Journal of neurophysiology最新文献

{"title":"Interlimb differences in reach-to-grasp coordination under goal- and dynamics-related perturbations.","authors":"Anna Akbaş, Mathew Yarossi, Hidetaka Hibino, Robert L Sainburg, Eugene Tunik, Mariusz P Furmanek","doi":"10.1152/jn.00260.2026","DOIUrl":"10.1152/jn.00260.2026","url":null,"abstract":"<p><p>Interlimb asymmetries in motor control are well documented in simplified tasks, but their expression in coordinated reach-to-grasp actions under perturbation remains unclear. Here, we examined whether differences between the dominant (DH) and nondominant hand (NDH) emerge during online adjustments of reach-to-grasp movements. Participants (<i>n</i> = 12; 5 females, 7 males) performed reach-to-grasp actions in a virtual environment under control, visual perturbation, and mechanical perturbation conditions. Kinematic and electromyographic (EMG) measures were analyzed, and baseline-corrected values were used to isolate perturbation-specific effects. Under control conditions, differences between hands were minimal and limited to peak transport velocity and proximal muscle activity. During perturbations, analyses performed prior to baseline correction revealed a significant Hand × Perturbation interaction for index-finger curvature, indicating hand-dependent distal reorganization during mechanical perturbation. Crucially, applying baseline correction to isolate perturbation-driven effects eliminated most global kinematic asymmetries, while revealing greater transport deceleration and triceps brachii activity in the NDH and greater index-finger curvature and extensor indicis activity in the DH during mechanical perturbation. In contrast, visual perturbations elicited largely symmetric responses across both limbs. These results indicate that interlimb differences in reach-to-grasp are not expressed as stable, fixed traits, but emerge selectively under mechanical perturbation. The observed pattern suggests that lateralized coordination strategies depend on the specific demands of the task, with the DH showing greater distal reorganization and the NDH exhibiting stronger proximal stabilization-related responses.<b>NEW & NOTEWORTHY</b> Although manual asymmetries are well known, their role in coordinated reach-to-grasp actions remains unclear. We show that interlimb differences are minimal under stable conditions but emerge selectively during mechanical perturbations. The dominant hand exhibits greater distal reorganization, whereas the nondominant hand shows stronger proximal deceleration and triceps activation. These findings suggest that motor lateralization is context-dependent and expressed through distinct responses to mechanical uncertainty.</p>","PeriodicalId":16563,"journal":{"name":"Journal of neurophysiology","volume":" ","pages":"1607-1622"},"PeriodicalIF":2.3,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149001947","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Epidermal microstructure and tactile sensitivity in the glabrous skin of hands and feet.","authors":"James R E Hall, Gabriela Gonzalez Salas Duhne, Olivia M Wallis, Clare Howarth, Hannes P Saal","doi":"10.1152/jn.00279.2026","DOIUrl":"10.1152/jn.00279.2026","url":null,"abstract":"<p><p>Glabrous skin on the human palms and soles is specialized for mechanical interaction and is characterized by papillary ridges, an absence of hair follicles, and a thick stratum corneum. Although gross morphological differences, such as the increased thickness of the plantar stratum corneum, are well-documented, the fine-scale structural features associated with individual ridges and whether they help explain differences in tactile perception remain poorly understood. Here, we employed optical coherence tomography, automated image segmentation, and three-dimensional (3-D) reconstruction to generate high-resolution models of the stratum corneum and viable epidermis across six sites on the hand and foot for 27 participants. Our morphological analysis revealed that while the stratum corneum was thicker on the foot than the hand, the thickness of the viable epidermis remained remarkably consistent across all sites. Furthermore, papillary ridge width increased in a distal-to-proximal fashion and was larger on the foot. We also found that internal ridge architecture was considerably more pronounced than the topography observable on the skin surface. Correlating these structural parameters with psychophysical measures, specifically absolute force and two-point discrimination thresholds, demonstrated distinct drivers for tactile sensitivity. Force thresholds were primarily governed by a combination of skin thickness and innervation density, and additionally, on the foot by papillary ridge width and internal ridge depth. In contrast, spatial acuity was best predicted by innervation and papillary ridge width. These findings precisely quantify glabrous skin morphology and offer new insights into the process of mechanotransduction by highlighting how tissue architecture might contribute to human tactile perception.<b>NEW & NOTEWORTHY</b> Using in vivo volumetric optical coherence tomography, we quantify and compare epidermal microstructure across glabrous skin on the hands and feet. Correlating these measures with absolute force and spatial acuity thresholds reveals that fine-scale microstructural features predict tactile sensitivity beyond coarse layer thickness and neural innervation. These findings suggest that papillary ridge width and internal ridge geometry contribute to human tactile perception.</p>","PeriodicalId":16563,"journal":{"name":"Journal of neurophysiology","volume":" ","pages":"1640-1653"},"PeriodicalIF":2.3,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149039402","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influence of force direction on motor-unit activity during low-force isometric contractions with the first dorsal interosseous muscle.","authors":"Kelsey Koger, Negar Rahimi, Logan E Alarcon-Weinman, Nicholas Toninelli, Mélanie Henry, Roger M Enoka","doi":"10.1152/jn.00269.2026","DOIUrl":"10.1152/jn.00269.2026","url":null,"abstract":"<p><p>The purpose of this study was to compare the discharge characteristics of motor units in the first dorsal interosseous (FDI) muscle when it performed low-force isometric contractions in the directions of index finger abduction, flexion, or concurrent abduction + flexion (combined). Motor-unit activity was identified from high-density surface electromyography (HD-sEMG) recordings obtained with grid electrodes attached to the skin over FDI while participants performed low-force isometric contractions at 10% of maximum in the three directions. A total of 378 motor units were identified across all participants and tasks with an average of 10.4 motor units per participant tracked across 2-3 tasks. Mean and peak discharge rates were greater during abduction than during flexion or the combined task, whereas discharge rates at recruitment and derecruitment were lower during abduction. Factor analysis identified a single dominant mode that explained >93% of the variance in motor-unit discharge rates across all directions despite directional differences in Mode 1 loadings, discharge characteristics, and correlations between motor-unit-derived signals and fluctuations in force. These findings indicate that the motor-unit discharge rates in FDI during low-force isometric contractions are organized within a single dominant low-dimensional structure that is preserved across force directions despite the modulation of discharge characteristics across directions. High-density surface electromyography (HD-sEMG) was used to identify the discharge characteristics of motor units in the first dorsal interosseous muscle during low-force isometric contractions in three directions: abduction, flexion, and concurrent abduction + flexion. A single dominant mode explained >93% of the variance in motor-unit discharge rates across the three force directions. Mode 1 loadings and the strength of coupling between motor-unit-derived signals and force fluctuations differed across directions, but the low-dimensional structure underlying motor-unit activity was preserved. These findings indicate that although motor-unit discharge characteristics were modulated across force directions, the variability in motor-unit discharge rates emerged from a single dominant mode.<b>NEW & NOTEWORTHY</b> Discharge characteristics of motor units in the first dorsal interosseous (FDI) muscle differed during low-force isometric contractions applied in three different directions: abduction, flexion, or abduction + flexion (combined). Despite these differences, a single dominant mode explained at least 93% of the variance in discharge rates across all directions. These findings indicate the low-dimensional organization underlying motor-unit activity during low-force isometric contractions with the FDI muscle is preserved across directions despite differences in discharge characteristics.</p>","PeriodicalId":16563,"journal":{"name":"Journal of neurophysiology","volume":" ","pages":"1392-1404"},"PeriodicalIF":2.3,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148919678","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hypoglossal motor output is altered by C4 epidural electrical stimulation via ascending spinal and peripheral feedback pathways.","authors":"Alyssa R Mickle, Jesús D Peñaloza-Aponte, Caitlin Brennan, Erica A Dale","doi":"10.1152/jn.00272.2026","DOIUrl":"10.1152/jn.00272.2026","url":null,"abstract":"<p><p>After cervical spinal cord injury (cSCI), upper airway dysfunction is highly prevalent, including a dramatically increased incidence of obstructive sleep apnea and swallowing dysfunction. Although these deficits have often been attributed to secondary sources such as damage from complications of injury management or anatomical changes, there has recently been a greater appreciation for the modulatory role of spinal populations in upper airway behaviors that are disrupted by injury. Here, we illustrate in a rodent model of cSCI that epidural spinal stimulation of the phrenic motor nucleus at spinal segment C4 alters motor output at the hypoglossal motor nucleus through activation of excitatory ascending spinal pathways and inhibitory peripheral sensory feedback mechanisms. These findings highlight the importance of spinal-brainstem communication in shaping the motor program of upper airway musculature and suggest that stimulation of the cervical spinal cord may be a viable therapeutic target for augmenting upper airway motor output after spinal injury.<b>NEW & NOTEWORTHY</b> In two different models of spinal cord injury, we demonstrate the effects of spinal cord stimulation at C4 on the distal hypoglossal motor nucleus. We show that despite being anatomically distant, electrical stimulation near the phrenic motor nucleus increases hypoglossal motor output through ascending spinal pathways and dampens it through peripheral pathways. These findings highlight the importance of spinal-brainstem communication and illustrate the ability of spinal stimulation to restore this communication after injury.</p>","PeriodicalId":16563,"journal":{"name":"Journal of neurophysiology","volume":" ","pages":"1557-1565"},"PeriodicalIF":2.3,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13641834/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148977145","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rotating a petavoxel reconstruction exposes the viewing angle bias inherent to Golgi-Cox and confocal dendritic spine classification.","authors":"Elias Manjarrez, Sandra T Hernández, Miguel A Zamora-Ursulo, Amira Flores","doi":"10.1152/jn.00280.2026","DOIUrl":"10.1152/jn.00280.2026","url":null,"abstract":"<p><p>Dendritic spines are the principal postsynaptic sites of excitatory transmission. For over a century, their shape has been sorted into discrete categories such as filopodia, thin, long-thin, stubby, mushroom, and branched, largely by Golgi-Cox impregnation and, more recently, confocal microscopy. Yet both approaches share a fundamental limitation. Here, using the human H01 petavoxel reconstruction imaged by electron microscopy, we show that spine shape classification depends strongly on viewing angle. A total of 445 spines on layer 4 basal dendrites of five pyramidal neurons were classified from an arbitrary initial viewpoint (<i>angle 1</i>) and then reclassified after rotation in Neuroglancer (<i>angle 2</i>). Only 20.9% kept their category, so chance-corrected agreement was negligible (Cohen's kappa = 0.027), and a McNemar-Bowker test showed that the reclassifications were directional rather than random. Comparing morphometric measurements against three-dimensional ground-truth shapes further showed that spine length is systematically distorted by rotation across spine types, whereas caliber parameters (neck diameter, head diameter, and head area) generally remain stable except in mushroom spines, which are highly sensitive to viewing angles in both length and caliber. These observations demonstrate that the rigid Golgi-Cox and confocal taxonomies conflate true spine morphology with the arbitrary angle of view, cautioning against treating spine categories from single-viewpoint imaging as reliable descriptors of shape. Our results therefore support, as best practice, the use of continuous and coarse morphometric descriptors. More broadly, they mark the limits of optical resolution for dendritic spine analysis and signal a shift toward three-dimensional, electron microscopy-based reconstruction as the reference for studying spine morphology.<b>NEW & NOTEWORTHY</b> Discrete classification of dendritic spines underpins research on synaptic plasticity, development, and disease yet rests on two-dimensional images whose viewing angle is uncontrolled. By arbitrary rotation of dendrites, four of five spines changed category with viewpoint alone, exposing bias in Golgi-Cox and confocal classifications. Comparing morphometric measurements against ground-truth shapes also showed that spines are distorted by rotation. Our results support, as best practice, replacing the rigid six-category scheme with continuous and coarse morphometric descriptors.</p>","PeriodicalId":16563,"journal":{"name":"Journal of neurophysiology","volume":" ","pages":"1464-1474"},"PeriodicalIF":2.3,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149001916","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Anterior cruciate ligament injury: beyond the ligament-a neurophysiological perspective.","authors":"Hedaya N Rizeq, Tyler T Whittier","doi":"10.1152/jn.00247.2026","DOIUrl":"10.1152/jn.00247.2026","url":null,"abstract":"<p><p>The anterior cruciate ligament (ACL) is not merely a passive stabilizer of the knee, yet its injuries are still commonly treated as a mechanical problem despite growing evidence implicating the central nervous system (CNS). This mini-review highlights the ACL as a critical sensory organ, housing mechanoreceptors that provide afferent feedback regarding the knee position. We further examine evidence across peripheral, cortical, and supraspinal levels to characterize CNS involvement in ACL injury.</p>","PeriodicalId":16563,"journal":{"name":"Journal of neurophysiology","volume":" ","pages":"1387-1391"},"PeriodicalIF":2.3,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148912573","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"No evidence for an effect of M1 cTBS on schema-mediated motor sequence learning.","authors":"Serena Reverberi, Koen Cuypers, Bradley Ross King, Genevieve Albouy","doi":"10.1152/jn.00168.2026","DOIUrl":"10.1152/jn.00168.2026","url":null,"abstract":"<p><p>The availability of a pre-existing cognitive-motor schema accelerates the learning of novel motor information. The encoding of a novel schema-compatible, compared with -incompatible, motor sequence was recently shown to be supported by the left primary motor cortex (M1). However, causal evidence for the role of M1 in schema-mediated motor learning is currently lacking. In the current study, we aimed to address this knowledge gap by transiently disrupting M1 using inhibitory continuous theta-burst stimulation (cTBS). Forty-eight young healthy participants learned a bimanual motor sequence task (cognitive-motor schema). Twenty-four hours later, they learned a novel sequence whose ordinal schematic structure was compatible with that learned on the previous day. To provide causal evidence for a role of M1 on such schema-mediated motor learning, we applied either cTBS or sham stimulation to the left M1 immediately before encoding the schema-compatible novel sequence. Electromyography results showed no evidence for an effect of left M1 cTBS on corticospinal excitability as measured with motor-evoked potentials. Similarly, behavioral results indicated no significant effect of cTBS on subsequent schema-mediated motor sequence learning. Altogether, the present data do not provide evidence for a causal role of the left M1 in schema-mediated motor sequence learning.<b>NEW & NOTEWORTHY</b> Primary motor cortex (M1) continuous theta-burst stimulation (cTBS) did not impair schema-mediated motor sequence learning compared with sham. M1 cTBS did not suppress corticospinal excitability at the group level. Across individuals, greater motor-evoked potential (MEP) suppression was related to higher baseline MEPs. Postintervention changes in MEP amplitude did not correlate with motor performance.</p>","PeriodicalId":16563,"journal":{"name":"Journal of neurophysiology","volume":" ","pages":"1566-1579"},"PeriodicalIF":2.3,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149012003","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Task-dependent cortical modulation for stepping movement preparation.","authors":"Ali Doroodchi, Sean Lai, Sue Peters","doi":"10.1152/jn.00578.2025","DOIUrl":"10.1152/jn.00578.2025","url":null,"abstract":"<p><p>The brain contributes to maintaining balance both while standing and during step initiation, where cortical preparatory activity and sensory modulation may be tuned to the task goal. Standing requires maintaining postural equilibrium, whereas stepping involves propelling the body toward a target while preserving stability. These demands change with the intended step direction, suggesting that cortical processing may be flexibly adjusted according to directional goals. Foot-sole cutaneous receptors are relevant to postural control, as they signal load distribution that supports upright posture and step initiation. This project aimed to investigate how sensory modulation and preparatory cortical processes differ across stepping tasks with differing directional goals. Quiet standing, straight stepping, and diagonal stepping tasks were performed by 31 healthy participants, while EEG was recorded. Standing trials were conducted only with electrical stimulation, whereas stepping trials were performed both with and without stimulation (2 Hz at 125% perceptual threshold) delivered to the left (stance) foot sole to elicit somatosensory-evoked potentials (SEPs). Trials without stimulation allowed examination of cortical preparatory activity. eLORETA source localization was applied across all conditions to identify cortical generators. SEP amplitudes were larger during both stepping tasks compared with standing, and diagonal stepping SEPs were larger compared with straight stepping. In nonstimulation trials, frontal, central, and parietal regions showed greater preparatory activity during diagonal compared with straight stepping, particularly in early preparation stages. These findings suggest that somatosensory processing and preparatory cortical activity are flexibly tuned to the directional goal of the task, consistent with optimal feedback control principles.<b>NEW & NOTEWORTHY</b> This study demonstrates that preparatory cortical processes and somatosensory processing may be modulated according to the stepping direction. Somatosensory-evoked potential (SEP) amplitudes were larger during stepping compared with standing and were further increased during diagonal stepping compared with straight stepping. In addition, frontal, central, and parietal regions showed greater preparatory activity during diagonal compared with straight stepping, suggesting these areas adjusted in preparation to the stepping direction and may contribute to modulating somatosensory information.</p>","PeriodicalId":16563,"journal":{"name":"Journal of neurophysiology","volume":" ","pages":"1590-1605"},"PeriodicalIF":2.3,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149061854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Automated inference of respiratory and syringeal biomechanical trajectories from birdsong acoustics.","authors":"Lauren M Ostrowski, Jorge M Méndez, Pablo Tostado-Marcos, Brenton G Cooper, Timothy Q Gentner","doi":"10.1152/jn.90042.2026","DOIUrl":"10.1152/jn.90042.2026","url":null,"abstract":"<p><p>Songbirds, in particular zebra finches (<i>Taeniopygia guttata</i>), provide a powerful model for investigating the neural mechanisms of learned vocal behavior. Researchers typically rely on the acoustic structure of birdsong to quantify vocal behavior. As a more direct measure of motor control, we present VIBE, vocal acoustic inversion to biomechanical estimates, an open-source pipeline that recovers the biomechanical control parameters of song production from the pitch and amplitude of the acoustic waveform. Biomechanical models of the songbird syrinx describe vocal production with two continuously varying parameters: α and β, representing subsyringeal air sac pressure and syringeal muscle tension, respectively. Recovering these parameters from song acoustics provides a motor-based coordinate system against which neural activity or other dependent variables can be directly compared. Because α and β are the coupled control parameters of a nonlinear oscillator, their joint recovery is nontrivial. VIBE addresses this through iterative optimization of the governing normal-form equations. We validate VIBE against recorded air sac pressure across 44 songs from 12 birds, showing that the recovered α corresponds to empirically measured air sac pressure. Pairing VIBE with Neuropixels recordings from RA in five birds, we find that RA activity is well predicted by the recovered parameters, and that α and β add predictive power beyond the acoustic features of song. By recovering biomechanical control parameters from the acoustic signal, VIBE makes the biomechanical coordinate system of song production accessible to the broader songbird research community.<b>NEW & NOTEWORTHY</b> VIBE provides a novel, fully automated pipeline to recover the biomechanical control parameters of the avian vocal organ, α and β, as continuously varying quantities from the pitch and amplitude of the acoustic waveform, making the full biomechanical model of song production accessible at the scale of modern datasets.</p>","PeriodicalId":16563,"journal":{"name":"Journal of neurophysiology","volume":" ","pages":"1696-1708"},"PeriodicalIF":2.3,"publicationDate":"2026-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149111059","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatiotemporal spinal integration of descending and spinal volleys in spinal motor circuits revealed by compound motor evoked potentials.","authors":"Yousuke Tanaka, Atsushi Sasaki, Nadaka Hakariya, Hiroki Arakawa, Yume Mashiki, Ryo Aoki, Yohei Masugi, Dimitry G Sayenko, Kimitaka Nakazawa","doi":"10.1152/jn.00263.2026","DOIUrl":"https://doi.org/10.1152/jn.00263.2026","url":null,"abstract":"<p><p>Descending corticospinal and afferent pathways underlying spinally evoked motor potential both contribute to motor output, yet how their interaction at the spinal and peripheral levels is organized spatially within a muscle remains unclear. This study investigated the spatiotemporal characteristics of descending modulation of spinally evoked motor potentials by combining subthreshold transcranial magnetic stimulation (TMS) with transcutaneous spinal cord stimulation (tSCS) delivered at the L1-L2 interspinous space in nine participants and at the T12-L1 interspinous space in one participant. In Experiment 1, spinally evoked motor potentials were recorded from multiple lower-limb muscles at various interstimulus intervals (ISIs) defined relative to central conduction time (CCT). Subthreshold TMS facilitated spinally evoked motor potentials from CCT onward across all recorded muscles, with additional bilateral facilitation observed at longer ISIs. In Experiment 2, high-density surface electromyography (HDsEMG) revealed distinct intramuscular activation patterns in the tibialis anterior. The center of gravity (CoG) of TMS-induced motor evoked potentials was located more proximally than that of spinally evoked motor potentials. Notably, the CoG of facilitation maps was shifted further proximally than that of both single-stimulus responses. These findings suggest that descending and afferent inputs preferentially recruit partially distinct motoneuron pools within the same muscle. The proximal bias of facilitation indicates recruitment of additional motoneurons rather than uniform amplification of existing activity. Together, these results demonstrate that the interaction between descending and afferent inputs is both timing-dependent and spatially non-uniform, providing new insight into sensorimotor integration in the human lower limb.</p>","PeriodicalId":16563,"journal":{"name":"Journal of neurophysiology","volume":" ","pages":""},"PeriodicalIF":2.3,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149025148","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}