Abstract
Evidence shows altered somatosensory temporal discrimination threshold (STDT) in Parkinson’s disease in comparison to normal subjects. In healthy subjects, movement execution modulates STDT values through mechanisms of sensory gating. We investigated whether STDT modulation during movement execution in patients with Parkinson’s disease differs from that in healthy subjects. In 24 patients with Parkinson’s disease and 20 healthy subjects, we tested STDT at baseline and during index finger abductions (at movement onset “0”, 100, and 200 ms thereafter). We also recorded kinematic features of index finger abductions. Fifteen out of the 24 patients were also tested ON medication. In healthy subjects, STDT increased significantly at 0, 100, and 200 ms after movement onset, whereas in patients with Parkinson’s disease in OFF therapy, it increased significantly at 0 and 100 ms but returned to baseline values at 200 ms. When patients were tested ON therapy, STDT during index finger abductions increased significantly, with a time course similar to that of healthy subjects. Differently from healthy subjects, in patients with Parkinson’s disease, the mean velocity of the finger abductions decreased according to the time lapse between movement onset and the delivery of the paired electrical stimuli for testing somatosensory temporal discrimination. In conclusion, patients with Parkinson’s disease show abnormalities in the temporal coupling between tactile information and motor outflow. Our study provides first evidence that altered temporal processing of sensory information play a role in the pathophysiology of motor symptoms in Parkinson’s disease.
Highlights
Sensorimotor integration is the process whereby incoming sensory information is continuously monitored so as to allow the current motor plan to be adjusted and voluntary movements to be executed accurately [1,2,3,4,5]
Post hoc analysis performed to evaluate percentage changes in the mean velocity of index finger abductions during somatosensory temporal discrimination threshold (STDT) testing showed that the mean velocity in PD patients, unlike that in healthy subjects (P > 0.05), significantly decreased across time lapses, with lower values being recorded at 200 ms than at 0 ms interval (Figure 2B)
We show that sensory information processing related to STDT is abnormally gated during movement execution in PD patients OFF therapy if compared with healthy subjects and those ON therapy
Summary
Sensorimotor integration is the process whereby incoming sensory information is continuously monitored so as to allow the current motor plan to be adjusted and voluntary movements to be executed accurately [1,2,3,4,5]. Sensorimotor integration depends on the temporal processing of sensory information. In a recent study on healthy subjects, we used the STDT to provide new evidence showing that movement execution brings about changes in the temporal processing of tactile information through the interplay between the basal ganglia and thalamus [10]. The aim of this study was to investigate whether STDT modulation during movement execution in PD patients differs from that in healthy subjects and to evaluate changes in the kinematic properties of movements during the sensorimotor integration task. We investigated possible correlations between neurophysiological and clinical variables
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