3.3 Neurobiology of Learning and Memory - Learning and Memory

MCAT Behavioral Sciences Review - Kaplan Test Prep 2021–2022

3.3 Neurobiology of Learning and Memory
Learning and Memory

LEARNING OBJECTIVES

After Chapter 3.3, you will be able to:

· Describe neuroplasticity and changes that occur throughout the human life span

· Recall the terms involved with removing and strengthening memory connections

Even as you read this text, your brain is changing. Memory, and therefore learning, involves changes in brain physiology, such that with each new concept you learn your brain is altering its synaptic connections in response. You may have heard that it is far easier for children to learn a new language than it is for adults. Indeed, the cliché you can’t teach an old dog new tricks, while not strictly true, does have its roots in neurobiology.

As infants, we are born with many more neurons than we actually need. As our brains develop, neural connections form rapidly in response to stimuli via a phenomenon called neuroplasticity (also known as neural plasticity). In fact, the brains of young children are so plastic that they can reorganize drastically in response to injury, as evidenced by studies of children who have had entire hemispheres of their brains removed to prevent severe seizures. The remaining hemisphere will change to take over functions of the missing parts of the brain, allowing these children to grow up to lead essentially normal lives. While our brains do maintain a degree of plasticity throughout our lives, adult brains display nowhere near the degree of plasticity as those of a child. Another way our brains change is through a process called synaptic pruning. As we grow older, weak neural connections are broken while strong ones are bolstered, increasing the efficiency of our brains’ ability to process information.

This concept of plasticity is important because it is closely linked to learning and memory. As you learned in Chapter 4 of MCAT Biology Review, stimuli cause activation of neurons, which release their neurotransmitters into the synaptic cleft, the gap between a neuron and a target cell. These neurotransmitters continue to stimulate activity until degradation, reuptake, or diffusion out of the synaptic cleft. In the interim, this neural activity forms a memory trace that is thought to be the cause of short-term memory. As discussed earlier, if the stimulus isn’t repeated or rehearsed, the memory trace disappears, and the consequence is the loss of the short-term memory. However, as the stimulus is repeated, the stimulated neurons become more efficient at releasing their neurotransmitters and at the same time receptor sites on the other side of the synapse increase, increasing receptor density. The strengthening of neural connections through repeated use is known as long-term potentiation, and is believed to be the neurophysiological basis of long-term memory.

MCAT Expertise

Recent research has begun to elucidate the mechanism of long-term potentiation. It has been observed that a specific type of glutamate receptor, the NMDA receptor, is required for the strengthening of synaptic connections.

mnemonic

The word potentiate means to increase the potency or strength of something. Long-term potentiation can be thought of as the strengthening of a "long-term" synaptic connection.

As described in the previous section, a memory begins its life as a sensory memory in the projection area of a given sensory modality. This sensory memory is brief, unless maintained in consciousness and moved, as a short-term memory, into the hippocampus in the temporal lobe. The memory can then be manipulated through working memory while in the hippocampus (in tandem with the frontal and parietal lobes), and even stored for later recall. Over very long periods of time, memories are gradually moved from the hippocampus back to the cerebral cortex. Note that this general pathway is a drastic oversimplification of the complex interplay of brain regions involved in memory, but is a useful paradigm for Test Day.

MCAT Concept Check 3.3:

Before you move on, assess your understanding of the material with these questions.

1. What is neuroplasticity? How does neuroplasticity change during life?

2. What is the term for removing weak neural connections? What is the term for strengthening memory connections through increased neurotransmitter release and receptor density?

o Removing weak connections:


o Strengthening connections: