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Abstract:
According to recent studies, both humans and macaques share face-selective brain regions. Among the active regions in the monkey, the anterior STS, and to a lesser degree TE, contain neurons selective to facial expressions and gaze or head direction. Results from human fMRI suggest the STS is sensitive to gaze direction, whereas the amygdala is the hallmark region showing activity for facial affect, particularly negative affect. To clarify which brain regions, if any, may be biased towards the processing of facial expressions or gaze/head direction, we presented blocks of face stimuli or Fourier-phase scrambled images to the awake Rhesus macaque placed in a 4.7 T magnet. The stimulus blocks contained images of the same 12 monkeys, grouped by gaze/head direction (towards or away) and facial expression (aggressive, neutral, or appeasing), for a total of 6 face groups and 6 corresponding scramble groups. Eight-segment GE-EPIs (3s TR) were obtained at a resolution of 1x1x2mm, smoothed with a Gaussian kernel at 2mm FWHM. Regions of face activation from previous reports were subsumed by regions of activation in the present study: large extents of STS were active bilaterally from posterior regions near FST to anterior regions co-extensive with the amygdala. Anterior activation spread over the lip of STS into TE (peak activation for face versus scrambled images, T = 18.38). Aggressive facial expressions produced amygdala activation, whereas appeasing faces activated a patch in area TF. The overall STS face activation, and amygdala activation to aggressive stimuli are consistent with BOLD activity reported in humans; however, the extensive STS activity was, as a whole, not sensitive to gaze or facial expressions.
