Training in a ballistic task but not a visuomotor task increases responses to stimulation of human corticospinal axons

Giesebrecht S, van Duinen H, Todd G, Gandevia SC, Taylor JL. Training in a ballistic task but not a visuomotor task increases responses to stimulation of human corticospinal axons. J Neurophysiol 107: 2485-2492, 2012. First published February 8, 2012; doi:10.1152/jn.01117.2010.-Short periods of training in motor tasks can increase motor cortical excitability. This study investigated whether changes also occur at a subcortical level. Subjects trained in ballistic finger abduction or visuomotor tracking. The right index finger rotated around the metacarpophalangeal (MCP) joint in a splint. Surface EMG was recorded from the first dorsal interosseous. Transcranial magnetic stimulation over the back of the head (double-cone coil) elicited cervicomedullary motor evoked potentials (CMEPs) by stimulation of corticospinal axons. Responses were recorded from the relaxed muscle before, between, and after two sets of training. In study 1 (n = 7), training comprised two sets of 150 maximal finger abductions. Feedback of acceleration was provided. With training, acceleration increased significantly. CMEPs increased to 248 +/- 152% (+/- SD) of baseline immediately after training (P = 0.007) but returned to control level (155 +/- 141%) 10 min later. In study 2 (n = 7), subjects matched MCP joint angle to a target path on a computer screen. After similar to 30 min of training, tracking improved as shown by increased correlation between joint angle and the target pathway, reduced time lag, and reduced EMG(rms). However, CMEPs remained unchanged. These results show that transmission through the corticospinal pathway at a spinal level increased after repeated ballistic movements but not after training in a visuomotor task. Thus, changes at a spinal level may contribute to improved performance in some motor tasks.