Motor and spatial representations of action: corticospinal excitability in M1 after training with a bimanual skill.

The purpose of the study was twofold: (1) determine if different time delays (30 min or 6 h) between training and a post-training test with a rhythmic bimanual pattern (90° relative phase) would be associated with different levels of consolidation for the motor and spatial representations of the pattern; and (2) determine if training with the rhythmic bimanual pattern would lead to enhanced corticospinal excitability in M1 linked to changes in motor and spatial performance measures. Coordination accuracy and stability of the 90° pattern improved over practice. Coordination accuracy and stability were the same after a 30-min or 6-h delay between training and the post-training test, indicating equivalent levels of consolidation in the motor representation. The 6-h delay interval resulted in shorter visual recognition times compared to the 30-min delay and was centered on the trained 90° pattern. These findings indicate the consolidation of the spatial representation was more time sensitive compared to the motor representation in the current task. Motor evoked potentials (MEPs) from the first dorsal interosseous muscle (FDI) generated by single-pulse transcranial magnetic stimulation (TMS) were measured at baseline (before training) and at 6-min and 21-min intervals post-training with the 90° pattern. Increased corticospinal excitability in M1 was evidenced by larger MEPs of the FDI muscle at the 6-min interval. This increased excitability after training is a novel finding after training with a difficult and initially unstable rhythmic bimanual pattern. No significant correlations were found between the MEP data and behavioral data; thus, the increased excitability in M1 may have been linked to the difficulty in performing the pattern, consolidation processes, or both.

Application of anodal tDCS at primary motor cortex immediately after practice of a motor sequence does not improve offline gain.

Tecchio et al. (J Neurophysiology 104: 1134-1140, 2010) reported that the application of anodal tDCS at primary motor cortex (M1) immediately after practice of a procedural motor skill enhanced consolidation, which in turn improved offline gain. Tecchio et al. noted, however, that this study did not account for known after-effects associated with this form of non-invasive stimulation. The present study was designed to explicitly reevaluate Tecchio et al.'s claim. As in the original study, individuals experienced either anodal or sham stimulation at M1 after practice of a serial reaction time task (SRTT) followed by test trials 15-min later. Two additional novel conditions experienced the test trials after 120-min rather than 15-min thus allowing potential stimulation after-effects to dissipate. The expectation was that if anodal stimulation influences post-practice consolidation leading to offline gain, this effect would be present not only at 15-min but also after 120-min. In agreement with the working hypothesis, findings revealed offline gain at both 15-min and the longer 2-h time period. Unexpectedly, we found no interaction between real and sham conditions. The lack of difference between Real and Sham effects weakens confidence in the potential of post-practice tDCS for consolidation enhancement, while it is more consistent with other claims that decoupling practice and anodal tDCS stimulation in time can reduce the effectiveness of exogenous stimulation for procedural skill gain.

Expert monitoring and verbal feedback as sources of performance pressure.

The influence of monitoring-pressure and verbal feedback on the performance of the intrinsically stable bimanual coordination patterns of in-phase and anti-phase was examined. The two bimanual patterns were produced under three conditions: 1) no-monitoring, 2) monitoring-pressure (viewed by experts), and 3) monitoring-pressure (viewed by experts) combined with verbal feedback emphasizing poor performance. The bimanual patterns were produced at self-paced movement frequencies. Anti-phase coordination was always less stable than in-phase coordination across all three conditions. When performed under conditions 2 and 3, both bimanual patterns were performed with less variability in relative phase across a wide range of self-paced movement frequencies compared to the no-monitoring condition. Thus, monitoring-pressure resulted in performance stabilization rather than degradation and the presence of verbal feedback had no impact on the influence of monitoring pressure. The current findings are inconsistent with the predictions of explicit monitoring theory; however, the findings are consistent with studies that have revealed increased stability for the system's intrinsic dynamics as a result of attentional focus and intentional control. The results are discussed within the contexts of the dynamic pattern theory of coordination, explicit monitoring theory, and action-focused theories as explanations for choking under pressure.