Carbon dioxide can provoke fear

February 4th, 2013 by Nature

Zawadi Mungu at Oregon Zoo breathes out C02 as he yawns on 8 January 2012 (click image to expand - image courtesy of Major Clanger Flickr photostream, published under creative commons license)

The amygdala, a small region of the brain, is not necessarily required for fear and panic in people, according to a study published in the paper ‘Fear and panic in humans with bilateral amygdala damage‘ in the journal Nature Neuroscience.

These results are surprising, because decades of research in humans and animals had suggested that the amygdala has an influential role in fear.

To show this, Jon Wemmie and colleagues tested three rare patients with damage to their amygdala, who do not experience fear.

Inhaling carbon dioxide (CO2) stimulates breathing and can provoke fear and even trigger panic attacks, as was experienced by the three patients in this study.

For one of the patients, it was the first time since childhood that she had experienced fear.

Previous work, with this patient and others with similar damage, had suggested that damage to the amygdala resulted in a lack of fear in response to a variety of fear-provoking stimuli, even life-threatening traumatic events.

The current findings from Jon Wemmie and colleagues indicate that there are conditions in which the amygdala is not necessary for the expression of fear.

The authors do not know why CO2 can provoke fear without the amygdala when other stimuli cannot.

However, most things that provoke fear are sensed by the visual and auditory pathways, which project to the amygdala.

In contrast, high levels of CO2 are sensed by receptors in the brainstem and can cause a range of physiological changes, which could activate several different brain areas in addition to the amygdala.

1 Response to “Carbon dioxide can provoke fear”

  1. Maria

    1. The response to CO2 inhalation is PHYSIOLOGICAL, which means that this is a systemic response from your body to get Oxygen. If you were having a heart attack and you didn’t have an amygdala you would still have all the symptoms and response that are normal, and could die. All of this without being afraid for your life.
    2. These patients NEVER felt fear (not since their childhood…), so they can’t possibly know how it feels.

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