Objective: To explore differences in kinematic parameters of reach in those with Parkinson’s disease (PD) classified into normal cognition (PD-NC), mild cognitive impairment (PD-MCI) and dementia (PDD).

Background: Reaching is a motor action controlled by a highly specialised neural pathway involving the posterior parietal and premotor frontal cortices. Reach has previously been studied in PD-NC and there is evidence of a greater reliance on visual feedback to guide the reaching arm compared to healthy controls (HC). Reach has not been studied in PD-MCI or PDD.

Methods: Twenty-two PD-NC, 23 PD-MCI, 10 PDD and 19 HC performed a reaching task under three conditions at a natural speed: a) full vision (FULL); b) towards an illuminated target in a darkened room (VIS); c) with eyes closed (MEM). All PD subjects were tested whilst on. Movement sensing equipment was used and calculated kinematic parameters were compared using standard statistical tests.

Results: Age, MDS-UPDRS Motor Score and levodopa equivalent daily dose were not significantly different between the PD groups. PDD had significantly longer duration of disease (p = 0.007) and average Montreal Cognitive Assessment score was significantly different between the PD groups (PD-NC 26.9, PD-MCI 22.1, PDD 17.6, p = <0.001). PD-NC had a significantly longer reach time (RT) compared to HC in MEM (p = <0.001) but not in FULL or VIS. PDD had the longest RT in all three conditions compared to PD-NC and PD-MCI with a trend towards significance in MEM (p = 0.081). In addition, time to attain peak acceleration, velocity and deceleration were significantly different between the PD groups in MEM and were longest for PDD (p = <0.05). There were no significant differences in kinematic reach parameters between PD-NC and PD-MCI in any condition.

Conclusions: The only condition that resulted in a slower reach for PD-NC compared to HC was when they had their eyes closed. The reaching movement profile of PDD differed significantly compared to PD-NC, particularly when visual input was omitted. These results suggest an increased reliance on visual feedback to guide reach in PD-NC compared to HC and in PDD compared to PD-NC. Impairment of visual spatial memory in PD may explain these findings, as may direct damage to the parietal reach region by infiltration of alpha-synuclein.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/how-does-cognition-affect-reaching-in-parkinsons-disease/