From a neurobiological perspective, emotion involves a complex interaction between core limbic structures and overlying cortex. Recent evidence suggests that the two cerebral hemispheres play different roles in modulating the components of emotional behavior, although the precise manner by which this occurs is controversial. The global right hemisphere model posits that neural systems within the right hemisphere are crucially involved in all aspects of emotional behavior. In contrast, the bivalent model posits that anterior regions of the right hemisphere (RH) mediate the experience of negative/withdrawal emotions, whereas the left hemisphere (LH) mediates positive/approach emotions. To address this, patients with strokes of the RH or LH will be presented standardized sets of emotion-eliciting stimuli (affective slides, emotional nonverbal sounds, emotional sentences) that are positively and negatively toned. During these tasks, multiple measures of emotional responsivity will be obtained including psychophysiological (heart rate, bilateral SCR), somatic (bilateral facial EMG), startle eyeblinks, and verbal report measures. As designed, the proposed studies will enable us to determine how focal cortical lesions of the LH or RH differentially alter emotional reactivity, and whether their alteration is valence- specific, material-specific, modality-specific, or """"""""measure"""""""" specific. The following questions will be addressed: (a) Is there differential decoupling among the emotion response systems (i.e., HR, SCR, facial EMG, eyeblink, verbal report) due to the integrity of right vs. left cortical regions? To date, prior neurobehavioral studies of emotion have relied almost exclusively on evaluation of only one response system of emotion (i.e., verbal report, or SCR) at a time; (b) Is valence modulation of the startle response differently affected by lesions within the right versus left hemisphere, and is intrahemispheric lesion site important? Recent evidence from normals suggests that the magnitude of the startle eyeblink reflex is augmented during negative affective states and diminished during positive affective states. No human data currently exist concerning which cortical area(s) might contribute to affective modulation of the startle response, or whether hemispheric asymmetries might exist; (c) Are findings more consistent with a global right hemisphere versus a bivalent model of emotional processing?
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