Not Too Much, Not Too Little: New Discoveries on How Our Brains Regulate Fear

A pack of wolves hunting a, presumably fearful, bison.

A pack of wolves hunting a presumably fearful bison.

Human history is full of praise for brave people and often downplays fearful individuals.

But our inclination to perceive fear as a flaw of character does not do justice to the relevance of this feature for human survival and evolution. This deeply wired emotional reaction has played a central role in helping animals like us to stay alert, avoid threats, and preserve our overall well-being.

Fear can be as simple as a reflexive fight-or-flight response to encountering a dangerous predator in nature, or as complex as modern-day anxiety disorders.

This innate response for coping with perceived danger is so important for our lives that it can be detrimental if unbalanced, whether it is lacking or in excess.

Unbalanced levels of fear can lead to several undesired conditions, including stress and anxiety, excessive risk-taking and difficulties in the pursuit of important needs. Thus, abnormal levels of fear can significantly affect people’s lives for the worse. But how can the mind know and adjust the appropriate level of fear in each context? This has been an unanswered question for a long time, but scientists just took a new step towards answering it.

Fear has the power to evoke strong bodily reactions, including changes in heart and breathing rates, as well as behavioral and emotional responses.

Our brain becomes hyperalert, our pupils dilate, we breathe faster, and our blood pressure increases. Non-vital organs, such as those in the gastrointestinal system, slow down, so our body can focus on whatever the threat is.

Curiously, some of the main chemicals involved in this chain of effects are also present in other intense emotional states, such as happiness and excitement. Through reasoning, our thinking brain analyses the context and signals to our body whether we should be terrified or not. Thus, context is key. More precisely, perceived context is key.

The hippocampus and prefrontal cortex of the brain are central in the interpretation of perceived threats, helping in the assessment of whether the danger is real.

The hippocampus is closely connected with the amygdala, an almond-shaped region of the brain dedicated to detecting the emotional relevance of different stimuli.

The fear response starts in the amygdala, so, for instance, if you encountered a lion in the wild, you would typically become hyperalert and trigger a fight-or-flight response. But if your brain interprets the situation as safe – say, you’re in a zoo and the lion can’t harm you – you might respond with other emotions, such as curiosity and excitement. This happens because the hippocampus and prefrontal cortex inhibit the fear response from the amygdala, basically providing chemical reassurance to your body that you are ok.

The human amygdala.

The human amygdala.

The amygdala modulates fear responses in humans and other animals.

Several brain imaging studies have found that fearful stimuli activate the amygdala. When this happens and we experience stress, our brains release two kinds of stress hormones, cortisol and adrenaline, preparing our bodies to fight or flee the situation. These hormones increase blood flow to muscles, increasing our strength and speed, expand our airways so we can breathe more intensely, increase blood sugar for immediate energy release, dilate pupils to improve our vision for faster responses, and so on. But even though this physiological program was inarguably useful to early humans, it can be problematic in the modern world if it becomes overly activated when relatively minor situations such as stress from office work or family arguments are perceived as threats to our survival.

Illustration of internal fear.

Illustration of internal fear.

That is why the mechanisms behind how the mind and body work together to balance fear within an adequate range have intrigued scientists for such a long time.

The insular cortex – a small lobe folded deep within the cerebral cortex – acts in the processing of bodily signals, and previous research suggested that it might also play a role in fear maintenance and extinction.

In a recent study, Dr. Alexandra Klein, from the Circuits for Emotion Research Group, at the Max Planck Institute of Neurobiology, in Germany, and colleagues investigated this topic through a series of experiments conducted in mice. They observed that the insular cortex plays an important parallel role in either enhancing or suppressing fear, by using bodily feedback signals to assess the internal fear-state of the animal.

In other words, the insular cortex of the brain uses bodily signals to regulate fear responses. Because of the similarities in how our brains and the brains of other mammals, like mice, process fear, this bodily feedback mechanism may have huge therapeutic potential for anxiety disorders in humans.

Coincidentally, the insular cortex has long been known to be responsible for our body homeostasis – the state of steady internal, physical, and chemical conditions necessary for survival. Now we know that this same brain region is also responsible for our emotional homeostasis, which is an interesting, albeit not surprising, link between the physical and mental makeup of the human being.

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