In sum, we have seen that variation in temporal performance is reflected in slow brain potential (CNV) changes. On the one hand, in normal subjects CNV amplitude progressively increases over progressive learning of temporal parameters and decreases as temporal accuracy approaches the maximum level of performance. On the other hand, CNV amplitude is consistently reduced in elderly adults compared to young ones and in Parkinson's disease patients compared with controls, particularly at the frontal sites. Moreover, latency of CNV resolution shows a positive correlation with accuracy in duration estimation, probably reflecting the conscious decision to respond after the formation of the temporal judgment. Studies in patients with Parkinson's disease suggest that the cortical-basal ganglia-thalamo-cortical circuit plays a major role in the generation of the CNV. The combination of EEG and PET data further indicates that cortical activity may underlie cognitive processes associated with the preparation and organization of forthcoming responses. Finally, there is some intriguing evidence of a right hemispheric bias for processing temporal information.

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