Abstracts

Rationale: In various neurological and psychiatric disorders, deficits in emotional response are associated with abnormalities in amygdala functioning. Although emotion recognition itself is often performed well, individuals with neurological or psychiatric conditions are often found to have abnormal autonomic response to emotional stimuli, however this has rarely been assessed as a function of amygdala atrophy. The purpose of this study was to examine the relationship between skin conductance responses and amygdala volume to emotional stimuli in patients with medial temporal lobe damage compared with healthy volunteers. Methods: The study involved two tasks: an implicit and an explicit task. The implicit task was presented first and involved viewing a series of 24 faces that expressed one of six emotions (happiness, fear, sadness, anger, disgust, and neutral). Each face was presented with a choice of two ages and the subject had to decide which number best represented how old they thought the person in the picture was. In the explicit task, the subjects were presented with similar pictures but for this task they had to choose which of two emotion labels best represented the face on the screen. During both tasks, electrodes were attached to the subjects fingers on both hands to measure skin conductance while responses were spoken. Bilateral recordings are not the norm in this field, but in patients with unilateral temporal lobe pathology, subtle differences related to lateralization may be relevant. Following completion of the tasks, subjects underwent a high resolution structural MRI scan in a 3 Tesla magnet. After appropriate preprocessing of the scans, amygdalae were segmented manually and volumes calculated using inhouse software. Results: Contrasting with the classic view that skin conductance only distinguishes valenced stimuli from neutral, the response profile to different emotions in our healthy volunteers showed an interesting pattern, specifically with the right hand. We found higher responses to fight or flight emotions such as fear and disgust, especially when the data was presented explicitly. In comparison, patients with epilepsy primarily affecting their left hemisphere showed atypical responses: Compared with their healthy counterparts they showed relatively greater response to faces depicting sadness in our implicit task, and reduced response to faces depicting disgust in the explicit task. As would be expected, amygdala volume in healthy control subjects was unrelated to skin conductance response to emotional faces. Conclusions: These initial results point to differences in reaction to certain emotions in patients with subtle damage to the medial temporal lobe. The differences most likely reflect structural and functional changes in the temporal lobe emotion circuitry. The nature of the differences, specifically heightened reaction to sad faces in patients with left sided pathology, may underpin the exaggerated prevalence of depression in this patient population.