Tatsunori Watanabe

Transcranial static magnetic stimulation (tSMS) is a non-invasive neuromodulation technique that reduces cortical excitability. Although tSMS has been reported to attenuate interhemispheric inhibition (IHI) within the motor cortex, its effects on IHI within the primary somatosensory cortex (S1) remain unclear. The purpose of this study was to determine whether tSMS over the S1 modulates somatosensory IHI using a paired somatosensory evoked potentials (pSEPs) paradigm. In a randomized crossover design, twenty-five healthy young adults received either tSMS or sham stimulation over the right S1 (C4 in the international 10–20 system) for 20 min. SEPs were elicited by a test stimulus delivered to the right median nerve, preceded by a conditioning stimulus (CS) delivered to the left median nerve at an interstimulus interval of 10 ms. Recordings were obtained before, immediately after, and 20 min after stimulation. In addition to the N20 and P27 SEP components, high-frequency oscillations (HFOs) were extracted and classified into early (eHFOs) and late (lHFOs) components relative to the N20 peak latency. TSMS over the right S1 significantly reduced CS-induced suppression of lHFOs in the left S1 immediately after stimulation, whereas eHFOs and N20/P27 components remained unchanged. Given that N20/P27 components, eHFOs, and lHFOs are thought to reflect activity in Brodmann area 3b of the S1, thalamocortical input, and GABAergic interneuron activity, respectively, these findings are consistent with the possibility that tSMS modulates transcallosal interactions involving intracortical inhibitory processing within the somatosensory system.

Transcranial static magnetic field stimulation (tSMS) is a non-invasive brain stimulation technique known to reduce cortical excitability. Although its effectiveness has been demonstrated in various cortical regions, it remains unclear whether somatosensory processing is influenced by this stimulation. The purpose of this study was to investigate whether tSMS over the primary somatosensory cortex (S1) modulates somatosensory evoked potentials (SEPs) and high-frequency oscillations superimposed on them (somatosensory HFOs). In a randomized crossover study, twenty healthy young adults received tSMS or sham stimulation over the left S1 (corresponding to C3 of the international 10–20 system) for 20 min. SEPs were recorded in response to right median nerve stimulation before, immediately after, and 20 min after stimulation. Somatosensory HFOs were extracted by applying a 400–800 Hz band-pass filter to SEP waveforms and separated into early and late components relative to the N20 peak latency. TSMS over the left S1 significantly reduced the amplitude of early HFOs 20 min after stimulation, whereas late HFOs remained unchanged. No effects of tSMS were observed on the N20 component of standard SEPs, which reflects neural activity in area 3b of the S1. Early and late HFOs are thought to reflect the action potentials of thalamocortical fibers and the activity of GABAergic interneurons, respectively. These findings therefore suggest that tSMS over the S1 selectively attenuates thalamocortical input while exerting no effect on GABAergic interneuron activity.

Background: Precise finger force control is essential for performing everyday tasks such as writing, buttoning, and eating. While the neurophysiological basis of cognitive skill learning has been extensively studied, much less is known about the neural mechanisms supporting the acquisition of fine motor skills involving finger force control. This study aimed to investigate changes in cortical oscillatory activity and event-related potentials (ERPs) associated with the acquisition of fine finger force control. Results: Eighteen right-handed healthy young adults practiced a visual target-matching task using a left-hand pinch grip. Force control performance and electroencephalogram (EEG) recordings were assessed before and after training. Behavioral analyses revealed significant improvements in time to target, velocity to target, mean force error, and force variability, with no changes in reaction time. EEG analysis showed enhanced alpha- and beta-band event-related desynchronization after learning. ERP analysis further revealed a significant reduction in N2 amplitude and a significant increase in P3 amplitude following learning. Conclusions: These results suggest that learning fine finger force control is accompanied by enhanced visuomotor processing, more efficient stimulus discrimination, and greater attentional allocation. This study provides novel insights into the neurophysiological underpinnings of fine motor skill acquisition.

Interventions to improve activities of daily living (ADL) remain undeveloped for unilateral spatial neglect (USN). This case study examined the effects of combining visual scanning training (VST) and electrical stimulation during walking on ADL for USN. The patient was a 62-year-old right-handed man with dissection and occlusion of the right middle cerebral artery, who was transferred to our hospital on the 11th day from stroke onset. After approximately two months of conventional therapy, he was able to walk without an aid, but frequently overlooked objects and people on the left, requiring assistance. Thereafter, he underwent 14 days of combined VST with transcutaneous electrical nerve stimulation on his left posterior neck muscle during walking in addition to conventional physical therapy. The effectiveness of the intervention was assessed using the Behavior Inattention Test conventional subtest (BIT-c), Catherine Bergego Scale (CBS), and a computer-based assessment of top-down and bottom-up attention. Following the intervention, the BIT-c and CBS scores improved from 141 to 145 and from 11 to 2, respectively, and he rarely overlooked objects while walking. In addition, there was an improvement in attention automatically directed by external stimuli (bottom-up attention). These improvements were maintained at two-week follow-up. These findings suggest that the combined training during walking may have contributed to the improvement of ambulatory ADL in this stroke patient with USN, highlighting its potential relevance for functional independence in similar cases.