![]() ![]() ![]() This and other evidence suggests that the amygdala may play multiple roles in processing emotional faces: it may rapidly decode emotional content and then “reflectively” decode ambiguity in facial expressions ( 11). The amygdala has also been implicated in encoding the relevance of the expression to the self, responding more when an expression is perceived as more intense, rather than gaze direction per se ( 10). The lateral extended amygdala, which is more responsive to averted gaze than directed gaze, has been implicated in the perception of ambiguous stimuli ( 9). This is congruent with other analyses of amygdala function that have placed an emphasis on its role in processing of ambiguity or uncertainty rather than negative emotion per se ( 7) or in directing attention to stimuli whose consequences have become uncertain ( 8). Fear grins may represent a particularly ambiguous type of emotional stimulus because they can represent the submissive gesture of a social inferior or a fearful response to an external stimulus. It is tempting to speculate that this may represent some differential involvement of the amygdala in processing certain types of social and emotional stimuli. It is notable that processing of fear grins appeared to be particularly resilient to amygdala damage, relative to other emotional expressions. Thus, selective damage to the amygdala extensively alters the neural processing of emotion within IT cortex, supporting the view that the amygdala is the engine that drives neural coding of emotional identity in this part of the brain. These responses appeared to be driven by small amounts of preserved amygdala tissue that retained selectivity for fear grins in hemispheres where the anterior or posterior amygdala was completely eliminated, there was no response even to fear grins in the corresponding region of IT cortex (anterior or posterior). There was practically no response to threat or lip smack expressions, even though responses to fear grins were largely preserved in the same cortical areas. In the three monkeys with amygdala damage, the pattern of modulation within IT was altered. Similar modulations of face-selective activity were seen in the amygdala itself in these monkeys. ( 1) showed greater activation, in both anterior and posterior face-selective regions of IT, to different emotional expressions (threat, fear grin, or lip smack, an affiliative expression) relative to a neutral face that showed no particular emotional expression. Most control monkeys in the study by Hadj-Bouziane et al. The anatomical connections of the amygdala and IT cortex would allow the amygdala to modulate activity of the cortex in response to the emotional valence of faces, but it is equally possible that information about facial identity and emotion is independently extracted within IT cortex, passed to the amygdala through feed-forward connections, and, from there on, modulates behavior. Signal in the amygdala was also modulated by faces and by emotional valence. Some of the emotion-responsive areas did not overlap with the face-selective areas, potentially pointing toward independent cortical processing streams for face identity and emotion. ( 6) identified face-specific cortical areas in the anterior and posterior inferior temporal (IT) cortex of macaque monkeys, as well as regions within IT whose activity was modulated by the emotional valence of faces. An initial study in monkeys by Hadj-Bouziane et al. Neuroimaging with functional MRI (fMRI) provides a means by which neural activity, inferred by changes in relative levels of blood oxygenation, can be mapped across large regions of the brain in awake, behaving monkeys and humans. The mechanisms by which brain structures may interact in processing facial identity and emotion have been difficult to elucidate. ![]()
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