Observing social gestures: an fMRI study.

We investigated the effects of social content of gestures on brain activation patterns. We used a 3 x 3 x 3 factorial design in an event-related functional magnetic resonance imaging experiment with participants observing gestures varied by type (fascist salute, wave, or arm lift), number of images shown at a time, and face frequency. We sought to determine whether increasing the social content of the gesture spreads activation from traditional sensorimotor regions engaged in mirror neuron activity to prefrontal regions concerned with social behavior. Results indicate that viewing a highly provocative gesture (fascist salute) compared to a less provocative but still socially meaningful gesture (wave) reveals activation in prefrontal and limbic areas. In addition, as expected there was more inferior frontal gyrus activation when participants observed a greater number of gesturing actors. Additionally, the psychological characteristics of shame and defeat affected activation in the inferior parietal lobe, which is part of the mirror neuron system, for the fascist salute compared to the wave contrast. We conclude that observing social gestures activates social- and emotion-processing areas of the brain, and the activation varies depending on the observer's psychological characteristics.