Further evidence for excitability changes in human primary motor cortex during ipsilateral voluntary contractions

Liang Nan

Murakami Tsuneji

Funase Kozo

Narita Tomohiro

Kasai Tatsuya

Neuroscience Letters

The present study aimed to further investigate whether the intracortical neural circuits within the primary motor cortex (M1) are modulated during ipsilateral voluntary finger movements. Single- and paired-pulse (interstimulus intervals, ISIs; 3 ms and 12 ms) transcranial magnetic stimulations of the left M1 were applied to elicit motor evoked potential (MEP) in the right first dorsal interosseous (Rt-FDI) muscle during voluntary contractions (10% and 30% maximum voluntary contraction) of the left FDI (Lt-FDI) muscle. F-waves of Rt-FDI muscle were recorded under these left index-finger conditions for ensuring that the excitability changes occur at the supraspinal level. MEPs were also recorded during motor imagery of the left index-finger abduction instead of overt movement. The results showed that, in single-pulse transcranial magnetic stimulation (TMS) paradigm, MEPs in Rt-FDI muscle were markedly enhanced during voluntary contractions of Lt-FDI muscle compared with the complete resting state. In paired-pulse TMS paradigm, the short intracortical inhibition was significantly reduced in proportion to increments of the ipsilateral muscle contraction, whereas the intracortical facilitation had no change. F-wave of Rt-FDI muscle was unchanged under these conditions, while MEP in Rt-FDI muscle was also enhanced during motor imagery of the left index-finger abduction. Based on the present results, it is suggested that the intracortical inhibitory neural circuits may be modulated in the transition from rest to activity of the ipsilateral homonymous muscle. The excitability changes in M1 might be induced by overflows of voluntary drive given to the ipsilateral limb, probably via the transcallosal pathway.

short intracortical inhibition

SICI

intracortical facilitation

ICF

motor imagery

primary motor cortex

motor evoked potential

MEP

transcranial magnetic stimulation

TMS

Sports and physical training [ 780 ]

Medical sciences [ 490 ]

eng

Elsevier Ireland Ltd

Copyright (c) 2008 Elsevier Ireland Ltd.

[ISSN] 0304-3940

[DOI] 10.1016/j.neulet.2007.12.058

[NCID] AA00754925

[DOI] http://dx.doi.org/10.1016/j.neulet.2007.12.058