Prism adaptation in Parkinson disease: comparing reaching to walking and freezers to non-freezers

Abstract

Visuomotor adaptation to gaze-shifting prism glasses requires recalibration of the relationship between sensory input and motor output. Healthy individuals flexibly adapt movement patterns to many external perturbations; however, individuals with cerebellar damage do not adapt movements to the same extent. People with Parkinson disease (PD) adapt normally, but exhibit reduced after-effects, which are negative movement errors following the removal of the prism glasses and are indicative of true spatial realignment. Walking is particularly affected in PD, and many individuals experience freezing of gait (FOG), an episodic interruption in walking, that is thought to have a distinct pathophysiology. Here, we examined how individuals with PD with (PD + FOG) and without (PD - FOG) FOG, along with healthy older adults, adapted both reaching and walking patterns to prism glasses. Participants completed a visually guided reaching and walking task with and without rightward-shifting prism glasses. All groups adapted at similar rates during reaching and during walking. However, overall walking adaptation rates were slower compared to reaching rates. The PD - FOG group showed smaller after-effects, particularly during walking, compared to PD + FOG, independent of adaptation magnitude. While FOG did not appear to affect characteristics of prism adaptation, these results support the idea that the distinct neural processes governing visuomotor adaptation and storage are differentially affected by basal ganglia dysfunction in PD.

Fig. 1

Average trial-by-trial angular error during reaching (a) and walking (b) in all groups for baseline, adaptation, and post-adaptation phases. Continuous lines represent the exponential fit to data; vertical dashed lines distinguish the phase (baseline, adaptation, post-adaptation); horizontal dotted lines mark the location of the target edges. Error bars are ±SEM

Fig. 2

Representative walking adaptation data showing good (left column) and poor fits (right column) in CTRL (top row), PD − FOG (middle row), and PD + FOG (bottom row). Continuous lines are monotonic exponential fits

Fig. 3

Relationship between magnitude of adaptation (abscissa) and after-effect (ordinate) during reaching (squares) and walking (circles) adaptation. Error bars are ±SEM. *Significant post hoc differences in M_Post between PD − FOG and PD + FOG (p = 0.009). In addition, M_Post was significantly different across tasks (reaching > walking; F_36,1 = 54.314, p < 0.001)