The amygdala is known to influence processing of threat-related stimuli in distant brain regions, including visual cortex. The time-course of these distant influences is unknown, although this information is important for resolving debates over likely pathways mediating an apparent rapidity in emotional processing. To address this, we recorded event-related potentials (ERPs) to seen fearful face expressions, in preoperative patients with medial temporal lobe epilepsy who had varying degrees of amygdala pathology, plus healthy volunteers. We found that amygdala damage diminished ERPs for fearful versus neutral faces within the P1 time-range, approximately 100-150 ms, and for a later component at approximately 500-600 ms. Individual severity of amygdala damage determined the magnitude of both these effects, consistent with a causal amygdala role. By contrast, amygdala damage did not affect explicit perception of fearful expressions nor a distinct emotional ERP effect at 150-250 ms. These results demonstrate two distinct time-points at which the amygdala influences fear processing. The data also demonstrate that while not all aspects of expression processing are disrupted by amygdala damage, there is a crucial impact on an early P1 component. These findings are consistent with the existence of multiple processing stages or routes for fearful faces that vary in their dependence on amygdala function.
(c) 2009 Wiley-Liss, Inc.