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.

Priming Effects of Water Immersion on Paired Associative Stimulation-Induced Neural Plasticity in the Primary Motor Cortex

“…Priming the activity of specific interneurons synapsing in M1 was found to alter the neural plasticity without modifying M1 excitability [43,44], thus supporting the notion that heterosynaptic plasticity may account for the effects of priming. Experiments 2 and 3 indicated that WI did not alter corticospinal excitability or intracortical excitability, consistent with previous studies [39,45]. In contrast, the cholinergic activity, as evaluated by SAI, significantly increased for at least 8.5 min after WI and returned to baseline at 21.5 min post-WI.…”

Nonpainful wide-area compression inhibits experimental pain

“… 20 , 43 , 54 Increase in M1 excitability was also reported in response to large-area non-noxious somatosensory stimuli. This was demonstrated by reduced motor activity threshold, increased amplitude of motor-evoked potentials, and increased intracortical facilitation in response to whole-hand or whole-body water flow stimulation 60 , 61 and in response to whole-hand mesh-flow electrical stimulation. 23 , 24 Thus, the theoretical increase in M1 excitability in large-body compression can be attributed to CIA in our study.…”

Energetic responses of head-out water immersion at different temperatures during post-exercise recovery and its consequence on anaerobic mechanical power

“…In contrast, the performance improvement seen after HWI could be attributed to the increase in muscle temperature through heat conduction and by peripheral vasodilation, contributing to faster restoration of energy stores and acceleration of the rate of cross-bridge disconnection (Stienen et al 1996;He et al 2000). Although con rmed only when associated with water movement at thermoneutral temperatures (Sato et al 2014;Sato et al 2015), stimulation of peripheral thermoreceptors during immersions at 40°C could contribute to increased performance by virtue of increased corticospinal excitability, decreased intracortical inhibition and increased intracortical facilitation (Sato et al 2015). All these factors could explain the increase in muscle contraction speed.…”