Different patterns of excitation and inhibition of the small hand and forearm muscles from magnetic brain stimulation in humans

Lin Wu, Yoshinobu Goto, Takayuki Taniwaki, Naoko Kinukawa, Shozo Tobimatsu

Research output: Contribution to journalArticle

43 Citations (Scopus)

Abstract

Objectives: The objective of the present study is to quantify the effects of voluntary muscle contraction of the small hand (abductor pollicis brevis, first dorsal interosseus (FDI)) and forearm muscles (extensor carpi radialis (ECR), extensor carpi ulnaris (ECU), flexor carpi radialis (FCR) and flexor carpi ulnaris (FCU)) on motor evoked potentials (MEPs). Methods: MEPs were recorded in 12 healthy subjects by a circular coil placed over the vertex at 1.2 times the resting motor threshold at different levels of the muscle contraction (0-100% of maximum voluntary contraction (MVC)). The effects of transcranial magnetic stimulation (TMS) on the onset latency, MEP area and silent period (SP) as a function of the %MVC were evaluated using a piecewise linear regression analysis. Results: The MEP areas for the small hand muscles were almost completely saturated at 20% of MVC. In contrast, the MEP areas for radial muscles (ECR, FCR) had a dual increase at 40% of MVC while the ulnar muscles (ECU, FCU) had a dual increase at 20% of MVC. A uniform latency shift (1.5-3ms reduction) was observed in all muscles with a changing point at 10% of MVC. The SPs were the longest for FDI and were not significantly influenced by MVC for any muscles. Conclusions: The excitatory and inhibitory effects of TMS on the MEPs differed for the small hand and forearm muscles and also between the ulnar and radial muscles. These results probably resulted from the different degrees of direct corticomotoneuronal inputs to each muscle and the inherent properties of the spinal motoneurons.

Original languageEnglish
Pages (from-to)1286-1294
Number of pages9
JournalClinical Neurophysiology
Volume113
Issue number8
DOIs
Publication statusPublished - Aug 23 2002

All Science Journal Classification (ASJC) codes

  • Sensory Systems
  • Neurology
  • Clinical Neurology
  • Physiology (medical)

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