Normative data of cortical excitability measurements obtained by transcranial magnetic stimulation in healthy subjects

Females with painful temporomandibular disorders present higher intracortical facilitation relative to pain-free controls

OBJECTIVES

This study aimed to investigate cortical excitability differences in the primary motor cortex (M1) hand representation between individuals with temporomandibular disorders (TMD) and healthy controls. We assessed resting motor thresholds, motor-evoked potentials (MEPs), intracortical inhibition, and intracortical facilitation and explored potential associations with clinical and psychosocial characteristics in the TMD group.

MATERIALS AND METHODS

We recruited 36 female participants with TMD and 17 pain-free controls. Transcranial magnetic stimulation (TMS) was used to assess M1 cortical excitability. Correlations between clinical and psychosocial factors and cortical excitability measures were also evaluated.

RESULTS

Patients with TMD showed significantly higher intracortical facilitation at 12 ms (z = 1.98, p = 0.048) and 15 ms (z = 2.65, p = 0.008) when compared to controls. Correlations revealed associations between intracortical facilitation and pain interference, sleep quality, depressive symptoms, and pain catastrophizing in the TMD group.

CONCLUSIONS

Females with TMD exhibit heightened motor cortex intracortical facilitation in the hand representation, potentially indicating altered cortical excitability beyond the motor face area. This suggests a role for cortical excitability in TMD pathophysiology, influenced by psychosocial factors.

CLINICAL RELEVANCE

Understanding cortical excitability in TMD may inform targeted interventions. Psychosocial variables may play a role in cortical excitability, emphasizing the multidimensional nature of TMD-related pain. Further research is needed to confirm and expand upon these findings, with potential implications for the management of TMD and related pain conditions.

Parkinson's Disease-related Pains are Not Equal: Clinical, Somatosensory and Cortical Excitability Findings in Individuals With Nociceptive Pain

Chronic pain is a frequent and burdensome nonmotor symptom of Parkinson's disease (PD). PD-related chronic pain can be classified as nociceptive, neuropathic, or nociplastic, the former being the most frequent subtype. However, differences in neurophysiologic profiles between these pain subtypes, and their potential prognostic and therapeutic implications have not been explored yet. This is a cross-sectional study on patients with PD (PwP)-related chronic pain (ie, started with or was aggravated by PD). Subjects were assessed for clinical and pain characteristics through questionnaires and underwent quantitative sensory tests and motor corticospinal excitability (CE) evaluations. Data were then compared between individuals with nociceptive and non-nociceptive (ie, neuropathic or nociplastic) pains. Thirty-five patients were included (51.4% male, 55.7 ± 11.0 years old), 20 of which had nociceptive pain. Patients with nociceptive PD-related pain had lower warm detection threshold (WDT, 33.34 ± 1.39 vs 34.34 ± 1.72, P = .019) and mechanical detection threshold (MDT, 2.55 ± 1.54 vs 3.86 ± .97, P = .007) compared to those with non-nociceptive pains. They also presented a higher proportion of low rest motor threshold values than the non-nociceptive pain ones (64.7% vs 26.6%, P = .048). In non-nociceptive pain patients, there was a negative correlation between WDT and non-motor symptoms scores (r = -.612, P = .045) and a positive correlation between MDT and average pain intensity (r = .629, P = .038), along with neuropathic pain symptom scores (r = .604, P = .049). It is possible to conclude that PD-related chronic pain subtypes have distinctive somatosensory and CE profiles. These preliminary data may help better frame previous contradictory findings in PwP and may have implications for future trial designs aiming at developing individually-tailored therapies. PERSPECTIVE: This work showed that PwP-related nociceptive chronic pain may have distinctive somatosensory and CE profiles than those with non-nociceptive pain subtypes. These data may help shed light on previous contradictory findings in PwP and guide future trials aiming at developing individually-tailored management strategies.

Beyond trial-and-error: Individualizing therapeutic transcranial neuromodulation for chronic pain

BACKGROUND AND OBJECTIVE

Repetitive transcranial magnetic stimulation (rTMS) applied to the motor cortex provides supplementary relief for some individuals with chronic pain who are refractory to pharmacological treatment. As rTMS slowly enters treatment guidelines for pain relief, its starts to be confronted with challenges long known to pharmacological approaches: efficacy at the group-level does not grant pain relief for a particular patient. In this review, we present and discuss a series of ongoing attempts to overcome this therapeutic challenge in a personalized medicine framework.

DATABASES AND DATA TREATMENT

Relevant scientific publications published in main databases such as PubMed and EMBASE from inception until March 2023 were systematically assessed, as well as a wide number of studies dedicated to the exploration of the mechanistic grounds of rTMS analgesic effects in humans, primates and rodents.

RESULTS

The main strategies reported to personalize cortical neuromodulation are: (i) the use of rTMS to predict individual response to implanted motor cortex stimulation; (ii) modifications of motor cortex stimulation patterns; (iii) stimulation of extra-motor targets; (iv) assessment of individual cortical networks and rhythms to personalize treatment; (v) deep sensory phenotyping; (vi) personalization of location, precision and intensity of motor rTMS. All approaches except (i) have so far low or moderate levels of evidence.

CONCLUSIONS

Although current evidence for most strategies under study remains at best moderate, the multiple mechanisms set up by cortical stimulation are an advantage over single-target 'clean' drugs, as they can influence multiple pathophysiologic paths and offer multiple possibilities of individualization.

SIGNIFICANCE

Non-invasive neuromodulation is on the verge of personalised medicine. Strategies ranging from integration of detailed clinical phenotyping into treatment design to advanced patient neurophysiological characterisation are being actively explored and creating a framework for actual individualisation of care.

Retest reliability of repetitive transcranial magnetic stimulation over the healthy human motor cortex: a systematic review and meta-analysis

Introduction

Repetitive transcranial magnetic stimulation (rTMS) is used to induce long-lasting changes (aftereffects) in cortical excitability, which are often measured via single-pulse TMS (spTMS) over the motor cortex eliciting motor-evoked potentials (MEPs). rTMS includes various protocols, such as theta-burst stimulation (TBS), paired associative stimulation (PAS), and continuous rTMS with a fixed frequency. Nevertheless, subsequent aftereffects of rTMS are variable and seem to fail repeatability. We aimed to summarize standard rTMS procedures regarding their test-retest reliability. Hereby, we considered influencing factors such as the methodological quality of experiments and publication bias.

Methods

We conducted a literature search via PubMed in March 2023. The inclusion criteria were the application of rTMS, TBS, or PAS at least twice over the motor cortex of healthy subjects with measurements of MEPs via spTMS as a dependent variable. The exclusion criteria were measurements derived from the non-stimulated hemisphere, of non-hand muscles, and by electroencephalography only. We extracted test-retest reliability measures and aftereffects from the eligible studies. With the Rosenthal fail-safe N, funnel plot, and asymmetry test, we examined the publication bias and accounted for influential factors such as the methodological quality of experiments measured with a standardized checklist.

Results

A total of 15 studies that investigated test-retest reliability of rTMS protocols in a total of 291 subjects were identified. Reliability measures, i.e., Pearson's r and intraclass correlation coefficient (ICC) applicable from nine studies, were mainly in the small to moderate range with two experiments indicating good reliability of 20 Hz rTMS (r = 0.543) and iTBS (r = 0.55). The aftereffects of rTMS procedures seem to follow the heuristics of respective inhibition or facilitation, depending on the protocols' frequency, and application pattern. There was no indication of publication bias and the influence of methodological quality or other factors on the reliability of rTMS.

Conclusion

The reliability of rTMS appears to be in the small to moderate range overall. Due to a limited number of studies reporting test-retest reliability values and heterogeneity of dependent measures, we could not provide generalizable results. We could not identify any protocol as superior to the others.

Acute pain drives different effects on local and global cortical excitability in motor and prefrontal areas: insights into interregional and interpersonal differences in pain processing

Pain-related depression of corticomotor excitability has been explored using transcranial magnetic stimulation-elicited motor-evoked potentials. Transcranial magnetic stimulation-electroencephalography now enables non-motor area cortical excitability assessments, offering novel insights into cortical excitability changes during pain states. Here, pain-related cortical excitability changes were explored in the dorsolateral prefrontal cortex and primary motor cortex (M1). Cortical excitability was recorded in 24 healthy participants before (Baseline), during painful heat (Acute Pain), and non-noxious warm (Warm) stimulation at the right forearm in a randomized sequence, followed by a pain-free stimulation measurement. Local cortical excitability was assessed as the peak-to-peak amplitude of early transcranial magnetic stimulation evoked potential, whereas global-mean field power measured the global excitability. Relative to the Baseline, Acute Pain decreased the peak-to-peak amplitude in M1 and dorsolateral prefrontal cortex compared with Warm (both P < 0.05). A reduced global-mean field power was only found in M1 during Acute Pain compared with Warm (P = 0.003). Participants with the largest reduction in local cortical excitability under Acute Pain showed a negative correlation between dorsolateral prefrontal cortex and M1 local cortical excitability (P = 0.006). Acute experimental pain drove differential pain-related effects on local and global cortical excitability changes in motor and non-motor areas at a group level while also revealing different interindividual patterns of cortical excitability changes, which can be explored when designing personalized treatment plans.

On the reliability of motor evoked potentials in hand muscles of healthy adults: a systematic review

Aims

Motor evoked potentials (MEP) elicited by transcranial magnetic stimulation (TMS) over the primary motor cortex are used as a neurophysiological marker of cortical excitability in clinical and scientific practice. Though, the reliability of this outcome parameter has not been clarified. Using a systematic approach, this work reviews and critically appraises studies on the reliability of MEP outcome parameters derived from hand muscles of healthy subjects and gives a proposal for most reliable TMS practice.

Methods

A systematic literature research was performed in PubMed, according to the PRISMA guidelines. Articles published up to March 2023 that were written in English, conducted repeated measurements from hand muscles of healthy subjects and reliability analysis were included. The risk of publication bias was determined. Two authors conducted the literature search and rated the articles in terms of eligibility and methodological criteria with standardized instruments. Frequencies of the checklist criteria were calculated and inter-rater reliability of the rating procedure was determined. Reliability and stimulation parameters were extracted and summarized in a structured way to conclude best-practice recommendation for reliable measurements.

Results

A total of 28 articles were included in the systematic review. Critical appraisal of the studies revealed methodological heterogeneity and partly contradictory results regarding the reliability of outcome parameters. Inter-rater reliability of the rating procedure was almost perfect nor was there indication of publication bias. Identified studies were grouped based on the parameter investigated: number of applied stimuli, stimulation intensity, reliability of input-output curve parameters, target muscle or hemisphere, inter-trial interval, coil type or navigation and waveform.

Conclusion

The methodology of studies on TMS is still subject to heterogeneity, which could contribute to the partly contradictory results. According to the current knowledge, reliability of the outcome parameters can be increased by adjusting the experimental setup. Reliability of single pulse MEP measurement could be optimized by using (1) at least five stimuli per session, (2) a minimum of 110% resting motor threshold as stimulation intensity, (3) a minimum of 4 s inter-trial interval and increasing the interval up to 20 s, (4) a figure-of-eight coil and (5) a monophasic waveform. MEPs can be reliably operationalized.

Exploratory genome-wide analyses of cortical inhibition, facilitation, and plasticity in late-life depression

Late-life depression (LLD) is a heterogenous mood disorder influenced by genetic factors. Cortical physiological processes such as cortical inhibition, facilitation, and plasticity may be markers of illness that are more strongly associated with genetic factors than the clinical phenotype. Thus, exploring the relationship between genetic factors and these physiological processes may help to characterize the biological mechanisms underlying LLD and improve diagnosis and treatment selection. Transcranial magnetic stimulation (TMS) combined with electromyography was used to measure short interval intracortical inhibition (SICI), cortical silent period (CSP), intracortical facilitation (ICF), and paired associative stimulation (PAS) in 79 participants with LLD. We used exploratory genome-wide association and gene-based analyses to assess for genetic correlations of these TMS measures. MARK4 (which encodes microtubule affinity-regulating kinase 4) and PPP1R37 (which encodes protein phosphatase 1 regulatory subunit 37) showed genome-wide significant association with SICI. EGFLAM (which encodes EGF-like fibronectin type III and laminin G domain) showed genome-wide significant association with CSP. No genes met genome-wide significant association with ICF or PAS. We observed genetic influences on cortical inhibition in older adults with LLD. Replication with larger sample sizes, exploration of clinical phenotype subgroups, and functional analysis of relevant genotypes is warranted to better characterize genetic influences on cortical physiology in LLD. This work is needed to determine whether cortical inhibition may serve as a biomarker to improve diagnostic precision and guide treatment selection in LLD.

Developmental models of motor-evoked potential features by transcranial magnetic stimulation across age groups from childhood to adulthood

To derive the maturation of neurophysiological processes from childhood to adulthood reflected by the change of motor-evoked potential (MEP) features. 38 participants were recruited from four groups (age mean in years [SD in months], number (males)): children (7.3 [4.2], 7(4)), preadolescents (10.3 [6.9], 10(5)), adolescents (15.3 [9.8], 11(5)), and adults (26.9 [46.2], 10(5)). The navigated transcranial magnetic stimulation was performed on both hemispheres at seven stimulation intensity (SI) levels from sub- to supra-threshold and targeted to the representative cortical area of abductor pollicis brevis muscle. MEPs were measured from three hand- and two forearm-muscles. The input-output (I/O) curves of MEP features across age groups were constructed using linear mixed-effect models. Age and SI significantly affected MEP features, whereas the stimulated side had a minor impact. MEP size and duration increased from childhood to adulthood. MEP onset- and peak-latency dropped in adolescence, particularly in hand muscles. Children had the smallest MEPs with the highest polyphasia, whereas I/O curves were similar among preadolescents, adolescents, and adults. This study illustrates some of the changing patterns of MEP features across the ages, suggesting developing patterns of neurophysiological processes activated by TMS, and to motivate studies with larger sample size.

Motor corticospinal excitability abnormalities differ between distinct chronic low back pain syndromes

OBJECTIVES

It is not known whether cortical plastic changes reported in low-back pain (LBP) are present in all etiologies of LBP. Here we report on the assessment of patients with three LBP conditions: non-specific-LBP (ns-LBP), failed back surgery syndrome (FBSS), and sciatica (Sc).

METHODS

Patients underwent a standardized assessment of clinical pain, conditioned pain modulation (CPM), and measures of motor evoked potential (MEPs)-based motor corticospinal excitability (CE) by transcranial magnetic stimulation, including short interval intracortical inhibition (SICI), and intracortical facilitation (ICF). Comparisons were also made with normative data from sex- and age-matched healthy volunteers.

RESULTS

60 patients (42 women, 55.1±9.1 years old) with LBP were included (20 in each group). Pain intensity was higher in patients with neuropathic pain [FBSS (6.8±1.3), and Sc (6.4±1.4)] than in those with ns-LBP (4.7±1.0, P<0.001). The same was shown for pain interference (5.9±2.0, 5.9±1.8, 3.2±1.9, P<0.001), disability (16.4±3.3, 16.3±4.3, 10.4±4.3, P<0.001), and catastrophism (31.1±12.3, 33.0±10.4, 17.4±10.7, P<0.001) scores for FBSS, Sc, and ns-LBP groups, respectively. Patients with neuropathic pain (FBSS, Sc) had lower CPM (-14.8±1.9, -14.1±16.7, respectively) compared to ns-LBP (-25.4±16.6; P<0.02). 80.0% of the FBSS group had defective ICF compared to the other two groups (52.5% for ns-LBP, P=0.025 and 52.5% for Sc, P=0.046). MEPs (140%-rest motor threshold) were low in 50.0% of patients in the FBSS group compared to 20.0% of ns-LBP (P=0.018) and 15.0% of Sc (P=0.001) groups. Higher MEPs were correlated with mood scores (r=0.489), and with lower neuropathic pain symptom scores(r=-0.415) in FBSS.

CONCLUSIONS

Different types of LBP were associated with different clinical, CPM and CE profiles, which were not uniquely related to the presence of neuropathic pain. These results highlight the need to further characterize patients with LBP in psychophysics and cortical neurophysiology studies.

Corticomotor excitability is altered in central neuropathic pain compared with non-neuropathic pain or pain-free patients

OBJECTIVES

Central neuropathic pain (CNP) is associated with altered corticomotor excitability (CE), which can potentially provide insights into its mechanisms. The objective of this study is to describe the CE changes that are specifically related to CNP.

METHODS

We evaluated CNP associated with brain injury after stroke or spinal cord injury (SCI) due to neuromyelitis optica through a battery of CE measurements and comprehensive pain, neurological, functional, and quality of life assessments. CNP was compared to two groups of patients with the same disease: i. with non-neuropathic pain and ii. without chronic pain, matched by sex and lesion location.

RESULTS

We included 163 patients (stroke=93; SCI=70: 74 had CNP, 43 had non-neuropathic pain, and 46 were pain-free). Stroke patients with CNP had lower motor evoked potential (MEP) in both affected and unaffected hemispheres compared to non- neuropathic pain and no-pain patients. Patients with CNP had lower amplitudes of MEPs (366 μV ±464 μV) than non-neuropathic (478 ±489) and no-pain (765 μV ± 880 μV) patients, p < 0.001. Short-interval intracortical inhibition (SICI) was defective (less inhibited) in patients with CNP (2.6±11.6) compared to no-pain (0.8±0.7), p = 0.021. MEPs negatively correlated with mechanical and cold-induced allodynia. Furthermore, classifying patients' results according to normative data revealed that at least 75% of patients had abnormalities in some CE parameters and confirmed MEP findings based on group analyses.

DISCUSSION

CNP is associated with decreased MEPs and SICI compared to non-neuropathic pain and no-pain patients. Corticomotor excitability changes may be helpful as neurophysiological markers of the development and persistence of pain after CNS injury, as they are likely to provide insights into global CE plasticity changes occurring after CNS lesions associated with CNP.

Sex differences in mild vascular cognitive impairment: A multimodal transcranial magnetic stimulation study

BACKGROUND

Sex differences in vascular cognitive impairment (VCI) at risk for future dementia are still debatable. Transcranial magnetic stimulation (TMS) is used to evaluate cortical excitability and the underlying transmission pathways, although a direct comparison between males and females with mild VCI is lacking.

METHODS

Sixty patients (33 females) underwent clinical, psychopathological, functional, and TMS assessment. Measures of interest consisted of: resting motor threshold, latency of motor evoked potentials (MEPs), contralateral silent period, amplitude ratio, central motor conduction time (CMCT), including the F wave technique (CMCT-F), short-interval intracortical inhibition (SICI), intracortical facilitation, and short-latency afferent inhibition, at different interstimulus intervals (ISIs).

RESULTS

Males and females were comparable for age, education, vascular burden, and neuropsychiatric symptoms. Males scored worse at global cognitive tests, executive functioning, and independence scales. MEP latency was significantly longer in males, from both sides, as well CMCT and CMCT-F from the left hemisphere; a lower SICI at ISI of 3 ms from the right hemisphere was also found. After correction for demographic and anthropometric features, the effect of sex remained statistically significant for MEP latency, bilaterally, and for CMCT-F and SICI. The presence of diabetes, MEP latency bilaterally, and both CMCT and CMCT-F from the right hemisphere inversely correlated with executive functioning, whereas TMS did not correlate with vascular burden.

CONCLUSIONS

We confirm the worse cognitive profile and functional status of males with mild VCI compared to females and first highlight sex-specific changes in intracortical and cortico-spinal excitability to multimodal TMS in this population. This points to some TMS measures as potential markers of cognitive impairment, as well as targets for new drugs and neuromodulation therapies.

Transcranial Magnetic Stimulation Indices of Cortical Excitability Enhance the Prediction of Response to Pharmacotherapy in Late-Life Depression

BACKGROUND

Older adults with late-life depression (LLD) often experience incomplete or lack of response to first-line pharmacotherapy. The treatment of LLD could be improved using objective biological measures to predict response. Transcranial magnetic stimulation (TMS) can be used to measure cortical excitability, inhibition, and plasticity, which have been implicated in LLD pathophysiology and associated with brain stimulation treatment outcomes in younger adults with depression. TMS measures have not yet been investigated as predictors of treatment outcomes in LLD or pharmacotherapy outcomes in adults of any age with depression.

METHODS

We assessed whether pretreatment single-pulse and paired-pulse TMS measures, combined with clinical and demographic measures, predict venlafaxine treatment response in 76 outpatients with LLD. We compared the predictive performance of machine learning models including or excluding TMS predictors.

RESULTS

Two single-pulse TMS measures predicted venlafaxine response: cortical excitability (neuronal membrane excitability) and the variability of cortical excitability (dynamic fluctuations in excitability levels). In cross-validation, models using a combination of these TMS predictors, clinical markers of treatment resistance, and age classified patients with 73% ± 11% balanced accuracy (average correct classification rate of responders and nonresponders; permutation testing, p < .005); these models significantly outperformed (corrected t test, p = .025) models using clinical and demographic predictors alone (60% ± 10% balanced accuracy).

CONCLUSIONS

These preliminary findings suggest that single-pulse TMS measures of cortical excitability may be useful predictors of response to pharmacotherapy in LLD. Future studies are needed to confirm these findings and determine whether combining TMS predictors with other biomarkers further improves the accuracy of predicting LLD treatment outcome.

Acute High-Intensity Interval Exercise Modulates Corticospinal Excitability in Older Adults

INTRODUCTION

Acute exercise can modulate the excitability of the non-exercised upper-limb representation in the primary motor cortex (M1). Measures of M1 excitability using transcranial magnetic stimulation (TMS) are modulated following various forms of acute exercise in young adults, including high intensity interval training (HIIT). However, the impact of HIIT on M1 excitability in older adults is currently unknown. Therefore, the purpose of the current study was to investigate the effects of lower-limb cycling HIIT on bilateral upper-limb M1 excitability in older adults.

METHODS

We assessed the impact of acute lower-limb HIIT or rest on bilateral corticospinal excitability, intracortical inhibition and facilitation, and interhemispheric inhibition of the non-exercised upper-limb muscle in healthy older adults (aged 66 ± 8). We used single and paired-pulse TMS to assess motor evoked potentials (MEPs), short-interval intracortical inhibition (SICI), intracortical facilitation (ICF) and the ipsilateral silent period (iSP). Two groups of healthy older adults completed either HIIT exercise or seated rest for 23 min, with TMS measures performed pre (T0), immediately post (T1) and 30 min post (T2) HIIT/rest.

RESULTS

MEPs were significantly increased after HIIT exercise at T2 compared to T0 in the dominant upper-limb. Contrary to our hypothesis we did not find any significant change in SICI, ICF or iSP following HIIT.

CONCLUSIONS

Our findings demonstrate that corticospinal excitability of the non-exercised upper-limb is increased following HIIT in healthy older adults. Our results indicate that acute HIIT exercise impacts corticospinal excitability in older adults, without affecting intracortical or interhemispheric circuitry. These findings have implications for the development of exercise strategies to potentiate neuroplasticity in healthy older and clinical populations.

The distribution and reliability of TMS-evoked short- and long-latency afferent interactions

Short-latency afferent inhibition (SAI) and long-latency afferent inhibition (LAI) occur when the motor evoked potential (MEP) elicited by transcranial magnetic stimulation (TMS) is reduced by the delivery of a preceding peripheral nerve stimulus. The intra-individual variability in SAI and LAI is considerable, and the influence of sample demographics (e.g., age and biological sex) and testing context (e.g., time of day) is not clear. There are also no established normative values for these measures, and their reliability varies from study-to-study. To address these issues and facilitate the interpretation of SAI and LAI research, we pooled data from studies published by our lab between 2014 and 2020 and performed several retrospective analyses. Patterns in the depth of inhibition with respect to age, biological sex and time of testing were investigated, and the relative reliability of measurements from studies with repeated baseline SAI and LAI assessments was examined. Normative SAI and LAI values with respect to the mean and standard deviation were also calculated. Our data show no relationship between the depth of inhibition for SAI and LAI with either time of day or age. Further, there was no significant difference in SAI or LAI between males and females. Intra-class correlation coefficients (ICC) for repeated measurements of SAI and LAI ranged from moderate (ICC = 0.526) to strong (ICC = 0.881). The mean value of SAI was 0.71 ± 0.27 and the mean value of LAI was 0.61 ± 0.34. This retrospective study provides normative values, reliability estimates, and an exploration of demographic and testing influences on these measures as assessed in our lab. To further facilitate the interpretation of SAI and LAI data, similar studies should be performed by other labs that use these measures.

Biological sex differences in afferent-mediated inhibition of motor responses evoked by TMS

Sensorimotor integration can be assessed by pairing electrical peripheral nerve stimulation with transcranial magnetic stimulation (TMS). The resulting afferent inhibition is observed when TMS precedes nerve stimulation by ∼ 20-25 ms, termed short-latency afferent inhibition (SAI), or by 200 ms, termed long-latency afferent inhibition (LAI). The purpose of this study was to determine whether biological sex influences the magnitude of SAI or LAI. SAI and LAI were assessed in fifteen males (21.5 ± 2.7 years) and fifteen females (20.2 ± 2.3 years). TMS was delivered to the primary motor cortex (M1) following stimulation of the contralateral median nerve at the wrist or digital nerve of the index finger, and motor-evoked potentials (MEPs) were obtained from the right first dorsal interosseous (FDI) muscle. SAI evoked by median and digital nerve stimulation, and LAI evoked by median nerve stimulation, were not different between males and females. LAI evoked by digital nerve stimulation was increased in females compared to males, but this difference between sexes was no longer present following the removal of datapoints where inhibition was not observed. This study is the first to investigate biological sex differences in afferent inhibition.

Clinical and Neurophysiological Effects of Botulinum Neurotoxin Type A in Chronic Migraine

Chronic pain syndromes present a subversion of both functional and structural nociceptive networks. We used transcranial magnetic stimulation (TMS) to evaluate changes in cortical excitability and plasticity in patients with chronic migraine (CM) treated with botulinum neurotoxin type A (BoNT/A). We enrolled 11 patients with episodic migraine (EM) and 11 affected by CM. Baseline characteristics for both groups were recorded using single- and paired-pulse TMS protocols. The same TMS protocol was repeated in CM patients after four cycles of BoNT/A completed in one year. At baseline, compared with EM patients, patients with CM had a lower threshold in both hemispheres (right hemisphere: 46% ± 7.8 vs. 52% ± 4.28, p = 0.03; left hemisphere: 52% ± 4.28 vs. 53.54% ± 6.58, p = 0.02). In EM, paired-pulse stimulation elicited a physiologically shaped response, whereas in CM, physiological intracortical inhibition (ICI) between 1 and 3 ms intervals was absent at baseline. On the contrary, increasing intracortical facilitation (ICF) was observed for all interstimulus intervals (ISIs). In CM, cortical excitability was partially reduced after BoNT/A treatment, along with a significant decrease observed in MIDAS score (from 20.7 to 9.8; p = 0.008). The lower motor threshold in CM reflects a higher cortical hyperexcitability. The lack of physiological ICI in CM could indicate sensitisation of the trigeminovascular system. Although reduced, this type of response is still observable after treatment, despite a marked clinical improvement. Our study suggests a long-term alteration of cortical plasticity due to chronic pain.

Brain-Derived Neurotrophic Factor Modulates the Effect of Sex on the Descending Pain Modulatory System in Healthy Volunteers

OBJECTIVES

We investigated sex differences and the influence of brain-derived neurotrophic factor (BDNF) in the descending pain modulatory system (DPMS), as measured by change on the numerical pain scale (NPS; 0-10) during conditioned pain modulation (CPM task; primary outcome) and by function of the corticospinal motor pathway and heat pain thresholds (HPTs; secondary outcomes).

METHODS

This cross-sectional study included healthy volunteers ranging in age from 18 to 45 years (32 male and 24 female). Assessment included serum BDNF, HPT, change on the NPS (0-10) during the CPM task, and motor-evoked potential (MEP) using transcranial magnetic stimulation (TMS).

RESULTS

The MEP (Mv) amplitude was larger in male participants compared with female participants (mean [SE] = 1.55 [0.34] vs mean [SE] = 1.27 [0.27], respectively, P = 0.001). The mean NPS (0-10) during CPM task changed more substantially for female compared with male participants (mean [SE] = -3.25 [2.01] vs mean [SE] = -2.29 [1.34], respectively, P = 0.040). In addition, a higher serum BDNF (adjusted index for age) was associated with a larger decrease of the NPS during CPM task (P = 0.003), although further regression analyses by sex showed that this was only significant for females (P = 0.010).

CONCLUSIONS

Significant sex differences were identified in DPMS function and corticospinal motor pathway integrity. Nevertheless, BDNF was associated with the function of the DPMS in female but not male participants, indicating that sex and neuroplasticity state are crucial factors for pain perception in healthy subjects.

Evaluation of Changes in Preoperative Cortical Excitability by Navigated Transcranial Magnetic Stimulation in Patients With Brain Tumor

Background: This prospective study aimed to evaluate the cortical excitability (CE) of patients with brain tumors surrounding or directly involving the corticospinal tract (CST) using navigated transcranial magnetic stimulation (nTMS).

Methods: We recruited 40 patients with a single brain tumor surrounding or directly involving the CST as well as 82 age- and sex-matched healthy controls. The patients underwent standard nTMS and CE evaluations. Single and paired pulses were applied to the primary motor area (M1) of both affected and unaffected cerebral hemispheres 1 week before surgery. The CE parameters included resting motor threshold (RMT), motor evoked potential (MEP) ratio for 140 and 120% stimulus (MEP 140/120 ratio), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF). Motor outcome was evaluated on hospital discharge and on 30-day and 90-day postoperative follow-up.

Results: In the affected hemispheres of patients, SICI and ICF were significantly higher than in the unaffected hemispheres (p=0.002 and p=0.009, respectively). The 140/120 MEP ratio of patients' unaffected hemispheres was lower than that in controls (p=0.001). Patients with glioblastomas (GBM) had a higher interhemispheric RMT ratio than patients with grade II and III gliomas (p = 0.018). A weak correlation was observed among the RMT ratio and the preoperative motor score (R² = 0.118, p = 0.017) and the 90-day follow-up (R² = 0.227, p = 0.016).

Conclusion: Using preoperative nTMS, we found that brain hemispheres affected by tumors had abnormal CE and that patients with GBM had a distinct pattern of CE. These findings suggest that tumor biological behavior might play a role in CE changes.

Cortical inhibition, facilitation and plasticity in late-life depression: effects of venlafaxine pharmacotherapy

BACKGROUND

Late-life depression is often associated with non-response or relapse following conventional antidepressant treatment. The pathophysiology of late-life depression likely involves a complex interplay between aging and depression, and may include abnormalities in cortical inhibition and plasticity. However, the extent to which these cortical processes are modifiable by antidepressant pharmacotherapy is unknown.

METHODS

Sixty-eight patients with late-life depression received 12 weeks of treatment with open-label venlafaxine, a serotonin-norepinephrine reuptake inhibitor (≤ 300 mg/d). We combined transcranial magnetic stimulation of the left motor cortex with electromyography recordings from the right hand to measure cortical inhibition using contralateral cortical silent period and paired-pulse short-interval intracortical inhibition paradigms; cortical facilitation using a paired-pulse intracortical facilitation paradigm; and short-term cortical plasticity using a paired associative stimulation paradigm. All measures were collected at baseline, 1 week into treatment (n = 23) and after approximately 12 weeks of treatment.

RESULTS

Venlafaxine did not significantly alter cortical inhibition, facilitation or plasticity after 1 or 12 weeks of treatment. Improvements in depressive symptoms during treatment were not associated with changes in cortical physiology.

LIMITATIONS

The results presented here are specific to the motor cortex. Future work should investigate whether these findings extend to cortical areas more closely associated with depression, such as the dorsolateral prefrontal cortex.

CONCLUSION

These findings suggest that antidepressant treatment with venlafaxine does not exert meaningful changes in motor cortical inhibition or plasticity in late-life depression. The absence of changes in motor cortical physiology, alongside improvements in depressive symptoms, suggests that age-related changes may play a role in previously identified abnormalities in motor cortical processes in latelife depression, and that venlafaxine treatment does not target these abnormalities.

Transcranial magnetic stimulation reveals diminished homoeostatic metaplasticity in cognitively impaired adults

Homoeostatic metaplasticity is a neuroprotective physiological feature that counterbalances Hebbian forms of plasticity to prevent network destabilization and hyperexcitability. Recent animal models highlight dysfunctional homoeostatic metaplasticity in the pathogenesis of Alzheimer's disease. However, the association between homoeostatic metaplasticity and cognitive status has not been systematically characterized in either demented or non-demented human populations, and the potential value of homoeostatic metaplasticity as an early biomarker of cognitive impairment has not been explored in humans. Here, we report that, through pre-conditioning the synaptic activity prior to non-invasive brain stimulation, the association between homoeostatic metaplasticity and cognitive status could be established in a population of non-demented human subjects (older adults across cognitive spectrums; all within the non-demented range). All participants (n = 40; age range, 65-74, 47.5% female) underwent a standardized neuropsychological battery, magnetic resonance imaging and a transcranial magnetic stimulation protocol. Specifically, we sampled motor-evoked potentials with an input/output curve immediately before and after repetitive transcranial magnetic stimulation to assess neural plasticity with two experimental paradigms: one with voluntary muscle contraction (i.e. modulated synaptic activity history) to deliberately introduce homoeostatic interference, and one without to serve as a control condition. From comparing neuroplastic responses across these experimental paradigms and across cohorts grouped by cognitive status, we found that (i) homoeostatic metaplasticity is diminished in our cohort of cognitively impaired older adults and (ii) this neuroprotective feature remains intact in cognitively normal participants. This novel finding suggests that (i) future studies should expand their scope beyond just Hebbian forms of plasticity that are traditionally assessed when using non-invasive brain stimulation to investigate cognitive ageing and (ii) the potential value of homoeostatic metaplasticity in serving as a biomarker for cognitive impairment should be further explored.

Neurophysiological basis of manual force asymmetries in young and senior adults

In this study, we investigated age differences in manual force production to explore their neurophysiological basis. Manual pinching and gripping forces were first measured during unilateral and bilateral efforts in two groups of right-handed adults (young, n = 12, senior, n = 11). Then, transcranial magnetic stimulation (TMS) was applied to each hemisphere to assess central motor inhibition via the contralateral and ipsilateral silent period (cSP, iSP). Laterality quotients (LQs) were computed to determine asymmetries for unimanual strength tests and hemispheric asymmetries in TMS measures. Bilateral indices (BLI) were computed to assess the bilateral force deficit (BFD). During unilateral efforts, both young and senior participants exhibited similar degrees of asymmetry. Similarly, no age difference was detected when comparing LQs derived from TMS measures. During bilateral efforts, although BLI tended to be lower in seniors, no age difference was detected. Asymmetry in strength and BLI showed no association with hemispheric asymmetry in TMS measures, except for the asymmetry in pinch strength, which was associated with asymmetry in the iSP duration. These observations confirm that asymmetries in manual strength and BFD are little affected by age. Also, our results show that hemispheric asymmetries in transcallosal inhibition are associated with pinch strength asymmetry.

An inverse relationship between cortical plasticity and cognitive inhibition in late-life depression

Executive dysfunction is a common and disabling component of late-life depression (LLD), yet its neural mechanisms remain unclear. In particular, it is not yet known how executive functioning in LLD relates to measures of cortical physiology that may change with age and illness, namely cortical inhibition/excitation and plasticity. Here, we used transcranial magnetic stimulation (TMS) to measure cortical inhibition/excitation (n = 51), and the potentiation of cortical activity following paired associative stimulation, which is thought to reflect long-term potentiation (LTP)-like cortical plasticity (n = 32). We assessed the correlation between these measures of cortical physiology and two measures of executive functioning: cognitive inhibition, assessed using the Delis-Kaplan Executive Function System Color-Word Interference ["Stroop"] Test, and cognitive flexibility, assessed using the Trail Making Test. Correlations with recall memory and processing speed were also performed to assess the specificity of any associations to executive functioning. A significant correlation was found between greater LTP-like cortical plasticity and poorer cognitive inhibition, a core executive function (rp = -0.56, p < 0.001). We did not observe significant associations between cortical inhibition/excitation and executive functioning, or between any neurophysiological measure and cognitive flexibility, memory, or processing speed. Our finding that elevated cortical plasticity is associated with diminished cognitive inhibition emphasizes the importance of balanced synaptic strengthening to healthy cognition. More specifically, our findings suggest that hyper-excitability of cortical circuits following repeated cortical activation may promote inappropriate prepotent responses in LLD. LTP-like cortical plasticity might therefore represent a neural mechanism underlying an inhibitory control cognitive endophenotype of LLD.

Changes of motor cortical excitability and response inhibition in patients with obsessive–compulsive disorder

BACKGROUND

Deficits in cortical inhibitory processes have been suggested as underlying pathophysiological mechanisms of obsessive–compulsive disorder (OCD). We examined whether patients with OCD have altered cortical excitability using paired-pulse transcranial magnetic stimulation (TMS). We also tested associations between TMS indices and OCD-related characteristics, including age of onset and response inhibition in the go/no-go paradigm, to examine whether altered cortical excitability contributes to symptom formation and behavioural inhibition deficit in patients with OCD.

METHODS

We assessed motor cortex excitability using paired-pulse TMS in 51 patients with OCD and 39 age-matched healthy controls. We also assessed clinical symptoms and response inhibition in the go/nogo task. All patients were undergoing treatment with serotonin reuptake inhibitors. We performed repeated-measures multivariate analysis of covariance to compare TMS indices between patients with OCD and controls.

RESULTS

Compared to controls, patients with OCD showed a shorter cortical silent period and decreased intracortical facilitation. However, we found no significant difference between groups for resting motor threshold or short-interval intracortical inhibition. In the OCD group, the shortened cortical silent period was associated with a prompt reaction time in the go/no-go task and with early onset of OCD.

LIMITATIONS

We could not exclude the influence of medications on motor cortex excitability.

CONCLUSION

These findings suggest abnormal cortical excitability in patients with OCD. The associations between cortical silent period and response inhibition and age of onset further indicate that altered cortical excitability may play an important role in the development of OCD.

Age, Height, and Sex on Motor Evoked Potentials: Translational Data From a Large Italian Cohort in a Clinical Environment

Introduction

Motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) are known to be susceptible to several sources of variability. However, conflicting evidences on individual characteristics in relatively small sample sizes have been reported. We investigated the effect of age, height, and sex on MEPs of the motor cortex and spinal roots in a large cohort.

Methods

A total of 587 subjects clinically and neuroradiologically intact were included. MEPs were recorded during mild tonic contraction through a circular coil applied over the "hot spot" of the first dorsal interosseous and tibialis anterior muscles (TAs), bilaterally. Central motor conduction time (CMCT) was estimated as the difference between MEP cortical latency and the peripheral motor conduction time (PMCT) by cervical or lumbar magnetic stimulation. Peak-to-peak MEP amplitude to cortical stimulation and right-to-left difference of each parameter were also measured.

Results

After Bonferroni correction, general linear (multiple) regression analysis showed that both MEP cortical latency and PMCT at four limbs positively correlated with age and height. At lower limbs, an independent effect of sex on the same measures was also observed (with females showing smaller values than males). CMCT correlated with both age (negatively) and height (positively) when analyzed by a single regression; however, with a multiple regression analysis this significance disappeared, due to the correction for the multicollinearity within the dataset.

Conclusion

Physical individual features need to be considered for a more accurate and meaningful MEPs interpretation. Both in clinical practice and in research setting, patients and controls should be matched for age, height, and sex.

Changes in motor cortical excitability in schizophrenia following transcranial direct current stimulation

Schizophrenia is a disorder associated with cortical inhibition deficits. Transcranial direct current stimulation (tDCS) induces changes in cortical excitability in healthy subjects and individuals with neuropsychiatric disorders depending on the stimulation parameters. Our aim was to investigate whether a previously published tDCS protocol associated with symptomatic improvement in schizophrenia would induce changes in motor cortical excitability, assessed by transcranial magnetic stimulation paradigms, i.e., short-interval intracortical inhibition (SICI) and intra-cortical facilitation (ICF). We assessed cortical excitability measurements in 48 subjects with schizophrenia before and after a single session of active tDCS (20 min, 2 mA, anode over left dorsolateral prefrontal cortex, cathode over left temporoparietal cortex) or sham. Those who received active tDCS had a significant increase of SICI in the left motor cortex compared to those who received sham stimulation (Cohen's d = 0.54, p = .019). No changes were observed for ICF. In addition, lower SICI was associated with higher age (β = -0.448, p < .01). Increase in intracortical inhibition may indicate a mechanism of action of tDCS in this population. Future studies should investigate whether this finding is a biomarker of treatment response for schizophrenia.

Age, Height, and Sex on Motor Evoked Potentials: Translational Data From a Large Italian Cohort in a Clinical Environment

INTRODUCTION

Motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) are known to be susceptible to several sources of variability. However, conflicting evidences on individual characteristics in relatively small sample sizes have been reported. We investigated the effect of age, height, and sex on MEPs of the motor cortex and spinal roots in a large cohort.

METHODS

A total of 587 subjects clinically and neuroradiologically intact were included. MEPs were recorded during mild tonic contraction through a circular coil applied over the "hot spot" of the first dorsal interosseous and tibialis anterior muscles (TAs), bilaterally. Central motor conduction time (CMCT) was estimated as the difference between MEP cortical latency and the peripheral motor conduction time (PMCT) by cervical or lumbar magnetic stimulation. Peak-to-peak MEP amplitude to cortical stimulation and right-to-left difference of each parameter were also measured.

RESULTS

After Bonferroni correction, general linear (multiple) regression analysis showed that both MEP cortical latency and PMCT at four limbs positively correlated with age and height. At lower limbs, an independent effect of sex on the same measures was also observed (with females showing smaller values than males). CMCT correlated with both age (negatively) and height (positively) when analyzed by a single regression; however, with a multiple regression analysis this significance disappeared, due to the correction for the multicollinearity within the dataset.

CONCLUSION

Physical individual features need to be considered for a more accurate and meaningful MEPs interpretation. Both in clinical practice and in research setting, patients and controls should be matched for age, height, and sex.

Reduced GABAergic cortical inhibition in aging and depression

The neurobiology underlying depression in older adults is less extensively evaluated than in younger adults, despite the putative influence of aging on depression neuropathology. Studies using transcranial magnetic stimulation (TMS), a neurophysiological tool capable of probing inhibitory and excitatory cortical neurotransmission, have identified dysfunctional GABAergic inhibitory activity in younger adults with depression. However, GABAergic and glutamatergic cortical neurotransmission have not yet been studied in late-life depression (LLD). Here, we used single- and paired-pulse TMS to measure cortical inhibition and excitation in 92 LLD patients and 41 age-matched healthy controls. To differentiate the influence of age and depression, we also compared these TMS indices to those of 30 younger depressed adults and 30 age- and sex-matched younger healthy adults. LLD patients, older healthy adults, and younger depressed adults demonstrated significantly lower GABA_A receptor-mediated cortical inhibition than younger healthy controls. By contrast, no significant differences in cortical inhibition were observed between older adults with and without depression. No significant differences in GABA_B receptor-mediated inhibition or cortical excitation were found between the groups. Altogether, these findings suggest that reduced cortical inhibition may be associated with both advancing age and depression, which (i) supports the model of depression as a disease of accelerated aging, and (ii) prompts future investigation into diminished GABAergic neurotransmission in late-life as a biological predisposing factor to the development of depression. Given that cortical neurophysiology was similar in depressed and healthy older adults, future prospective studies need to establish the relative influence of age and depression on cortical inhibition deficits.

Altered cortical excitability in persistent idiopathic facial pain

Introduction

Persistent idiopathic facial pain is a refractory and disabling condition of unknown mechanism and etiology. It has been suggested that persistent idiopathic facial pain patients have not only peripheral generators of pain, but also central nervous system changes that would contribute to the persistence of symptoms. We hypothesized that persistent idiopathic facial pain would have changes in brain cortical excitability as measured by transcranial magnetic stimulation compared to healthy controls.

Methods

Twenty-nine persistent idiopathic facial pain patients were compared to age- and sex-matched healthy controls and underwent cortical excitability measurements by transcranial magnetic stimulation applied to the cortical representation of the masseter muscle of both hemispheres. Single-pulse stimulation was used to measure the resting motor threshold and suprathreshold motor-evoked potentials. Paired-pulse stimulation was used to assess short intracortical inhibition and intracortical facilitation. Clinical pain and associated symptoms were assessed with validated tools.

Results

Spontaneous pain was found in 27 (93.1%) and provoked pain was found in two (6.9%) persistent idiopathic facial pain patients. The motor-evoked potentials at 120% and 140% were significantly lower for both hemispheres compared to controls. Persistent idiopathic facial pain patients had lower short-interval intracortical inhibition compared with controls. These changes were correlated with some aspects of quality of life, and higher mood symptoms. These neurophysiological alterations were not influenced by analgesic medication, as similar changes were observed in patients with or without central-acting drugs.

Conclusions

Persistent idiopathic facial pain is associated with changes in intracortical modulation involving GABAergic mechanisms, which may be related to certain aspects of the pathophysiology of this chronic pain condition. Trial registration: NTC01746355.

Epigenetics insights into chronic pain: DNA hypomethylation in fibromyalgia-a controlled pilot-study

To evaluate changes in DNA methylation profiles in patients with fibromyalgia (FM) compared to matched healthy controls (HCs). All individuals underwent full clinical and neurophysiological assessment by cortical excitability (CE) parameters measured by transcranial magnetic stimulation. DNA from the peripheral blood of patients with FM (n = 24) and HC (n = 24) were assessed using the Illumina-HumanMethylation450 BeadChips. We identified 1610 differentially methylated positions (DMPs) in patients with FM displaying a nonrandom distribution in regions of the genome. Sixty-nine percent of DMP in FM were hypomethylated compared to HC. Differentially methylated positions were enriched in 5 genomic regions (1p34; 6p21; 10q26; 17q25; 19q13). The functional characterization of 960 genes related to DMPs revealed an enrichment for MAPK signaling pathway (n = 18 genes), regulation of actin cytoskeleton (n = 15 genes), and focal adhesion (n = 13 genes). A gene-gene interaction network enrichment analysis revealed the participation of DNA repair pathways, mitochondria-related processes, and synaptic signaling. Even though DNA was extracted from peripheral blood, this set of genes was enriched for disorders such as schizophrenia, mood disorders, bulimia, hyperphagia, and obesity. Remarkably, the hierarchical clusterization based on the methylation levels of the 1610 DMPs showed an association with neurophysiological measurements of CE in FM and HC. Fibromyalgia has a hypomethylation DNA pattern, which is enriched in genes implicated in stress response and DNA repair/free radical clearance. These changes occurred parallel to changes in CE parameters. New epigenetic insights into the pathophysiology of FM may provide the basis for the development of biomarkers of this disorder.

Altered Intracortical Inhibition in Chronic Traumatic Diffuse Axonal Injury

Background

Overactivation of NMDA-mediated excitatory processes and excess of GABA-mediated inhibition are attributed to the acute and subacute phases, respectively, after a traumatic brain injury (TBI). However, there are few studies regarding the circuitry during the chronic phase of brain injury.

Objective

To evaluate the cortical excitability (CE) during the chronic phase of TBI in victims diagnosed with diffuse axonal injury (DAI).

Methods

The 22 adult subjects were evaluated after a minimum of 1 year from the onset of moderate or severe TBI. Each of the subjects first had a comprehensive neuropsychological assessment to evaluate executive functions-attention, memory, verbal fluency, and information processing speed. Then, CE assessment was performed with a circular coil applying single-pulse and paired-pulse transcranial magnetic stimulation over the cortical representation of the abductor pollicis brevis muscle on M1 of both hemispheres. The CE parameters measured were resting motor threshold (RMT), motor-evoked potentials (MEPs), short-interval intracortical inhibition (SIICI), and intracortical facilitation (ICF). All data were compared with that of a control group that consisted of the healthy age-matched individuals.

Results

No significant differences between the left and right hemispheres were detected in the DAI subjects. Therefore, parameters were analyzed as pooled data. Values of RMT, MEPs, and ICF from DAI patients were within normal limits. However, SIICI values were higher in the DAI group-DAI SIICI = 1.28 (1.01; 1.87) versus the control value = 0.56 (0.33; 0.69)-suggesting that they had a disarranged inhibitory system (p < 0.001). By contrast, the neuropsychological findings had weak correlation with the CE data.

Conclusion

As inhibition processes involve GABA-mediated circuitry, it is likely that the DAI pathophysiology itself (disruption of axons) may deplete GABA and contribute to ongoing disinhibition of these neural circuits of the cerebrum during the chronic phase of DAI.

The variability of motor evoked potential latencies in neurosurgical motor mapping by preoperative navigated transcranial magnetic stimulation

Background

Recording of motor evoked potentials (MEPs) is used during navigated transcranial magnetic stimulation (nTMS) motor mapping to locate motor function in the human brain. However, factors potentially underlying MEP latency variability in neurosurgical motor mapping are vastly unknown. In the context of this study, one hundred brain tumor patients underwent preoperative nTMS-based motor mapping of the tumor hemisphere between 2010 and 2013. Fourteen predefined predictor variables were recorded, and MEP latencies of abductor pollicis brevis muscle (APB), abductor digiti minimi muscle (ADM), and flexor carpi radialis muscle (FCR) were analyzed using linear mixed-effect multiple regression analysis with the forward step-wise model comparison approach.

Results

Common factors (relevant to APB, ADM, and FCR) for MEP latency variability were gender, most likely due to body height, and antiepileptic drug (AED) intake. Muscle-specific factors (relevant to APB, ADM, or FCR) for MEP latency variability were resting motor threshold (rMT), tumor side, and tumor location.

Conclusions

Based on a large cohort of neurosurgical patients, this study provides data on a wide range of clinical factors that may underlie MEP latency variability. The factors that significantly contributed to MEP latency variability should be standardly recorded and taken into consideration during neurosurgical motor mapping.