Intraoperative neuromonitoring in Chiari I malformation surgery: a systematic review and meta-analysis.

Chiari Malformation Type I (CMI) is a prevalent neurosurgical condition characterized by the descent of cerebellar tonsils below the foramen magnum. Surgery, aimed at reducing symptomatology and syrinx size, presents risks, making intraoperative neuromonitoring (IONM) a potentially vital tool. Despite its widespread use in cervical spine surgery, the utility of IONM in CMI surgery remains controversial, with concerns over increased operative time, cost, restricted anesthetic techniques and tongue lacerations. This systematic review and meta-analysis followed the Cochrane Group standards and PRISMA framework. It encompassed an extensive search through PubMed, Embase, and Web of Science up to December 2023, focusing on clinical and surgical outcomes of IONM in CMI surgery. Primary outcomes included the use of various IONM techniques, complication rates, clinical improvement, reoperation, and mortality. The review, registered at PROSPERO (CRD42024498996), included both prospective and retrospective studies, with rigorous selection and data extraction processes. Statistical analysis was conducted using R software. The review included 16 studies, comprising 1358 patients. It revealed that IONM techniques predominantly involved somatosensory evoked potentials (SSEPs), followed by motor evoked potentials (MEPs) and Brainstem auditory evoked potentials (BAEPs). The estimated risk of complications with IONM was 6% (95% CI: 2-11%; I2 = 89%), lower than previously reported rates without IONM. Notably, the clinical improvement rate post-surgery was high at 99% (95% CI: 98-100%; I2 = 56%). The analysis also showed lower reoperation rates in surgeries with IONM compared to those without. Interestingly, no mortality was observed in the included studies. This systematic review and meta-analysis indicate that intraoperative neuromonitoring in Chiari I malformation surgery is associated with favorable clinical outcomes, including lower complication and reoperation rates, and high rates of clinical improvement.

Artificial embodiment displaces cortical neuromagnetic somatosensory responses.

Integrating artificial limbs as part of one's body involves complex neuroplastic changes resulting from various sensory inputs. While somatosensory feedback is crucial, plastic processes that enable embodiment remain unknown. We investigated this using somatosensory evoked fields (SEFs) in the primary somatosensory cortex (S1) following the Rubber Hand Illusion (RHI), known to quickly induce artificial limb embodiment. During electrical stimulation of the little finger and thumb, 19 adults underwent neuromagnetic recordings before and after the RHI. We found early SEF displacement, including an illusion-brain correlation between extent of embodiment and specific changes to the first cortical response at 20 ms in Area 3b, within S1. Furthermore, we observed a posteriorly directed displacement at 35 ms towards Area 1, known to be important for visual integration during touch perception. That this second displacement was unrelated to extent of embodiment implies a functional distinction between neuroplastic changes of these components and areas. The earlier shift in Area 3b may shape extent of limb ownership, while subsequent displacement into Area 1 may relate to early visual-tactile integration that initiates embodiment. Here we provide evidence for multiple neuroplastic processes in S1-lasting beyond the illusion-supporting integration of artificial limbs like prostheses within the body representation.

Brain Encoding of Naturalistic, Continuous, and Unpredictable Tactile Events.

Studies employing EEG to measure somatosensory responses have been typically optimized to compute event-related potentials in response to discrete events. However, tactile interactions involve continuous processing of nonstationary inputs that change in location, duration, and intensity. To fill this gap, this study aims to demonstrate the possibility of measuring the neural tracking of continuous and unpredictable tactile information. Twenty-seven young adults (females, 15) were continuously and passively stimulated with a random series of gentle brushes on single fingers of each hand, which were covered from view. Thus, tactile stimulations were unique for each participant and stimulated fingers. An encoding model measured the degree of synchronization between brain activity and continuous tactile input, generating a temporal response function (TRF). Brain topographies associated with the encoding of each finger stimulation showed a contralateral response at central sensors starting at 50 ms and peaking at ∼140 ms of lag, followed by a bilateral response at ∼240 ms. A series of analyses highlighted that reliable tactile TRF emerged after just 3 min of stimulation. Strikingly, topographical patterns of the TRF allowed discriminating digit lateralization across hands and digit representation within each hand. Our results demonstrated for the first time the possibility of using EEG to measure the neural tracking of a naturalistic, continuous, and unpredictable stimulation in the somatosensory domain. Crucially, this approach allows the study of brain activity following individualized, idiosyncratic tactile events to the fingers.

A multidisciplinary non-invasive approach to monitor response to intravenous immunoglobulin treatment in neurodegenerative Langerhans cell histiocytosis: a real-world study.

Aims: Early detection and treatment of neurodegenerative Langerhans cell histiocytosis (ND-LCH) have been suggested to prevent neurodegenerative progression. The aim of the study is to validate a standardized multidisciplinary diagnostic work-up to monitor the intravenous immunoglobulins (IVIG) treatment response and the natural course of the disease in untreated patients. Methods: Patients with abnormal somatosensory evoked potentials (SEPs) received monthly 0.5 g/kg IVIG. The diagnostic protocol included structural 3T MRI, neurological examination, brainstem auditory evoked potentials (BAEPs) and SEPs. Results: Twenty-two patients were followed for 5.2 years (median) from the first MRI evidence of ND-LCH. Eleven patients received IVIG for 1.7 years (median). At treatment start neurological examination was abnormal in 10 patients, of whom two had severe clinical impairment and four had abnormal BAEPs. At last follow-up, 1/11 remained stable and 7/11 improved, while worsening of neurological or neurophysiological findings, or both, occurred in 3/11. Risk factors for worsening were a severe clinical or MRI ND-LCH at treatment initiation and prolonged exposure to LCH. Of the 11 untreated patients, none improved and three worsened. Conclusions: Using a standardized diagnostic protocol, we demonstrated that IVIG treatment can lead to clinical stabilization or improvement in all pauci-symptomatic patients with an MRI grading of less than 4.

Resting-state functional connectivity involved in tactile orientation processing.

BACKGROUND: Grating orientation discrimination (GOD) is commonly used to assess somatosensory spatial processing. It allows discrimination between parallel and orthogonal orientations of tactile stimuli applied to the fingertip. Despite its widespread application, the underlying mechanisms of GOD, particularly the role of cortico-cortical interactions and local brain activity in this process, remain elusive. Therefore, we aimed to investigate how a specific cortico-cortical network and inhibitory circuits within the primary somatosensory cortex (S1) and secondary somatosensory cortex (S2) contribute to GOD. METHODS: In total, 51 healthy young adults were included in our study. We recorded resting-state magnetoencephalography (MEG) and somatosensory-evoked magnetic field (SEF) in participants with open eyes. We converted the data into a source space based on individual structural magnetic resonance imaging. Next, we estimated S1- and S2-seed resting-state functional connectivity (rs-FC) at the alpha and beta bands through resting-state MEG using the amplitude envelope correlation method across the entire brain (i.e., S1/S2-seeds × 15,000 vertices × two frequencies). We assessed the inhibitory response in the S1 and S2 from SEFs using a paired-pulse paradigm. We automatically measured the GOD task in parallel and orthogonal orientations to the index finger, applying various groove widths with a custom-made device. RESULTS: We observed a specific association between the GOD threshold (all P < 0.048) and the alpha rs-FC in the S1-superior parietal lobule and S1-adjacent to the parieto-occipital sulcus (i.e., lower rs-FC values corresponded to higher performance). In contrast, no association was observed between the local responses and the threshold. DISCUSSION: The results of this study underpin the significance of specific cortico-cortical networks in recognizing variations in tactile stimuli.

Methodologies to elicit and record pudendal somatosensory evoked potentials in adult humans: A systematic review.

OBJECTIVE: The purpose of this systematic review was to characterize methodologies reported in the literature to elicit and record pudendal somatosensory evoked potentials (SEPs) in human adults. METHODS: We conducted an electronic literature search in MEDLINE, Embase, CENTRAL, and CINAHL for studies that elicited pudendal SEPs via electrical stimulation and recorded responses though electroencephalography. From included studies, we extracted methodological details of how the SEPs were evoked and recorded. RESULTS: 132 studies were included in our review. The majority of participants were male (n = 6742/8526, 79%). Almost all studies stimulated the dorsal nerve of penis/clitoris. Stimulus parameters varied, with most standardizing stimulus intensity to 2-4x perceptual threshold, pulse duration to 0.1-0.2 ms, and frequency to 3 Hz. The number of stimuli recorded varied by clinical population. CONCLUSIONS: Our results demonstrate the inconsistencies of pudendal SEP methodology in the literature, with the majority (77%) of publications not reporting enough detail to reasonably replicate their protocol. Most research to date has been conducted in males, highlighting the paucity of female pelvic neurophysiology research. SIGNIFICANCE: We propose a Pudendal SEP Reporting Checklist for adequate reporting of pudendal SEP protocols. Optimal sex- and patient-specific methodologies to investigate all branches of the pudendal nerve need to be established.

High frequency oscillations may improve somatosensory evoked potential detection of good outcomes in disorders of consciousness secondary to acute neurologic injury.

BACKGROUND: Somatosensory evoked potentials (SEPs) are highly specific predictors of poor prognosis in hypoxic-ischemic coma when cortical responses (N20s) are absent. However, bilateral N20 presence is nonspecific for good outcomes. High-frequency oscillations (HFOs) in the SEP waveform predict neurologic recovery in animals, but clinical applications are poorly understood. We sought to develop a clinical measure of HFOs to potentially improve detection of good outcomes in coma. MATERIALS AND METHODS: We collected SEP waveform data from all comatose inpatients (GCS<=8) who underwent neurologic prognostication from 2020 to 2022 at Johns Hopkins Hospital. We developed a novel measure - HFO evoked to spontaneous ratios (HFO-ESRs) - and applied this to those patients with bilaterally present N20s using both standard univariate classification and cubic kernal vector machine (SVM) models to predict the last documented in-hospital Glasgow Coma Scale (GCS) prior to discharge or death. RESULTS: Of 58 total patients, 34 (58.6%) had bilaterally present N20s. Of these, 14 had final GCS>=9, and 20 had final GCS<=8. Mean age was 52 (+/- 17) years, 20.1% female. Etiologies of coma were primarily global hypoxic-ischemic brain injury (79.4%), intracranial hemorrhage (11.8%), and traumatic brain injury (2.9%). In univariate classification, the addition of averaged HFO-ESRs to bilaterally present N20s predicted final GCS>=9 with 68% specificity. The SVM model further improved specificity to 85%. CONCLUSIONS: In this pilot investigation, we developed a novel clinical measure of SEP HFOs. Incorporation of this measure may improve the specificity of the SEP to predict in-hospital GCS outcomes in coma, but requires further validation in specific neurologic injuries and with longitudinal outcomes.

Usefulness of somatosensory evoked potentials for monitoring the clinical course of patients with chronic inflammatory demyelinating polyradiculoneuropathy.

INTRODUCTION/AIMS: Somatosensory evoked potentials (SSEPs) are described as a supportive tool to diagnose chronic inflammatory demyelinating polyradiculoneuropathy (CIDP); however, there is a lack of studies determining the effectiveness of SSEPs in monitoring the clinical course of individuals with this condition. The aims of this study are to evaluate the utility of SSEPs in monitoring patients with CIDP and to assess their association with clinical outcomes following immunomodulatory therapy. METHODS: This was a single-center retrospective observational study that included patients who met European Federation of Neurological Societies and Peripheral Nerve Society criteria for CIDP between 2018 and 2023. SSEPs were performed at diagnosis and during follow-up after the start of immunomodulatory treatment. Fisher's exact test was employed to assess the association between clinical improvement and SSEP improvement. RESULTS: Eighteen patients were included in the study. Ten patients had a typical CIDP pattern and 11 were male. In 17, SSEPs were abnormal prior to the start of immunomodulatory treatment. In patients who showed clinical improvement with immunomodulatory therapy, we observed that 15/17 had partial or complete improvement in SSEPs. Patients who showed no clinical improvement with first-line treatment exhibited worsening SSEPs. There was a significant association between clinical and SSEPs improvement (p = 0.009). DISCUSSION: We observed a positive association between improvement in SSEPs and clinical improvement in patients with CIDP. Our data suggest that SSEPs may be useful for monitoring the clinical course of patients with CIDP, but additional, larger studies are needed.

Interference haptic stimulation and consistent quantitative tactility in transparent electrotactile screen with pressure-sensitive transistors.

Integrating tactile feedback through haptic interfaces enhances experiences in virtual and augmented reality. However, electrotactile systems, which stimulate mechanoreceptors directly, often yield inconsistent tactile results due to variations in pressure between the device and the finger. In this study, we present the integration of a transparent electrotactile screen with pressure-sensitive transistors, ensuring highly consistent quantitative haptic sensations. These transistors effectively calibrate tactile variations caused by touch pressure. Additionally, we explore remote-distance tactile stimulations achieved through the interference of electromagnetic waves. We validated tactile perception using somatosensory evoked potentials, monitoring the somatosensory cortex response. Our haptic screen can stimulate diverse electrotactile sensations and demonstrate various tactile patterns, including Morse code and Braille, when integrated with portable smart devices, delivering a more immersive experience. Furthermore, interference of electric fields allows haptic stimulation to facilitate diverse stimulus positioning at lower current densities, extending the reach beyond direct contact with electrodes of our screen.

CutFEM-based MEG forward modeling improves source separability and sensitivity to quasi-radial sources: A somatosensory group study.

Source analysis of magnetoencephalography (MEG) data requires the computation of the magnetic fields induced by current sources in the brain. This so-called MEG forward problem includes an accurate estimation of the volume conduction effects in the human head. Here, we introduce the Cut finite element method (CutFEM) for the MEG forward problem. CutFEM's meshing process imposes fewer restrictions on tissue anatomy than tetrahedral meshes while being able to mesh curved geometries contrary to hexahedral meshing. To evaluate the new approach, we compare CutFEM with a boundary element method (BEM) that distinguishes three tissue compartments and a 6-compartment hexahedral FEM in an n = 19 group study of somatosensory evoked fields (SEF). The neural generators of the 20 ms post-stimulus SEF components (M20) are reconstructed using both an unregularized and a regularized inversion approach. Changing the forward model resulted in reconstruction differences of about 1 centimeter in location and considerable differences in orientation. The tested 6-compartment FEM approaches significantly increase the goodness of fit to the measured data compared with the 3-compartment BEM. They also demonstrate higher quasi-radial contributions for sources below the gyral crowns. Furthermore, CutFEM improves source separability compared with both other approaches. We conclude that head models with 6 compartments rather than 3 and the new CutFEM approach are valuable additions to MEG source reconstruction, in particular for sources that are predominantly radial.

Altered somatosensory processing in adult attention deficit hyperactivity disorder.

BACKGROUND: Tactile sensitivity and sensory overload in ADHD are well-documented in clinical-, self-, and parent- reports, but empirical evidence is scarce and ambiguous and focuses primarily on children. Here, we compare both empirical and self-report tactile sensitivity and ADHD symptomatology in adults with ADHD and neurotypical controls. We evaluate whether tactile sensitivity and integration is more prevalent in ADHD and whether it is related to ADHD symptom severity. METHODS: Somatosensory evoked potential (SEP) amplitudes were measured in 27 adults with ADHD and 24 controls during four conditions (rest, stroking of the own arm, stroking of the arm by a researcher, and stroking of an object). Participants also filled out questionnaires on tactile sensitivity and ADHD symptoms and performed a Qb-test as an objective measure of ADHD symptom severity. RESULTS: Participants with ADHD self-reported greater tactile sensitivity and ADHD symptom severity than controls and received higher scores on the Qb-test. These values correlated with one another. ADHD participants showed lower tolerable threshold for electrical radial nerve stimulus, and greater reduction in cortical SEP amplitudes during additional tactile stimuli which was correlated with ADHD symptoms. CONCLUSIONS: We find that ADHD symptomatology and touch sensitivity are directly linked, using both self-reports and experimental measures. We also find evidence of tactile sensory overload in ADHD, and an indication that this is linked to inattention specifically. Tactile sensitivity and sensory overload impact the functioning and life quality of many people with ADHD, and clinicians should consider this when treating their patients.

Electrotactile BCI for Top-Down Somatosensory Training: Clinical Feasibility Trial of Online BCI Control in Subacute Stroke Patients.

This study investigates the feasibility of a novel brain-computer interface (BCI) device designed for sensory training following stroke. The BCI system administers electrotactile stimuli to the user's forearm, mirroring classical sensory training interventions. Concurrently, selective attention tasks are employed to modulate electrophysiological brain responses (somatosensory event-related potentials-sERPs), reflecting cortical excitability in related sensorimotor areas. The BCI identifies attention-induced changes in the brain's reactions to stimulation in an online manner. The study protocol assesses the feasibility of online binary classification of selective attention focus in ten subacute stroke patients. Each experimental session includes a BCI training phase for data collection and classifier training, followed by a BCI test phase to evaluate online classification of selective tactile attention based on sERP. During online classification tests, patients complete 20 repetitions of selective attention tasks with feedback on attention focus recognition. Using a single electroencephalographic channel, attention classification accuracy ranges from 70% to 100% across all patients. The significance of this novel BCI paradigm lies in its ability to quantitatively measure selective tactile attention resources throughout the therapy session, introducing a top-down approach to classical sensory training interventions based on repeated neuromuscular electrical stimulation.

Performance of the ERC/ESICM-recommendations for neuroprognostication after cardiac arrest: Insights from a prospective multicenter cohort.

AIM: To investigate the performance of the 2021 ERC/ESICM-recommended algorithm for predicting poor outcome after cardiac arrest (CA) and potential tools for predicting neurological recovery in patients with indeterminate outcome. METHODS: Prospective, multicenter study on out-of-hospital CA survivors from 28 ICUs of the AfterROSC network. In patients comatose with a Glasgow Coma Scale motor score ≤3 at ≥72 h after resuscitation, we measured: (1) the accuracy of neurological examination, biomarkers (neuron-specific enolase, NSE), electrophysiology (EEG and SSEP) and neuroimaging (brain CT and MRI) for predicting poor outcome (modified Rankin scale score ≥4 at 90 days), and (2) the ability of low or decreasing NSE levels and benign EEG to predict good outcome in patients whose prognosis remained indeterminate. RESULTS: Among 337 included patients, the ERC-ESICM algorithm predicted poor neurological outcome in 175 patients, and the positive predictive value for an unfavourable outcome was 100% [98-100]%. The specificity of individual predictors ranged from 90% for EEG to 100% for clinical examination and SSEP. Among the remaining 162 patients with indeterminate outcome, a combination of 2 favourable signs predicted good outcome with 99[96-100]% specificity and 23[11-38]% sensitivity. CONCLUSION: All comatose resuscitated patients who fulfilled the ERC-ESICM criteria for poor outcome after CA had poor outcome at three months, even if a self-fulfilling prophecy cannot be completely excluded. In patients with indeterminate outcome (half of the population), favourable signs predicted neurological recovery, reducing prognostic uncertainty.

Assessment of TENS-Evoked Tactile Sensations for Transradial Amputees via EEG Investigation.

Most of current prostheses can offer motor function restoration for limb amputees but usually lack natural and intuitive sensory feedback. Many studies have demonstrated that Transcutaneous Electrical Nerve Stimulation (TENS) is promising in non-invasive sensation evoking for amputees. However, the objective evaluation and mechanism analysis on sensation feedback are still limited. This work utilized multi-channel TENS with diverse stimulus patterns to evoke sensations on four non-disabled subjects and two transradial amputees. Meanwhile, electroencephalogram (EEG) was collected to objectively assess the evoked sensations, where event-related potentials (ERPs), brain electrical activity maps (BEAMs), and functional connectivity (FC) were computed. The results show that various sensations could be successfully evoked for both amputees and non-disabled subjects by customizing stimulus parameters. The ERP confirmed the sensation and revealed the sensory-processing-related components like N100 and P200; the BEAMs confirmed the corresponding regions of somatosensory cortex were activated by stimulation; the FC indicated an increase of interactions between the regions of sensorimotor cortex. This study may shed light on how the brain responds to external stimulation as sensory feedback and serve as a pilot for further bidirectional closed-loop prosthetic control.

Utility of Intraoperative Neuromonitoring to Protect against Adjacent Nerve Injury in Musculoskeletal and Lymph Nodal Cryoablation.

PURPOSE: To demonstrate the utility of intraoperative neuromonitoring (IONM) as an effective method of passive thermoprotection against cryogenic injury to neural structures during musculoskeletal and lymph node cryoablation. MATERIAL AND METHODS: Twenty-nine patients (16 men; mean age among men, 68.6 years [range, 45-90 years]; mean age among women, 62.6 years [range, 28-88 years]) underwent 33 cryoablations of musculoskeletal and lymph node lesions. Transcranial electrical motor-evoked potentials (MEPs) and somatosensory-evoked potentials (SSEPs) of target nerves were recorded throughout the ablations. Significant change was defined as waveform amplitude reduction greater than 30% (MEP) and 50% (SSEP). The primary outcomes of this study were immediate postprocedural neurologic deficits and frequency of significant MEP and SSEP amplitude reductions. RESULTS: Significant amplitude reductions were detected in 54.5% (18/33) of MEP tracings and 0% (0/33) of SSEP tracings. Following each occurrence of significant amplitude reductions, freeze cycles were promptly terminated. Intraprocedurally, 13 patients had full recovery of amplitudes to baseline, 11 of whom had additional freeze cycles completed. In 5 of 33 (15.2%) cryoablations, there were immediate postprocedural neurologic deficits (moderate adverse events). Unrecovered MEPs conferred a relative risk for neurologic sequela of 23.2 (95% CI, 3.22-167.21; P < .001) versus those with recovered MEPs. All 5 patients had complete neurologic recovery by 12 months. CONCLUSIONS: IONM (with MEP but not SSEP) is a reliable and safe method of passive thermoprotection of neurologic structures during cryoablation. It provides early detection of changes in nerve conduction, which when addressed quickly, may result in complete restoration of MEP signals within the procedure and minimize risk of cryogenic neural injury.

Intraoperative somatosensory evoked potential (SEP) monitoring: an updated position statement by the American Society of Neurophysiological Monitoring.

Somatosensory evoked potentials (SEPs) are used to assess the functional status of somatosensory pathways during surgical procedures and can help protect patients' neurological integrity intraoperatively. This is a position statement on intraoperative SEP monitoring from the American Society of Neurophysiological Monitoring (ASNM) and updates prior ASNM position statements on SEPs from the years 2005 and 2010. This position statement is endorsed by ASNM and serves as an educational service to the neurophysiological community on the recommended use of SEPs as a neurophysiological monitoring tool. It presents the rationale for SEP utilization and its clinical applications. It also covers the relevant anatomy, technical methodology for setup and signal acquisition, signal interpretation, anesthesia and physiological considerations, and documentation and credentialing requirements to optimize SEP monitoring to aid in protecting the nervous system during surgery.

Electrophysiological responses to digit stimulation in a tactile oddball paradigm.

Sensory memory traces are assessed via oddball paradigms in which deviant (infrequent) stimuli are interspersed into a string of standard (frequent) stimuli. Once a memory trace for the standard is established, the deviant spurs a change detection response measured via the resulting event related potential (ERP). Response magnitude is sensitive to the differences in stimuli properties or categories and influenced by individual experience. The goal of the present study was to use ERPs to test the relation between individual digits in the somatosensory cortex and the extent to which digit representations are influenced by individual differences in experience such as independent mobility and playing video games. The present study of 60 undergraduates utilized a passive tactile oddball paradigm, stimulating the thumb, middle, and little fingers. The oddball paradigm was fully matched with each digit serving as the standard and deviant. A temporal principal component analysis (tPCA) identified factors that matched three a priori ERP components: N80, somatosensory mismatch negativity (sMMN), and P300. Analyses confirmed the anticipated differences between standards and deviants and provided some support for prior ERP work suggesting the thumb is in a different functional category than the other digits. Independent control of individual digits (such as the little finger) was positively related to only one aspect of the ERP (P3a) while video game experience was not associated with ERP differences. Cumulatively, these results provide a more nuanced examination of tactile oddball paradigms and how ERP methods can shed light on the relations between different digits.

Bilateral median nerve stimulation and High-Frequency Oscillations unveil interhemispheric inhibition of primary sensory cortex.

OBJECTIVE: This study aimed at investigating the effect of median nerve stimulation on ipsilateral cortical potentials evoked by contralateral median nerve electrical stimulation. METHODS: We recorded somatosensory-evoked potentials (SEPs) from the left parietal cortex in 15 right-handed, healthy subjects. We administered bilateral median nerve stimulation, with the ipsilateral stimulation preceding the stimulation on the contralateral by intervals of 5, 10, 20, or 40 ms. We adjusted these intervals based on each individual's N20 latency. As a measure of S1 excitability, the amplitude of the N20 and the area of the High Frequency Oscillation (HFO) burst were analyzed for each condition. RESULTS: The results revealed significant inhibition of N20 amplitude by ipsilateral median nerve stimulation at interstimulus intervals (ISIs) between 5 and 40 ms. Late HFO burst was suppressed at short ISIs of 5 and 10 ms, pointing to a transcallosal inhibitory effect on S1 intracortical circuits. CONCLUSIONS: Findings suggest interhemispheric interaction between the primary somatosensory areas, supporting the existence of transcallosal transfer of tactile information. SIGNIFICANCE: This study provides valuable insights into the interhemispheric connections between primary sensory areas and underscore the potential role of interhemispheric interactions in somatosensory processing.