The intensity of continuous theta burst stimulation, but not the waveform used to elicit motor evoked potentials, influences its outcome in the human motor cortex

Takuya Sasaki; Satoshi Kodama; Naohiko Togashi; Yuichiro Shirota; Yusuke Sugiyama; Shin-Ichi Tokushige; Satomi Inomata-Terada; Yasuo Terao; Yoshikazu Ugawa; Masashi Hamada

doi:10.1016/j.brs.2017.12.003

The intensity of continuous theta burst stimulation, but not the waveform used to elicit motor evoked potentials, influences its outcome in the human motor cortex

Brain Stimul. 2018 Mar-Apr;11(2):400-410. doi: 10.1016/j.brs.2017.12.003. Epub 2017 Dec 15.

Affiliations

¹ Department of Neurology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
² Department of Neurology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; Department of Neurology, Kyorin University School of Medicine, Tokyo, Japan.
³ Department of Neurology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; Department of Cell Physiology, Kyorin University School of Medicine, Tokyo, Japan.
⁴ Department of Neurology, School of Medicine, Fukushima Medical University, Fukushima, Japan; Fukushima Global Medical Science Center, Advanced Clinical Research Center, Fukushima Medical University, Fukushima, Japan.
⁵ Department of Neurology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan. Electronic address: mhamada-tky@umin.net.

PMID: 29258807
DOI: 10.1016/j.brs.2017.12.003

Abstract

Background: Responses to continuous theta burst stimulation (cTBS) applied to the human primary motor cortex are highly variable between individuals. However, little is known about how to improve the after-effects of cTBS by adjusting the protocol characteristics.

Objective: We examined whether current directions adopted in the measurement of cortical motor excitability indexed as motor evoked potentials (MEPs) affect the responses to cTBS. We also tested whether the stimulus intensity of cTBS influences the after-effects.

Methods: Thirty-one healthy volunteers participated. The after-effects of cTBS with the conventional intensity of 80% of individual active motor threshold (AMT) (cTBS_80%) were tested by measuring MEP amplitudes induced by not only posterior-anterior (PA) but also anterior-posterior (AP) and biphasic (PA-AP) currents. We also investigated cTBS with 65% AMT (cTBS_65%) and 100% AMT (cTBS_100%) in subjects who showed depression of MEP amplitudes after cTBS_80%, as well as cTBS_65% in subjects in whom facilitation of MEPs was induced by cTBS_80%. RESULTS: Current directions in MEP measurement had no influence on the cTBS responses. In subjects whose MEPs were depressed by cTBS_80%, cTBS_100% partly induced MEP facilitation, while cTBS_65% abolished the after-effects. In subjects who showed MEP facilitation by cTBS_80%, cTBS_65% partly induced MEP depression.

Conclusions: Stimulus intensity of cTBS influenced the responses to cTBS, and lowering stimulus intensity induced the expected after-effects of cTBS in some subjects.

Keywords: Continuous theta burst stimulation (cTBS); Motor cortex; Plasticity; Transcranial magnetic stimulation (TMS); Variability.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adult
Evoked Potentials, Motor*
Female
Humans
Male
Middle Aged
Motor Cortex / physiology*
Neuronal Plasticity
Theta Rhythm*
Transcranial Magnetic Stimulation