Tactile/proprioceptive integration during arm localization is intact in individuals with Parkinson's disease

Abstract

It has been theorized that sensorimotor processing deficits underlie Parkinson's disease (PD) motor impairments including movement under proprioceptive control. However, it is possible that these sensorimotor processing deficits exclude tactile/proprioception sensorimotor integration: prior studies show improved movement accuracy in PD with endpoint tactile feedback, and good control in tactile-driven precision-grip tasks. To determine whether tactile/proprioceptive integration in particular is affected by PD, nine subjects with PD (off-medication, UPDRS motor=19-42) performed an arm-matching task without visual feedback. In some trials one arm touched a static tactile cue that conflicted with dynamic proprioceptive feedback from biceps brachii muscle vibration. This sensory conflict paradigm has characterized tactile/proprioceptive integration in healthy subjects as specific to the context of tactile cue mobility assumptions and the intention to move the arm. We found that the individuals with PD had poorer arm-matching accuracy than age-matched control subjects. However, PD-group accuracy improved with tactile feedback. Furthermore, sensory conflict conditions were resolved in the same context-dependent fashion by both subject groups. We conclude that the somatosensory integration mechanism for prioritizing tactile and proprioception feedback in this task are not disrupted by PD, and are not related to the observed proprioceptive deficits.

Figure 1

Left: Apparatus and setup. For ‘touch’ conditions the cue-arm index fingertip touched the cue-surface, located 20cm above the tabletop. The cue-surface was stationary throughout experimental trials, but was rotated about a hinge in between the 2 trial-blocks to demonstrate mobility potential. For PD-group subjects, the cue-surface was moved to the more PD-involved side. Right: Experimental design included 2 blocks with 8 conditions, separated by an ‘interlude’. Left-to-right order represents protocol order.

Figure 2

Means±SD (n=9) of peak discrepancies of forearm orientation across all conditions with vibration, before (trial block I, white bars) and after (block II, dark bars) being made aware of the cue-surface’s potential to move. All errors correspond to greater report-arm extension. All no-vibration results are collapsed.