Neurophysiological Aspects of postural control training in Parkinson's disease

Introduction: Postural instability is an obvious symptom in Parkinson's disease (PD) and documented in various studies. However, some experiments report no differences between PD patients and age matched controls. This divergence might be explainable by methodical differences in postural control analyses e.g. perturbed or unperturbed, on or off medication. Further more the basic pathological mechanisms as well as treatment strategies are widely discussed. Some authors consider disturbances in peripheral mechanisms to be fundamentally involved in postural instability others refer to a reduced cortical excitability. Comparable differences can be identified in the field of medication. Anyway, in earlier studies we found that mechanical stochastic-resonance stimuli lead to postural control improvements in PD. The guiding aim of this study was to prove the influence of medication and proprioceptive performance on postural control training effects.

Fig. 1 Treatment related Sway-Changes

Fig. 2 Changes in Prioprioception

Methods: For both experiments the treatment was based on mechanical stochastic-resonance (SR) stimuli. In experiment one 57 PD patients were subdivided in two comparable groups. Patients of one group were treated and tested in the off status i.e. after they were withdrawn from L-Dopa for 12 hours. Participants of the other group absolved treatment and testing under the influence of routine L-Dopa doses. Postural control was analysed in three sessions pre- and post-treatment using a 2-D moveable platform. In experiment two proprioceptive capabilities of 25 Parkinson's disease patients were tested. Subjects were asked to reproduce an oscillating target-course via knee extension and flexion movements. Each participant performed 5 pre- and post-test series.

Results and Discussion: As presented before subjects show improved postural control after the treatment. However, effects were stronger in patients that were withdrawn from L-Dopa (on: 11% reduced sway, off: 28% reduced sway, Fig. 1). Referring to proprioception no significant differences became evident in any parameter or group (Fig. 2). In conclusion although dopamine medication improves controlling of internally triggered movements it seems to suppress functional reflex adaptations. However, this neuromuscular capability is not directly related to proprioceptive performance.