Dissociable neural responses to facial expressions of sadness and anger

Previous neuroimaging and neuropsychological studies have investigated the neural substrates which mediate responses to fearful, disgusted and happy e xpressions, No previous studies have investigated the neural substrates whi ch mediate responses to sad and angry expressions. Using functional neuroim aging, we tested two hypotheses. First, we tested whether the amygdala has a neural response to sad and/or angry facial expressions. Secondly, we test ed whether the orbitofrontal cortex has a specific neural response to angry facial expressions. Volunteer subjects were scanned, using PET, while they performed a sex discrimination task involving static grey-scale images of faces expressing varying degrees of sadness and anger. We found that increa sing intensity of sad facial expression was associated with enhanced activi ty in the left amygdala and right temporal pole. In addition, we found that increasing intensity of angry facial expression was associated with enhanc ed activity in the orbitofrontal and anterior cingulate cortex. We found no support for the suggestion that angry expressions generate a signal in the amygdala, The results provide evidence for dissociable, but interlocking, systems for the processing of distinct categories of negative facial expres sion.