P104. The impact of timing of cerebellar anodal transcranial direct current stimulation on motor performance in a sequential finger tapping task

Abstract

Background Transcranial direct current stimulation (tDCS) of the cerebellum could constitute an innovative approach in understanding the role of cerebellar function in healthy and pathological conditions. Recently, attention has grown toward cerebellar neuromodulation in motor learning using tDCS. An important point of discussion regarding this modulation is the optimal timing of tDCS. As this parameter could significantly influence the outcome, we aimed to compare the effect of anodal cerebellar tDCS applied at different times on the motor performance and retention using a sequential finger tapping task (FTT). Methods Fifty-six healthy young, right-handed subjects performed two days of FTT on a custom keyboard. The task was presented with OpenSesame software and lasted 40 s followed by 20 s rest forming one trial. Each participant performed 20 trials on the first day (20 min) and 10 trials on the following one (10 min). tDCS (2 mA, sponge electrodes of 25 cm2, duration 20 min) was applied to the ipsilateral cerebellar hemisphere on day 1 at the following times: (1) before ‘tDCS-before’, (2) sham during ‘tDCS-sham’, (3) active during ‘tDCS-active’ or (4) after the training ‘tDCS-after’. Motor skill performance and retention were assessed. Results All participants showed significant effects of learning ( p 0.0001 ). The mean performance on day 1 was significantly different ( p 0.0001 ): The tDCS-after group performed better than all the other groups, whereas the tDCS-active group performed worse than the tDCS-before group. Similarly, there was a significant difference in the mean performance on day 2 ( p 0.0001 ): tDCS-after was associated with a better performance on day 2, compared to tDCS-sham and tDCS-active. The tDCS-before group also performed better than the tDCS-sham or the tDCS-active groups. Motor skill retention was not different between the groups (p = 0.15). Discussion Cerebellar tDCS applied during the FTT (‘on-line’) interfered with task execution, resulting in an impaired performance on days 1 and 2 compared to the other groups. This inhibitory effect of anodal tDCS may caution against a simple transfer of tDCS’ effects on the motor cortex to regions with a different architecture like the cerebellum. It calls for a careful attention to the timing of stimulation when designing experiments with tDCS. Cerebellar tDCS did not facilitate the retention of the motor skill in the FTT – however, it cannot be excluded that young healthy subjects already performed at a near optimal level with little room for further improvement. Future work will evaluate the effect of cerebellar tDCS in a population where motor learning and cerebellar volume are known to decline.