Cause-effect Relationships Between Brain Networks and Bimanual Coordination in Older Adults

A single-blind, pseudo-randomised, sham-controlled within-subject design will be used. The study consists of three experimental sessions. In each session, one out of three stimulation conditions was applied: (1) in-phase stimulation; (2) anti-phase stimulation; (3) sham stimulation. The order of the three stimulation conditions over sessions will be pseudo-randomised across participants. Within each session, stimulation is applied during the performance of two tasks: a 2-back task for assessing pure spatial working memory (sWM), and a complex bimanual tracking task (BTT) for assessing bimanual skill acquisition. To minimise learning and carry-over effects over sessions, a wash-out period of 6 weeks in between sessions is used and three different variants of the BTT task (one for each session). The order of these variants was also pseudo-randomised across participants.

For assessing sWM, participants perform an adapted version of the 2-back visuospatial match-to-sample test used in Alekseichuk et al., 2016. Participants are seated on a chair, with their right hand resting on a response box. A computer screen is placed in front of the participant. On the screen, a blue 3x3 grid is drawn on a black background. Each trial consists of three events: a stimulus, a probe, and a response period. During the stimulus, two or three white dots appear somewhere in the grid for 2150ms. After a time interval of 50ms, this is followed by the appearance of the probe, consisting of one small blue dot, lasting for 300ms. During the response period (2000ms duration), the participant is requested to either press or to not press the response button, indicating whether the location of the probe matches the location of the stimulus in the previous trial or not (i.e., 2-back condition).

For familiarisation purposes, participants are first instructed what the goal of the task is. Next, they practiced a series of ten or twenty trials without stimulation.

For the experiment (i.e., task performance during stimulation), a complete set of trials is organised in five blocks, consisting of 30 trials (i.e. 150 trials per set). The five blocks are separated by 1-minute breaks. The distribution of 2-dot or 3-dot stimulus conditions in the 150-trial set was 50%-50%, presented in random order. Forty % of the trials are matched trials (i.e. 58 trials) and 60% are non-matched trials (i.e. 87 trials).

For this study, we use three fixed sets of trials, i.e. one for each session. The order of these sets over sessions will be pseudo-randomised across participants.