Where does fear come from?

Fear often becomes fear as a burden, and most want to get rid of it. Unfortunately there is no quick solution for that. Yet it is possible to follow a strategy that allows you to overcome your unnecessary fears. To build such a strategy, you must consciously deal with your fears, and therefore it is useful to know where they come from. That is why we now provide a brief overview of what we know about the neurobiology of anxiety. We structure this information into three topics:

1. Two types of fear.
2. How is a fear-triggering stimulus processed?
3. The brainstem, our primitive brain.

 

1. Two types of fear

There are two types of fear: state anxiety and trait anxiety. Strictly speaking, only state anxiety is important for cycling. State anxiety is evoked by a stimulus, and trait anxiety is constantly present, independent of the presence of a fear-triggering stimulus. Typical fear-triggering stimuli while cycling are other road users, objects on the road, and images that indicate that one is getting off the road.

Trait anxiety is a person characteristic: some people are on average more anxious than others, and they are so independent of the environment in which they find themselves (i.e., the stimuli with which they are confronted). People with a high trait anxiety are more often afraid of a stimulus and their anxiety is more intens. In other words, state anxiety depends on trait anxiety. That is why trait anxiety is also indirectly important for cycling: cyclists with a high trait anxiety are more likely to suffer from anxiety.

 

2. How is a fear-triggering stimulus processed?

Processing a fear-triggering stimulus involves two steps: (1) detecting, and (2) responding. These two steps are performed by different brain regions, with the first brain area (for detection) activating the second (responding). Detecting dangerous stimuli is done by the amygdala. The amygdala can detect dangerous stimuli thanks to its learning ability: a stimulus that initially did not evoke fear (e.g., a cyclist in front of you who brakes hard), does so after being associated with a painful experience (e.g., a fall as a result of a collision with that cyclist). The learning process within the amygdala involves that, as a result of the association between the neutral stimulus and the painful experience, new connections are made between specialised neurons within the amygdala.

When the amygdala is activated, it sends signals to two other brain areas that are responsible for the response to the stimulus: the hypothalamus and the periaquaductal gray, and especially the latter is important for cycling. In response to the signal from the amygdala, the hypothalamus causes a series of bodily changes: higher breathing rate, increased blood circulation in the skin, increased muscular tension, etc. The periaquaductal gray can evoke a so-called “freeze” reaction, a stiffening of the whole body. If you are riding on a bicycle and you are frightened of something, then such stiffening is the last thing you are waiting for: the subtle movements that are necessary to steer away and thus avoid any danger are made impossible by that stiffening. In this way the cyclist ends up in a vicious circle: the impossibility of avoiding a possible danger (as a result of the stiffening) creates even more fear, and that in turn provides even more stiffening. This also applies to the automated movements that are under the control of the cerebellum: activation of the periaquaductal gray closes off the cerebellum from the sensory feedback that is needed to control the motor cortex.

 

3. The brainstem, our primitive brain

The periaquaductal gray is part of the medulla oblongata, which in turn is part of the brainstem. The brainstem is a structure that can also be found in most lower animal species (e.g., fish and reptiles). The big difference between the brains of lower animal species and that of humans is in the cortex (the brown-pink part in the picture on the right): relative to his body weight, man has a larger cortex. The cortex contains structures that we call upon for staying upright and steering: the motor and the prefrontal cortex. We need our cortex to make fine controlled movements. Lower animal species usually have no arms and legs with which they can make fine controlled movements, and therefore they do not need such a highly developed cortex. In comparison with humans, lower animal species rely much more on their brainstem for controlling their movements. The brainstem can also control movements in humans, but in the course of evolution two important changes occurred in this control: (1) the motor cortex can directly control the muscles without the intervention of the brainstem, and (2) the prefrontal and the motor cortex control the motor areas in the brainstem.

The processing of fear-triggering stimuli has undergone a similar evolution, from pure control by the brainstem to a predominant control by the cortex. The control by the cortex starts with the detection of a dangerous stimulus by the amygdala. Unlike the brainstem, the amygdala is able to detect complex dangerous stimuli. The brainstem can only detect very simple stimuli (including rapid movements), and therefore lacks the precision that is needed to make the distinction that is often needed to survive (e.g., to be able to distinguish a dormant from an awake tiger). It is surprising that the amygdala (a part of the cortex) does not control the motor cortex but the periaquaductal gray (a part of the brainstem). This means that the amygdala uses an evolutionary old brain structure to trigger the fear response.

The above does not mean that our fear responses are fully dictated by a cortical detection mechanism (the amygdala) and a primitive reaction mechanism in the brainstem (the periaquaductal gray), and this is good news for cyclists with fear. During evolution, the role of the prefrontal cortex has increased, and this affects both the amygdala and the periaquaductal gray. The prefrontal cortex can prevent the amygdala from rushing to conclusions and the periaquaductal gray from reacting too quickly. In this way, the prefrontal cortex allows us to overcome unnecessary fears.