Neural feel for seeing: emotion may mold early visual activity in brain.

We don't just react emotionally to what we see. What we see is shaped by what we feel, a new study suggests.

When looking at faces displaying fearful expressions, people with intact brains or with brain damage that spares the amygdala, an emotion-regulating neural structure, exhibit pronounced activity in certain parts of the brain that deal with visual information, say neuroscientist Patrik Vuilleumier of the University of Geneva in Switzerland and his colleagues. People respond to neutral faces with less activity in these visual-cortex areas.

Moreover, when people with amygdala damage view fearful faces, they show sparse activity in these areas, the scientists report in the November Nature Neuroscience. People with the most-extensive tissue loss in the amygdala display the least activity.

Taken together, the results indicate that the amygdala uses its connections to far-flung areas of the brain to shape the visual perception of fearful objects, according to Vuilleumier's group. "Enhanced activation to fearful stimuli in distant sensory regions depends on amygdala function" the scientists conclude.

Yet, in a separate trial, people with amygdala damage recognized the emotion depicted in faces displaying any of six expressions, including fear.

Vuilleumier and his coworkers studied 26 people who had brain-damaging epilepsy. Over many years, the disease had left half of them with varying degrees of amygdala damage; in the rest, neural losses had spared the amygdala. The team also studied 13 participants with healthy brains.

The scientists used a functional magnetic resonance imaging (fMRI) scanner to measure blood flow throughout the brains of participants as they viewed a sequence of images on a computer screen. Each image contained a pair of faces and a pair of houses, with one pair aligned vertically and the other horizontally. Both faces in a pair showed either a fearful or a neutral expression.

Participants were told to pay attention only to vertically aligned pairs on half the trials and only to horizontally aligned pairs on the rest.

When paying attention to fearful faces, only the participants with an intact amygdala displayed substantial blood flow, a sign of robust neural activity, in visual-cortex areas implicated in the brain's initial responses to visual information, including one area specific to images of faces.

When looking at houses and neutral faces, individuals with amygdala damage exhibited the same pattern of brain activity as did those without it.

Researchers now need to investigate how perceptions of emotional faces differ between people with amygdala damage and healthy individuals, remarks neuroscientist Ralph Adolphs of the University of Iowa in Iowa City, in a comment published with the new study.

People with amygdala-linked mental disorders such as mania and depression may perceive facial expressions differently than others do, thus fostering their previously reported tendency to misread others' intentions, Adolphs theorizes.