Time course of corticospinal excitability changes following a novel motor training task.

Motor learning is known to take place over several days, and there are a number of studies investigating the time course of improvements in motor performance, yet only a limited number that have investigated the time course of neurophysiological changes that accompany motor learning. The aim of this study was to investigate the time course of changes to corticospinal excitability, following novel motor training in the dominant hand, during two sessions of motor training and testing. This study used the slope of transcranial magnetic stimulation (TMS) input-output (I/O) curves elicited at stimulator intensities between 90 and 150% of resting motor threshold for the first dorsal interosseous (FDI) muscle in order to measure corticospinal excitability. The I/O curves for 12 right-handed males (M age: 21.9+-0.5 years, [Laterality Index]=83.42 SD=4.9) were elicited before and after the performance of novel motor tracing task performed with the right hand on two different testing days. Participants had significant improvements in motor performance during both the initial (mean error improvement=31%, SD=7%, F(1, 11)=22.439 with p=0.001) and follow up session (mean error improvement=19%, SD=6%, F(1, 11)=17.85 with p=0.001). The slope of the TMS I/O curve decreased significantly over the four training blocks, F(1,11)=8.149, p=0.016, however pre-planned contrasts within the repeated measures ANOVA indicated that the decrease was only significant relative to baseline following the first day of training F(1,11)=10.476, p=0.008. This study found that corticospinal excitability measured using I/O curves decreases in response to performance of a novel motor training task, and the majority of this excitability change occurs on the first training day.