specialized for the monitoring of emotional arousal, of either valence. But positive emotional states also enhance motivation and readiness to act, left hemisphere attributes. The direction of shift of balance of activation is determined by the quality of personal response to the positive circumstance. If the subject is passive, as in input paradigms that call for perceptual judgments, the right sided activation predominates. If the subject's role involves overt responding, or covert response planning (as in formulating answers to questions), the left hemisphere intervenes ( Davidson & Fox, in press).
The studies of normal subjects support the main conclusions about emotional lateralization based on the clinical literature. Though systematic, the findings are not as stable as would be expected if a structural brain abnormality were being measured. The balance of activation between brain areas has many determinants, not all of which can be held constant in the laboratory. Nevertheless, it is clear that no striking differences have been discovered between brain activity patterns in emotional states within the normal range, emotional states in psychopathology, and structurally based emotional impairment. In all three, brain mechanisms react compensatorily to the displacements from homeostasis brought about by experimental manipulation, mental illness, and brain damage respectively.
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