Expressive and response dimensions of human emotion : neural mechanisms

This thesis is about the neural mechanisms that underpin the expression of emotion in the human face and emotional modulation of behavioural responses. I designed 5 integrated studies and used functional magnetic resonance imaging (fMRI) to address specifically the neural mechanisms underlying human facial expression and emotional response. This work complements studies of emotion perception and subjective affective experience to provide a more comprehensive understanding of human emotions. I examined the neural underpinnings of emotional facial expression in three studies. I first demonstrated that emotional (compared to non-emotional) facial expression is not a purely motoric process but engages affective centres, including amygdala and rostral cingulate gyrus. In a second study I developed the concept of emotion contagion to demonstrate and verify a new interference effect (emotion expression interference, EEI). There is a cost (in reaction time and effort) to over-riding pre-potent tendency to mirror the emotional expressions of others. Several neural centres supporting EEI were identified (inferior frontal gyrus, superior temporal sulcus and insula), with their activity across subject predicting individual differences in personal empathy and emotion regulation. In a third study I examined an interesting phenomenon in our daily social life: how our own emotional facial expressions influence our judgment of the emotional signals of other people? I explored this issue experimentally to examine the behavioural and neural consequences of posing positive (smiling) and negative (frowning) emotional expressions on judgments of perceived facial expressions. Reciprocal interactions between an emotion centre (amygdala) and a social signal processing region (superior temporal sulcus) were quantified. My analysis further revealed that the biasing of emotion judgments by one’s own facial expression works through changes in connectivity between posterior brain regions (specifically from superior temporal sulcus to post-central cortex). I further developed two versions of an emotion GO/NOGO task to probe the impact of affective processing on behavioural responses. GO represents response execution and NOGO represents response inhibition. I therefore investigated how different emotions modulate both these complementary response dimensions (i.e. execution and inhibition). This research line is pertinent to a major theme within emotion theory, in which emotion is defined in terms of response patterns (e.g. approach and withdrawal). My results confirmed that both emotional processing and induced emotional states have robust modulatory effects on neural centres supporting response execution and response inhibition. Importantly, my results argue for emotion as a context for response control. My work extends our understanding of human emotion in terms of the nature and effect of its expression and its influence on response system. I hereby declare that I have initiated, performed, and completed all aspects of the work described in this thesis by myself. This work includes conceptualization of the experimental questions, experimental design, execution of the experiments, data analyses, and write-up of the thesis.