Comparison of subjective peripheral sensation, F-waves, and somatosensory evoked potentials in response to a unilateral pinch task measured on the contractile and non-contractile sides

Depression of sensory input during voluntary muscle contractions has been demonstrated using electrophysiological methods in both animals and humans. However, the association between electrophysiological responses of the sensory system and subjective peripheral sensation (SPS) during a voluntary muscle contraction remains unclear. Our aim in this study was to describe the changes in SPS, spinal α-motoneuron excitability (F-wave to M-wave amplitude), and somatosensory evoked potentials (SEPs) during a unilateral pinch-grip task. Outcome variables were measured on the side ipsilateral and contralateral to the muscle contraction, and at rest (control). Participants were 8 healthy men, 20.9±0.8 years of age. The isometric pinch-grip task was performed at 30% of the maximum voluntary isometric force measured for the right and left hand separately. The appearance rate of the F-wave during the task was significantly higher for the ipsilateral (right) hand than for the contralateral (left) hand and control condition. Although there was no difference in F-wave latency between hands and the control condition, the amplitude of the F-wave was significantly higher for the ipsilateral (right) hand than for the contralateral (left) hand and the control condition. There was no difference in the amplitude of the SEP at N20. However, the amplitude at P25 was significantly lower for the ipsilateral (right) hand than for the contralateral (left) hand and the control condition. The accuracy rate of detecting tactile stimulation, evaluated for 20 repetitions using a Semmes–Weinstein monofilament at the sensory threshold for each participant, was significantly lower during the pinch-grip task for both the ipsilateral (right) and contralateral (left) hand compared to the control condition. Overall, our findings show that SPS and neurophysiological parameters were not modulated in parallel during the task, with changes in subjective sensation preceding changes in electrophysiological indices during the motor task. Our findings provide basic information on sensory-motor coordination.


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When peripheral nerves are electrically stimulated, the ascending afferent input is projected to the [11] and contralateral [9] muscles. SEP gating has also been observed in the primary sensory cortex on 58 the side contralateral to active muscle contraction [12], although there is no consensus on this finding [13].

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Moreover, although depression of sensory input during voluntary muscle contraction has been 60 demonstrated using electrophysiological methods in both animal and human studies, the association 61 between the electrophysiological response of the sensory system and subjective peripheral sensation (SPS)

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during an active muscle contraction remains unclear.

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In a previous study, we reported a reduction in cutaneous sensation on the dorsal surface of the hand 64 during an isometric pinch-grip task under submaximal conditions compared to a no-motion (rest) condition

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[10]. However, it is not clear whether this response occurred locally only in the hand on the side of the 66 contraction or would also be observed on the non-contracting side. Therefore, our aim in this study was to 67 evaluate the changes in SPS, spinal α-motoneuron excitability, and SEPs on the side ipsilateral and 68 contralateral to an active contraction of a hand muscle, the right abductor pollicis brevis (APB).

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Epochs with artifacts due to eye movement or blinking (> ±6 μV from baseline) were excluded 110 automatically prior to averaging. A plate electrode was used to record the evoked electroencephalogram 111 (Ag/AgCl electrode, NE-132B (Φ, 10 mm), Nihon Kohden, Japan). The peak-to-peak amplitude of the 112 SPE at N20 and N20-P25, from baseline, which are early components after electrostimulation, were 113 analyzed.

SPS measurement
115 Prior to the experiment, the SPS threshold on the dorsal surface of the right hand was measured using

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A typical example of the M-and F-waves is shown in Fig 1A. The appearance rate of the F-wave (Fig   152  1B)   A typical example of SEP waveforms is shown in Fig 2A. There were no differences in the SEP 167 amplitude at N20 (Fig 2B) Fig 3).

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The source of the SEP at N20 is considered to be the 3b area of the primary somatosensory cortex,

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representing the stage when the sensory stimulation reaches the primary sensory cortex via the thalamus

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[19]. The source of the SEP at P25 is considered to be higher than the 3b area [20]. Therefore, the 215 submaximal isometric pinch-grip task performed with the right hand in our study caused suppression of 216 the ipsilateral somatosensory input at a higher level than the 3b area. Previous studies on SEP gating during 217 voluntary movement have reported an absence of gating in components corresponding to N20, which is 218 consistent with findings from previous studies. For these reasons, although the electrophysiological input 10 219 that is projected to the primary somatosensory area is the same for a given amount of physical stimulation 220 (regardless of the presence or absence of the motor task), this electrophysiological input is suppressed 221 during the subsequent more complex phase of information processing. Additionally, as the amplitude of 222 all components of the SEPs was not different between the left (contralateral) hand and the control (rest)

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condition, it appears that the electrophysiological sensory input is projected from the periphery to the 224 primary somatosensory cortex, without influence from the contralateral muscle contraction.

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In our study, we used the accuracy rate for cutaneous stimulation at the sensory threshold in the right in amplitude. This phenomenon is also observed during muscle contraction on the contralateral side of the 236 filament stimulation. These results suggest that localized muscle contraction modulates the SPS even in 237 areas that are not related to a muscle contraction or movement.

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The primary limitation to generalization of our findings is that the F-wave, SEP, and SPS measurements 239 were conducted in separate sessions and not measured simultaneously in real time. As such, identification