Motor-cognitive Functions in Parkinson’s Disease Patients across the Program of "Dry" Immersion: a Pilot Study

• ¹ Petrozavodsk State University, Russia
• ² Institute of Biomedical Problems (RAS), Russia

Motor and cognitive signs of Parkinson's disease (PD) have specific progression speed (Lawton et al., 2018). Some motor-cognitive instrumented tasks, e.g. choice reaction time (CRT) appear as cognitively demanding, while others, e.g. simple reaction time (SRT) or tapping test (TT) - as ones with lower need for cognitive effort (Müller et al., 2002). In PD patients, the program of "dry" immersion (DI) sessions provoked decrease of UPDRS-III and rigidity scores by 16%, while that of Hamilton’s depression rate scale - by 40% (Meigal et al., 2018). Therefore, we hypothesize that the cognitively demanding tasks might have been more affected by a program of DI in comparison to merely motor tasks. To proceed, we compared the effect of DI on a set of reaction time tasks with different share of mental operation - TT, SRT, SRT at distraction of attention (SRT/DA), CRT, and prediction motion task (PMT). A total of 10 PD patients (9 m, 1 f, Hoehn and Yahr staged 1-3) participated in the program of DI. They stood immersed in a bathtub (MEDSIM, IBMP, Moscow, Russia, Twater=31-32°C), wrapped in a thin waterproof material, head-out-of-water, 7 times (45 min each session) within 35 days. The data was collected at 4 study points: before the 1st (preDI), after the 7th immersion (DI7), 2 weeks (2W) and 2 months post-DI (2M). Six PD patients (all males) without application of DI formed the reference group. The study was performed with a help of PC-based tester (NS-Psychotest, Neirosoft Ltd., Ivanovo, Russia). To execute the TT task, the subjects performed tapping as quickly as possible on a contact board (55x60 mm) with a contact pencil, within 30 s. The count of taps was measured. The visual SRT task was evaluated as the time between light (red flash) stimulus (n=30) on PC-based portable control panel and pressing the button with the thumb of the dominant hand on the same panel. The SRT/DA paradigm appeared as a SRT task (red circle, 20 mm in diameter, emerging on the center of PC screen, random in time, n=30) supplemented by distracting visual stimuli (circles of varied color and size, appearing irregularly in time and space of PC screen). In the CRT paradigm subjects had to press the appropriate panel button (red button on red light stimulus, and green button - on the green one, n=20). In all these tests reaction time (ms) was measured. To perform PMT, subjects pressed the button on control panel (n=30) when a dynamic object (growing red segment, 135°/s) on PC screen was colliding with a static object (green radius, 45 mm). The accuracy (% of precise hits) was estimated. The SPSS 21.0 (IBM Corp., USA) was used for statistics (multiply comparisons between 4 study points by Friedman non-parametric test with further post-hoc corrections). In the reference group, none of the tests has significantly modified along the investigation period. In the study group, before the program of DI, SRT centered around 290 ms (249-335 ms, 25-75%), SRT/DA was 343 ms (300-358.5 ms), and CRT - 486 ms (407-724 ms). The SRT has not changed across the study, while the SRT/DA has decreased by some 8% (315.5, 308-353, p=0.042), and the CRT - by 20% (417, 355-457 ms, p=0.022) at 2W study point. At the point 2M all parameters tended to restore their values. Normalized values of SRT, SRT/DA and CRT along the study are presented on figure 1. The count of hand taps during TT task centered around 185 per 30 s (6.05 Hz), and it stood unchanged by DI in both groups (see Figure 1). In the PMT, precise hits were 51% (40-62) and did not change over the study. Before the DI program, the three RT tasks clearly ranged by their duration from the shortest (SRT) through SRT/DA to the longest (CRT) thus reflecting gradually increasing cognitive complexity of the task. The reaction to DI program has also ranged from a prominent (20% decrease) effect on CRT, through a modest effect (8% decrease) on SRT/DA to a negligible effect (<2% decrease) on SRT. Such finding prompts that the more the task was cognitively demanding, the more it was affected by the DI program. Thus, the motor component of the reaction time tasks was not modified by DI. That conclusion is supported by the fact that the tapping count in TT task and proportion of accurate hits in PMT have not changed through the DI program. That result is in line with earlier finding that performance of complex, but not simple motor tasks is improved by anti-PD therapy (Müller et al., 2003), what supports the original hypothesis of that study. As the reaction time tasks have well-established neurophysiologic basis, they can be used to evaluate the mechanisms of DI therapy. In further studies, the battery of motor-cognitive tasks could be expanded to the more complex ones, e.g. recognition/discrimination tasks. This study is financially supported by the Ministry of Education and Science of the Russian Federation (project 17.7302.2017/6.7, to A.M.)