Amygdala responses to valence and its interaction by arousal revealed by MEG

Charalampos Styliadis, Andreas A Ioannides, Panagiotis D Bamidis, Christos Papadelis, 

Journal of Psychophysiology (pre-press)

Abstract: It is widely accepted that the amygdala plays a crucial role in the processing of emotions. The precise nature of its involvement is however unclear. We hypothesized that ambivalent findings from  neuroimaging studies that report amygdala's activity in emotions, are due to distinct functional specificity of amygdala's sub-divisions and specifically to differential reactivity to arousal and valence.  The goal of the present study is to characterize the amygdala response to affective stimuli by disentangling the contributions of arousal and valence. Our hypothesis was prompted by recent reports claiming anatomical sub-divisions of amygdala based on cytoarchitecture and the functional

maps obtained from diverse behavioural, emotional, and physiological stimulation. We measured magnetoencephalography (MEG) recordings from 12 healthy individuals passively exposed to affective stimuli from the International Affective Picture System (IAPS) collection using a 2 (Valence levels) x 2  (Arousal levels) design. Source power was estimated using a beamformer technique with the activations referring to the amygdala sub-divisions defined through probabilistic zytoarchitectonic  maps. Right laterobasal amygdala activity was found to mediate negative valence (elicited by unpleasant stimuli) while left centromedial activity was characterized by an interaction of valence by  arousal (arousing pleasant stimuli). We did not find a main effect for amygdala activations in any of its sub-divisions for arousal modulation. To the best of our knowledge, our findings from non-invasive  MEG data, indicate for the first time, a distinct functional specificity of amygdala anatomical subdivisions in the emotional processing.