A PATIENT who cannot read fear on other people鈥檚 faces has given researchers a valuable clue to how the human brain processes emotions. Her confusion shows for the first time that the brain processes fear and mixed emotions through a different pathway from those used to process other feelings.
The woman, known as S. M., has a rare disease which has damaged the amygdala region of her brain. She also has problems perceiving other 鈥渘egative鈥� emotions, such as anger and surprise, if expressed at the same time.
The amygdala is an almond-shaped structure at a crossroads in the brain鈥檚 circuitry: it links the cortex, which is responsible for conscious thought, with regions of the brain that control the body鈥檚 emotional responses. 快猫短视频s knew that the amygdala helps regulate reactions associated with strong emotion 鈥� such as quickened heart rate and sweating. But what exactly does it do?
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Brain researchers determine the function of a part of the brain by studying people whose brains are damaged in that region. But patients with damage to the amygdala alone are very unusual, according to Antonio Damasio of the University of Iowa, who led the team that made the new discovery.
S. M. first turned up at a hospital suffering from epilepsy. Later, when her doctors looked for the root of the problem using magnetic resonance imaging, they found that her amygdala was destroyed. This was the result of Urbach-Wiethe disease, which deposits calcium in the amygdala. With S. M.鈥檚 consent, the Iowa researchers subjected her to a battery of psychological tests devised by Damasio鈥檚 colleague Ralph Adolphs, asking her to say what emotions were being expressed by the people pictured in a series of photographs.
S. M. failed what Damasio calls 鈥渢he Doris Day test鈥�. 鈥淲hen we showed her a film clip of Doris Day screaming, she asked, 鈥榃hat is she doing?鈥�,鈥� he says. In fact, S. M. was baffled by any picture showing a fearful expression. She also had problems deciphering mixtures of negative emotions, such as anger and surprise. By contrast, she had no difficulty with 鈥減ositive鈥� emotions such as happiness. She was also perfectly able to recognise familiar faces (Nature, vol 376, p 669).
These results, says Damasio, indicate that the amygdala has a pivotal role in linking frightening signals from the environment with the body鈥檚 fear responses. Fear is universally important for survival in animals, Damasio notes, so it is reasonable that a special brain system has evolved to deal with it. The amygdala also seems to help us respond correctly to complex mixtures of negative emotions expressed by other people. Because she often fails to recognise criticism or aggression, S.M. has difficulty interacting socially.
Positive emotions seem to be processed in another region of the brain. Just where is a mystery. 鈥淲e鈥檝e never seen a patient who can鈥檛 recognise a happy face,鈥� says Adolphs.