FIGURE 1.

Following completion of a MSL task with the nondominant left hand inside the MRI scanner, participants were randomly assigned to either an anodal or sham tDCS experimental condition (anodal electrode centered above right primary motor cortex). MRS from the right sensorimotor cortex (contralateral to the hand used to perform the motor task) and whole brain RS fMRI data were obtained prior to and following the MSL task/tDCS intervention. The experiment was completed between approximately 11 a.m. and 1 p.m. for all participants. The approximate durations (in minutes) for each of the various measurements are provided in the figure. As the number of sequence repetitions was held constant in the MSL task, the duration of the training session varied depending on the participants movement speed (mean = 16 min; range = 12–24 min). Note that participants were removed from the MRI scanner and taken to an adjacent testing room to complete the stimulation session. The tDCS electrode positions were marked, but not attached, prior to entering the scanner in order to minimize the time between end of the learning episode and the onset of stimulation (mean duration = 8 min; range = 5–16 min). As the participants were removed from the scanner for the tDCS, the delay between post‐learning/stimulation MRS time point and the end of MSL training and the end of stimulation varied. The post‐MRS measurements started approximately 32 min (range = 27–40) and 8 min (range = 5–15) after the completion of the MSL and stimulation, respectively. Previous research in young healthy adults has indicated that modulations in GABA are detectable up to 20–50 min after a learning or stimulation intervention (Bachtiar et al., 2018; Floyer‐Lea et al., 2006; Patel et al., 2019). Changes in RS connectivity have been observed hours following motor learning (e.g., Sami, Robertson, & Miall, 2014). fMRI, functional magnetic resonance imaging; GABA, gamma‐aminobutyric acid; MRS, magnetic resonance spectroscopy; MSL, motor sequence learning; tDCS, transcranial direct current stimulation; RS, resting state