Median nerve conduction study findings in various arm positions.

OBJECTIVES: To investigate the effects of various arm positions on median nerve conduction studies (NCSs). METHODS: This prospective cohort study, conducted at Adana City Training and Research Hospital between January and July 2023, included 20 healthy participants. Median NCSs were performed on the participants in three different standing positions with the elbow as the stimulation point: 1) with the arm adducted (P1), 2) with the arm anteflexed (P2), and 3) with the arm raised upwards (P3). We obtained median nerve compound muscle action potential (CMAP) latency, duration, peak-to-peak (PP) amplitude, onset-to-negative peak (OP) amplitude, negative area/duration. Three CMAPs were obtained in each position, and the mean and minimum/maximum values at each position were analyzed. RESULTS: The mean age (minimum-maximum) of the participants (11 male, 9 female) was 28.5±6.5 (20-42) years. Median nerve CMAP means (median) of latency/negative duration in the P1, P2, and P3 positions were 6.82±0.59 (6.83)/5.50±0.76 (5.39) ms, 6.99±0.56 (7.02)/5.72±0.73 (5.73) ms, and 7.03±0.58 (7.12)/5.79±0.80 (5.83) ms. Median nerve CMAP mean/minimum latency and negative duration were lowest in the P1 position (p<0.05). The mean median nerve CMAP OP amplitude was highest in P3 than P1 or P2 (p=0.042 and p=0.048). CONCLUSION: Median NCS results differed based on the position of the arm.

Nerve conduction, latency, and its association with hand function in young men.

INTRODUCTION: The median and ulnar nerves have been suggested to play a significant role in hand function; however, there are insufficient data to determine the strength of this association. This study aimed to investigate the correlation between hand function as measured with the Grooved pegboard test (GPT) and conduction velocity and latency of the median and ulnar nerves. METHODS: We collected convenience samples in the College of Medicine, KSAU-HS. We used GPT to characterize hand function and performed measured nerve conduction velocity (NCV) and latency of the ulnar and median nerves of both hands. We used the Edinburgh handedness inventory (EHI) to determine hand dominance. RESULTS: We recruited 28 healthy medical students aged 20-29 years (mean: 21.46 ± 1.62 years). Most were right-handed (n = 25, 89.3%), with a mean EHI score of 302 ± 210. The mean GPT time was significantly faster in the dominant (65.5 ± 6.4 s) than in the non-dominant (75.0 ± 9.6 s) hand. The NCV for the ulnar nerve of the dominant hand was significantly correlated with GPT (r = -0.52, p = 0.005) while median nerve was not correlated (0.24, p = 0.21). Regression analysis and collinearity test showed that the ulnar NCV explained 20% of the variance in GPT of the dominant hand (R2 = 0.203, p = 0.016). CONCLUSION: The ulnar nerve conduction velocity, explained 20% of the variance in GPT times of the young men. Performance on this biomarker of neurological health seems to be more influenced by other factors in healthy young individuals.

Comparison of a hand-held high-end resolution infrared thermography (FLIR P640) and a smartphone infrared thermographic device (FLIR One) for the assessment of skin surface temperature after anaesthetising the median nerve in Healthy horses.

Accuracy of a median nerve block is normally assessed by testing skin sensitivity on the medial and dorsal aspects of fetlock and pastern. The present study evaluated subjective and objective analysis of skin surface temperature obtained with two different infrared (IR) thermography cameras (a high-end [FLIR P640] and a smartphone IR thermography device [FLIR One®]) before and after anaesthesia of the median nerve. Thermographic images were obtained at 0, 30, 60 and 90 minutes after performing a median nerve block with 2% mepivacaine hydrochloride. The subjective analysis of thermographic images using the FLIR P640 camera found assessors had >50% agreement for the presence of a nerve block (p<0.01) based on assessment of skin temperature within the expected dermatome of the median nerve. The objective analysis found skin temperature increases in the treated leg using the FLIR One® in the dorsal fetlock, dorsal pastern and medial pastern at 60 minutes, and the lateral pastern at 90 minutes (p<0.05). The treated leg, imaged using the FLIR P640 camera, had increases in skin temperature at the medial aspect of the fetlock at 60 minutes and lateral pastern at 90 minutes (p<0.05). Images obtained with the P640 camera had higher resolution and finer thermal detail. The images obtained with the FLIR One® camera had a wider temperature range with overall higher temperature measurements than the images obtained using the P640 camera (p<0.001). Skin temperatures in horses should be interpreted with caution when using the FLIR One® camera. Furthermore, the FLIR One® device detected an increase in skin surface temperature in both treated and non-treated legs and should not be used for assessment of a median nerve block. Infrared thermography appears to be useful for determining the presence of a high regional nerve block such as the median nerve block by observing increased temperatures of the skin surface after perineural anaesthesia. Further studies with a larger sample size as well as investigating the use of thermography for assessment of other regional nerve blocks are warranted.

Effect of Forearm Supination and Pronation on Median & Ulnar Nerve Conduction Velocity Among Throwers, Archers, and Non-Athletes.

The distinct and specialized movements performed in different sports disciplines may significantly influence nerve performance, potentially affecting nerve responses and the overall function within the respective athletic activities. The purpose of this study is to find the effect of forearm supination and pronation across the elbow joint on ulnar and median nerve conduction velocity (NCV) in throwers, archers, and non-athletes. A total of 34 participants both male and females were recruited with a body mass index (BMI) between 18.5 and 24.9 kg/m2. Nerve conduction study (NeuroStim NS2 EMG/NCV/EP System) was used for measuring ulnar and median NCV across the elbow joint at different angles with the forearm in supination and pronation. Repeated measure analysis of variance (RMANOVA) revealed that there are statistically significant differences in mean values of forearm positions, angles, nerves and groups (p < .05). This study illuminates distinctive NCV variations across diverse athletic groups during forearm supination and pronation movements. Pronation consistently exhibited faster ulnar NCV compared to the median nerve across throwers, archers, and non-athletes, while in supination specific joint positions revealed notable differences within sports groups and nerve function.

Effect of cervical contralateral lateral flexion on the median nerve and fascia at the wrist - Cadaveric study.

BACKGROUND: Neurodynamic tests are an essential aspect of the physical examination of the patient when suspicion of neural involvement exists. A manoeuvre that is hypothesised to move nerves differentially relative to other structures (structural differentiation) has been proposed as a necessary part of neurodynamic testing for differential diagnosis. However, although the specificity of structural differentiation for peripheral nerve over muscle has been demonstrated in some body regions, no study has tested specificity of nerve movement relative to fascia. OBJECTIVES: The aim of this study was to measure the effect of the cervical contralateral lateral flexion (CCLF) as an structural differentiation manoeuvre for the median nerve compared to fascia (superficial and deep) at the wrist during the upper limb neurodynamic test 1 (ULNT1). DESIGN: A cross-sectional study was performed in 5 fresh frozen cadavers. METHODS: Excursion and strain in the fascia (superficial and deep) and the median nerve were measured at the wrist with structural differentiation during the ULNT1. KINOVEA software was used to measure kinematic parameters. RESULTS: CCLF resulted in significant proximal excursion in the median nerve (p < 0.001*) but not in the strain. CCLF neither produced changes in strain nor excursion in the superficial and deep fascia (p > 0.05). CONCLUSION: This study showed that CCLF produced significant differential excursion in the median nerve at the wrist compared to the local superficial and deep fascia during the ULNT1. The data support CCLF in mechanical differentiation between nerve and fascia in this area in diagnosis of local sources of wrist pain.

Modulation of the somatosensory blink reflex under fear.

OBJECTIVE: This study evaluated the isolated and combined effects of fear and PPS paradigms on SBR. METHOD: The prospective study was conducted with healthy participants. After stimulation of the right median nerve at the wrist, bilateral recordings were randomized under the following conditions: First experiment (with the right hand on the chair armrest): i. baseline recordings, ii. while watching fearful facial expressions from the Karolinska Emotional Faces battery (fear), iii. post-watching (post-fear), iv. while watching neutral facial expressions from the same battery (neutral), v. Immediately after viewing (post-neutral). Second experiment (right hand 2 cm away from the right eye, PPS): i. reference condition (PPS), ii. while watching fearful facial expressions (PPS-fear), iii. while watching neutral facial expressions (PPS-neutral). In each condition, SBR latency, area, duration, and amplitudes were measured and compared between conditions. RESULTS: We included 16 participants. SBR could be recorded in 11 (mean age:30.7 ± 5.2, F/M:5/6). First experiment: SBR amplitude was significantly reduced in fear condition (p = 0.008), and SBR area was reduced considerably in fear and post-fear conditions (p = 0.004) compared to the baseline. Second experiment: The SBR area was higher in the PPS (p = 0.009) compared to the baseline and even higher in the fearPPS compared to the PPS (p = 0.038). In neutral or PPS-neutral conditions, the area of the SBR did not change significantly. CONCLUSION: Fear suppressed SBR, but fear increased SBR when a threat stimulus was present. The findings were unrelated to habituation or attention, indicating cortical-amygdala-bulbar connections.

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.

Further characterisation of late somatosensory evoked potentials using electroencephalogram and magnetoencephalogram source imaging.

Beside the well-documented involvement of secondary somatosensory area, the cortical network underlying late somatosensory evoked potentials (P60/N60 and P100/N100) is still unknown. Electroencephalogram and magnetoencephalogram source imaging were performed to further investigate the origin of the brain cortical areas involved in late somatosensory evoked potentials, using sensory inputs of different strengths and by testing the correlation between cortical sources. Simultaneous high-density electroencephalograms and magnetoencephalograms were performed in 19 participants, and electrical stimulation was applied to the median nerve (wrist level) at intensity between 1.5 and 9 times the perceptual threshold. Source imaging was undertaken to map the stimulus-induced brain cortical activity according to each individual brain magnetic resonance imaging, during three windows of analysis covering early and late somatosensory evoked potentials. Results for P60/N60 and P100/N100 were compared with those for P20/N20 (early response). According to literature, maximal activity during P20/N20 was found in central sulcus contralateral to stimulation site. During P60/N60 and P100/N100, activity was observed in contralateral primary sensorimotor area, secondary somatosensory area (on both hemispheres) and premotor and multisensory associative cortices. Late responses exhibited similar characteristics but different from P20/N20, and no significant correlation was found between early and late generated activities. Specific clusters of cortical activities were activated with specific input/output relationships underlying early and late somatosensory evoked potentials. Cortical networks, partly common to and distinct from early somatosensory responses, contribute to late responses, all participating in the complex somatosensory brain processing.

Somatosensory evoked spikes in normal adults detected by magnetoencephalography.

OBJECTIVE: Somatosensory evoked spikes (SESs) have been reported only in children aged under 14 years and are considered as an age-dependent phenomenon. However, we detected SESs in adult patients with epilepsy using magnetoencephalography (MEG). The present study investigated whether MEG can detect SESs in normal adults. METHODS: Spontaneous MEG was recorded during measurement of somatosensory evoked fields (SEFs) for bilateral electrical median nerve stimuli in 30 healthy adults. RESULTS: Bilateral SESs were observed in 10 adults but none in the other 20 subjects. SESs consisted of one or two peaks, and the first peak latency corresponded to that of the second peak (M2) of SEFs. The first SES peak was identical to the M2 in isofield map pattern, as well as location and orientation of the equivalent current dipole (ECD). M2 ECD strength in the 10 subjects with SESs was larger (p <0.0001) than in 20 without SESs. CONCLUSIONS: All-or-nothing detection of bilateral SESs by MEG in normal adults must depend on the signal-to-noise issue of symmetrical SEFs and background brain activity. SIGNIFICANCE: Our results further confirm the higher sensitivity of MEG compared to scalp EEG for the detection of focal cortical sources tangential to the scalp such as SESs.

Concurrent spinal and brain imaging with optically pumped magnetometers.

BACKGROUND: The spinal cord and its interactions with the brain are fundamental for movement control and somatosensation. However, brain and spinal electrophysiology in humans have largely been treated as distinct enterprises, in part due to the relative inaccessibility of the spinal cord. Consequently, there is a dearth of knowledge on human spinal electrophysiology, including the multiple pathologies that affect the spinal cord as well as the brain. NEW METHOD: Here we exploit recent advances in the development of wearable optically pumped magnetometers (OPMs) which can be flexibly arranged to provide coverage of both the spinal cord and the brain in relatively unconstrained environments. This system for magnetospinoencephalography (MSEG) measures both spinal and cortical signals simultaneously by employing custom-made scanning casts. RESULTS: We evidence the utility of such a system by recording spinal and cortical evoked responses to median nerve stimulation at the wrist. MSEG revealed early (10 - 15 ms) and late (>20 ms) responses at the spinal cord, in addition to typical cortical evoked responses (i.e., N20). COMPARISON WITH EXISTING METHODS: Early spinal evoked responses detected were in line with conventional somatosensory evoked potential recordings. CONCLUSION: This MSEG system demonstrates the novel ability for concurrent non-invasive millisecond imaging of brain and spinal cord.

Investigating the effects of dopamine on short- and long-latency afferent inhibition.

Short- and long-latency afferent inhibition (SAI and LAI respectively) are phenomenon whereby the motor evoked potential induced by transcranial magnetic stimulation (TMS) is inhibited by a sensory afferent volley consequent to nerve stimulation. It remains unclear whether dopamine participates in the genesis or modulation of SAI and LAI. The present study aimed to determine if SAI and LAI are modulated by levodopa (l-DOPA). In this placebo-controlled, double-anonymized study Apo-Levocarb (100 mg l-DOPA in combination with 25 mg carbidopa) and a placebo were administered to 32 adult males (mean age 24 ± 3 years) in two separate sessions. SAI and LAI were evoked by stimulating the median nerve and delivering single-pulse TMS over the motor hotspot corresponding to the first dorsal interosseous muscle of the right hand. SAI and LAI were quantified before and 1 h following ingestion of drug or placebo corresponding to the peak plasma concentration of Apo-Levocarb. The results indicate that Apo-Levocarb increases SAI and does not significantly alter LAI. These findings support literature demonstrating increased SAI following exogenous dopamine administration in neurodegenerative disorders. KEY POINTS: Short- and long-latency afferent inhibition (SAI and LAI respectively) are measures of corticospinal excitability evoked using transcranial magnetic stimulation. SAI and LAI are reduced in conditions such as Parkinson's disease which suggests dopamine may be involved in the mechanism of afferent inhibition. 125 mg of Apo-Levocarb (100 mg dopamine) increases SAI but not LAI. This study increases our understanding of the pharmacological mechanism of SAI and LAI.

Changes in the excitability of anterior horn cells in a mental rotation task of body parts.

INTRODUCTION/AIMS: Mental rotation (MR), a tool of implicit motor imagery, is the ability to rotate mental representations of two- or three-dimensional objects. Although many reports have described changes in brain activity during MR tasks, it is not clear whether the excitability of anterior horn cells in the spinal cord can be changed. In this study, we examined whether MR tasks of hand images affect the excitability of anterior horn cells using F-wave analysis. METHODS: Right-handed, healthy participants were recruited for this study. F-waves of the right abductor pollicis brevis were recorded after stimulation of the right median nerve at rest, during a non-MR task, and during an MR task. The F-wave persistence and the F/M amplitude ratio were calculated and analyzed. RESULTS: Twenty participants (11 men and 9 women; mean age, 29.2 ± 4.4 years) were initially recruited, and data from the 18 that met the inclusion criteria were analyzed. The F-wave persistence was significantly higher in the MR task than in the resting condition (p = .001) or the non-MR task (p = .012). The F/M amplitude ratio was significantly higher in the MR task than in the resting condition (p = .019). DISCUSSION: The MR task increases the excitability of anterior horn cells corresponding to the same body part. MR tasks may have the potential for improving motor function in patients with reduced excitability of the anterior horn cells, although this methodology must be further verified in a clinical setting.

Effects of finger pinch motor imagery on short-latency afferent inhibition and corticospinal excitability.

Motor imagery is a cognitive process involving the simulation of motor actions without actual movements. Despite the reported positive effects of motor imagery training on motor function, the underlying neurophysiological mechanisms have yet to be fully elucidated. Therefore, the purpose of the present study was to investigate how sustained tonic finger-pinching motor imagery modulates sensorimotor integration and corticospinal excitability using short-latency afferent inhibition (SAI) and single-pulse transcranial magnetic stimulation (TMS) assessments, respectively. Able-bodied individuals participated in the study and assessments were conducted under two experimental conditions in a randomized order between participants: (1) participants performed motor imagery of a pinch task while observing a visual image displayed on a monitor (Motor Imagery), and (2) participants remained at rest with their eyes fixed on the monitor displaying a cross mark (Control). For each condition, sensorimotor integration and corticospinal excitability were evaluated during sustained tonic motor imagery in separate sessions. Sensorimotor integration was assessed by SAI responses, representing inhibition of motor-evoked potentials (MEPs) in the first dorsal interosseous muscle elicited by TMS following median nerve stimulation. Corticospinal excitability was assessed by MEP responses elicited by single-pulse TMS. There was no significant difference in the magnitude of SAI responses between motor imagery and Control conditions, while MEP responses were significantly facilitated during the Motor Imagery condition compared to the Control condition. These findings suggest that motor imagery facilitates corticospinal excitability, without altering sensorimotor integration, possibly due to insufficient activation of the somatosensory circuits or lack of afferent feedback during sustained tonic motor imagery.

Utility of shear wave elastography for diagnosing carpal tunnel syndrome with psoriatic arthritis.

BACKGROUND: Carpal tunnel syndrome (CTS) is a type of peripheral entrapment neuropathy and common for the patients with psoriatic arthritis (PsA). Shear wave elastography (SWE) is a new ultrasonography technique that can be used for diagnosing CTS, but not studied in PsA patients. AIMS: The aim of this study to measure the stiffness of median nerve and hand muscles by quantitative SWE to identify whether SWE can be used for diagnosing CTS in patients with PsA or not. METHODS: To diagnose CTS, all patients had electrodiagnostic study. The stiffness values of the median nerve, abductor pollicis brevis, and abductor digiti minimi were determined using SWE. Muscle stiffness ratio was also calculated. RESULTS: Consideration is given to 48 patients with PsA (93 wrists) and 29 healthy volunteers (57 wrists). Median nerve stiffness was found to be significantly higher, and abductor pollicis brevis' stiffness and muscle stiffness ratio were significantly lower in PsA patients' wrists compared to control group (p = 0.002, p < 0.001, p = 0.001, respectively) and in CTS wrists compared to others (p < 0.001, p < 0.001, p = 0.001, respectively). Receiver operating characteristic analysis identified 28.2 kPA as the median nerve stiffness cut-off point for differentiating CTS in PsA patients (p = 0.001). CONCLUSIONS: We found that SWE has a good diagnostic value for CTS with PsA patients; hence, we can conclude that SWE could diagnose CTS in PsA patients.

Long latency reflexes of the median nerves in healthy adults.

INTRODUCTION/AIMS: Long latency reflexes (LLRs) are late responses in nerve conduction studies seen after peripheral nerve stimulation during submaximal muscle contraction. They follow a short latency reflex, also known as the H reflex, and are thought to involve transcortical pathways, providing a measure of proximal nerve and central conduction. For this reason, they have been evaluated in several central nervous system diseases, but reference values are not widely published and are mostly based on old studies with very small numbers of participants. Therefore, in this work we aim to provide comprehensive reference values for LLR testing. METHODS: LLRs were tested in a cohort of 100 healthy participants, testing the median nerve bilaterally. RESULTS: Mean latencies for short latency reflex (SLR), LLR1, LLR2, and LLR3 were 27.00, 38.50, 47.60, and 67.34 milliseconds, respectively. The allowable side-to-side difference was approximately 3 to 4 milliseconds. No significant sex-related differences were seen. Height correlated moderately with the SLR latency, but only weakly with LLR1, LLR2, and LLR3. DISCUSSION: This work provides normal LLR values for comparison with future studies in disease. The technique used may allow for improved evaluation of central nervous system or proximal peripheral nerve disorders.

Central sensitization mechanisms in chronic migraine with medication overuse headache: a study of thalamocortical activation and lateral cortical inhibition.

BACKGROUND: It is unclear whether cortical hyperexcitability in chronic migraine with medication overuse headache (CM-MOH) is due to increased thalamocortical drive or aberrant cortical inhibitory mechanisms. METHODS: Somatosensory evoked potentials (SSEP) were performed by electrical stimulation of the median nerve (M), ulnar nerve (U) and simultaneous stimulation of both nerves (MU) in 27 patients with CM-MOH and, for comparison, in 23 healthy volunteers (HVs) of a comparable age distribution. We calculated the degree of cortical lateral inhibition using the formula: 100 - [MU/(M + U) × 100] and the level of thalamocortical activation by analyzing the high frequency oscillations (HFOs) embedded in parietal N20 median SSEPs. RESULTS: Compared to HV, CM-MOH patients showed higher lateral inhibition (CM-MOH 52.2% ± 15.4 vs. HV 40.4% ± 13.3; p = 0.005), which positively correlated with monthly headache days, and greater amplitude of pre-synaptic HFOs (p = 0.010) but normal post-synaptic HFOs (p = 0.122). CONCLUSION: Our findings suggest that central neuronal circuits are highly sensitized in CM-MOH patients, at both thalamocortical and cortical levels. The observed changes could be due to the combination of dysfunctional central pain control mechanisms, hypersensitivity and hyperresponsiveness directly linked to the chronic intake of acute migraine drugs.

Strength-duration time constant and rheobase measurements: Comparison of the threshold tracking method and a manual procedure.

OBJECTIVE: To compare the strength-duration time constant (SDTC) and rheobase measurements obtained by the threshold tracking method (TT) and by a non-automated method (MM). METHODS: The MM procedure involved measuring, using a routine electrodiagnostic device, the intensity required to evoke a motor response whose amplitude corresponds to 40% of the maximum amplitude for four stimulus duration (1.0, 0.7, 0.5, 0.2 ms), and studying the linear relationship between stimulus charge and stimulus duration (slope = rheobase, intercept on the x-axis = SDTC). Using TT and MM, 30 successive healthy subjects (mean age = 38 years old) underwent a prospective evaluation of SDTC and rheobase of the median nerve motor axons at the wrist. Nerve stimulation and bipolar recording of evoked motor responses were performed with disposable self-adhesive surface electrodes. RESULTS: The Spearman correlations between the two methods were 0.78 (p < 0.0001) for SDTC and 0.96 (p < 0.0001) for the rheobase. The Bland-Altman analysis did not reveal any systematic bias of MM compared to TT. CONCLUSIONS: The MM procedure was reliable for strength-duration relationship analysis. SIGNIFICANCE: We encourage neurophysiologists, who do not have dedicated threshold tracking equipment, not to hesitate to use these simple tools to assess peripheral nerve excitability.

The Rise Slope of the Compound Sensory Nerve Action Potential in Normal and Pathological Human Nerves.

In spite of the diagnostic importance of the early phase of the sensory nerve action potential (SNAP), reliable electrodiagnostic metrics for this part of the recorded waveform are lacking. The average rise slope of the SNAP appreciates the steepness of the initial negative deflection of the waveform, which might be a useful metric for the first part of the potential. Sural nerve sensory neurography was performed in patients with various axonal neuropathies, and median nerve sensory studies were carried out in patients with carpal tunnel syndrome. Age-matched healthy individuals served as controls. The rise slope was compared to conventional SNAP parameters such as conduction velocity, latency, duration, and rise time. Overall, 537 sensory studies were prospectively analyzed. The rise slope of the sural SNAP demonstrated superior classification performance in terms of sensitivity (92.5%), specificity (97%), and area under the receiver operating characteristic curve (0.986), as compared to conventional SNAP parameters. Its diagnostic power was similarly excellent in median nerve studies, whereas here a slightly better classification performance was obtained by SNAP latency and conduction velocity. The average rise slope appears to do justice to the tight interplay between amplitude and rise time of the initial negative spike deflection, outperforming many conventional measures. This composite metric proved high diagnostic potency in particular with regard to axonal sensory nerve dysfunction.

Skin type and nerve effects on cortical tactile processing: a somatosensory evoked potentials study.

Somatosensory evoked potential (SEP) studies typically characterize short-latency components following median nerve stimulations of the wrist. However, these studies rarely considered 1) skin type (glabrous/hairy) at the stimulation site, 2) nerve being stimulated, and 3) middle-latency (>30 ms) components. Our aim was to investigate middle-latency SEPs following simple mechanical stimulation of two skin types innervated by two different nerves. Eighteen adults received 400 mechanical stimulations over four territories of the right hand (two nerves: radial/median; two skin types: hairy/glabrous skin) while their EEG was recorded. Four middle-latency components were identified: P50, N80, N130, and P200. As expected, significantly shorter latencies and larger amplitudes were found over the contralateral hemisphere for all components. A skin type effect was found for the N80; glabrous skin stimulations induced larger amplitude than hairy skin stimulations. Regarding nerve effects, median stimulations induced larger P50 and N80. Latency of the N80 was longer after median nerve stimulation compared with radial nerve stimulation. This study showed that skin type and stimulated nerve influence middle-latency SEPs, highlighting the importance of considering these parameters in future studies. These modulations could reflect differences in cutaneous receptors and somatotopy. Middle-latency SEPs can be used to evaluate the different steps of tactile information cortical processing. Modulation of SEP components before 100 ms possibly reflects somatotopy and differential processing in primary somatosensory cortex.NEW & NOTEWORTHY The current paper highlights the influences of stimulated skin type (glabrous/hairy) and nerve (median/radial) on cortical somatosensory evoked potentials. Mechanical stimulations were applied over four territories of the right hand in 18 adults. Four middle-latency components were identified: P50, N80, N130, and P200. A larger N80 was found after glabrous skin stimulations than after hairy skin ones, regardless of the nerve being stimulated. P50 and N80 were larger after median than radial nerve stimulations.

Reduced somatosensory evoked potentials and paired-pulse inhibition in the primary somatosensory cortex of athletes with chronic pain.

PURPOSE: Chronic pain impedes athletic training and performance. However, it is challenging to identify the precise causes of chronic pain for effective treatment. To examine possible neuroplastic changes in sensory transmission and cortical processing, we compared somatosensory evoked potentials (SEPs) and paired-pulse inhibition (PPI) in primary sensory cortex (S1) between athletes with chronic pain and control athletes. METHODS: Sixty-six intercollegiate athletes (39 males and 27 females) were recruited for this study, 45 control athletes and 21 reporting persistent pain for > 3 months. Sensory-evoked potentials were induced in S1 by constant-current square-wave pulses (0.2-ms duration) delivered to the right median nerve, while PPI was induced by paired stimulation at interstimulus intervals of 30 and 100 ms (PPI-30 and PPI-100 ms, respectively). All participants were randomly presented with total 1,500 (each 500 stimuli) single stimuli and stimulus pairs at 2 Hz. RESULTS: Both N20 amplitude and PPI-30 ms were significantly lower in athletes with chronic pain compared to control athletes, while P25 amplitude and PPI-100 ms did not differ significantly between groups. CONCLUSION: Chronic pain in athletes is associated with substantially altered excitatory-inhibitory balance within the primary somatosensory cortex, possibly due to reduced thalamocortical excitatory transmission and suppressed cortical inhibitory transmission.