Asymmetric influences of pointing on saccade latency in hemi-Parkinson's disease

The objective of this study was to investigate whether eye-hand coupling wa s preserved or not in PD. We studied predictive saccade performance during hand pointing in six Parkinson's disease (PD) patients with asymmetrical mo tor signs compared to nine age-matched healthy subjects. The motor response s (saccades and hand pointing) were elicited under open loop conditions (wi thout vision of the hand), by a visual target stepping at a predictable loc ation (10 degrees right and left from the centre) and time. The subjects ha d to simultaneously move the eyes and point with the finger to the visual t arget alternating at one of three fixed frequencies (0.25, 0.5 and 1 Hz), f or 30 cycles. This task was performed in two sessions balanced over the sub jects: one session of ocular saccades only and another session of combined ocular saccades and manual pointing. In the PD group, motor performance was perturbed particularly in terms of increased latencies of hand movements. Interestingly, during pointing, associated predictive saccade disorders wer e tightly related to the defects of the pointing hand. Indeed, with respect to the latency of predictive saccades alone, the predictive saccade latenc y during hand pointing significantly decreased in the control group and in the PD group when using the non-affected hand. In contrast, for the PD grou p when using the affected hand, the saccade latency was increased from the latency values of predictive saccades induced without pointing. Moreover, i n the control and in the PD groups, the correlation between eye and hand la tencies was highly significant, suggesting an intact eye-hand coupling. No saccadic amplitude disorders were found in either condition. These results demonstrate that eye-hand coupling is preserved in PD, as revealed by the p ossible beneficial or adverse effects on the ocular saccades, respectively, of the less- or more-affected hand motor responses. This eye-hand coupling mechanism likely involves regions other than the nigro-striatal pathways a ffected in PD. (C) 2001 Elsevier Science Ltd. All rights reserved.