Differences in corticospinal system activity and reaction response between karate athletes and non-athletes.

Background/Objectives: The impact of stroke on upper extremity function in the older adult population underscores the need for accurate recovery prediction. Motor evoked potential (MEP) has been explored as a predictor of upper extremity function recovery in patients with stroke. However, research specifically targeting the geriatric population remains limited. Therefore, this study focused specifically on patients aged 65 years and older to investigate correlations between MEP parameters and upper extremity function. This study investigates correlations between MEP parameters (amplitude and latency) and upper extremity function-related measures, including Medical Research Council (MRC) scale, the Korean version of the Modified Barthel Index (K-MBI), and the Hand Function Test (HFT), including grip strength, pinch strength, the Box and Block Test, and the 9-Hole Peg Test, in older adults with stroke. Methods: A multiple linear regression model predicts upper extremity outcomes using initial MEP parameters, time, and function. The dataset includes 90 patients with stroke categorized by timing of the first MEP assessment: ≤3 months (n = 42) or >3 months (n = 48). Results: MEP amplitude and latency were significantly correlated with upper extremity function in both groups. No significant correlations were found between MEP amplitude or latency and outcome measures. Regression analysis showed that initial MEP amplitude had a limited association with outcomes, whereas latency was significantly associated with grip strength (β: -10.205, 95% CI: -19.374~-1.036) and the Box and Block Test (β: -10.204, 95% CI: -20.254~-0.154). Initial upper extremity parameters were significantly associated with K-MBI and HFT follow-up results (p < 0.05). Conclusions: Larger MEP amplitude and faster initial MEP latency were associated with improved upper extremity function in patients with stroke. In older patients, MEP latency, rather than amplitude, demonstrated greater predictive value for upper extremity function recovery, possibly due to age-related muscle atrophy, a factor not fully addressed in existing prognostic frameworks such as PREP2. These findings support the integration of MEP latency assessment into geriatric stroke prognostication, complementing existing frameworks such as PREP2, and may guide personalized rehabilitation planning to optimize functional recovery and independence.

Motor evoked potentials (MEPs) induced through transcranial magnetic stimulation (TMS) are susceptible to several sources of variability including gender, hand dominance, and upper extremity length. Conflicting evidence on the relationship between MEPs and subject characteristics has been reported. The purposes of this study were to determine if MEPs are different between genders and between right- and left-hand dominant subjects, and to determine if MEPs are correlated with upper extremity length. Using a case-control design, we recorded MEPs from 45 healthy subjects (age 21.6 ± 2.0 years; 24 females, 21 males) with a MagStim200 stimulating coil positioned over the primary motor cortex. Evoked responses were recorded by surface EMG electrodes from the abductor pollicis brevis, abductor digiti minimi and first dorsal interosseous muscles contralateral to the site of TMS. Evoked responses were analyzed to determine motor thresholds, latencies and amplitudes. Central motor conduction time (CMCT) was estimated from MEP, M response, and F wave latencies. Gender and hand dominance did not significantly influence thresholds, MEP amplitudes, or CMCT (P > .05). MEP latencies were moderately correlated with upper extremity length (R = .62 right median, R = .50 left median, R = .45 right ulnar, R = .51 left ulnar MEP latency, P < .01). An ANCOVA using upper extremity length as the covariate demonstrated no significant differences between genders (Wilk's λ = .89, F = 2.45, P = .10). After adjusting MEP latencies to upper limb length, no significant differences were observed between dominant and non-dominant limbs (F = .002, P = .97 median, and F = .03, P = .56 ulnar) nor between genders (F = 2.7, P = .11 median; F = .05, P = .82 ulnar). Variability in MEP latencies between genders was due to differences in upper extremity length. Adjusting MEP latencies to upper limb length is recommended for more accurate comparison and meaningful interpretation between subjects. Hand dominance and gender do not significantly influence motor thresholds, MEP amplitude, or CMCT.

Introduction: It has been shown from invasive epidural recordings that in transcranial magnetic stimulation (TMS) a current in the brain flowing from a posterior to an anterior (p.a.) direction mainly evokes I1, I2 and I3 waves whereas a current flowing from an anterior to a posterior direction mainly evokes I3 waves. This leads to the hypotheses that in p.a. current direction the motor threshold (MT) is lower, motor evoked potentials (MEPs) are higher and latency is shorter than in a.p. direction. The aim of this study was to re-evaluate the inconsistent results in literature by means of a stimulation technique that enabled us to change the current direction without turning the coil. Methods: We investigated n=23 healthy subjects (female: n=12; mean age: 26.2±1.9 years). We recorded the MT, MEP amplitude to target 400µV (SI400µV), MT adapted IO curves and maximum stimulator output (MSO) adapted IO curves in a.p. and p.a. current direction (monophasic waveform) with the P-Stim 160 stimulator (Mag and More, Germany). Results: MT was significantly lower (p=0.003), MEP amplitudes (SI400µV) were significantly higher (p<0.001) and latencies significantly shorter (p<0.001) in p.a. current direction. RmANOVA revealed a significant influence of current direction in MSO adapted IO curves on both, MEP amplitude and latency. We observed a significant influence of current direction on latencies in MT adapted recording of IO-curves but not on MEP amplitudes. Discussion: Our results consistently demonstrate for the first time a significant influence of current direction on MT, MEP amplitude and latency at fixed stimulus intensities as well as in IO curves due to the hypotheses generated from the specific I-wave pattern. The high consistency of the results when changing the current direction without altering coil position offers the opportunity of I wave specific evaluation and stimulation in TMS.

This study aimed to assess the effects of thoracic anodal and cathodal transcutaneous spinal direct current stimulation (tsDCS) on upper and lower limb corticospinal excitability. Although there have been studies assessing how thoracic tsDCS influences the spinal ascending tract and reflexes, none has assessed the effects of this technique over upper and lower limb corticomotor neuronal connections. In 14 healthy subjects we recorded motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) from abductor hallucis (AH) and hand abductor digiti minimi (ADM) muscles before (baseline) and at different time points (0 and 30 min) after anodal or cathodal tsDCS (2.5 mA, 20 min, T9-T11 level). In 8 of the 14 subjects we also tested the soleus H reflex and the F waves from AH and ADM before and after tsDCS. Both anodal and cathodal tsDCS left the upper limb MEPs and F wave unchanged. Conversely, while leaving lower limb H reflex unchanged, they oppositely affected lower limb MEPs: whereas anodal tsDCS increased resting motor threshold [(mean ± SE) 107.33 ± 3.3% increase immediately after tsDCS and 108.37 ± 3.2% increase 30 min after tsDCS compared with baseline] and had no effects on MEP area and latency, cathodal tsDCS increased MEP area (139.71 ± 12.9% increase immediately after tsDCS and 132.74 ± 22.0% increase 30 min after tsDCS compared with baseline) without affecting resting motor threshold and MEP latency. Our results show that tsDCS induces polarity-specific changes in corticospinal excitability that last for >30 min after tsDCS offset and selectively affect responses in lower limb muscles innervated by lumbar and sacral motor neurons.

We aimed to determine, using transcranial magnetic stimulation (TMS), the number of elicited motor evoked potentials (MEPs) that induces the highest intra- and inter-sessions reliability for the extensor carpi radialis (ECR) and first dorsal interosseus (FDI) muscles. Twelve healthy subjects participated in this study on two separate days. Single pulse magnetic stimuli were triggered with Magstim 2002 to obtain MEPs from the muscles of interest, with the subjects in a relaxed position. Reliability of MEP responses was investigated in three blocks of 5, 10 and 15 trials. The intra- and inter-session reliability of the MEPs' amplitudes and latencies were assessed using intraclass correlation coefficients (ICCs). Repeated measures ANOVA and paired t-tests revealed no significant time effect in the MEP amplitude and latency measurements (P>0.05). The ICCs indicated high intra-session reliability in the MEPs' amplitudes for the ECR and FDI muscles (0.77 to 0.99, 0.90 to 0.99, respectively) and latency (0.80 to 1.00, 0.75 to 0.97, respectively). The MEPs' amplitudes also had high inter-session reliability (0.84 to 0.97, 0.88 to 0.93, respectively), as did their latency (0.80 to 0.90, 0.75 to 0.97, respectively). Highest intra- and inter-session reliability was achieved for blocks of 10 and 15 trials. Our data suggest that intra- and inter-session comparisons should be performed using at least 10 MEPs in “combined hotspot” stimulation technique to ensure highest reliability.

Cortical silent period evoked by transcranial magnetic stimulation in ischemic stroke

Effects of intravenous antidepressant drugs on the excitability of human motor cortex: a study with paired magnetic stimulation on depressed patients

Introduction: A practical solution to the incidental unreliability of intraoperative neuromonitoring (IONM) may be the simultaneous neurophysiological recording and control of the surgical field through a camera (the concept of “Real-time” IONM). During “Real-time” IONM, the surgeon is immediately warned about the possibility of damage to the neural structures during, but not after, standard idiopathic scoliosis (IS) corrective surgery procedures (the concept of “Surgeon–neurophysiologist” interactive, verbal IONM). This study aimed to compare the advantages, utilities, reliabilities, and time consumption of the two IONM scenarios. Methods: Studies were performed in two similar groups of patients undergoing surgery primarily due to Lenke 2 idiopathic scoliosis (N = 120), when both IONM approaches were applied. Neurophysiological evaluations of the spinal transmission were performed pre- (T0), intra- (before (T1) and after (T2) surgery), and postoperatively (T3), as well as once in healthy volunteers (control, N = 60). Non-invasive and innovative recordings of the motor evoked potentials (MEPs) bilaterally from the peroneal (PER) nerve and tibialis anterior (TA) muscle were performed with surface electrodes as a result of transcranial magnetic stimulation (TMS) or electrical stimulation (TES) at T0–T3. Results: In both groups, the MEP amplitudes and latencies recorded from the PER nerve were approximately 67% lower and 3.1 ms shorter than those recorded from the TA muscle. The MEP recording parameters differed similarly at T0–T3 compared to the control group. In all patients, the MEP parameters induced by TMS (T0) and TES (T1) did not differ. The MEP amplitude parameters recorded from the TA and PER at T1 and T2 indicated a bilateral improvement in the neural spinal conduction due to the surgical intervention. The TMS-induced MEP amplitude at T3 further increased bilaterally. In both IONM groups, an average 51.8 BIS level of anesthesia did not affect the variability in the MEP amplitude, especially in the PER recordings when the applied TES strength was 98.2 mA. The number of fluctuations in the MEP parameters was closely related to the number of warnings from the neurophysiologist during the transpedicular screw implantation, corrective rod implantation, and distraction, derotation, and compression procedures, and it was higher in the “Surgeon–neurophysiologist” IONM group. The average duration of surgery was shorter by approximately one hour in the “Real-time” IONM group. The number of two-way communications between the surgeon and the neurophysiologist and vice versa in the “Real-time” IONM group decreased by approximately half. Conclusions: This study proves the superiority of using “Real-time” IONM over the standard “Surgeon–neurophysiologist” IONM procedure in increasing the safety and non-invasiveness, shortening the time, and lowering the costs of the surgical treatment of IS patients. The modifications of the MEP nerve-conduction-recording technology with surface electrodes from nerves enable precise and reliable information on the pediatric patient’s neurological condition at every stage of the applied surgical procedures, even under conditions of slight fluctuations in anesthesia.

P 160. The “dormant potential” of the non-dominant hemisphere: In teremispheric a symmetry of cortial plasticity

The purpose of this study was to determine the form of the relation between the mean amplitude and variance of motor-evoked potentials (MEP). To this end, single-pulse transcranial magnetic stimulation (TMS) was applied over the motor cortex of seventeen neurologically normal adult human subjects. The coil was positioned at a locus on the scalp that elicited an MEP in the first dorsal interosseous (FDI) at the lowest stimulus intensity. The subjects were instructed to maintain tonic activity in the FDI of 5 or 10% of the maximum voluntary contraction (MVC). The relation between MEP variance and amplitude was found to have an inverted parabolic shape, with maximal variance occurring near the half-maximal MEP amplitude. The coefficient of variation [Formula: see text] of MEPs decreased approximately as a rectangular hyperbolic function of MEP amplitude (i.e. ~ 1/MEP). A probabilistic model is proposed to explain the inverted parabolic relation between MEP variance and MEP amplitude, as well as the sigmoid shape of the MEP input-output relation (i.e. stimulus-response curve). The model is based on a description of α-motoneurons as binary threshold units, with unit thresholds distributed according to a positively skewed probability density function. The units are driven by noisy synaptic input currents having a Gaussian distribution. The model predicts an inverse parabolic relation between MEP variance and amplitude and a sigmoid input-output relation, as experimentally observed. Furthermore, increasing model motoneuron excitability by increasing the background synaptic drive increases MEP variability independently of MEP size, a surprising prediction. The model also explains the approximately rectangular hyperbolic relation between [Formula: see text] and MEP amplitude. The implications of these results for the interpretation of neurophysiological experiments and the statistical analysis of MEPs are discussed.

Prestimulus cortical EEG oscillations can predict the excitability of the primary motor cortex

Comparison of low frequency repetitive transcranial magnetic stimulation parameters on motor cortex excitability in normal subjects

The present study aimed to investigate the effects of changes in motor-evoked potential (MEP) amplitude on short-latency afferent inhibition (SAI) and short-interval intracortical inhibition (SICI). MEPs in response to transcranial magnetic stimulation (TMS) of the left primary motor cortex were measured from the right first dorsal interosseous muscle of 10 healthy participants. SAI was evaluated by measuring MEPs in response to variable-intensity test TMS pulses delivered 22 ms following electrical stimulation of the right ulnar nerve (intensity fixed at the motor threshold). SICI was evaluated by pairing a constant conditioning TMS pulse [80% of resting motor threshold (RMT)] with a second variable-intensity TMS test pulse (interstimulus interval of 2 ms). The intensity of the test stimulus was set at 110, 115, 120, 125, or 130%RMT on a given trial. SAI was significantly reduced when evoked by a 125%RMT test TMS pulse compared with 110%RMT, and absent at 130%RMT. There was no significant difference in SICI at 110-130%RMT. Significant positive correlations were detected between the unconditioned and conditioned MEP amplitudes at both SAI and SICI. This study demonstrated that SAI and SICI are highly sensitive to the MEP amplitude and SAI decreases with increasing MEP amplitude, whereas SICI does not change. The different responses for SAI and SICI to the increasing MEP amplitude is interpreted as evidence that different inhibitory neural circuits may be involved in SAI and SICI.

The influence of non-visual information on visual awareness judgments has recently gained substantial interest. Using single-pulse transcranial magnetic stimulation (TMS), we investigate the potential contribution of evidence from the motor system to judgment of visual awareness. We hypothesized that TMS-induced activity in the primary motor cortex (M1) would increase reported visual awareness as compared to the control condition. Additionally, we investigated whether TMS-induced motor-evoked potential (MEP) could measure accumulated evidence for stimulus perception. Following stimulus presentation and TMS, participants first rated their visual awareness verbally using the Perceptual Awareness Scale (PAS), after which they responded manually to a Gabor orientation identification task. Delivering TMS to M1 resulted in higher average awareness ratings as compared to the control condition, in both correct and incorrect identification task response trials, when the hand with which participants responded was contralateral to the stimulated hemisphere (TMS-response-congruent trials). This effect was accompanied by longer PAS response times (RTs), irrespective of the congruence between TMS and identification response. Moreover, longer identification RTs were observed in TMS-response-congruent trials in the M1 condition as compared to the control condition. Additionally, the amplitudes of MEPs were related to the awareness ratings when response congruence was taken into account. We argue that MEP can serve as an indirect measure of evidence accumulated for stimulus perception and that longer PAS RTs and higher amplitudes of MEPs in the M1 condition reflect integration of additional evidence with visual awareness judgment. In conclusion, we advocate that motor activity influences perceptual awareness judgments.

Recent transcranial magnetic stimulation studies have shown that the motor output pathway shows a profound inhibition during the preparation of an action. This phenomenon, called “preparatory inhibition”, remains incompletely understood, as it is still unclear which neural structures support it and what function it exactly serves during action preparation. In the current study, we tested this preparatory inhibition in Parkinson’s disease (PD) patients and matched healthy control subjects. The aim was to better understand the role of basal ganglia (which are dysfunctional in PD) and the influence of dopamine replacement therapy on motor inhibition during action preparation.