Reversed Effects of Intermittent Theta Burst Stimulation following Motor Training That Vary as a Function of Training-Induced Changes in Corticospinal Excitability.

Tino Stöckel,Mark R Hinder,Jeffery J Summers

doi:10.1155/2015/578620

Abstract

Intermittent theta burst stimulation (iTBS) has the potential to enhance corticospinal excitability (CSE) and subsequent motor learning. However, the effects of iTBS following motor learning are unknown. The purpose of the present study was to explore the effect of iTBS on CSE and performance following motor learning. Therefore twenty-four healthy participants practiced a ballistic motor task for a total of 150 movements. iTBS was subsequently applied to the trained motor cortex (STIM group) or the vertex (SHAM group). Performance and CSE were assessed before motor learning and before and after iTBS. Training significantly increased performance and CSE in both groups. In STIM group participants, subsequent iTBS significantly reduced motor performance with smaller reductions in CSE. CSE changes as a result of motor learning were negatively correlated with both the CSE changes and performance changes as a result of iTBS. No significant effects of iTBS were found for SHAM group participants. We conclude that iTBS has the potential to degrade prior motor learning as a function of training-induced CSE changes. That means the expected LTP-like effects of iTBS are reversed following motor learning.

Highlights

Theta burst stimulation (TBS) is a noninvasive brain stimulation (NBS) technique whereby high frequency, subthreshold, bursts of transcranial magnetic stimulation can induce plastic change within human motor cortex (M1)
While the results showed that Intermittent theta burst stimulation (iTBS), when applied following the longer motor learning protocol, facilitated corticospinal excitability (CSE) without affecting motor performance, this finding was based on data from only 5 participants
Following iTBS, these improvements were reduced to 63% (MD = −0.45; confidence intervals (CI): −0.64, −0.26) in the STIM group but remained stable in the SHAM group (MD = 0.04; CI: −0.16, 0.23)

Summary

Introduction

Theta burst stimulation (TBS) is a noninvasive brain stimulation (NBS) technique whereby high frequency, subthreshold, bursts of transcranial magnetic stimulation can induce plastic change within human motor cortex (M1). Huang and colleagues [1] reported that intermittent TBS (iTBS) elicited increases in motor evoked potential (MEP) amplitude (indicative of enhanced cortical excitability), whereas continuous TBS (cTBS) resulted in the opposite effects. These and subsequent findings [2,3,4] are consistent with the view that iTBS and cTBS induce long-term potentiation- (LTP-) like plasticity and long-term depression- (LTD-) like plasticity, respectively. Understanding the nature of the metaplastic interaction (i.e., homeostatic versus nonhomeostatic) between NBS and motor learning is of particular interest in regard to clinical applications for NBS, where gains in motor performance are the desired behavioral outcome

Objectives

Methods

Results

Discussion

Conclusion