Median Nerve Somatosensory Evoked Potentials Research Articles

The P22 median nerve SEP component: precentral or postcentral origin? Dipole source analysis from subdural grid recordings

The P22 median nerve SEP component: precentral or postcentral origin? Dipole source analysis from subdural grid recordings

Effects of Remote Ischemic Preconditioning on Biochemical Markers and Neurologic Outcomes in Patients Undergoing Elective Cervical Decompression Surgery

Remote ischemic preconditioning (RIPC) may protect the spinal cord from ischemic injury. This randomized clinical trial was designed to assess whether a large clinical trial testing the effect of RIPC on neurologic outcome in patients undergoing spine surgery is warranted. This trial was registered with ClinicalTrials.gov, number NCT00778323. Forty adult cervical spondylotic myelopathy patients undergoing elective decompression surgery were randomly assigned to either the RIPC group (n=20) or the control group (n=20). Limb RIPC consisted of three 5-minutes cycles of upper right limb ischemia with intervening 5-minute periods of reperfusion. Neuron-specific enolase and S-100B levels were measured in serum at set time points. Median nerve somatosensory-evoked potentials (SEPs) were also recorded. Neurologic recovery rate was evaluated using a Japanese Orthopaedic Association scale. RIPC significantly reduced serum S-100B release at 6 hours and 1 day after surgery, and reduced neuron-specific enolase release at 6 hours, and then at 1, 3, and 5 days after surgery. No differences were observed in SEP measurements or the incidence of SEP changes during surgery between the control and RIPC groups. Recovery rate at 7 days, and at 1 and 3 months after surgery was higher in the RIPC group than in the control group (P<0.05). Our results for markers of neuronal ischemic injury and rate of recovery suggest that a clinical trial with sufficient statistical power to detect an effect of RIPC on the incidence of neurologic complications (paresis, palsy, etc) due to spinal cord ischemia-reperfusion injury after spine surgery is warranted [corrected].

Inducing Homeostatic-Like Plasticity in Human Motor Cortex Through Converging Corticocortical Inputs

Transcranial stimulation techniques have revealed homeostatic-like metaplasticity in the hand area of the human primary motor cortex (M1(HAND)) that controls stimulation-induced changes in corticospinal excitability. Here we combined two interventional protocols that induce long-term depression (LTD)-like or long-term potentiation (LTP)-like plasticity in left M1(HAND) through different afferents. We hypothesized that the left M1(HAND) would integrate LTP- and LTD-like plasticity in a homeostatic fashion. In ten healthy volunteers, low-intensity repetitive transcranial magnetic stimulation (rTMS) of the left dorsal premotor cortex (PMD) was first applied to produce an LTP-like increase (5 Hz rTMS) or LTD-like decrease (1 Hz rTMS) in corticospinal excitability in left M1(HAND) via premotor-to-motor inputs. Following PMD rTMS, paired-associative stimulation (PAS) was applied to the right median nerve and left M1(HAND) to induce spike-time-dependent plasticity in sensory-to-motor inputs to left M1(HAND). We adjusted the interstimulus interval to the N20 latency of the median nerve somatosensory-evoked cortical potential to produce an LTP-like increase (PAS(N20+2ms)) or an LTD-like decrease (PAS(N20-5ms)) in corticospinal excitability. The amplitude of motor-evoked potentials was recorded from intrinsic hand muscles to assess stimulation-induced changes in corticospinal excitability. Premotor-to-motor preconditioning triggered a homeostatic response to subsequent sensory-to-motor PAS. After facilitatory 5 Hz rTMS, "facilitatory" PAS(N20+2ms) suppressed corticospinal excitability. Likewise, "inhibitory" PAS(N20-5ms) facilitated corticospinal excitability after "inhibitory" 1 Hz rTMS. There was a negative linear relationship between the excitability changes induced by PMD rTMS and those elicited by subsequent PAS. Excitability changes were not paralleled by changes in performance during a finger-tapping task. These results provide evidence for a homeostatic response pattern in the human M1(HAND) that integrates acute plastic changes evoked through different "input channels."

Changes of Recovery Function in Median Nerve Somatosensory Evoked Potentials From Awake to Sleep

To investigate how the sleep affects the recovery functions of somatosensory evoked potential, we studied somatosensory evoked potential recovery functions of the median nerve during awake to sleep in eight healthy adults, using the paired conditioning and test stimulus paradigm. The most notable difference between wakefulness and sleep was the much greater enhancement of parietal P26 and frontal P22 in sleep than in awake state at interstimulus intervals of 20 to 100 milliseconds of paired stimulus paradigm. Although the enhanced P26 and P22 were observed in control somatosensory evoked potential during sleep, the augmentation was much greater when conditioned by preceding stimulus. In contrast, the parietal P40-N60 and frontal fP40-fN60 of test response were more depressed in sleep than in wakefulness. As a whole, the recovery curves in sleep appeared to be shifted to the right as compared with those in the awake, suggesting delayed recovery function in sleep. The augmentation of frontal P22 and parietal P26 in sleep, contrasting depressed other components, most notably fP40-fN60 and parietal P40-N60, imply that the former components reflect inhibitory and the latter to the excitatory process. This is the first study that demonstrates the somatosensory evoked potential recovery functions are different from those of awake state.

PO3.11 Comparison between Median and Tibial Nerve Somatosensory Evoked Potentials (SEPs) in Patients with High Cervical Dorsal Column Lesions

PO3.11 Comparison between Median and Tibial Nerve Somatosensory Evoked Potentials (SEPs) in Patients with High Cervical Dorsal Column Lesions

Multimodality-evoked potential study of anti-aquaporin-4 antibody-positive and -negative multiple sclerosis patients

Neuromyelitis optica (NMO) is claimed to be a distinct disease entity from multiple sclerosis (MS) because of its strong association with NMO-IgG/anti-AQP4 antibody; however, the in vivo role of the antibody remains unknown. Therefore, we aimed to clarify whether the presence of anti-AQP4 antibody is associated with any abnormalities in multimodality-evoked potentials in 111 patients with relapsing–remitting or relapsing-progressive MS, including the opticospinal form of MS, 18 of whom were seropositive for anti-AQP4 antibody. More patients with anti-AQP4 antibody showed a lack of the P100 component on visual-evoked potentials (VEPs) than those without the antibody (11/17, 64.7% vs. 20/84, 23.8%, p = 0.003), whereas the frequency of delayed P100 latency was significantly higher in the latter group than in the former (1/17, 5.9% vs. 28/84, 33.3%, p = 0.021). The frequencies of non-responses and delayed central sensory conduction times in median and posterior tibial nerve somatosensory-evoked potentials (SEPs) were not significantly different between anti-AQP4 antibody-positive and -negative patients. In terms of upper and lower limb motor-evoked potentials (MEPs), the frequencies of non-responses and delayed central motor conduction times did not differ significantly based on the presence or absence of anti-AQP4 antibody. The frequency of optic nerve lesions on MRI was significantly higher in anti-AQP4 antibody-positive patients than in anti-AQP4 antibody-negative patients ( p = 0.0137). Multiple logistic analyses revealed that anti-AQP4 antibody positivity (OR = 8.406, p = 0.02) and unevoked VEP responses (OR = 35.432, p < 0.001) were significantly related to development of severe visual impairment. Such an association of anti-AQP4 antibody with disability was not found for either severe motor or sensory impairment. These findings suggest a distinctive nature of optic nerve lesions between anti-AQP4 antibody-positive and -negative patients; lesions are supposed to be more necrotic in the former group and more demyelinating in the latter.

128-Channel somatosensory evoked potentials in the differential diagnosis of parkinsonian disorders

Purpose The differential diagnosis of parkinsonian disorders can be very difficult, especially at an early stage. In this study, we investigated whether SEP amplitude recorded by 128-channel EEG is useful for diagnosis of parkinsonian disorders, and in particular whether SEP asymmetry can differentiate corticobasal degeneration (CBGD) from other parkinsonian disorders. Methods We recorded median nerve SEPs in 47 patients suspected of CBGD, supranuclear palsy or definite Parkinson's disease at an early stage. We compared SEP asymmetry and parietal peak amplitudes of the patients after grouping them based on their clinical diagnosis after 1–5 years of follow-up. In nine subjects the diagnosis remained unclear. Results Three of 13 patients with a clinical diagnosis of CBGD had an abnormal SEP asymmetry. Furthermore, we found extremely high N20 amplitudes in three other patients with CBGD. However, similar asymmetry abnormalities were found in patients with other Parkinsonian disorders. Conclusion Despite the use of 128-channel SEP recordings and analysis techniques, which are more accurate than conventional techniques, sensitivity and specificity of cortical median nerve SEP asymmetry and parietal amplitude for differentiating CBGD from other parkinsonian disorders were low at an early stage of the disease. A possible reason for this may be that the hand area of the primary somatosensory cortex was not yet affected in most CBGD patients.

Does Stimulus Rate Matter When Performing Somatosensory Evoked Potentials for Coma Patients?

It is unclear whether the rate of stimulation for somatosensory evoked potentials (SEPs) can influence the presence or absence of cortical responses to median nerve stimulation in comatose patients. If so, this could affect how SEPs are performed and interpreted for prognostication in coma. Our objective was to determine how frequently our comatose patients had absent median nerve SEP responses at 3 Hz stimulation, but present responses at 1 Hz stimulation, and to report outcomes of these patients. We reviewed SEP recordings in 639 comatose patients over a 9-year period. All had stimulation at 3 Hz and 1 Hz. This is a retrospective review. There were seven patients who had absent median nerve SEP responses at 3 Hz stimulation bilaterally, but had present responses at 1 Hz on one or both sides. Six of the seven died. One 16-year-old patient with traumatic brain injury awoke, but had moderate disability. Stimulation rate is an important determinant of presence or absence of cortical responses in about 1% of comatose patients. It is unclear whether such patients have a different outcome that those with absent responses at both rates of stimulation.

Relationship between median nerve somatosensory evoked potentials and spinal cord injury levels in patients with quadriplegia

Cross-sectional study. To observe if there is a relationship between the level of injury by the American Spinal Cord Injury Association (ASIA) and cortical somatosensory evoked potential (SSEP) recordings of the median nerve in patients with quadriplegia. Rehabilitation Outpatient Clinic at the university hospital in Brazil. Fourteen individuals with quadriplegia and 8 healthy individuals were evaluated. Electrophysiological assessment of the median nerve was performed by evoked potential equipment. The injury level was obtained by ASIA. N(9), N(13) and N(20) were analyzed based on the presence or absence of responses. The parameters used for analyzing these responses were the latency and the amplitude. Data were analyzed using mixed-effect models. N(9) responses were found in all patients with quadriplegia with a similar latency and amplitude observed in healthy individuals; N(13) responses were not found in any patients with quadriplegia. N(20) responses were not found in C5 patients with quadriplegia but it was present in C6 and C7 patients. Their latencies were similar to healthy individuals (P>0.05) but the amplitudes were decreased (P<0.05). This study suggests that the SSEP responses depend on the injury level, considering that the individuals with C6 and C7 injury levels, both complete and incomplete, presented SSEP recordings in the cortical area. It also showed a relationship between the level of spinal cord injury assessed by ASIA and the median nerve SSEP responses, through the latency and amplitude recordings.

Cutaneous Silent Periods in the Assessment of Mild Cervical Spondylotic Myelopathy

Clinical, neuroradiologic, and neurophysiologic description of 21 patients with compressive cervical spondylotic myelopathy (CCSM). To describe the utility of cutaneous silent periods (CSPs) for functional evaluation of mild CCSM. Electroneurography, electromyography, and somatosensory and motor evoked potentials (SEPs, MEPs) are routinely used for comprehensive functional neurophysiological evaluation of CCSM. CSPs have been reported in various intramedullary spinal cord lesions, however, they have not been systematically studied in mild CCSM. We investigated 21 patients with multilevel CCSM as documented by magnetic resonance imaging. We recorded CSPs in thenar muscles after noxious digit II stimulation and compared them with median and tibial nerve SEPs and MEPs obtained from abductor digiti minimi and tibialis anterior muscles. Electroneurography and electromyography were obtained in affected myotomes. CSP onset and end latencies were delayed, and CSP duration was shortened, in CCSM patients. CSP abnormalities were present in 17 patients of whom all, but 1 presented with intramedullary magnetic resonance imaging hyperintensity. All 11 limbs affected by hypalgesia and thermhypesthesia had abnormal CSPs, whereas no spinothalamic deficit was noted in any limb with normal CSPs. CSP onset latency was inversely correlated with JOA score and N13 amplitude, and was positively correlated with central motor conduction time to abductor digiti minimi. CSP duration was inversely correlated with central motor conduction time to tibialis anterior. Electromyographic abnormalities were found in 7 patients. We confirm the value of neurophysiological evaluation of CCSM. MEPs were more frequently abnormal than SEPs. CSP abnormalities were almost equally sensitive as upper limb MEPs, and were highly associated with spinothalamic dysfunction. The high correlation of CSP abnormalities with corticospinal tract dysfunction suggests supraspinal influence on CSPs. Our findings corroborate the utility of CSP testing in the comprehensive assessment of intramedullary spinal cord dysfunction in CCSM.

11. The impact of stimulus properties on low- and high-frequency median nerve SEPs

11. The impact of stimulus properties on low- and high-frequency median nerve SEPs

Utility of somatosensory evoked potentials in chronic acquired demyelinating neuropathy

Chronic acquired demyelinating polyneuropathy (CADP) is a heterogeneous syndrome that may be classified into a number of subtypes. Somatosensory evoked potentials (SSEPs) assess proximal segments of sensory nerves, inadequately assessed by routine nerve conduction studies (NCSs). The aim of the present study was to determine the utility of SSEPs in diagnosing and classifying different CADP subtypes. Forty-seven patients with CADP were studied and classified in five groups based on conventional NCSs and SSEPs. Some patients in Group 1 were initially misdiagnosed as having either motor neuron disease or multifocal motor neuropathy due to normal sensory NCSs, but they exhibited abnormal tibial and median nerve SSEPs, as evidenced by marked prolongation or absence of peripheral potentials (N9-median nerve, and N20-tibial nerve). These were reclassified as having chronic inflammatory demyelinating neuropathy (CIDP). In CIDP patients (Group 2), SSEPs were abnormal, thereby confirming the presence of demyelination in the proximal peripheral nerves. Patients with distal acquired demyelinating neuropathy (DADS) (Group 3), as defined by conventional NCS, exhibited abnormal SSEPs when anti-MAG antibodies were present. Anti-MAG-negative DADS patients (Group 3) had normal SSEPs. In the pure sensory ataxic group (Group 4), SSEP studies disclosed poorly formed and delayed cortical potentials with absent lumbar (N20) potentials, thereby suggesting the presence of proximal demyelination. SSEPs were normal in the pure motor CIDP and multifocal motor neuropathy patients (MMN) (Group 5), thereby differentiating asymmetric forms of CIDP from MMN. These findings suggest that SSEPs may be an important complementary investigation to conventional NCSs in the diagnosis of CADP.

Effect of spinal transcutaneous direct current stimulation on somatosensory evoked potentials in humans

Objective Invasive stimulation of the spinal cord is used to treat a number of pathological conditions. Aiming to modulate human spinal cord function non-invasively, we evaluated whether transcutaneous direct current (DC) stimulation induces long-lasting changes in conduction along the sensory spinal pathways. Methods Somatosensory evoked potentials (SEPs) by posterior tibial nerve and by median nerve stimulation were recorded, before, at current offset and at 20 min after transcutaneous anodal or cathodal DC stimulation over the thoracic spinal cord (2.5 mA, 15 min) in a group of 12 healthy subjects. Results Whereas both polarities left the spinal (N22) and the cortical potentials (P39) unchanged, anodal transcutaneous spinal DC stimulation decreased significantly by about 25% the amplitude of the cervico-medullary component of posterior tibial nerve SEPs (P30) for at least 20 min. Thoracic transcutaneous spinal cord stimulation left median nerve SEPs unchanged. Conclusions Transcutaneous DC stimulation over the thoracic spinal cord induces changes in conduction along human lemniscal pathway that persist after stimulation ends. Significance Our results support the use of transcutaneous DC stimulation as a novel tool for non-invasive spinal neuromodulation. Because the method is non-expensive and simple, it can be tested in patients with disorders presently treated with invasive procedures.

Somatosensory Evoked Potentials by Median Nerve Stimulation in Children During Thiopental/Sevoflurane Anesthesia and the Additive Effects of Ketoprofen and Fentanyl

Somatosensory evoked potentials (SEPs) are used to determine the spinal cord and brain function during surgical procedures. In general, SEPs are sensitive to volatile anesthetics, but little is known about the effects of anesthesia maintenance with sevoflurane on SEPs in children. Analgesics are often provided during anesthesia, and supplementary drugs may also affect the SEPs. In this prospective clinical trial of 27 healthy, 3- to 8-yr-old children, we evaluated the effects of sevoflurane anesthesia after IV induction with benzodiazepine and barbiturate on median nerve SEP. In addition, the effects of two analgesics (ketoprofen and fentanyl) on SEPs were evaluated. Median nerve SEPs were recorded before premedication with midazolam 0.1 mg/kg IV, and at three separate times during anesthesia maintenance with sevoflurane 2% end-tidal concentration in air/oxygen (after 15 min of sevoflurane inhalation), supplemented with/without ketoprofen 1 mg/kg (after 25 min) and fentanyl 1 microg/kg (after 35 min). Compared with baseline measurements, an increase both in N20 latency (P = 0.015) and in central conduction time (P = 0.001) was noted during anesthesia maintenance with sevoflurane. The administration of analgesics did not have an influence on the N20 latency or central conduction time. In children 5 to 8 yr of age, the mean cortical N20-P25 amplitude was decreased (P = 0.008). In addition, in older children, the N20-P25 amplitude decreased after the co-administration of ketoprofen and fentanyl compared with the values measured before the analgesics (P = 0.03). These decreases were not seen in the younger children. In children, anesthesia maintenance with 2% sevoflurane prolongs median SEP latencies in a manner that is similar to those reported for other volatile anesthetics. However, SEP monitoring can be done with sevoflurane inhalation, but the dosage should be adjusted due to interindividual variability. Co-administration of ketoprofen, and fentanyl did not affect the SEP latencies, but post hoc analysis suggested that older children had a decrease in cortical amplitudes.

Somatosensory evoked potentials (SEPs) for the evaluation of cervical spondylotic myelopathy: Utility of the onset-latency parameters

Objective Peak latencies have been traditionally employed for the evaluation of somatosensory evoked potentials (SEPs). Some authors have argued for the theoretical superiority of the onset latencies, which has never been verified in actual clinical cases. We aimed to investigate the utility of onset-latency parameters of median nerve SEPs in the cervical spondylotic myelopathy (CSM) patients, as well as several other issues concerned with the SEP diagnosis of CSM. Methods We retrospectively enrolled 42 CSM patients and investigated their SEP findings. Results The N9o (N9 onset)-P13/14o interval showed the highest sensitivity (83%) followed by N9o-N20o (74%). The sensitivities of corresponding peak latency parameters were lower (62% and 33%). The amplitude of the lower cervical N13 also showed the highest sensitivity (83%). The sensitivity of tibial nerve SEPs examined in 21 patients was lower (71%) than that of median nerve SEPs (90%). When clinical signs alone were used as the gold standard, the sensitivity of median SEPs was 90% whereas that of MRI was 88%. Conclusions Higher diagnostic yield of onset-latency parameters of median nerve SEPs has been documented in CSM. Significance SEPs are useful in the diagnosis of CSM having equal sensitivity and probably higher specificity than MRI.

Electrophysiological features of myoclonus‐dystonia

Inherited myoclonus-dystonia (M-D) is an autosomal dominant disorder characterized by myoclonus and dystonia that often improves with alcohol. To examine the electrophysiologic characteristics of M-D, we studied 6 patients from 4 different families and 9 age-matched healthy subjects. Neurophysiological studies performed include electromyography (EMG)-electroencephalography (EEG) polygraphy, jerk-locked back-averaged EEG, somatosensory evoked potentials (SEP), long-latency reflex (LLR) to median and digital nerve stimulation, and transcranial magnetic stimulation studies with short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), and long-interval intracortical inhibition (LICI). All 6 patients showed myoclonus and dystonia on clinical examination and EMG testing. The EMG burst durations ranged from 30.4 to 750.6 milliseconds (mean, 101.5 milliseconds). Jerk-locked back-averaged EEG failed to reveal any preceding cortical correlates. Median nerve SEP revealed no giant potential. No patients had exaggerated LLR to median or digital nerve stimulation. There was no significant difference in SICI, ICF, and LICI between M-D patients and normal subjects. Myoclonus in inherited M-D is likely of subcortical origin. Normal intracortical inhibition and facilitation suggest that the GABAergic circuits in the motor cortex are largely intact and that the mechanisms of myoclonus and dystonia are different from those for cortical myoclonus and other dystonic disorders.

Somatosensory evoked potentials reflect the upper limb motor performance in multiple sclerosis

Objective The aim of this multicentric study was to multidimensionally evaluate the relationship among somatosensory evoked potentials (SEPs) parameters, patient's perspective and clinical measures of the upper limb impairment in patients with multiple sclerosis (MS). Methods We consecutively enrolled 39 MS patients. For median nerve SEPs we acquired the N9, P14, N20 responses and the N9–P14 and P14–N20 interpeak latencies on the dominant side. We also used a validated patient-oriented questionnaire (Disabilities of the Arm, Shoulder and Hand — DASH) and a test of dexterity quantification as the 9-Hole Peg Test (9-HPT). Results A significant longer time to complete the 9-HPT ( p < 0.00006) was observed in patients with abnormal SEPs. Patients with undetectable N20 or P14 responses performed the 9-HPT in a significant longer time than patients with detectable responses ( p < 0.0006 and p < 0.001 respectively). Concerning the perspective of patient (evaluated with the DASH questionnaire) significant differences in patients with undetectable P14 response ( p < 0.01) were observed. Conclusions Our data provide further information useful for interpretation of SEPs results, being the median nerve SEPs related to the upper limb performance in MS patients. Significance These data increase the significance of SEPs both in clinical practice and in experimental studies in MS.

The Impact of Stimulus Properties on Low- and High-Frequency Median Nerve Somatosensory Evoked Potentials

Questioning whether stimulation properties in median nerve somatosensory evoked potentials show interactions multichannel recordings were performed in a three-factorial repeated measures design with the parameters (i) eyes opened versus eyes closed, (ii) stimulation intensity above motor threshold versus intensity sub motor threshold, (iii) stimulation rate 0.5 Hz versus 9 Hz resulting in somatosensory evoked potentials recorded during eight different conditions. Varying the stimulation intensity revealed an impact on the amplitude and the latency of the N20 source activity and on the amplitude, the duration and the number of peaks of the high frequency oscillatory (HFOs) sources. Modifying the stimulation rate lead to an effect on the amplitude and latency of the N20 and on the amplitude of the high-frequency oscillatory sources. The condition opened/closed eyes had an impact on the duration and number of high-frequency oscillatory. No relevant interactions between the stimulation properties were found. In consequence, varying one stimulus parameter already leads to a saturation of the low as well as high-frequency somatosensory evoked potentials components. Thus, the careful choice of stimulation parameters is a condition precedent for reasonable data interpretation.

Quantifying Interhemispheric Symmetry of Somatosensory Evoked Potentials With the Intraclass Correlation Coefficient

Although large intersubject variability is reported for cortical somatosensory evoked potentials (SEPs), variability between hemispheres within one subject is thought to be small. Therefore, interhemispheric comparison of SEP waveforms might be clinically useful to detect unilateral abnormalities in cortical sensory processing. We developed and evaluated a new technique to quantify interhemispheric SEP symmetry that uses a time interval including multiple SEP components, measures similarity of SEP waveforms between both hemispheres and results in high symmetry values even in the presence of small interhemispheric anatomic differences. Median nerve SEPs were recorded in 50 healthy subjects (20-70 years) using 128-channel EEG. Symmetry was quantified by the intraclass correlation coefficient and correlation coefficient between global field power of left and right median nerve SEPs. In 74% of subjects left-right intraclass correlation coefficient was higher than 0.60, implying high SEP hemispheric symmetry in terms of shape and amplitude. Left-right intraclass correlation coefficients lower than 0.60 were due to differences in amplitude, unilateral absence of peaks, or shape differences. We quantified SEP waveform interhemispheric symmetry and found it to be high in most healthy subjects. This technique may therefore be useful for detection of unilateral abnormalities in cortical sensory processing.

Short-latency median-nerve somatosensory-evoked potentials and induced gamma-oscillations in humans

Recent studies have suggested that cortical gamma-oscillations are tightly linked with various forms of physiological activity. In the present study, the dynamic changes of intracranially recorded median-nerve somatosensory-evoked potentials (SEPs) and somatosensory-induced gamma-oscillations were animated on a three-dimensional MR image, and the temporal and spatial characteristics of these activities were analysed in 10 children being evaluated for epilepsy surgery. Visual and quantitative assessments revealed that short-latency SEPs and somatosensory-induced gamma-oscillations predominantly involved the post-central gyrus and less intensely involved the pre-central gyrus and the anterior parietal lobule. Formation of a dipole of N20 peak with opposite polarities across the central sulcus was well delineated in animation movies. High-frequency (100-250 Hz) somatosensory-induced gamma-oscillations emerged in the post-central gyrus at 13.6-17.5 ms after median-nerve stimulation, gradually slowed down in frequency around and below 100 Hz, and progressively involved the neighbouring areas. A substantial proportion of somatosensory-induced gamma-oscillations was initially phase-locked and the proportion of a non-phase-locked component gradually increased over time. The primary motor hand areas proven by cortical stimulation frequently coincided with the sites showing the largest N20 peak and the largest somatosensory-induced gamma oscillations. In vivo animation of SEPs and somatosensory-induced gamma oscillations both may be utilized to localize the primary sensory-motor hand area in pre-surgical evaluation. The dipole on SEPs is consistent with the previously accepted notion that the cortices along the central sulcus are activated. The high-frequency somatosensory-induced gamma-oscillations in the post-central gyrus may represent the initial neural processing for external somatosensory stimuli, whereas the subsequent lower-frequency oscillations might represent the reafferent cortical activity occurring in larger cortical networks.