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A variety of recent research indicates that when subjects are induced to experience certain negative emotions, there is greater suppression of alpha power in the right than left frontal region, while during the experience of positive emotion, alpha power asymmetry in this region shows the opposite pattern. We have conceptualized this assymetry as reflecting specialization for approach and withdrawal processes in the left and right frontal regions, respectively. In this experiment, reward and punishment contingencies were directly manipulated to produce approach and withdrawal response motional states. In addition, subjects responded to imperative stimuli using either an approach response (finger press) or a withdrawal response (finger lift). EEG was recorded from multiple scalp locations. During the foreperiod prior to the response to the imperative stimuli, the EEG was extracted, Fourier-transformed and power computed in the theta, alpha and beta frequency bands. In addition, the contingent negative variation (CNV) was derived from the identical epoch. Reward trials were associated with greater left frontal alpha power suppression than punishment trials, while during the latter trials, there was greater right-sided frontal alpha power suppression than during reward trials. There was also some evidence to indicate that withdrawal responses were associated with greater right-sided alpha power suppression in the temporo-parietal region compared with approach responses. Power in the theta and beta bands did not systematically vary with condition. The CNV was larger during trials on which subjects responded quickly compared with slow trials, but did not differentiate between reward and punishment contingencies. The findings support the hypothesis that approach-related processes can be differentiated from withdrawal-related processes on the basis of asymmetrical shifts in alpha power in the frontal region. They also indicate that the CNV and spectral power estimates from the identical epochs reflect different neural processes.
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