Anodal tDCS over Primary Motor Cortex Provides No Advantage to Learning Motor Sequences via Observation

Abstract

When learning a new motor skill, we benefit from watching others. It has been suggested that observation of others' actions can build a motor representation in the observer, and as such, physical and observational learning might share a similar neural basis. If physical and observational learning share a similar neural basis, then motor cortex stimulation during observational practice should similarly enhance learning by observation as it does through physical practice. Here, we used transcranial direct-current stimulation (tDCS) to address whether anodal stimulation to M1 during observational training facilitates skill acquisition. Participants learned keypress sequences across four consecutive days of observational practice while receiving active or sham stimulation over M1. The results demonstrated that active stimulation provided no advantage to skill learning over sham stimulation. Further, Bayesian analyses revealed evidence in favour of the null hypothesis across our dependent measures. Our findings therefore provide no support for the hypothesis that excitatory M1 stimulation can enhance observational learning in a similar manner to physical learning. More generally, the results add to a growing literature that suggests that the effects of tDCS tend to be small, inconsistent, and hard to replicate. Future tDCS research should consider these factors when designing experimental procedures.

The time course of ineffective sham‐blinding during low‐intensity (1 mA) transcranial direct current stimulation

“…Secondly, 10 min of 1 mA anodal tDCS to the primary motor cortex failed to reduce reaction times relative to sham. These results add to previously reported null findings relating to stimulation of the primary motor cortex (Apšvalka, Ramsey, & Cross, ; Conley, Fulham, Marquez, Parsons, & Karayanidis, ; Conley et al., ; Horvath, Vogrin, Carter, Cook, & Forte, ; Turkakin et al., ). Since Minarik et al.…”

The Time Course of Ineffective Sham Blinding During 1mA tDCS

“…As a secondary finding, we also failed to find a difference in reaction times during anodal tDCS relative to sham, adding to previous null results relating to stimulation of the primary motor cortex [26][27][28][29][30]. Since Minarik et al (2016) did not include a sham protocol, it was not possible to determine whether the anodal tDCS resulted in improved reaction times, or whether the cathodal protocol had actively inhibited motor learning throughout the task.…”

Double transcranial direct current stimulation of the brain increases cerebral energy levels and systemic glucose tolerance in men

“…Because tDCS also affects the contralateral hemisphere of the brain, it is likely that stimulation in another area of the cortex would lead to a similar increase in cerebral energy consumption, with anodal stimulation over the motor cortex not being essential for the observed effect. However, when discussing the targeted stimulation area, it should be noted that the chosen electrode montage in the present study is a commonly used and established procedure of anodal tDCS of the primary motor cortex and, moreover, this enables a good comparison with our previous investigation, as well as a variety of other studies applying the same stimulation protocol. Nevertheless, the assumed excitatory effects of anodal tDCS cannot be considered as a standing rule because anodal tDCS could also evoke inhibitory effects .…”