Abstract
The amygdala has been regarded as a key substrate for emotion processing. However, the engagement of the left and right amygdala during the early perceptual processing of different emotional faces remains unclear. We investigated the temporal profiles of oscillatory gamma activity in the amygdala and effective connectivity of the amygdala with the thalamus and cortical areas during implicit emotion-perceptual tasks using event-related magnetoencephalography (MEG). We found that within 100 ms after stimulus onset the right amygdala habituated to emotional faces rapidly (with duration around 20–30 ms), whereas activity in the left amygdala (with duration around 50–60 ms) sustained longer than that in the right. Our data suggest that the right amygdala could be linked to autonomic arousal generated by facial emotions and the left amygdala might be involved in decoding or evaluating expressive faces in the early perceptual emotion processing. The results of effective connectivity provide evidence that only negative emotional processing engages both cortical and subcortical pathways connected to the right amygdala, representing its evolutional significance (survival). These findings demonstrate the asymmetric engagement of bilateral amygdala in emotional face processing as well as the capability of MEG for assessing thalamo-cortico-limbic circuitry.
Highlights
Rapid detection of facial expressions and emotional salience is critical for social communication and interaction
We found that angry faces elicited amygdala activity on the right side at 60–70 ms and on the left side at 65–70 ms and 90–105 ms (Fig. 2A)
In response to happy faces, the left amygdala was activated at 35–70 ms and 90–100 ms, and the right amygdala was activated at 80–110 ms (Fig. 2B)
Summary
Rapid detection of facial expressions and emotional salience is critical for social communication and interaction. A dual-route model [1] has been proposed that rapid brain responses to emotional facial expressions through two pathways, one from the subcortical colliculo-pulvinar to the amygdala and the other from cortical visual areas to amygdala, within 120 ms [2]. Such rapid amygdala engagement is biologically crucial for survival under threatening confrontation [3,4]. In a meta-analysis of 54 fMRI and PET studies, found that there were more reports of left amygdala engagement (41 out of 54 studies) than right (30 out of 54 studies) This left-predominant phenomenon may be explained by rapid habituation of the right amygdala and sustained activity of the left amygdala. Using neuroimaging tools to determine the temporal profiles of the left and right amygdala activity would help clarify the asymmetric activity and habituation rates of the left and right amygdala in early perceptual processing of emotions
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