Publications by authors named "Syusaku Sasada"
Article Synopsis
- The study explores how the intensity of a pre-contraction (Test 1) affects the EMG activity of the biceps brachii during a weak elbow flexion task (Test 2) after strong contractions (conditioning).
- Results indicated that a 2% test contraction intensity (TCI) led to increased EMG activity in Test 2, while a 20% TCI resulted in decreased EMG activity.
- Additionally, spectral analysis showed that lower intensity levels improve certain brain wave patterns (α- and β-band power ratios) in EMG signals after intensive muscle contraction, highlighting the importance of test contraction intensity on muscle response.
Article Synopsis
- - The study examined the impact of ankle joint position on cutaneous reflexes in the peroneus longus (PL) muscle among patients with chronic ankle instability (CAI) compared to age-matched controls.
- - Researchers stimulated the sural nerve while participants stood in different ankle positions, revealing that CAI patients had a more pronounced suppressive middle latency cutaneous reflex (MLR) during neutral standing than controls, but not during extreme inversion.
- - The results indicated that CAI patients experienced deterioration in their sensory-motor system, affecting both reflex response and ankle position sense, highlighting differences between them and healthy controls.
Objective: The aim of this study was to assess safety issues of self-controlled repetitive trans-vertebral magnetic stimulation (rTVMS) in humans.
Methods: We investigated effects of self-controlled rTVMS (≤20 Hz, ≤90% intensity) on vital signs and subjective sensations in 1690 trials of 30 healthy volunteers and 12 patients with spinal cord disorders.
Results: Healthy volunteers and the patients received 4595 ± 2345, and 4450 ± 2304 pulses in one day, respectively.
Article Synopsis
- - The study examines the CPN reflex, an involuntary response triggered by low-intensity electrical stimulation of the common peroneal nerve, which supports body weight during walking and shows increased activity during heel strikes.
- - Researchers tested 28 subjects who performed arm cycling while measuring changes in the CPN reflex, finding that the reflex was significantly stronger during cycling than before it, with modulation occurring only at specific stimulation intensities.
- - The increase in CPN reflex during arm cycling suggests a neural connection between arm and leg movements, indicating that locomotion of the arms may influence how knee extensor muscles respond to ankle signals, although the exact mechanisms remain unclear.
Sprint motor performance, such as in short-distance running or cycling, gradually decreases after reaching a maximum speed or cadence. This may be attributed to the central nervous system. Brain stimulation studies have recently revealed the plastic nature of the human brain and spinal cord, but it is unclear how direct current stimulation (DCS) affects sprint motor performance.
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- * ELCR amplitudes were found to be higher during simultaneous arm and leg cycling compared to when each limb was cycled separately, indicating some form of neural integration.
- * The research suggests that there is a shared neural mechanism in the spinal cord that activates the ELCR reflex pathway specifically during rhythmic movements, receiving coordination from both arms and legs.
Controlling a neuroprosthesis requires learning a novel input-output transformation; however, how subjects incorporate this into limb control remains obscure. To elucidate the underling mechanisms, we investigated the motor adaptation process to a novel artificial recurrent connection (ARC) from a muscle to a peripheral nerve in healthy humans. In this paradigm, the ulnar nerve was electrically stimulated in proportion to the activation of the flexor carpi ulnaris (FCU), which is ulnar-innervated and monosynaptically innervated from Ia afferents of the FCU, defined as the "homonymous muscle," or the palmaris longus (PL), which is not innervated by the ulnar nerve and produces similar movement to the FCU, defined as the "synergist muscle.
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- The study investigates the changes in middle latency cutaneous reflexes (MLRs) in the peroneus longus (PL) muscle after an ankle sprain, focusing on how these changes relate to the number of sprains someone has experienced.
- Twenty-three subjects with varying histories of ankle sprains were compared to an age-matched control group while their MLRs were measured through nerve stimulation during ankle movements.
- Results indicated that MLR gains increased 4 weeks post-injury, with first-time sprainers returning to baseline in 3 months, while those with recurrent sprains showed prolonged MLR changes, correlating with their functional recovery.
Gait disturbance in individuals with spinal cord lesion is attributed to the interruption of descending pathways to the spinal locomotor center, whereas neural circuits below and above the lesion maintain their functional capability. An artificial neural connection (ANC), which bridges supraspinal centers and locomotor networks in the lumbar spinal cord beyond the lesion site, may restore the functional impairment. To achieve an ANC that sends descending voluntary commands to the lumbar locomotor center and bypasses the thoracic spinal cord, upper limb muscle activity was converted to magnetic stimuli delivered noninvasively over the lumbar vertebra.
View Article and Find Full Text PDFThe corpus callosum is essential for neural communication between the left and right hemispheres. Although spatiotemporal coordination of bimanual movements is mediated by the activity of the transcallosal circuit, it remains to be addressed how transcallosal neural activity is involved in the dynamic control of bimanual force execution in human. To address this issue, we investigated transcallosal inhibition (TCI) elicited by single-pulse transcranial magnetic stimulation (TMS) in association with the coordination condition of bimanual force regulation.
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- Voluntary muscle contractions lead to similar electrical activity (EMG) in the opposite muscle, not just in infants or patients but also in healthy adults, indicating a "mirror-like" response.
- This study analyzed how skin reflexes in the left hand are influenced by this mirror activity when participants quickly moved their right index finger during a reaction time task.
- Results showed that the reflexes in the left hand were enhanced around the same time as the right hand's muscle activity began, suggesting that these reflexes are closely linked to the voluntary movements happening in the opposite side.
The functional coupling of neural circuits between the upper and lower limbs involving rhythmic movements is of interest to both motor control research and rehabilitation science. This coupling can be detected by examining the effect of remote rhythmic limb movement on the modulation of reflex amplitude in stationary limbs. The present study investigated the extent to which rhythmic leg pedaling modulates the amplitude of an early latency (peak 30-70 ms) cutaneous reflex (ELCR) in the upper limb muscles.
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