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This past year has seen significant advances in our understanding of the physiology of emotion. Attention continues to focus on the amygdala and its interconnections with prefrontal cortical regions. New evidence underscores the importance of lateralization for emotion. There are also new findings on the physiological predictors of individual differences in emotional behavior and experience, and on the role of autonomic arousal in emotional memory.
BACKGROUND: Functional magnetic resonance imaging (fMRI) techniques were used to identify the neural circuitry underlying emotional processing in control and depressed subjects. Depressed subjects were studied before and after treatment with venlafaxine. This new technique provides a method to noninvasively image regional brain function with unprecedented spatial and temporal resolution. METHOD: Echo-planar imaging was used to acquire whole brain images while subjects viewed positively and negatively valenced visual stimuli. Two control subjects and two depressed subjects who met DSM-IV criteria for major depression were scanned at baseline and 2 weeks later. Depressed subjects were treated with venlafaxine after the baseline scan. RESULTS: Preliminary results from this ongoing study revealed three interesting trends in the data. Both depressed patients demonstrated considerable symptomatic improvement at the time of the second scan. Across control and depressed subjects, the negative compared with the positive pictures elicited greater global activation. In both groups, activation induced by the negative pictures decreased from the baseline scan to the 2-week scan. This decrease in activation was also present in the control subjects when they were exposed to the positive pictures. In contrast, when the depressed subjects were presented with the positive pictures they showed no activation at baseline, whereas after 2 weeks of treatment an area of activation emerged in right secondary visual cortex. CONCLUSION: While preliminary, these results demonstrate the power of using fMRI to study emotional processes in normal and depressed subjects and to examine mechanisms of action of antidepressant drugs.
Separate, extended series of positive, negative, and neutral pictures were presented to 24 (12 men, 12 women) undergraduates. Each series was presented on a different day, with full counterbalancing of presentation orders. Affective state was measured using (a) orbicularis oculi activity in response to acoustic startle probes during picture presentation, (b) corrugator supercilii activity between and during picture presentation, and (c) changes in self-reports of positive and negative affect. Participants exhibited larger eyeblink reflex magnitudes when viewing negative than when viewing positive pictures. Corrugator activity was also greater during the negative than during the positive picture set, during both picture presentation and the period between pictures. Self-reports of negative affect increased in response to the negative picture set, and self-reports of positive affect were greatest following the positive picture set. These findings suggest that extended picture presentation is an effective method of manipulating affective state and further highlight the utility of startle probe and facial electromyographic measures in providing on-line readouts of affective state.
Measures of left-right asymmetry in resting brain activity were derived from spectral estimates of electroencephalogram (EEG) alpha-band power density in 13 homologous scalp electrode pairs from 81 right-handed individuals (43 F) on two occasions separated by 6 weeks. At a third, later session, these individuals completed a cognitive task, comparing word-pairs that systematically differed in affective tone. For an extended series of paired-comparisons, the subject chose the one word-pair that 'went together best'. Objectively, associative strength was comparable for both word-pairs. Individuals with relatively greater left-sided anterior frontal resting activity were more likely to select the more pleasant word-pair. Relations between word-pair selection and asymmetry in resting brain activity at central and posterior sites were not significant.