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Abstract

The amygdala has been associated with the perception of (and responses to) socially-relevant stimuli such as facial expressions, yet the relative roles of the component nuclei are largely unknown. Here, Rhesus macaques passively viewed blocks of faces or Fourier phase-scrambled images while being scanned in a 4.7 T magnet. Stimulus blocks contained the same 12 unfamiliar monkeys displaying one of three expressions (aggressive, neutral, or appeasing) with gaze/head position either directed or averted. Anatomically-defined regions of interest were applied to the eight-segment GE-EPIs (3s TR) acquired at a resolution of 1x1x2mm. The basolateral amygdala nuclei showed greater activation for aggressive than for appeasing expressions, irrespective of gaze, consistent with previous reports of amygdala sensitivity to threatening or fearful stimuli. Significant interactions between basolateral amygdala and temporal lobe neocortical areas were also observed. In contrast, the central nucleus showed greater responsivity to averted gaze, with no significant effects of expression. This unexpected result is nonetheless consistent with skin conductance response profiles in monkeys viewing these same stimuli (Mosher et al., 2006). The distinct response profiles seen in component amygdaloid nuclei may help to reconcile the dual roles attributed to amygdalar function, namely: detection of fearful stimuli and mediation of attentional/orienting responses.