title: Neural mechanisms underlying the changes in ipsilateral primary motor cortex excitability during unilateral rhythmic muscle contraction.
abstract: 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.
authors.affiliation: Human Motor Control Laboratory, Division of Human Sciences, Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Uehara
authors.forename: Takuya
authors.initials: T
authors.lastname: Morishita
authors.forename: Shinji
authors.initials: S
authors.lastname: Kubota
authors.forename: Kozo
authors.initials: K
authors.lastname: Funase
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D003463:Cues; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006225:Hand / Q000502:physiology*; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D017397:Prefrontal Cortex / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult