Motor cortical plasticity and corticospinal tract diffusion tensor image in patients with Parkinson’s disease and essential tremor

Abstract

s / Brain Stimulation 8 (2015) 326e342 342 Background: Non-invasive brain stimulation (NIBS) protocols can interfere with or even facilitate motor learning. However, it is still unclear whether the response to NIBS protocols, such as theta-burst stimulation (TBS), can predict its ability to interfere with or enhance learning of a motor task. We aim to investigate this question using TBS and a ballistic finger movement task. Methods: Eight right handed healthy human volunteers participated in the study. Experiment 1: We investigated the effects of continuous TBS (cTBS) and intermittent TBS (iTBS) on cortical excitability. Thirty motor evoked potentials (MEP) were measured before and after intervention (cTBS or iTBS) for 30 min. Experiment 2: In separate sessions, we tested the effects of cTBS or iTBS on a ballistic finger movement task. Subjects were required to make rapid index finger abduction movements of the right hand paced at a rate of 0.5 Hz. One block consists of 75 movements for 2.5 min and 4 blocks were tested in total. Between blocks 2 and 3, either cTBS or iTBS was applied over left M1. We quantified the learning effect by measuring the increase the mean peak acceleration (ACC) for each set of 30 consecutive movements. Results: In experiment 1, there was a non-significant trend for MEPs to get smaller after cTBS and larger after iTBS. In experiment 2, cTBS or iTBS did not change ACC immediately after application of TBS. However, ACC increased significantly more in the final block of trials after cTBS than it did after iTBS. The normalized ACC in the last block was negatively correlated with excitability changes induced by cTBS in experiment 1 (Spearman’s r 1⁄4 0.881, p 1⁄4 0.002). Conclusions: This preliminary result suggest that cTBS did not affect early consolidation in M1, but facilitated further performance gains in model-free learning. The effect on performance was correlated with the effect of cTBS on MEPs.