Motor skills are essential for daily activities in our life. In healthy and clinical populations who have neurological disorders / related impairment, such as stroke, patients require extensive physical practice to regain their motor skills respectively. Thus, a better understanding of how the brain adapts to new challenges, focusing on the neural processes underlying the learning of motor skills is of the utmost importance for patient rehabilitation and to maintaining a healthy lifestyle.

To achieve gains in motor skills, physical practice is essential, but how we organize these practice sessions has received less attention, a critical step toward optimizing and maximizing motor skills learning. Here is the story behind our paper, Improving online and offline gain from repetitive practice using anodal tDCS at dorsal premotor cortex.

The focus of our study was on new evidence illustrating the efficacy of learning multiple motor skills through greater contextual interference (CI) during training. CI is a scheduling protocol that has been demonstrated to garner greater motor skill acquisition by performing multiple motor tasks in an interleaved practice (IP) format. Conversely, repetitive practice (RP) creates significantly less interference because it involves the repeated execution of the same motor task before further practice with other motor tasks.

The most striking aspect of the CI effect is demonstrated after practice. In the retention test session, prior exposure to RP usually leads to significant forgetting of motor skills. By contrast, individuals trained via IP exhibit stable or even enhanced motor skills, often referred to as offline gain. This result suggests that the IP format during practice sessions benefits the improvement of motor skills. 

Since 2007, neuroimaging data has supported CI effect on motor skills learning. IP and RP results revealed the differential cost of movement preparation reflected an increase in attention demand was accompanied by distinct neural recruitment strategies during RP and IP formats. In particular, the relative contribution of the primary motor cortex (M1) as well as dorsal lateral premotor (PMd) and medial premotor regions (pre-SMA, SMA) in the human brain, increased dramatically across IP but not RP.

Recently, we reported that the upregulating on M1 and SMA activity during RP, via administration of anodal transcranial direct current stimulation (tDCS), can induce offline gains that are absent for participants that trained in an RP training condition, but were paired with sham tDCS. This result is observed consistently after the IP.  

In this study, we focused on the dorsal lateral premotor cortex (PMd) because previous work highlighted the importance of left PMd recruitment. This neural site was part of developing functional connectivity between Left-PMd and the sensorimotor network during encoding and offline learning. Thus, we used anodal tDCS to upregulate left and right PMd during RP to boost PMd recruitment during RP, a similar feature of IP.

We found that supplementing RP with anodal tDCS exhibited superior online motor skills. This online benefit, as increased encoding of motor memories showed, increased resistance of offline forgetting over 6 hours and significant offline improvement, which lasted for 72 hours compared to RP without stimulation.

The implications of this study suggest training under IP format as opposed to RP is more effective in acquiring motor skills and leads to superior long-term retention of these skills for up to 72 hours after training has been completed. Moreover, we confirmed that heightened activity of PMd had a positive effect on encoding of motor memories, which was reflected in a significant offline gain following overnight sleep.

We hope our findings provide an interesting insight to enhancing motor skills learning and the development of practice-based neurorehabilitation programs for motor recovery after motor impairment. We believe our study is a critical and necessary step prior to translation to a clinical setting.

Learn more by reading our research article: Improving online and offline gain from repetitive practice using anodal tDCS at dorsal premotor cortex published by npj Science of Learning.

Reference

Kim, T., Buchanan, J.J., Bernard, J.A. et al. Improving online and offline gain from repetitive practice using anodal tDCS at dorsal premotor cortex. npj Sci. Learn. 6, 31 (2021). https://doi.org/10.1038/s41539-021-00109-4