Motor output variability and putative deficits in kinaesthetic integration in deafferentation and Parkinson‘s Disease

Abstract

Objective In Parkinson‘s Disease (PD) progressive decline in motor output is well documented. Less understood are any deficits in integration of kinaesthetic feedback from erratic unfolding movements. Method We present evidence from the reaching movements in a deafferented subject and groups of subjects with variable severities of PD analysed using a new statistical method (see Torres, 2013, Front Integr Neurosci, 7, 50). Results Increasing severity in those with PD leads to their statistical signatures of movement becoming closer to those of IW. Conclusions We propose that some with PD may have deficits in kinaesthetic integration in addition to their problems with motor efference. These may result from problems with integration of persistent, noisy motor patterns and the resultant proprioceptive feedback as the disorder progresses. The results are interpreted in the light of the concept of kinaesthetic reafference (von Holst and Mittelstaedt, 1950 in Dodwell Ed.). In this context, motor output variability in PD leads to noisy afference caused in turn by those faulty movements and to possible disordered central integration of feedback and motor output. Key message Motor output and proprioceptive feedback are inextricably linked; primary deficits in one may affect function in the other or, at least, in the whole system‘s integration.