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Reliable individual differences in electrophysiological measures of prefrontal activation asymmetry exist and predict dispositional mood and other psychological and biological indices of affective style. Subjects with greater relative right-sided activation report more dispositional negative affect and react with greater intensity to negative emotional challenges than their left-activated counterparts. We previously established that such individual differences in measures of prefrontal activation asymmetry were related to basal NK function, with left-activated subjects exhibiting higher levels of NK function than right-activated subjects. The present study was designed to replicate and extend these earlier findings. Subjects were tested in five experimental sessions over the course of 1 year. During the first two sessions, baseline measures of brain electrical activity were obtained to derive indices of asymmetric activation. During sessions 3 and 4, blood samples were taken during a nonstressful period in the semester and then 24 h prior to the subjects' most important final examination. During session 5, subjects were presented with positive and negative film clips 30 min in duration. Blood samples were obtained before and after the film clips. Subjects with greater relative right-sided activation at baseline showed lower levels of basal NK function. They also showed a greater decrease in NK function during the final exam period compared to the baseline period. Subjects with greater relative left-sided activation showed a larger increase in NK function from before to after the positive film clip. These findings indicate that individual differences in electrophysiological measures of asymmetric prefrontal activation account for a significant portion of variance in both basal levels of, and change in NK function.
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.