Emotional valence modulates activity in the posterior fusiform gyrus and inferior medial prefrontal cortex in social perception.

Previous studies have shown that during the presentation of emotionally loaded visual stimuli, activity increases in the visual and limbic cortices. This study focuses on empathic reactions induced by presenting pictures of situations and facial expressions from a "third party" point of view only. We measured regional changes in blood flow (rCBF) in nine healthy subjects while they were looking at neutral, positive, or negative emotional pictures of low (facial expressions) and high (persons in real-life situations) social complexity. A significant rCBF increase occurred in the right posterior fusiform gyrus during presentation of emotional pictures of both low and high social complexity. We also observed an interaction between emotionality and social complexity in the left inferior occipital gyrus for situations, where emotionality produced a significantly larger rCBF increase for situations than faces. No significant rCBF changes were observed in the amygdala or other parts of the limbic system. A significant rCBF decrease was found in the right inferior medial prefrontal cortex during presentation of the emotional pictures. This is discussed with respect to the "default mode of the brain" theory. We suggest that there is a neural network in the posterior fusiform and inferior occipital gyrus specialized in identifying emotionally important visual clues. Messages from this and other areas converge to the medial prefrontal cortex, to be evaluated in terms of relevance for attention. We believe that this is a crucial part of a network used in normal empathic reactions and social interactions.