Fear is considered to be one of the oldest and most basic of emotions that humankind feels, and now a group of researchers may have discovered something new about it, as they have successfully caused fear in people who are thought to be fearless.

Fear is controlled by the amygdala, two small, almond-shaped areas in the centre of our brain that is responsible for most of our emotional responses. People with damaged amygdalas, either due to injury or disease, supposedly do not feel anything when confronted by objects or situations that promote fear in people with normal amygdalas.

This is the case with S.M., a woman who has undergone extensive studies ever since her amygdala was damaged by Urbach–Wiethe disease, a rare genetic disorder that impacted on her as a teenager. She is unable to feel fear when confronted by spiders, snakes, horror movies, or when threatened with a knife or at gunpoint. She is even incapable of recognizing fearful faces.

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In this latest study, she, along with two other women (identical twins), were asked to breathe in a mixture of air that included 35 per cent carbon dioxide (CO 2 ). Normal air only contains about 0.04% CO 2 , which is a good thing, since the gas is an 'asphyxiant' — our lungs will absorb it as easily as they absorb oxygen, but carbon dioxide doesn't provide the same benefit as oxygen (obviously), so if concentrations climb too high, this can lead to suffocation and death.

The control group (who all had normal amygdalas) suffered anxiety in anticipation of breathing in the CO 2 — sweating and having a higher heart-rate — but the asphyxiant effect of the gas is so pronounced that breathing in the CO 2 for just a short period of time caused panic attacks in 3 out of the 12 participants in the control group. This agrees with research that the amygdala specifically controls fear responses connected with external threats.

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Believing that the three women would not experience any fear at all, the researchers had them breathe in the same concentration. Amazingly, all three women experienced panic attacks, even with repeated testing, reporting higher levels of fear and panic than what the control group felt, and their physical responses were also more extreme than those of the control group.

According to the study, these results "indicate that the amygdala is not required for fear and panic," and that they "make an important distinction between fear triggered by external threats from the environment versus fear triggered internally by CO 2 ."

(Image courtesy: Iowa Neurological Patient Registry at the University of Iowa)

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