Excitability changes in the ipsilateral primary motor cortex during rhythmic contraction of finger muscles.

The aim of this study was to determine whether the excitatory ipsilateral primary motor cortex (ipsi-M1) is affected by changes in the frequency of rhythmic voluntary contraction of the left first dorsal interosseous (FDI) induced by repetitive abduction of the left index-finger. Transcranial magnetic stimulations were delivered to the left M1 during repetitive left index-finger abduction at 1, 2, and 3Hz, and motor evoked potentials (MEPs) were simultaneously evoked in the resting right (Rt)-FDI, Rt-abductor pollicis brevis, and Rt-abductor digiti minimi. The stimulus-response (S-R) curve of the MEP at each frequency was recorded. In addition, F-waves were recorded from the Rt-FDI during these rhythmic contraction tasks in order to examine the changes in spinal motoneuron excitability. MEPs were markedly increased under the 3Hz conditions compared with the other conditions. However, F-waves were hardly changed under these conditions. The S-R curve of the MEP induced under the 3Hz conditions was significantly steeper than the curves produced under other conditions. Our results indicate that the excitability of ipsi-M1 is affected by the frequency of rhythmic voluntary contraction of unilateral finger movement, which may be caused by neural inputs delivered via a transcallosal pathway.

Uehara K ，Morishita T ，Funase K 《-》

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

Liang N ，Murakami T ，Funase K ，Narita T ，Kasai T ... -  《NEUROSCIENCE LETTERS》

Neural mechanisms underlying the changes in ipsilateral primary motor cortex excitability during unilateral rhythmic muscle contraction.

The aim of this study was to investigate the neural mechanisms underlying the changes in the ipsilateral primary motor cortex (ipsi-M1) excitability induced during the unilateral rhythmic muscle contraction of the first dorsal interosseous (FDI) (rhythmic contraction) muscle with three different frequencies of auditory cues (1, 2, and 3 Hz). The effect of different frequencies of unilateral rhythmic contraction on changes in the ipsi-M1 excitability was assessed using a single-pulse transcranial magnetic stimulation (TMS) technique when subjects were performing the unilateral rhythmic contractions according to each auditory cue frequency. After that, the changes in short intracortical inhibition (SICI)/facilitation (ICF), long intracortical inhibition (LICI) within the ipsi-M1, and interhemispheric inhibition (IHI), as well as dorsal premotor cortex to M1 (PMd-M1), and dorsolateral prefrontal cortex to M1 (DLPFC-M1) connectivity from the contralateral hemisphere to the ipsi-M1 were assessed using paired-pulse TMS techniques. The motor evoked potentials (MEP) induced in the right FDI were recorded. In the results, the ipsi-M1 excitability induced in response to single-pulse TMS was significantly decreased in the 2 Hz conditions, compared with the 1Hz and 3Hz conditions. Furthermore, PMd-M1 connectivity and LICI were significantly modulated depending on the frequency of the unilateral rhythmic contraction. In contrast, the changes in the SICI, ICF, IHI, and DLPFC-M1 were not directly associated with the rhythm frequency. These results suggest that PMd-M1 connectivity and LICI within the ipsi-M1 are likely to preferentially operate to modulate ipsi-M1 excitability during the performance of unilateral rhythmic contraction with different frequencies.

Uehara K ，Morishita T ，Kubota S ，Funase K ... -  《-》

Functional plasticity of surround inhibition in the motor cortex during single finger contraction training.

Sugawara K ，Tanabe S ，Higashi T ，Suzuki T ，Tsurumi T ，Kasai T ... -  《-》

Modulation of long-interval intracortical inhibition and the silent period by voluntary contraction.

Hammond G ，Vallence AM 《BRAIN RESEARCH》