Selective changes in cerebellar-cortical processing following motor training.

The aim of this study was to investigate the effect of varying stimulation rate and the effects of a repetitive typing task on the amplitude of somatosensory evoked potential (SEP) peaks thought to relate to cerebellar processing. SEPs (2,000 sweep averages) were recorded following median nerve stimulation at the wrist at frequencies of 2.47, 4.98, and 9.90 Hz from 12 subjects before and after a 20-min repetitive typing task. Typing and error rate were recorded 2-min pre- and post-typing task. Effect of stimulation rate was analysed with ANOVA followed by pairwise comparisons (paired t tests). Typing effects were analysed by performing two-tailed paired t tests. Increasing stimulation frequency significantly decreased the N30 SEP peak amplitude (p < 0.02). Both the 4.98 and 9.90 Hz rates lead to significantly smaller N30 peak amplitudes compared to the 2.47 Hz (p ≤ 0.01). The N24 amplitude significantly increased following the typing task for both 4.98 and 2.47 Hz (p ≤ 0.025). In contrast, there was a highly significant decrease (p < 0.001) in the N18 peak amplitude post-typing at all frequencies. Typing rate increased (p < 0.001) and error rate decreased (p < 0.05) following the typing task. The results suggest that the N24 SEP peak amplitude is best recorded at 4.98 Hz since the N30 amplitude decreases and no longer contaminates the N24 peak, making the N24 visible and easier to measure, while still enabling changes due to repetitive activity to be measured. The decrease in N18 amplitude along with an increase in N24 amplitude with no change in N20 amplitude may be explained by the intervention reducing inhibition at the level of the cuneate nucleus and/or interior olives leading to alterations in cerebellar-cortical processing.