Anxiety: A Very Short Introduction - Daniel Freeman, Jason Freeman 2012

The three-systems theory of anxiety
What is anxiety?

Anxiety sets in motion a series of physiological changes, all designed to help us focus entirely on dealing with the sudden threat to our existence. These changes are associated with what is known as the autonomic nervous system (ANS), whose job is to oversee basic physiological processes — for example, breathing, temperature regulation, and blood pressure. The ANS comprises two complementary subsystems: the sympathetic nervous system (SNS), which prepares the body to respond to danger; and the parasympathetic nervous system (PNS), which controls and counterbalances the frenzied activity of the SNS.

So, for example, the sympathetic nervous system elevates our heart rate, allowing blood to reach our muscles faster (by as much as 1,200% in some instances). Our pupils dilate, relaxing the lens and allowing more light to reach the eye. The digestive system is put on hold, resulting in reduced production of saliva — hence the dry mouth we often experience when we’re afraid. And new research suggests that the facial expression people typically assume when frightened — eyes wide open, nostrils flared, eyebrows raised — actually helps us see better and detect scents more efficiently: attributes that could make all the difference in dangerous situations. Without fear and anxiety, humans would surely have disappeared long ago. After all, creatures that cannot recognize danger and respond accordingly are well suited only to being someone else’s prey, as the dodo would doubtless attest.

As we’ve seen, Darwin emphasized the way in which we express our emotions. But though this is clearly a crucial component, it doesn’t tell the whole story. There is more to emotions than the configuration our facial features assume, or the way we hold our body. This is what the psychologist Peter Lang was getting at when he formulated the ’three-systems’ model of anxiety. According to Lang, anxiety manifests itself in three ways:

1. What we say and how we think: for example, worrying about a problem, or voicing fear or concern.

2. How we behave: avoiding certain situations, for instance, or being constantly on guard against trouble.

3. Physical changes: for example, elevated heart beat or faster breathing, and facial expression.

These three systems are only loosely interrelated. If we want to know whether someone is anxious, we can’t base our judgement simply on what they tell us about how they’re feeling; they may cover up their true emotions, or even be unaware of them. Similarly, the fact that someone engages in an activity doesn’t mean they’re not anxious about it (just as a person might avoid doing something for any number of reasons other than fear). And it’s quite possible to be anxious without feeling as if your stomach is tied in knots or that your heart is about to pound its way through your chest.