Rapid and multiple-stage activation of the human amygdala for processing facial signals

Human faces transmit multiple valuable signals, and neuroimaging studies have shown that the amygdala is active in response to facial stimuli. However, little has been known about the temporal profile of amygdala activation during facial signal processing until recently. Here we review three recent studies conducted by our group in which we recorded amygdala intracranial electroencephalography in humans. The subjects were engaged in tasks that required automatic processing of faces, eye gazes and emotional expressions. Time-frequency statistical parametric mapping analyses revealed that the amygdala showed gamma-band activation in response to emotional expressions, gazes and faces, with peak latencies at about 100 ms, 200 ms and 250 ms, respectively. These results suggest that: (1) the amygdala performs multiple-stage processing in response to these facial signals using different visual input routes, and (2) amygdala activation for processing all of these facial signals is rapid, which could be prior to or simultaneous with conscious awareness of faces.