Biological and neuropsychology
Brain and behaviour
Loraine Townsend, Kirston Greenop & Mark Solms
After studying this chapter you should be able to:
•describe the organisation of the nervous system
•explain the structure and function of the different areas of the hindbrain, the midbrain and the forebrain
•apply knowledge about the cerebrum when trying to understand brain damage
•explain what happens in a split-brain patient
•compare the processes of the sympathetic and parasympathetic divisions of the peripheral nervous system
•describe the structure of neurons and synapses
•explain communication within neurons and between neurons
•describe the action and dysfunction of neurotransmitters
•explain why the hormones sent out by the endocrine system affect the body more slowly than the nerve impulses sent out by the nervous system
•identify and describe the origins and basic assumptions of neuropsychology
•discuss the role of neuropsychology in South Africa
•identify and describe the various methods used in modern neuropsychology, and describe the circumstances under which they are used.
Melinda became aware of the effects of brain damage when her granny had a stroke. Melinda’s granny was 66 years old and had had problems with her high blood pressure medications. A neighbour had found her granny unconscious on the floor at home and rushed her to hospital. When Melinda asked her granny if she recalled what had happened, she could only remember feeling dizzy while making tea.
Melinda often went to visit her granny in hospital, but noticed that her behaviour had changed. Melinda’s granny would only notice her and talk to her if she was on the right-hand side of her bed and ignored anyone standing on the left side of the bed. She also had trouble dressing and washing herself, as she seemed to ignore the left side of her body. She only washed the right side of her face and dressed the right side of her body and the nurse had to do the rest. A CT scan (a type of X-ray) revealed that her granny had had a stroke in the right occipital-parietal region at the back of her brain. From her studies in neuropsychology, Melinda could understand why her granny acted in this strange manner. The injury had resulted in what is known as unilateral neglect, where patients generally do not pay attention to the left side of their bodies.
Being a neuropsychologist was not something that Melinda had ever contemplated as a career choice. Like most people she hadn’t really known such a profession existed or what it was that neuropsychologists might do. She knew that there were medical specialists called neurosurgeons who operated on the brain, but she hadn’t really thought about how a psychologist might be involved in working with people who had experienced some kind of neurological problem. But as Melinda discovered how important the brain was for all our human experiences, she found herself growing increasingly fascinated with this relatively new but rapidly growing area in psychology.
People often spoke about the centre of themselves being their heart, but Melinda began to realise that it was more likely your brain that made you who you were. A brain injury could change everything about you, who you felt you were and how you experienced the world.
In the case study, Melinda witnessed the effects of an injury to the brain. To understand what happened to Melinda’s granny we have to understand the psychobiology of the brain, which is a part of the nervous system. However, the brain is also affected by the rest of the nervous system and by the endocrine system. Therefore this chapter deals with the brain, the way messages are communicated through the body via the nervous system, and it also touches on the endocrine system.
Psychologists could be involved in diagnosing different kinds of damage to the brain and helping people with the effects of these. Understanding more about this amazing organ might make it possible not only to help people who have suffered brain disease or injury, but also to understand the complex processes that occur in the minds of normal people. Understanding these better might help with all sorts of psychological problems. The psychologists who specialise in this area are called neuropsychologists.
Neuropsychology links knowledge from two disciplines: neurology and psychology. A neurologist is a medical doctor who specialises in brain and nervous system disorders, while a neuropsychologist looks for the relationships between the mind and the brain. This has often been called the mind—body or mind—brain problem and has been studied and debated for centuries.
Neuropsychology can be divided into two major divisions: research neuropsychology and clinical neuropsychology. The two overlap considerably. However, in general, research neuropsychologists are interested in how mental functions are organised in the brain, and what the study of the brain (both when healthy and when diseased) can reveal about the organisation of the mind. Clinical neuropsychologists, on the other hand, are more concerned with the practical application of this knowledge: the diagnosis and management of the mental aspects of neurological disease. These aspects will be described in more detail later in the chapter.
The nervous system
The nervous system is made up of over 100 billion cells called neurons. In a later section, we will describe the structure and functioning of neurons. The nervous system is responsible for collecting information from the environment, sending this information to the right places in the body and then enabling the body to respond to this information. The nervous system can be divided into the central nervous system and the peripheral nervous system.
The central nervous system
The central nervous system is made up of the spinal cord and the brain. The spinal cord is found in the spinal column that runs down the middle of the back. It communicates with all the muscles and sense organs of the body below the head. If you were to cut the spinal cord in half, you would see that it has two parts. The inner part looks like an H and is grey in colour. It is called grey matter. It is surrounded by lighter tissue, called white matter (the second part). The neurons in the white matter are more insulated than those in the grey matter. Pairs of spinal nerves are attached to the spinal cord at 31 points on the spine. These nerves pass signals from the environment to the spinal cord and then transmit the response from the spinal cord to the body. When the spinal cord is damaged, there is no way for the body to communicate with these nerves. At the top of the spinal cord a bulge starts to form which is the start of the brain (the medulla oblongata).
The brain is about the size of a large grapefruit, looks like a wrinkly walnut and has the consistency of porridge. Because of its important functions and soft consistency, it is the most well-protected organ in the body. Carlson (2005) notes that this protection takes the form of cerebrospinal fluid, meninges and the skull. The brain floats in cerebrospinal fluid, which both nourishes it and protects it from bumps and knocks. The meninges are the membranes that surround the brain, protecting it and storing the cerebrospinal fluid. Surrounding these is the skull, which forms a solid box that protects the brain. The major structures of the brain are shown in Figure 7.1.
Figure 7.1 The major structures of the brain (adapted from Kalat, 2001, p. 97)
We can take two approaches to describing the brain: (1) by looking at the regions of the brain in the order in which they developed during evolution, and (2) based on how it appears to be divided into two sides called hemispheres. We shall start by discussing the former, which divides the brain into the hindbrain, the midbrain and the forebrain (see Figure 7.2).
Figure 7.2 The brain can be divided into the forebrain, midbrain and hindbrain
•The central nervous system consists of the spinal cord and the brain.
•The spinal cord:
”is in the spinal column
”communicates with all the muscles and sense organs of the body below the head
”consists of grey matter surrounded by white matter (which provides insulation).
•Pairs of spinal nerves pass signals from the environment to the spinal cord and from the spinal cord to the body.
•The medulla oblongata at the top of the spinal cord is the start of the brain.
”is protected by cerebrospinal fluid, the meninges, and the skull
”can be described in terms of regions or in terms of its hemispheres.
The hindbrain, midbrain and forebrain
We can describe the different parts of the brain by looking at the regions of the brain in the order in which they developed during evolution. From this point of view, you will see that the earliest parts of our brain to evolve are the ones responsible for our most important survival functions. Only later in evolution did humans develop the skills of complex thinking such as planning and organising their worlds. The following categorisation of the brain into the hindbrain, midbrain and forebrain refers to when the regions of the brain evolved as well as to their location in the head. The hindbrain is at the bottom near the back, the midbrain is near the centre of the brain, and the forebrain is at the top and front of the brain.
7.1THE CASE OF HM
Source: Wortman, Loftus and Weaver (1999) and Ogden and Corkin (1991)
HM was a young man who suffered from debilitating epilepsy, often suffering up to 10 seizures a day. His epilepsy became worse and the drugs used to treat it were not working. As a result, relationships between the members of his family became strained. As surgery at that time was very popular and no other treatments were working, his doctors suggested psychosurgery in 1953. The surgeons decided to operate on HM’s brain and they used a silver straw to remove the parts of the brain (the amygdala and hippocampus) that were causing the seizures. Although subsequent studies of the regions that were removed did not locate the precise site of his epilepsy, HM’s seizures grew less and were not as intense. But the side effects of the surgery were extreme: HM could no longer remember things, his long-term memory was impaired and he could no longer form new memories. He could remember things from before the surgery, but nothing afterwards. He would complete the same crossword puzzle over and over because he forgot that he had seen it before and he ’met’ his doctors for the first time every day.
The hindbrain is made up of the medulla oblongata, the pons, the cerebellum and portions of the reticular formation (which is discussed as part of the midbrain).
The medulla oblongata is the first structure in the transition from the spinal cord to the brain. The medulla is responsible for breathing, circulation, the functioning of the heart, and other involuntary behaviours such as vomiting, coughing, sneezing, hiccupping and blinking if something flies towards your eye. From this description you can see that any damage to the medulla could result in death, as breathing or the functioning of the heart would be affected (Holt et al., 2012).
The pons (which means ’bridge’ in Latin) is directly above the medulla oblongata. The pons acts like a relay station, sending signals from the spine to the brain and from the brain to the spine. Holt et al. (2012) note that the pons also plays a role in sleeping and waking. Narcolepsy is a disorder in which a person may fall asleep anywhere and at any time, and people suffering from this have been shown to have unusual neural activity in the pons.
The cerebellum (or small brain) is located at the back of the brain. It is responsible for coordinated movement, balance and posture. This structure is affected when you are drunk. When the police test people who are drunk, they are determining the extent to which the cerebellum has been affected by alcohol, thus indicating the amount of alcohol they have had.
As an example, put your arm out sideways at shoulder height and face forward; then bend your arm and, using your index finger, touch your nose. People who are drunk cannot touch their noses and often miss or do it very slowly because they have to concentrate very hard.
The reticular formation is a structure that begins in the hindbrain and continues through to the midbrain. It is made up of many neurons that connect to all the areas of the brain.
The reticular formation is responsible for arousal and sleep/wake consciousness. Brain arousal is the state of readiness for activity and varies in intensity. For example, you would want a heightened state of arousal when you wrote an examination, but would need less arousal to watch television. If the reticular formation is damaged, a permanent state of sleep or coma (Holt et al., 2012) can result.
The forebrain was the last area of the brain to develop in the course of evolution and is involved in complex cognitive functions, sensory processes and emotions. The forebrain comprises the thalamus, the hypothalamus, the limbic system, the basal ganglia and the cerebrum. The cerebrum is part of the cortex or outer layer of the brain, but the thalamus, hypothalamus and limbic system are all subcortical structures as they are below the cortex.
The thalamus is the first structure to process incoming sensory information before relaying it to the appropriate area of the brain for further processing. This is similar to the information desk in a shopping centre — when you walk into a new shopping centre, you could go to the information desk to find out where you would find a specific shop. The thalamus is also active in emphasising certain messages over others.
The hypothalamus is a very small structure that is found below the thalamus. It is involved in many different activities. The hypothalamus controls the pituitary gland, which is the main gland affecting all the other glands in the body. This is the link between the nervous system and the endocrine (gland and hormone) system. The hypothalamus is involved in emotions, regulating body rhythms for sleep, sexual activity, temperature regulation, hunger and thirst.
The limbic system is not a single structure, but is made up of a few structures to create a system (see Figure 7.3). It is involved in emotion, memory, learning and motivation. The most important parts are the amygdala and the hippocampus. The amygdala is involved in experiencing many emotions, learning and memory for emotional events. Most importantly, the amygdala is responsible for recognising fear in other people and feeling fear. The hippocampus is responsible for certain kinds of memory (see Box 7.1).
Figure 7.3 The limbic system (adapted from Peterson, 1997)
The basal ganglia are involved in movement. When these structures are damaged, changes in posture, muscle tone and normal movements can occur (Chakravarty, Joseph & Bapi, 2010). When a person has Parkinson’s disease, the dopamine neurons start to die. These neurons are meant to project out to the basal ganglia and, if they no longer exist, those areas in the basal ganglia that received them also die. The basal ganglia have also been implicated in mood and memory.
The cerebrum makes up the largest section of the forebrain and is the most complex. It is covered by the cerebral cortex which consists of a layer of grey matter a bit more than 0.5 cm thick. The cortex is wrinkled like a crumpled piece of paper and so contains a relatively large surface area (about the size of a pillowcase if it was smoothed out). The cerebral cortex represents the furthest development in brain evolution. Fish do not have a cerebral cortex, whereas in humans, it forms 80 per cent of brain tissue.
The cerebrum comprises four lobes: the frontal, temporal, parietal and occipital lobes (see Figure 7.4). In these lobes there are primary areas and association areas. The primary areas are those areas of the cerebrum that process primary or raw sensory information. Information is received by the sensory receptors through the thalamus and is directed to the primary areas. These neurons are more specific (e.g. to vision or taste) than ones in the association areas. The association areas are involved in the more complex mental functions.
Figure 7.4 The frontal, parietal, temporal and occipital lobes
To illustrate the difference between the primary areas and the association areas, imagine that you see a bicycle. The sensory information about shape, lines, colour and movement would come from the eye, through the thalamus, to the occipital lobe of the cerebrum. The neurons in the primary areas in the occipital lobe are sensitive to noting specific lines, colours and movement, and are therefore stimulated by this information. The visual association area then receives this information and makes meaning from it, determining that it is a ’bicycle’. Knowing that those lines, shapes and colours represent a bicycle is a result of learning what a bicycle looks like.
The cerebrum’s frontal lobes are located in the front of the brain and are responsible for many abilities ranging from movement to higher cognitive functioning. The frontal lobes can also be divided into sub-areas. The motor cortex is located at the back of the frontal lobes and is responsible for movement. This area receives information from the spinal cord, the cerebellum and the basal ganglia, and is involved in voluntary movements such as walking, jumping, running and threading a needle. The motor cortex has different areas dedicated to different parts of the body. For example, one area is dedicated to the mouth and another to the hands. However, each body part has a different-sized area dedicated to it. Parts of the body that are sensitive, complex and used frequently, such as the hands, have larger areas dedicated to them than parts that are not as skillful, such as the thighs.
The association areas in the frontal lobes are involved in personality and in higher-order thinking such as planning, organisation, abstract thought, coordinating skilled movements and memory. If the frontal lobes are damaged, a person may experience difficulties with these aspects, for example losing the ability to think abstractly, to plan and organise behaviour and activities, to adjust socially, or to behave appropriately.
A specific area found in the left frontal lobes (in most people) is involved with language. This is Broca’s area, named after the man who isolated it. This area is responsible for the expression of speech or the motor activities that comprise speech. People with Broca’s aphasia may not be able to talk, but they can usually still understand speech (Davey, 2004).
The cerebrum’s temporal lobes are on the sides of the brain and are mainly responsible for hearing and language. The primary areas receive the frequency, amplitude and pitch of the sounds and the association areas combine these into words that we recognise. Language is also represented in this cortex and Wernicke’s area is located in the left temporal lobe (in most people). This area is responsible for understanding speech. If you had Wernicke’s aphasia, you would still be able to speak, but you would not make any sense and you would not understand what others were trying to say.
Although hearing and language are emphasised as the main functions of the temporal lobes, they are also involved in visual association. After information from the visual system has been processed in the primary areas in the occipital lobes, the visual association areas in the temporal lobes identify what an object is.
The cerebrum’s parietal lobes are located at the top of the brain and contain the somatosensory cortex. This is a band of brain area that mirrors the motor cortex and which receives sensory information from the body. The parietal lobes are also responsible for locating the position of objects, the sense of touch, detection of movement and spatial orientation (how one’s body is located in space). Damage to this area could result in the syndrome called unilateral neglect, where patients do not pay attention to one side of their bodies.
The cerebrum’s occipital lobes are located at the back of the brain and are responsible for vision. If someone hits you on the back of the head and you see stars, this is because the primary visual areas in the occipital lobes have been affected. Damage to the primary visual area can result in partial or complete blindness. The association areas in the occipital lobes extend to other areas of the cortex and are responsible for organising the information from the primary areas into more complex pictures of the features of objects.
A topic that has puzzled brain researchers for a long time is consciousness. What is consciousness? What parts of the brain or brain activity are necessary for consciousness? Consciousness mainly means being aware, alert and attentive, and also includes inner self-knowledge. From this definition you can see that consciousness is a very subjective experience and measuring it has proven to be very difficult. In terms of brain anatomy, researchers have not found one specific area of the brain related to consciousness (not least because it is such a hard concept to define).
The main area of research into brain anatomy and consciousness is the problem of binding — that is, the way in which the brain takes many different aspects of information from all over the brain and binds them together to form a subjective experience. This implies that different brain regions are involved, depending on what part of consciousness you are studying.
One important area of research into consciousness involves the frontal lobes. In this research the focus is on executive functioning in terms of self-reference and self-evaluation. But it is clear that research on consciousness is determined by the definition of consciousness and the aspects of consciousness being focused on. In general, every area in the brain has been shown to link to the study of consciousness (Zillmer & Spiers, 2001).
The left hemisphere and the right hemisphere of the brain
While the brain can be viewed as being made up of the hindbrain, the midbrain and the forebrain, it can also be viewed as being formed by two hemispheres, left and right. Thus, the hindbrain, midbrain and forebrain each have two parts, one that falls in the left hemisphere and one that falls in the right hemisphere. For example, you would have a left forebrain and a right forebrain. These hemispheres are linked to each other by a thick band of tissue called the corpus callosum, which allows communication between the two.
It seems that each hemisphere is responsible for, or dominant over, some specific functions. This division of tasks between the hemispheres is referred to as lateralisation because the functions differ depending on the side of the brain where located. Thus, when some ability is lateralised, it is understood to be located in either the left or the right hemisphere.
In many people, the left hemisphere has been implicated in speech and language, and the right hemisphere has been implicated in spatial functions (Holt at al., 2012). One source that supports the idea of lateralisation is the records doctors have made regarding ’split brain’ patients (Holt et al., 2012). Split-brain patients are people who have had their corpus callosum severed by a surgeon to stop debilitating epileptic seizures. In many cases these patients experience changes in their behaviour and functioning following surgery.
Figure 7.5 The visual pathway in the brain (adapted from Holt et al., 2012)
Figure 7.5 illustrates the normal visual pathway in the brain. Information from the left visual field goes to the right hemisphere and information from the right visual field goes to the left hemisphere. The information crosses over at the optic chiasma. However, if the corpus callosum were severed, the information would not be able to be communicated between the hemispheres.
According to Figure 7.5, if you showed a split-brain patient an ice-cream in their left visual field, this information would travel to the right hemisphere, but the right hemisphere could not tell the left hemisphere what it saw because language is controlled in the left hemisphere. The patient would therefore not be able to tell you what he/she saw.
However, if you showed the same patient a flower in the right visual field, which was then transmitted to the left hemisphere, he/she would be able to tell you what was seen because language is controlled in the left hemisphere.
•The brain can be categorised into hindbrain, midbrain and forebrain; in evolutionary terms, the hindbrain developed earliest.
•The hindbrain is made up of the medulla oblongata, the pons, the cerebellum, and portions of the reticular formation:
”The medulla is responsible for breathing, circulation, the functioning of the heart and other involuntary behaviours.
”The pons acts like a relay station, sending signals from the spine to the brain and from the brain to the spine.
”The cerebellum is responsible for coordinated movement, balance and posture.
•The midbrain consists of the reticular formation; this is responsible for arousal and sleep/wake consciousness.
•The forebrain consists of the thalamus, the hypothalamus, the limbic system, the basal ganglia and the cerebrum:
”The thalamus processes incoming sensory information before relaying it to other areas of the brain for further processing.
”The hypothalamus is involved in many different activities; it controls the pituitary gland and links with the endocrine system.
”The limbic system is made up of several parts (most importantly, the amygdala and hippocampus); it is involved in emotion, memory, learning and motivation.
”The basal ganglia are involved in movement, mood and memory.
”The cerebrum makes up the largest section of the forebrain and is the most complex. The cerebrum is covered by the cerebral cortex and comprises four lobes (frontal, temporal, parietal and occipital lobes); in these lobes there are primary areas (for processing sensory information) and association areas (for more complex mental functions):
”The frontal lobes contain the motor cortex which is responsible for movement.
”Broca’s area in the left frontal lobes is involved with language.
”The temporal lobes are on the sides of the brain and are mainly responsible for hearing and language; Wernicke’s area in the left temporal lobe is responsible for understanding speech.
”The parietal lobes are located at the top of the brain; they contain the somatosensory cortex which receives sensory information from the body.
”The occipital lobes are located at the back of the brain and are responsible for vision.
•The brain can also be viewed as having a left hemisphere and a right hemisphere. Thus, the hindbrain, midbrain and forebrain each have two parts, one in the left hemisphere and one in the right hemisphere.
•The hemispheres are joined by a thick band of tissue, the corpus callosum.
•Certain functions are dominant in one or other hemisphere; this is called lateralisation. Generally, the left hemisphere is associated with speech and language, and the right hemisphere with spatial functions.
•In terms of the visual pathway, information from the visual fields crosses over to the opposite hemisphere at the optic chiasma.
The peripheral nervous system
The peripheral nervous system consists of all the nerve structures that lie outside the brain and spinal cord. It constantly communicates with the central nervous system through two sets of nerve pathways. The first receives information from the environment through the sensory receptors and sends this information to the central nervous system. The second takes information from the central nervous system to the muscles and glands, giving them directions on how and when to act or move. The peripheral nervous system has two main parts: the somatic and autonomic nervous systems.
Figure 7.6 The organisation of the nervous system (Holt et al., 2012)
The somatic nervous system
The somatic nervous system carries messages from the sensory receptors to the brain and spinal cord and also carries messages from these central nervous system structures to all of the muscles attached to bones in the body. These muscles control voluntary movement and they allow you, for instance, to jump, walk, bend — or scratch your head.
The autonomic nervous system
The autonomic nervous system controls all the other muscles, which are attached to your internal organs and glands in the body. The muscles attached to the autonomic division control mainly involuntary actions, such as the secretion of hormones or the beating of the heart. However, this latter process is not completely involuntary, as people can often affect their heartbeat by using relaxation techniques.
The autonomic nervous system is divided into the sympathetic and parasympathetic nervous systems. These two systems are involved in the body’s reaction to stress: the fight-or-flight response. The two systems work together to maintain homeostasis (a balanced internal state). The sympathetic nervous system is used to get the body ready for action (whether this is fighting or preparing for an injury). This involves:
•dilating or widening the pupils to take in as much light as possible to see the stressor
•relaxing the bronchi in the lungs, allowing large amounts of air to come into the lungs
•increasing the heart rate so that more oxygen is pumped around the body
•closing down the digestive system slightly to make energy available to other areas of the body
•constricting the blood vessels so that blood pressure is increased.
Once the body has reacted to the stress by either fighting or running away, the parasympathetic system inhibits the action and relaxes the body. This is done by:
•contracting the pupils to normal size
•contracting the bronchi
•slowing the heart rate so that you do not constantly have a racing heart
•reactivating the digestive system
•dilating the blood vessels once again.
•The peripheral nervous system consists of all the nerve structures that lie outside the brain and spinal cord.
•The PNS constantly communicates with the CNS, sending information from the sensory receptors to the CNS and from the CNS to the muscles and glands.
•The PNS has two main parts, namely the somatic and autonomic nervous systems.
•The somatic nervous system controls voluntary movement.
•The autonomic nervous system (ANS) controls all the other muscles attached to internal organs and glands in the body, thereby controlling mainly involuntary actions. The ANS contains two systems (sympathetic and parasympathetic) which work together to keep a balanced internal state:
”The sympathetic nervous system gets the body ready for action (fight or flight).
”Once the stress is past, the parasympathetic system relaxes the body.
Neurons and neural transmission
The nervous system is made up of billions of interconnected cells that are constantly communicating with one another. A neuron is a type of cell found in both the central and peripheral nervous systems; it is specialised to receive and transmit electrochemical signals in the body. These signals use both electricity and chemicals to make sure that their message is transmitted.
The structure of neurons
Neurons can vary widely in shape and size, and many different types of neurons have already been identified (Davey, 2004). Figure 7.7 shows the structure of a typical neuron. Each neuron has three main parts: the soma (or cell body), the dendrites, which emerge from the cell body, and the axon, which carries electrical impulses to other neurons, or muscles and glands.
The electric impulse or message travels down the neuron and passes across to the next neuron. The message starts at the dendrites which receive the message from other neurons. Because the dendrites have so many branches, they can receive messages from 1 000 or more adjacent neurons (Davey, 2004). This message then travels through the cell body of the neuron (the soma), where the messages from the dendrites are processed. The message then travels down the axon of the neuron, which transmits the message to other neurons. The message arrives at the axon terminals (the end of the neuron) from where it is passed on to other neurons.
The neuron axon may be covered with a myelin sheath, which serves to insulate the axon and make the message stronger and travel faster. Similarly, myelinated axons transmit messages faster and more efficiently than non-myelinated axons. The myelin sheath develops in the early stages of human development. Multiple sclerosis is a disease that breaks down the myelin sheath and uncovers parts of the axon. This affects the transmission of messages that travel from the brain to the muscles, causing an interruption in the message and an effect on movement, for example (Feldman, 2014).
Figure 7.7 The components of a neuron
Some substances travel in the opposite direction, from the axon terminal buttons to the cell body, so that food and nourishment reach the cell body. Certain diseases (e.g. Lou Gehrig’s disease or amyotrophic lateral sclerosis) affect this reverse movement so that the neuron eventually dies from starvation. Other diseases, such as rabies, travel in a reverse direction up the neuron (Feldman, 2014).
The transmission of nerve impulses
Neurons are cells that have an electrical charge inside them. The electrical charge inside the neuron is maintained at about −70 millivolts (one thousandth of a volt). The message that travels down the neuron does so as a wave of electrical activity. But how does this actually work?
Atoms are the basic unit of matter. When an atom has all the electrons it is meant to have, it does not have an electrical charge. But when it has lost one or more electrons, or gained one or more electrons, it does have an electrical charge, and it is then called an ion. An atom that has lost one or more electrons is a positively charged ion, and an atom that gained one or more electrons is a negatively charged ion. The neuron’s cell membrane is like a sieve, allowing some ions to pass through ion channels but stopping or limiting others.
Figure 7.8 The action potential in the neuron (sodium ions travel into the cell and a small number of potassium ions travel out) (Coon & Mitterer, 2013, p. 42)
A neuron contains ion-filled fluid with protein molecules (negatively charged ’anions’) and potassium ions (positively charged). The neuron is surrounded by a slightly different ion-filled fluid containing chloride ions (with a negative charge) and sodium ions (with a positive charge). When the neuron is in a resting state, the inside of the neuron is mainly negatively charged and the outside is mainly positively charged. This state of tension between the ions is called the resting potential. When in this resting state, we say the neuron is polarised.
As with all things with electrical charges, like charges repel each other and opposite charges attract each other. As the inside of the neuron is negatively charged, chloride, which is also negatively charged, is repelled by the neuron and therefore stays outside the neuron. As the outside of the neuron is positively charged, potassium, which is also positively charged, is repelled by the outside fluid and therefore stays inside the neuron.
Sodium is also positively charged, and is therefore attracted to the inside of the cell, which is predominantly negative, and repelled by the outside of the cell, which is predominantly positive. Overall, the neuron’s semi-permeable membrane is not very permeable to sodium. This means that even though sodium is attracted to the inside of the cell, it cannot cross the membrane.
When a nerve impulse comes along, the interior voltage in the neuron changes from −70 mv to +40 mv. This takes about one millisecond and is called the action potential. The action potential is an electrochemical process as the neural message is electrical and the ions in the surrounding fluid are chemical (see Figure 7.8).
The graph in Figure 7.9 illustrates the different stages of an action potential. The straight line at −70 mv is the cell in the resting potential. According to Carlson (2005), when an action potential is realised, certain stages occur.
1.When the threshold of excitation is reached, the permeability of the cell membrane changes, causing sodium ions to rush into the cell. This stage is called depolarisation. The cell becomes positively charged (up to +40 mv).
2.As the cell becomes more positively charged, the potassium channels open and the potassium ions start to leave the cell. The sodium channels are now closed and no more sodium ions can flow into the cell. This is known as the refractory period (the cell cannot pass another message in this recovery state).
Figure 7.9 The process of an action potential (Holt et al., 2012, p. 102)
3.As the cell returns to its resting potential (−70 mv), the potassium channels close. The cell returns to its normal state and waits for the next depolarisation incident.
4.This sequence is repeated along the axon as the message is passed down the cell.
The electrical impulse that travels down the neuron follows an all-or-none law. This law states that the electrical impulse will either be passed down the cell or not. Feldman (2014) compares this to a gun: you either pull the trigger and the gun fires, or you do not pull the trigger and the gun does not fire — there is no in-between.
Some neurons fire at different rates to others. For example, some can fire at 200 times per second while others can fire far fewer times in the same period. The intensity of the stimulus (e.g. a loud noise versus a whisper) determines the rate of firing. Researchers can also measure the rate of firing to determine how intense our reactions are to various stimuli (Feldman, 2014).
When the electrical impulse reaches the end of the neuron it needs to pass the message onto another neuron. The difficulty is that the terminal buttons from the first neuron and the dendrites of the second neuron do not actually meet. Between the two neurons is a space called the synaptic gap. The electrical impulse has to pass over this gap to make sure that the message continues in the next neuron. The process of synaptic transmission is a chemical process, and is illustrated in Figure 7.10.
Figure 7.10 The synaptic gap (a) and the process of transmission (b) (adapted from Peterson, 1997)
The structure and action of a synapse
A synapse is the region where two neurons meet. The terminal buttons of the first neuron sit close to the dendrites of the second neuron. The gap in between the terminals and the dendrites is the synaptic gap. There are small sacs called vesicles in the first neuron that contain neurotransmitters. When a nerve impulse reaches the terminal buttons, it stimulates the vesicles to release the neurotransmitters into the synaptic gap. The receptor sites on the second neuron then pick up the neurotransmitters. However, receptor sites are specialised and will only receive the neurotransmitters for which they were designed. For example, in Figure 7.10 you can see that the circular receptor sites can only receive circular neurotransmitters and not triangular ones. This is similar to a lock-and-key mechanism: only one key can fit a lock and open it.
Once the receptor site has accepted the neurotransmitter, it starts or inhibits an action potential in the second neuron, depending on the function of the neurotransmitter. Excitatory neurotransmitters start an action potential in the following neuron while inhibitory neurotransmitters stop the next action potential.
Once the neurotransmitters have been released into the synaptic gap and all receptor sites have received neurotransmitters, there are likely to be extra neurotransmitters left in the gap. These extra neurotransmitters are either broken down by enzymes or taken back up into the first neuron’s terminal buttons.
Chapter 24 on psychopharmacology outlines the neurotransmitter process and explains how drugs can affect neurotransmitters and their action. Box 7.3 illustrates how Ecstasy, an illegal drug, affects neurotransmitters and their action.
7.3THE EFFECTS OF ECSTASY
Source: Burgess, O’Donohoe and Gill (2000)
Ecstasy, often called E, is an illegal drug that many people consider to be a safe party drug. Its chemical name is MDMA (3, 4-methyl-enedioxymethamphetamine) and it is usually taken in pill form and has effects lasting two to six hours. The immediate effects include feelings of euphoria, empathy towards others and a heightened sense of touch. Negative effects can include jaw clenching, jumpiness, mental problems such as confusion, anxiety, sleep disruption and poor judgement, headaches and nausea, as well as increased heart rate and blood pressure. After a few days, people report feeling sad, despondent and irritable. Prolonged use of Ecstasy results in the degradation of terminal buttons that secrete serotonin (a mood neurotransmitter). When these buttons are affected, people may develop depression, anxiety and sleep problems.
The way that Ecstasy works is that when extra neurotransmitters are taken back into the first cell, Ecstasy replaces serotonin, dopamine and norepinephrine. Since serotonin, dopamine and norepinephrine stay in the synaptic gap, they continue to stimulate the receptor sites. However, because the serotonin axons are then overstimulated they die off. Once this happens, they cannot be replaced.
Types of neurotransmitters
Over 50 different neurotransmitters have been identified. This section will concentrate on a few of the most well-known and well-researched neurotransmitters.
Dopamine is found in the brain, especially in the limbic system, the cerebellum and the basal ganglia. It is involved in thought disorders such as schizophrenia (too much dopamine) and movement disorders such as Parkinson’s disease (too little dopamine). Parkinson’s disease is a disorder of movement and causes people to have problems coordinating movement and to experience tremors when at rest. The drug L-Dopa provides temporary relief as it mimics or pretends to be dopamine. Drugs used to block dopamine may alleviate schizophrenia; however, one must be careful with these drugs because they may cause Parkinson’s-like symptoms when they are taken in large doses.
Norepinephrine is derived from epinephrine (adrenaline). It is involved with mood, sleep, eating and arousal. When their levels of norepinephrine are too low, people experience depression (Holt et al., 2012). Antidepressants, the drugs used to treat depression, work by either pretending to be a neurotransmitter involved in mood, or by blocking the uptake of neurotransmitters so that the mood neurotransmitters have a better chance to work at the synaptic gap.
Serotonin is one of the most well-known neurotransmitters and is involved in mood, sleep, eating and arousal. Low levels of serotonin result in depression. The drug Prozac is a selective serotonin re-uptake inhibitor (SSRI). This means that it stops serotonin from being taken back up into the first neuron, causing it to stay in the synaptic gap and stimulate the next neuron for longer.
Acetylcholine or ACh is involved at the level of muscle movement as well as learning and memory. An absence of ACh is associated with paralysis while on oversupply may lead to severe muscle contractions and convulsions (Holt et al., 2012). People with Alzheimer’s disease have lower levels of ACh than others. Alzheimer’s disease involves a gradual degeneration in terms of memory and cognition.
Gamma amino butyric acid (GABA)
Gamma amino butyric acid (GABA) is an inhibitory neurotransmitter and is involved in emotion, anxiety, arousal and sleep. Parrott, Morinan, Moss and Scholey (2004) note that many benzodiazepines (such as Valium, Xanax and Librium) act by increasing the effect of GABA. As GABA is inhibitory, increasing its effects will lower anxiety.
•The nervous system is made up of billions of interconnected cells.
•Neurons are cells found in both the CNS and the PNS.
•Neurons receive and transmit signals in the body using both electricity and chemicals.
•Neurons vary widely in shape and size; they consist of a soma, dendrites and an axon.
•Messages travel from the dendrites to the soma and on to the axon and axon terminals.
•Some axons are insulated by a myelin sheath which speeds the message; damage to the myelin sheath can disrupt messages, as can disease in which the direction of message travel is reversed.
•Neurons have an electrical charge inside them; the message that travels down the neuron does so as a wave of electrical activity — ions (either positively or negatively charged electrons) move in or out of the cell.
•When the neuron is in a resting state (polarised), there is a state of tension between the inside and the outside of the cell.
•Chloride (negative), sodium (positive) and potassium (positive) ions are involved in the transmission of messages; like charges repel each other, and opposite charges attract each other.
•When a nerve impulse comes along, the interior voltage in the neuron changes from −70 mv to +40 mv. This takes about one millisecond and is called the action potential.
•The action potential is an electrochemical process (the neural message is electrical and the ions are chemical).
•The stages of transmission include depolarisation, action potential and the refractory period.
•The electrical impulse will either be passed down the cell or not.
•Some neurons fire at different rates to others.
•The electrical impulse needs to pass from one neuron to the next, but there is a gap (the synaptic gap) between the terminal buttons from the first neuron and the dendrites of the second neuron.
•Small vesicles in the first neuron contain neurotransmitters; the nerve impulse stimulates the vesicles to release the neurotransmitters into the synaptic gap. The receptor sites on the second neuron then pick up the neurotransmitters.
•Receptor sites are specialised and will only receive the neurotransmitters for which they were designed.
•Once the receptor site has accepted the neurotransmitter, it starts (excitatory) or inhibits (inhibitory) an action potential in the second neuron.
•Leftover neurotransmitters are either broken down by enzymes or taken back up into the first neuron’s terminal buttons.
•There are more than 50 types of neurotransmitters.
The endocrine system
This chapter has dealt primarily with the nervous system, but there are other biological systems that have an effect on our psychology. One such system is the endocrine system, to which we referred in the discussion about the hypothalamus. The endocrine system is the system of hormones and glands in the body (see Figure 7.11). Hormones are chemicals that are secreted by the glands. They travel through the bloodstream (making them a lot slower than nerve impulses and also longer lasting) and they influence the organ to which they were sent.
The pituitary gland is known as the master gland as it regulates and controls all the other glands in the body. It is close to, and connects with, the hypothalamus in the brain. This link between the nervous system and the endocrine system allows the two to work in harmony. The pituitary gland is also responsible for growth and regulates salt and water metabolism.
The thyroid gland in the throat is responsible for the body’s metabolism. If one has an under-active thyroid gland, one is likely to be apathetic and sluggish, to put on weight, and to feel very despondent. As a result of this, doctors often first check a patient’s thyroid gland functioning before making a diagnosis of depression. An overactive thyroid gland leads to a person being very active and thin.
Figure 7.11 The endocrine system is made up of the glands in your body (Holt et al., 2012)
The adrenal glands are situated on top of the kidneys. They produce many different hormones. They are made up of the adrenal cortex and the adrenal medulla. The adrenal cortex regulates salt and carbohydrate metabolism, while the adrenal medulla prepares the body for the fight-or-flight reaction to stress. You will find more information about the endocrine system in the chapter on stress (Chapter 21).
The pancreas is situated in the abdomen and regulates levels of insulin and blood sugar. It is also involved in digestion. When the pancreas does not secrete enough insulin, the person will be diagnosed with diabetes (high blood sugar levels).
Lastly, a female’s ovaries and a male’s testes are also glands, and they are responsible for sexual behaviour, the development of the reproductive hormones, and general physical growth.
•The endocrine system (hormones and glands) also has an effect on our psychology; the nervous system and the endocrine system work in harmony.
•The pituitary gland is the master gland; it works closely with the hypothalamus, and regulates and controls all the other glands in the body.
•The thyroid gland is responsible for the body’s metabolism.
•The adrenal glands consist of the adrenal cortex and the adrenal medulla; they produce many different hormones.
•The pancreas regulates levels of insulin and blood sugar.
•A female’s ovaries and a male’s testes are responsible for sexual behaviour, the reproductive hormones, and general physical growth.
There is a special relationship between the brain and the mind. The functions and dysfunctions of the brain have immediate and direct effects on the mind — so much so that people often say that the brain is the organ of the mind. This means that everything that we deal with in psychology has an aspect of neurology to it. As mentioned earlier in the chapter, neuropsychology is the branch of psychology that tries to understand how brain structure and function relate to psychological processes and behaviour. Ultimately, the connection between brain and mind is not far removed from the connection between body and soul, and so continues to raise philosophical and theological debate. This section of the chapter will consider the roles of psychiatrists and neuropsychologists in understanding brain function.
Students may well wonder how psychiatry fits into this interdisciplinary picture. Traditionally a psychiatrist is a medical doctor who specialises in the diagnosis and treatment of mental illness and emotional disorders. It is becoming more and more common for neurology and psychiatry to deal with the same issues and problems. Historically, however, the two disciplines dealt with apparently different medical problems. In the 19th century (when this distinction first arose), doctors classified mental disorders that were caused by a structural change in the brain as neurological — they could see these changes when they did an autopsy on the brain. Mental disorders that could not be seen in brain changes were classified as psychiatric and were considered to be disorders of brain function.
This was the start of the trend where brain structures were viewed separately from brain functions. However, these days psychiatrists point out that many of the functional disorders (such as bipolar disorder and schizophrenia) are due to micro-level changes (such as over-activity or under-activity in a particular neurotransmitter system), and so they treat them with medicines that act on these neurotransmitter pathways. Many neurological disorders (such as epilepsy and Parkinson’s disease) have a similar basis and approach to treatment. This shows that the difference between structure and function is no longer clear-cut. These days some psychiatrists specialise in what they call neuropsychiatry; in other words, they specialise in the psychiatric or functional aspects of ’structural’ neurological disease.
In general, neuropsychology is still concerned primarily with neurological (as opposed to psychiatric) disorders, as it attempts to describe the mental changes that result from structural changes in the brain. In this respect, the difference between neuropsychology and neuropsychiatry corresponds roughly with the difference between cognition and affect (emotion). Clinical neuropsychology focuses mainly (but by no means exclusively) on cognitive rather than emotional disorders. The same does not apply to research neuropsychology, however. This chapter focuses mainly on clinical neuropsychology. This emphasis also reflects the fact that neuropsychology in South Africa is very much a clinical discipline. (For an introduction to neuropsychology, see Kalat, 2009; Martin, 2006; Solms & Turnbull, 2002.)
The early history of neuropsychology
In the 1860s, Pierre Paul Broca discovered that damage to a particular part of the left hemisphere of the human brain results in loss of language. This part of the brain is now known as Broca’s area (see Figure 7.4 earlier in this chapter). Broca’s discovery caused considerable excitement in the European scientific circles at the time because language is a mental function (and, more specifically, a human mental function). Therefore, a part of the brain had been identified where language production was located. This discovery led to an increase in research into the brain, but mainly focused on trying to localise mental functions. This included the work of Carl Wernicke who localised the ability to understand speech to the temporal lobes (see Figure 7.4 earlier in this chapter), and this area is now called Wernicke’s area.
These classical localisations were made by inferring a relationship between the mental function that was lost, and the damaged part of the brain seen when an autopsy was done. This research led to a school of thought that argued that all mental functions could be located in particular places in the brain.
Localisation was not completely accepted, however. In 1891, Sigmund Freud criticised the authoritative works of Broca, Wernicke and Ludwig Lichtheim, which argued that the various components of language — spontaneous speech, comprehension, repetition, reading and writing — were localised in a patchwork of centres on (and just below) the surface of the left hemisphere. Other authorities also criticised the diagram makers for reducing the dynamic complexities of the mind to simple models of nervous centres and their connections. Other theorists proposed that the brain functioned as an integrated unit and that mental functions were holistic things that depended on the concerted functioning of the brain as a whole.
Aleksandr Romanovich Luria argued that both these views were right to a degree. Luria said that although a whole mental capacity cannot be reduced to the activities of a limited zone of the cerebral cortex, it was also true that different cortical zones performed different functions. His compromise position put forward the idea that there were groups of cortical zones that worked together to produce each complex mental ability (like speech). Luria argued that mental abilities were combinations of many low-level or basic functions, and that only the low-level elements could be narrowly localised (like sound production or awareness of sounds). The abilities themselves were made up of dynamic interactions between the components. While this meant that the abilities as a whole could not be narrowly localised, Luria argued that the task of neuropsychology was to identify the localisable components of each complex ability. (For a good indication of Luria’s approach, see Luria, 1973a, 1973b, 1979.)
Luria’s idea that complex mental functions are produced by dynamic neural networks as opposed to static centres gained rapid support and is still the standard way of thinking in neuropsychology today.
The influence of cognitive psychology on neuropsychology
Cognitive psychology has been hugely influential in modern neuropsychology because it provided a way to divide our cognitive capacities into smaller and smaller processing units, which became closer and closer to describing the individual processing units of cortical tissues. Computer-based approaches have thus gained popularity as a means of simulating the way neural connections work in the brain.
However, such models have not been useful in the study of areas such as emotion, motivation, the structure of personality and intersubjective experiences such as empathy, free will and the self. Computer-based models do not seem able to describe the physiological processes that govern the instinctual and subjective poles of the mind. For these aspects of neuropsychology, molecular-biological, ethological and perhaps even psychoanalytical theories might offer more appropriate conceptual and observational tools for the neuropsychology of the future.
Research methods in neuropsychology
For more than a century, clinico-anatomical correlation provided the methodological backbone for all neuropsychological research. This relied on autopsy studies. However, with the increase in the number of head injuries in World Wars I and II, it became possible to infer the site of a patient’s brain damage during life by tracking the entry and exit points of bullet or shrapnel wounds. The developing use of X-rays for visualising the location of bullets, shrapnel and skull fragments embedded in the brain provided further localising information.
These methods were basic research methods in neuropsychology, which took a major leap forward with the development of brain imaging (see Figures 7.12−7.15). This allowed the soft tissue inside the skull to be visualised while the person was still alive. Researchers no longer required autopsy results to support their hypotheses. Clinical observations of behaviour could be related to the images of brain pathology that were displayed by the technology. However, these imaging techniques are very expensive.
Computerised tomographic (CT) scanning became widely available in the 1970s. By the 1980s, CT scanning had been widely replaced by a second generation of imaging technology known as magnetic resonance imaging (MRI). MRIs had better resolution, which meant that pathology and changes to the brain could be viewed with greater accuracy and precision.
Figure 7.12 An image from a CT scan
Figure 7.13 An image from an MRI scan
Figure 7.14 An image from a PET scan
Figure 7.15 An image from an fMRI scan
The latest advance is functional brain imaging which involves obtaining images of the brain while the person is performing a certain function or is exposed to a stimulus. There are two major forms: positron emission tomography (PET) and functional MRI (fMRI). In different ways, both of these technologies measure differences in the rate of metabolic activity in the brain. Looking at an image from a PET or fMRI scan, one is able to see how active certain parts of the brain are when a person is actually performing a task. Thus one can infer which parts of the brain are used for particular cognitive functions.
This research seems logical, but it is important not to misinterpret the results. Some reports write about a particular brain region as though it is the only one that performs a task. We must remember that mental functions are produced not by circumscribed cortical locations, but rather by dynamic constellations of cortical and sub-cortical zones working together.
The qualitative and quantitative approaches to clinical neuropsychology
The specialist neuropsychologist takes an integrated (quantitative and qualitative) approach in assessment. He or she starts with a particular clinical question and then proceeds flexibly, selecting the appropriate assessment tools as the clinical picture unfolds. (This was Luria’s approach.) The aim is to identify a particular pattern of cognitive symptoms and signs that makes clinic-anatomical sense, thereby integrating the observable clinical picture, via its causal mechanism, with the underlying neuropathology.
7.4THE CASE OF THE GIRL WHO NEARLY DROWNED
An eight-year-old girl slipped while playing next to her parents’ swimming pool, banged her head, and fell into the water. It is unclear how long she was submerged in the water before she was found by her mother. However, she was unconscious and blue in the face. The mother administered mouth-to-mouth resuscitation, and after this the child vomited violently and resumed breathing. She was taken to casualty, semi-conscious, and was admitted for a period of observation. The laceration over her right forehead required six stitches. Although she passed through a period of confusion and drowsiness, she appeared to have recovered completely by the following day. An MRI scan of her brain showed no abnormality. She was therefore discharged home on the following day and, a few days later, she returned to school. However, her teachers noticed a change in her. She was no longer her bright and cheerful self. She seemed far less confident both academically and socially, and at the end of term she performed poorly in her examinations. Both parents and teachers attributed the change to the near-drowning incident. However, the question remained: ’Was the change attributable to neurological or emotional factors?’
If this girl was referred to a clinical psychologist trained only in standard psychometric assessment techniques, the psychologist would carry out a battery of standardised intelligence tests (as discussed in Chapter 15), projective tests or behavioural inventories. If the results were — as they would be in this case — low average scores on the standardised intelligence tests, and evidence of anxiety and insecurity on the projective tests, how would that help a psychologist say whether the change in the girl was attributable to neurological or emotional factors?
The psychologist could also use tests that are known to be resistant to the effects of brain injury. The psychologist could then compare the child’s scores on tests that are sensitive to the effects of injury to her scores on tests that are resistant to the effects of injury. However, this would still only provide us with an idea of how the girl’s present performance is different from her past performance, and not whether the girl was struggling at school because of neurological or emotional factors.
Table 7.1 Differential diagnosis possibilities for the girl discussed in Box 7.4
Differential diagnosis possibilities
a) Closed-head injury
Cognitive tests known to correspond to anatomical regions associated with the injury
b) Anoxia (lack of oxygen)
Cognitive tests known to correspond to anatomical regions associated with the injury
Lack of syndromes of above two possibilities Clinical interview and projective tests
3.Both brain damage and emotional trauma
Both of the above
Features of all of the above
In a purely quantitative approach, by contrast, a general clinical psychologist or psychometrician typically uses a standardised battery of tests, which measure the patient’s performance across a range of mental functions. They then compare this measure to an established population norm. This approach is quantitative as it calculates the degree of abnormality in the functions assessed, but it may not answer the clinical questions that the patient was referred for in the first place. Consider the case that was referred for a neuropsychological assessment in Box 7.4.
In order to answer the question about whether the change was attributable to neurological or emotional factors, the specialist neuropsychologist would begin by considering the possible differential diagnoses. Table 7.1 sets out these possibilities for this case.
To assess for brain damage, the neuropsychologist would test for the cognitive symptoms that are typically seen in a patient with a closed-head injury or a patient with anoxia. If there is an absence of these symptoms, then it is reasonable to conclude that the girl is unlikely to have suffered brain damage. Then, by exclusion, the neuropsychologist would infer that the girl’s difficulties in school were due to emotional (functional) causes, rather than organic (structural) causes. This diagnosis would be more secure if positive features of an emotional trauma (such as post-traumatic stress disorder) were demonstrated.
While the quantitative and qualitative approaches have been contrasted here, in practice the two approaches overlap. The main difference is that in neuropsychological assessment, measurement and standardisation are servants of the assessment process, not its masters, while in general psychometric assessment the structure of the assessment is determined by the fixed requirements of the tests rather than the flexible, unfolding clinical picture in relation to the referral question.
This section has described the process of using neuropsychological assessment in a specific case. This kind of assessment may also be used in a variety of situations where cognitive performance has been impaired (Harvey, 2012). Overall, neuropsychological assessment may be needed for diagnosis (e.g. dementias, stroke, traumatic brain injury), differential diagnosis (e.g. distinguishing between different kinds of dementias), predicting a person’s potential (e.g. following a brain injury or the onset of dementia), evaluating response to treatment (e.g. cognitive remediation following a stroke) and matching clinical findings to imaging results (e.g. vascular lesions that indicate a risk of stroke) (Harvey, 2012). Neuropsychological assessments may also be required for workers who are applying to be ’boarded’ (granted early retirement on full benefits due to ill health) and for assessments of a person’s competence to manage their financial affairs.
7.5THE PROFESSIONAL ROLES OF THE CLINICAL NEUROPSYCHOLOGIST
Neuropsychologists usually work in hospitals and private practices. In hospitals, neuropsychologists are often based in neurology, neurosurgery and psychiatry departments. In neurology departments, they play a role in diagnosing neurological disease. In neurosurgery, they often assess a patient’s current cognitive status and the cognitive functions of particular brain areas during surgery.
In psychiatric departments, they help to differentiate between neurological disorders on the one hand and functional, psychotic or mood disorders on the other. This often means working with children as complex combinations of neurological and psychiatric problems are particularly common in paediatric cases.
In private practice, neuropsychologists may assess individuals for medico-legal reasons, as well as offering therapy and counselling. Neuropsychologists also work within educational, industrial and primary health settings.
Neuropsychology in South Africa
Because neuropsychology is still developing, the impact of individual practitioners in the field is more strongly felt than in other branches of psychology. Michael Saling — a research psychologist formerly from the University of the Witwatersrand — played a pioneering role in neuropsychology in South Africa, and his qualitative, Luria-based approach to neuropsychological assessment continues to be practised and propagated by his erstwhile students today.
However, different countries have different assessment practices for neuropsychology. In South Africa, where the population is diverse in terms of language, culture, literacy and socio-economic status, Luria’s approach is a suitable one, while the use of standardised psychometric tests has limited value. But in the UK, for example, the use of standardised assessments has more value as this population is more homogenous.
Because neuropsychology is still a young science, and because its official professional status is still evolving in relation to the other, more established psychological categories, whether a person is able to register as a neuropsychologist depends in part on his/her country of residence. In South Africa, the Professional Board for Psychology of the Health Professions Council has established a professional category for neuropsychology, and the training requirements for registration in this new category are now being finalised. In addition, aspirant neuropsychologists may undergo a certification process run by the South African Clinical Neuropsychological Association (SACNA), which is currently the only body that credentials neuropsychologists in South Africa.
•There is a special relationship between the brain and the mind.
•Neuropsychology is the branch of psychology that tries to understand how brain structure and function relate to psychological processes and behaviour.
•Psychiatry is a medical speciality in the diagnosis and treatment of mental illness and emotional disorders.
•Historically, brain structures (neurological) were viewed separately from brain functions (psychiatric). Neuropsychiatrists specialise in the psychiatric or functional aspects of ’structural’ neurological disease.
•Neuropsychology attempts to describe the mental changes that result from structural changes in the brain. Clinical neuropsychology focuses on cognitive rather than emotional disorders.
•In the 1860s, Broca identified a part of the brain where language production was located.
•Further research focused on trying to localise other mental functions; Wernicke localised the ability to understand speech to the temporal lobes.
•This research led to the idea that all mental functions could be located in particular places in the brain; however, other theorists proposed that the brain functioned as an integrated holistic unit.
•Luria argued that both these views were partially right; he argued that mental abilities were combinations of many low-level or basic functions.
•Cognitive psychology provided a way to divide cognitive capacities into smaller processing units, analogous to computer-based operations.
•However, computer-based models have not been useful for the instinctual and subjective aspects of mind; molecular-biological, ethological and psychoanalytical theories might be more appropriate here.
•For more than a century, neuropsychological research was based on clinico-anatomical correlation.
•After the world wars, X-rays were used for visualising the location of foreign bodies and skull fragments embedded in the brain.
•Brain imaging techniques have developed rapidly, allowing the soft tissue inside the skull to be visualised while the person is still alive. Techniques include computerised tomographic (CT) scanning, magnetic resonance imaging (MRI) and functional brain imaging (positron emission tomography (PET) and functional MRI (fMRI)).
•Looking at an image from a PET or fMRI scan, one is able to see how active certain parts of the brain are when a person is performing a task.
•The specialist neuropsychologist takes an integrated (quantitative and qualitative) approach in assessment.
•The aim is to identify a particular pattern of cognitive symptoms and signs that makes clinico-anatomical sense, thereby integrating the observable clinical picture, via its causal mechanism, with the underlying neuropathology.
•In a quantitative approach, a standardised battery of tests is used to measure the patient’s performance across a range of mental functions; these are compared to an established population norm.
•In practice, the quantitative and qualitative approaches overlap.
•Neuropsychology is still a developing discipline in South Africa.
•Michael Saling has developed a qualitative, Luria-based approach to neuropsychological assessment.
•Because of South Africa’s diverse population, Luria’s approach is more suitable.
•The Professional Board for Psychology of the HPCSA has established a professional category for neuropsychology.
•Certification is conducted by the South African Clinical Neuropsychological Association (SACNA).
Both the nervous system and the endocrine system affect our feelings, thoughts and behaviour, but the brain, in particular, has a pivotal role to play. Apart from describing these systems, this chapter has briefly outlined the history of neuropsychology and the main debates in this area. It has described neuropsychological research methods, analysed both the qualitative and quantitative approaches in clinical neuropsychology, and explained the area of neuropsychology in South Africa. These days no-one can afford to overlook the role of neuropsychology in the field of psychology, as each day researchers are linking what we know about people to certain areas of brain functioning. Because there is a huge demand for neuropsychological expertise in this country, it is hoped that some psychology students will devote their psychological skills and energies to this absolutely fascinating profession.
acetylcholine (ACh): a neurotransmitter that is involved with muscle movement, as well as learning and memory
action potential: the state of a neuron when something causes the permeability of its cell membrane to change, allowing sodium ions to rush into the cell, which results in the generally negative charge of the cell becoming more positive
adrenal cortex: an adrenal gland that regulates salt and carbohydrate metabolism
adrenal glands: glands that are made up of the adrenal medulla and the adrenal cortex
adrenal medulla: an adrenal gland that prepares the body for the fight-or-flight reaction to stress
amygdala: a part of the limbic system that is involved in learning, experiencing emotion, remembering emotional events and recognising fear in other people
association areas: areas of the cerebrum that are involved in the more complex mental functions
autonomic nervous system: a division of the peripheral nervous system that controls the muscles involved in mainly involuntary actions, such as heartbeat
autopsy: a detailed dissection and examination of a body, or parts of a body, after death
axon: that part of a neuron that transmits the electrical impulse or message to other neurons
axon terminal: the part of a neuron where an electrical impulse or message passes to another neuron
basal ganglia: parts of the limbic system that are involved in movement
brain: the ’centre’ of the central nervous system, which is responsible for higher nervous functions
brain imaging: imaging techniques where images of the soft tissue within the skull (the brain) are obtained
brain pathology: the study of the causes and nature of brain diseases and dysfunctions
Broca’s area: a particular part of the frontal lobes in the left hemisphere which, in most people, results in a loss of language if damaged
cerebellum: a part of the hindbrain that is responsible for coordinated movement, balance and posture, as well as being involved in some kinds of learning
cerebral cortex: the outermost layer of the cerebrum
cerebrospinal fluid: the fluid in which the brain floats, which nourishes the brain and protects it from bumps and knocks
cerebrum: the most complex section of the forebrain, comprising the frontal, temporal, parietal and occipital lobes
clinical neuropsychology: a discipline within neuropsychology that focuses on cognitive disorders and is mainly concerned with diagnosing and managing the mental aspects of neurological disease
clinico-anatomical correlation: a method used to detect localisations in the brain, whereby inferences of a relationship between a mental function that was lost and a damaged part of the brain when an autopsy was done are made
computerised tomographic (CT) scanning: an imaging technique where X-rayed images of cross-sections of the brain are combined into a three-dimensional image of its structure
corpus callosum: a thick band of tissue that connects the two hemispheres of the brain and allows communication between them
dendrites: those parts of a neuron that receive messages from other neurons
depolarisation: a process that occurs when the threshold of excitation in a neuron is reached and the permeability of the cell changes, causing sodium ions to rush into the cell
dopamine: a neurotransmitter found especially in the limbic system, the cerebellum and the basal ganglia of the brain, which is involved in thought disorders such as schizophrenia and movement disorders such as Parkinson’s disease
dynamic localisation: an argument put forward by Luria that complex mental functions are produced by dynamic ’neural networks’ made up of components in the brain as opposed to static ’centres’
endocrine system: the system of hormones and glands in the body
excitatory neurotransmitters: neurotransmitters that start the action potential in a neuron
forebrain: a part of the brain that is made up of the thalamus, the hypothalamus, the limbic system, the basal ganglia and the cerebrum, and which is involved in many of the activities that we consider to be human activities, such as complex cognitive functions, emotions and sensory processes
functional brain imaging: an imaging technique where images of the soft tissue within the skull are obtained while a person is performing certain functions or being exposed to certain stimuli
functional magnetic resonance imaging (fMRI): an imaging technique using magnetism where cross-sectional images of the brain are combined into three-dimensional images of its structure while a person is performing certain functions or being exposed to certain stimuli
gamma amino butyric acid (GABA): an inhibitory neurotransmitter that is implicated in emotion, anxiety, arousal and sleep
hindbrain: a part of the brain that is made up of the medulla oblongata, the pons, the cerebellum and portions of the reticular formation
hippocampus: a part of the limbic system that is responsible for certain kinds of memory
hypothalamus: a part of the forebrain that controls the pituitary gland and is involved in emotions, regulating body rhythms for sleep, sexual activity, temperature regulation, hunger and thirst
inhibitory neurotransmitters: neurotransmitters that stop the action potential in a neuron
lateralisation: the specific functions for which each hemisphere of the brain is responsible or dominant
limbic system: a number of structures in the forebrain that are involved in emotion, memory, learning and motivation
localisation: the idea that mental functions could be located in particular places in the brain
magnetic resonance imaging (MRI): an imaging technique using magnetism where cross-sectional images of the brain are combined into a three-dimensional image of its structure
medulla oblongata: a part of the hindbrain that is responsible for breathing, circulation, heart functioning and other involuntary behaviours such as vomiting, coughing, sneezing, hiccupping and blinking if something flies towards the eye
meninges: membranes that surround the brain, which serve to protect the brain and store the cerebrospinal fluid
motor cortex: the primary area in the frontal lobes that is responsible for movement, which receives information from the spinal cord, the cerebellum and the basal ganglia, and is involved in voluntary movements such as walking, jumping, running and threading a needle
multiple sclerosis: a disease that breaks down neurons’ myelin sheaths and uncovers parts of their axons, which affects the transmission of messages that travel from the brain to the muscles
myelin sheath: a coating around an axon that serves to insulate the axon and make the message stronger and faster
neurologist: a medical doctor who specialises in the disorders of the nervous system
neurology: the branch of medicine that deals with disorders of the nervous system
neuropsychiatry: the field of medicine that specialises in the structure and function of the brain, and how they relate to psychological processes and overt human behaviour
neuropsychologist: a non-medical specialist who deals with the structure and function of the brain, and how they relate to psychological processes and overt human behaviour
neuropsychology: the branch of psychology that combines with neurology to investigate how the structure and function of the brain relates to psychological processes and overt human behaviour
norepinephrine: a neurotransmitter that is derived from epinephrine (adrenaline), and which is involved with arousal, mood, eating and sleeping
occipital lobes: parts of the cerebrum that are located at the back of the brain and are responsible for vision
pancreas: organ in the abdomen that produces hormones (as part of the endocrine system) and digestive enzymes (as part of the digestive system)
parasympathetic system: a division of the autonomic nervous system that, once the body has reacted to a stressor by either fighting or running away, inhibits the action and relaxes the body
parietal lobes: parts of the cerebrum that are responsible for the sense of touch, the detection of movement, the ability to locate where something is in space, and the ability to perceive how one’s body is located in space
pituitary gland: the master gland that regulates all the other glands in the body, and which is also responsible for growth, and the regulation of the salt and water metabolism
pons: a part of the hindbrain that acts like a relay station, sending signals from the spine to the brain and from the brain to the spine
positron emission tomography (PET): a nuclear medicine technique where, as a result of injecting small quantities of radioisotopes into a person that find their way to the brain, early warning signs of diseases of the brain can be detected
primary areas: areas of the cerebrum that process raw sensory information
psychiatrist: a medical doctor who specialises in the prevention, assessment, diagnosis and treatment of mental illness and emotional disorders
psychiatry: the medical speciality that deals with the prevention, assessment, diagnosis and treatment of mental illness and emotional disorders
psychologist: a person who has undergone extensive training in order to study and assess the mental processes and behaviour of humans and animals
psychology: the study of the mental processes and behaviour of humans and animals
refractory period: the period when the membrane potential of a neuron returns to the state in which it was initially, waiting for the next depolarisation incident
research neuropsychology: a discipline within neuropsychology that is interested in how mental functions are organised in the brain, and what the study of the brain can reveal about the organisation of the mind
resting potential: a neuron’s resting state when it is mainly negatively charged, with its surrounding fluid being mainly positively charged
reticular formation: a structure in the hindbrain and midbrain that connects to all the areas of the brain and is responsible for arousal and sleep/wake consciousness
serotonin: a neurotransmitter that is involved in mood, sleep, eating and arousal
soma: the body of a neuron
somatic nervous system: a division of the peripheral nervous system that controls voluntary movement by controlling all the muscles attached to your bones
somatosensory cortex: an area in the parietal lobes that receives sensory information from the body
spinal cord: the part of the central nervous system that is responsible for sending and receiving messages from the muscles and the sensory organs of the body
sympathetic nervous system: a division of the autonomic nervous system that is used to get the body ready for action (whether this is fighting or running away)
synapse: the region where two neurons meet
synaptic gap: the space between the terminal buttons of one neuron and the dendrites of a second neuron
temporal lobes: parts of the cerebrum that are on the sides of the brain and are mainly responsible for hearing and language, but are also involved in visual association
thalamus: the first structure in the forebrain to process incoming sensory information before relaying it to the appropriate area of the brain for further processing
thyroid gland: a gland that is responsible for metabolism
vesicles: small sacs in neurons that contain neurotransmitters
Wernicke’s area: an area in the temporal lobes of the left cerebral hemisphere that is involved in the interpretation of speech
X-rays: images that are obtained by projecting electromagnetic rays into body tissues to varying degrees
Multiple choice questions
1.Neurons receive information from other neurons through their:
2.The purpose of the myelin sheath is to:
a)insulate the axon against cold
b)insulate the axon so that the neural messages remain strong and fast
d)route the neural impulse.
3.Vinesh is walking down the street one evening and sees someone following him. He starts feeling scared, his pupils widen, his heart rate speeds up, and he feels slightly sick in his stomach. What part of the nervous system is at work in this example?
a)the central nervous system
b)the nervous system
c)the parasympathetic nervous system
d)the sympathetic nervous system.
4.The period when a neuron cannot fire is called:
a)the refractory period
b)the all-or-none law
c)the action potential
5.Thandi was in an accident, during which a pipe entered her brain. Doctors find that some of her subcortical structures were damaged. When she awakes she has no fear of danger and does not recognise fear in other people’s faces. What area of the brain is likely to have been damaged?
6.Which of the following psychological abilities is usually disrupted after damage to Broca’s area?
7.The attempt to identify the ’seat’ of each mental function in a particular part of the brain is known as:
8.Which of the following methods has been in longest use in neuropsychology?
a)magnetic resonance imaging (MRI)
b)parallel distributed processing (PDP) models
9.Wernicke’s area is located in the __________________, and is involved in ______________
a)left hemisphere of the brain; language production
b)right hemisphere of the brain; the interpretation of speech
c)left hemisphere of the brain; the interpretation of speech
d)right hemisphere of the brain; language production.
10. Computerised tomographic (CT) scanning is:
a)an imaging technique where X-rayed images of cross-sections of the brain are combined into a three-dimensional image of its structure
b)an imaging technique where magnetic images of cross-sections of the brain are combined into a three-dimensional image of its structure while people are awake
c)an imaging technique where small quantities of radio-isotopes are injected into the brain
d)an imaging technique where X-rayed images of cross-sections of the brain are combined into a three-dimensional image of its structure while people are asleep.
1.Which neurotransmitters are involved in mood and how do they work?
2.Explain the function of the limbic system and describe what would happen if this area was damaged.
3.Design a table that allows you to list the areas of the cerebrum and to state the structures, functions and dysfunctions of each of these areas. Fill this table in.
4.What happens to a patient whose corpus callosum has been severed? What behaviour are you likely to see?
5.Why do the hormones sent out by the endocrine system affect the body more slowly than the nerve impulses sent out by the nervous system?
6.Describe the sorts of methods that are used in modern neuropsychology.
7.Discuss the localisationism versus equipotentialism debate.