Nature examines the biology of fear – and how researchers have succeeded in creating fear in the fearless:
Many studies on animals over the years have shown that the amygdala, a small, almond-shaped structure located deep inside the brain, is crucial for the fear response. This finding has been confirmed in studies of humans.
Justin Feinstein at the University of Iowa in Iowa City and his colleagues have now found that in certain situations the fear response may occur even in people who do not have a working amygdala. Their work is published online today in Nature Neuroscience.
One situation in which the amygdala triggers fear and panic attacks is when it detects unusually high concentrations of carbon dioxide — a sign of possible suffocation — by sensing increased acidity in the blood. This may occur even if CO2 is inhaled in concentrations that are not lethal. Feinstein and his colleagues therefore predicted that patients with damaged amygdalas would not feel fear after inhaling the gas.
To test this, they asked S.M., two other patients with Urbach-Wiethe disease, and 12 healthy controls to inhale 35% carbon dioxide through a mask. To their surprise, the researchers found that the brain-damaged patients did experience fear immediately after inhalation — and, in fact, became even more fearful and panicky than did the healthy volunteers.
“The patients experienced significantly more fear and panic than the controls,” says Feinstein. In interviews conducted afterwards, all three patients reported feeling scared of suffocating and dying while inhaling the gas. For S.M., this was the first time she had experienced fear since childhood.
No wonder dry ice looks so creepy.