Abstract
The ability to process faces is valuable for social interaction, aiding identity judgment and emotional expression. As such, numerous brain regions play a role in face processing. fMRI experiments have demonstrated that the amygdala responds to face stimuli, but the role of the amygdala in the face processing network remains unknown. We used magnetoencephalography (MEG) to investigate the timing and directionality of spectral activity in the amygdala in response to faces. We measured brain activity with MEG while subjects viewed a series of face and object stimuli. Subjects performed a 1-back task, pressing a button if the face or object matched the image presented on the previous trial. We collected a total of 160 trials per category (face or object). We found that the amygdala responded more strongly to faces relative to objects within the first 200 ms in the beta (20-30 Hz) and low gamma (30-50 Hz) frequency bands. In the low gamma-band, amygdala activity was phase-locked to the fusiform gyrus during the first 200 ms, with a phase-slope index suggesting communication from the amygdala to the cortex during this temporal window. Previous studies have demonstrated that faces, emotional expression, and eye gaze all evoke gamma-band amygdala activity (Sato et al, 2013; Liu et al, 2015). Our results build on these earlier studies by demonstrating the timing and directionality of functional band-limited connectivity between the amygdala and visual cortex during face processing, and suggest that computations in the amygdala immediately following stimulus onset may be communicated to cortex for further processing at later points in time.