title: Whole-body water flow stimulation to the lower limbs modulates excitability of primary motor cortical regions innervating the hands: a transcranial magnetic stimulation study.
abstract: Whole-body water immersion (WI) has been reported to change sensorimotor integration. However, primary motor cortical excitability is not affected by low-intensity afferent input. Here we explored the effects of whole-body WI and water flow stimulation (WF) on corticospinal excitability and intracortical circuits. Eight healthy subjects participated in this study. We measured the amplitude of motor-evoked potentials (MEPs) produced by single transcranial magnetic stimulation (TMS) pulses and examined conditioned MEP amplitudes by paired-pulse TMS. We evaluated short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) using the paired-TMS technique before and after 15-min intervention periods. Two interventions used were whole-body WI with water flow to the lower limbs (whole-body WF) and whole-body WI without water flow to the lower limbs (whole-body WI). The experimental sequence included a baseline TMS assessment (T0), intervention for 15 min, a second TMS assessment immediately after intervention (T1), a 10 min resting period, a third TMS assessment (T2), a 10 min resting period, a fourth TMS assessment (T3), a 10 min resting period, and the final TMS assessment (T4). SICI and ICF were evaluated using a conditioning stimulus of 90% active motor threshold and a test stimulus adjusted to produce MEPs of approximately 1-1.2 mV, and were tested at intrastimulus intervals of 3 and 10 ms, respectively. Whole-body WF significantly increased MEP amplitude by single-pulse TMS and led to a decrease in SICI in the contralateral motor cortex at T1, T2 and T3. Whole-body WF also induced increased corticospinal excitability and decreased SICI. In contrast, whole-body WI did not change corticospinal excitability or intracortical circuits.
authors.affiliation: Institute for Human Movement and Medical Sciences, Niigata University of Health and Welfare, Niigata City, Japan; Department of Health and Sports, Niigata University of Health and Welfare, Niigata City, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Sato
authors.affiliation: Institute for Human Movement and Medical Sciences, Niigata University of Health and Welfare, Niigata City, Japan; Department of Health and Sports, Niigata University of Health and Welfare, Niigata City, Japan.
authors.forename: Koya
authors.initials: K
authors.lastname: Yamashiro
authors.affiliation: Institute for Human Movement and Medical Sciences, Niigata University of Health and Welfare, Niigata City, Japan; Department of Physical Therapy, Niigata University of Health and Welfare, Niigata City, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Onishi
authors.affiliation: Department of Health and Sports, Niigata University of Health and Welfare, Niigata City, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Baba
authors.affiliation: Department of Health and Sports, Niigata University of Health and Welfare, Niigata City, Japan.
authors.forename: Sho
authors.initials: S
authors.lastname: Nakazawa
authors.affiliation: Department of Health and Sports, Niigata University of Health and Welfare, Niigata City, Japan.
authors.forename: Yoshimitsu
authors.initials: Y
authors.lastname: Shimoyama
authors.affiliation: Institute for Human Movement and Medical Sciences, Niigata University of Health and Welfare, Niigata City, Japan; Department of Health and Sports, Niigata University of Health and Welfare, Niigata City, Japan.
authors.forename: Atsuo
authors.initials: A
authors.lastname: Maruyama
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor; D006225:Hand / Q000294:innervation*; D006801:Humans; D007101:Immersion; D007866:Leg / Q000502:physiology*; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D055698:Touch Perception; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult