FRONTAL AND PARIETAL PREMOVEMENT SLOW BRAIN POTENTIALS IN PARKINSONS-DISEASE AND AGING

During the anticipation of a stimulus that induces a predetermined pat tern of behavior, a slowly increasing negative electric potential can be recorded from the human scalp at central and parietal electrodes an d has been named contingent negative variation (CNV). We used a simple and a choice reaction time paradigm to investigate premovement potent ials in patients with Parkinson's disease (PD) and in normal controls. There was a clear CNV in young subjects whereas it was negligible in the elderly control subjects and absent in the patients. In addition, we found a slowly increasing positive frontal potential. In normals th e steepness of this potential decreased with the complexity of the tas k (simple vs. choice) and with age. This difference was abolished in t he patients: If a slowly increasing positivity was observed at all, it was, on average, larger in the choice task. Reaction times of the pat ients were disproportionally prolonged in the simple compared to the c omplex task. These findings support the hypothesis that storing or ini tiating a simple preprogrammed motor response is more impaired in PD t han selecting and initiating a motor response of a more complex task. The electrophysiological recordings suggest that impaired activation o f the frontal lobes may be responsible for this deficit.