Decrease In Motor Evoked Potentials Amplitude Research Articles

The effect of transcranial ultrasound pulse repetition frequency on sustained inhibition in the human primary motor cortex: A double-blind, sham-controlled study

BackgroundNon-invasive brain stimulation techniques such as transcranial magnetic stimulation and transcranial direct current stimulation hold promise for inducing brain plasticity. However, their limited precision may hamper certain applications. In contrast, Transcranial Ultrasound Stimulation (TUS), known for its precision and deep brain targeting capabilities, requires further investigation to establish its efficacy in producing enduring effects for treating neurological and psychiatric disorders. ObjectiveTo investigate the enduring effects of different pulse repetition frequencies (PRF) of TUS on motor corticospinal excitability. MethodsT1-, T2-weighted, and zero echo time magnetic resonance imaging scans were acquired from 21 neurologically healthy participants for neuronavigation, skull reconstruction, and the performance of transcranial ultrasound and thermal modelling. The effects of three different TUS PRFs (10, 100, and 1000 Hz) with a constant duty cycle of 10 % on corticospinal excitability in the primary motor cortex were assessed using TMS-induced motor evoked potentials (MEPs). Each PRF and sham condition was evaluated on separate days, with measurements taken 5-, 30-, and 60-min post-TUS. ResultsA significant decrease in MEP amplitude was observed with a PRF of 10 Hz (p = 0.007), which persisted for at least 30 min, and with a PRF of 100 Hz (p = 0.001), lasting over 60 min. However, no significant changes were found for the PRF of 1000 Hz and the sham conditions. ConclusionThis study highlights the significance of PRF selection in TUS and underscores its potential as a non-invasive approach to reduce corticospinal excitability, offering valuable insights for future clinical applications.

Neuromonitoring in pre-post and intraoperative total hip replacement surgery in type 4 high-riding developmental dysplasia of the hip.

The choice approach to treating congenital dislocation of the hip joint is total hip replacement (THR). One of the severe but uncommon complications of THR is nerve damage. The most common nerve injury associated with total hip arthroplasty (THA) is sciatic nerve palsy, and the second typical nerve damage with THA is femoral nerve paralysis. In this prospective cohort study, 35 patients with type 4 high riding developmental dysplasia of the hip (DDH) who were candidates for THA were enrolled. The somatosensory evoked potential (SSEP), motor evoked potential (MEP), and electromyography (EMG) were measured pre-post and intraoperatively to check the status of the sciatic and femoral nerves. After collecting the mentioned information, the data was analyzed by SPSS V. 26 software. Out of 35 patients with DDH type 4 who were candidates for THR, nine patients showed a 50 percent decrease in SSEP amplitude, and six patients showed a 10 percent decrease in SSEP latency. One patient during and two patients after the surgery showed more than an 80 percent decrease in MEP amplitude. Meanwhile, 14 patients showed abnormal spikes during and two patients after surgery regarding EMG. All patients with disturbed neurophysiological findings reverted to normal in the further investigation during follow-up. No correlation was found between increasing limb shortness and these modalities. Using neuromonitoring techniques during Total Hip Arthroplasty (THA) can help identify potential early nerve damage, prevent post-surgical complications, and improve high-riding DDH patient outcomes.

Investigating the Effect of Transcutaneous Auricular Vagus Nerve Stimulation on Cortical Excitability in Healthy Males

ObjectivesAs a potential treatment for epilepsy, transcutaneous auricular vagus nerve stimulation (taVNS) has yielded inconsistent results. Combining transcranial magnetic stimulation with electromyography (TMS-EMG) and electroencephalography (TMS-EEG) can be used to investigate the effect of interventions on cortical excitability by evaluating changes in motor evoked potentials (MEPs) and TMS-evoked potentials (TEPs). The goal of this study is to objectively evaluate the effect of taVNS on cortical excitability with TMS-EMG and TMS-EEG. These findings are expected to provide insight in the mechanism of action and help identify more optimal stimulation paradigms. Materials and MethodsIn this prospective single-blind cross-over study, 15 healthy male subjects underwent active and sham taVNS for 60 min, using a maximum tolerated stimulation current. Single and paired pulse TMS was delivered over the right-sided motor hotspot to evaluate MEPs and TEPs before and after the intervention. MEP statistical analysis was conducted with a two-way repeated measures ANOVA. TEPs were analyzed with a cluster-based permutation analysis. Linear regression analysis was implemented to investigate an association with stimulation current. ResultsMEP and TEP measurements were not affected by taVNS in this study. An association was found between taVNS stimulation current and MEP outcome measures indicating a decrease in cortical excitability in participants who tolerated higher taVNS currents. A subanalysis of participants (n = 8) who tolerated a taVNS current ≥2.5 mA showed a significant increase in the resting motor threshold, decrease in MEP amplitude and modulation of the P60 and P180 TEP components. ConclusionstaVNS did not affect cortical excitability measurements in the overall population in this study. However, taVNS has the potential to modulate specific markers of cortical excitability in participants who tolerate higher stimulation levels. These findings indicate the need for adequate stimulation protocols based on the recording of objective outcome parameters.

Electrophysiological changes of the spinal cord during thoracoabdominal aortic clamping -- Experimental study

Severe neurological complications of the thoracoabdominal aortic clamping were published in numerous clinical and experimental studies. These hardly predictable, devastating consequences demanded to develop a monitoring system which might detect impending level of spinal cord ischemia in time – in order to introduce or enhance protective procedures and prevent permanent neurological deficit. The most widely used monitoring in clinical practice is the continuous surveillance of the motor evoked potentials (MEP) during and after thoracoabdominal aortic clamping. Much less used, but promising opportunity is to control the metabolic changes and cellular integrity utilizing specific markers like liquor lactate and neuron specific enolase (NSE) etc. In our earlier study we published data of our canine experiment related to coherencies between neurological outcome and specific perfusion of the spinal cord during and after one hour thoracoabdominal aortic clamping. In the present paper we investigate the behavior of motor evoked (MEP) and sensory evoked (SEP) potentials related to neurological changes. We conclude the behavior of SEP values hardly correlate with the neurologic outcome, meanwhile decrease of MEP amplitude provides reliable signal for developing spinal cord ischemia. We could not confirm a numeric correlation of these data and the level of the final neurologic outcome.

The effect of dexmedetomidine on motor-evoked potentials during pediatric posterior spinal fusion surgery: a retrospective case-control study.

Motor-evoked potentials (MEPs) are frequently used in pediatric posterior spinal fusion surgery (PSFS) to detect spinal cord ischemia. Dexmedetomidine is increasingly being used as an adjunct to total intravenous anesthesia, but its effect on MEP amplitude has been variably reported. The purpose of this study was to evaluate the effect of an infusion of dexmedetomidine on the amplitude of MEPs. We performed a retrospective case-control study of 30 pediatric patients who received a 0.5 µg·kg-1·hr-1 infusion of dexmedetomidine, ten patients who received 0.3 µg·kg-1·hr-1 dexmedetomidine, and 30 control patients who did not receive dexmedetomidine during PSFS. Two neurophysiologists reviewed the MEP amplitudes in six muscle groups at three time points: when the patient was turned prone (baseline; T1), one hour after incision (T2), and after exposure of the spine but before insertion of the first screw (T3). In all muscles tested, the mean MEP amplitude was reduced by T3 when dexmedetomidine was infused at 0.5 µg·kg-1·hr-1. The greatest reduction from baseline MEP amplitude was 829 µV (95% confidence interval, 352 to 1230; P < 0.001) seen in first right dorsus interosseous. When dexmedetomidine was infused at 0.3 µg·kg-1·hr-1, there was a significant reduction in MEP amplitude in four of the six muscles tested at T3 compared with the control group. Dexmedetomidine at commonly used infusion rates of 0.3 µg·kg-1·hr-1 or 0.5 µg·kg-1·hr-1 causes a significant decrease in MEP amplitude during pediatric PSFS. We suggest that dexmedetomidine should be avoided in children undergoing PSFS so as not to confuse the interpretation of this important neurophysiological monitor.

Assessment of vestibulocortical interactions during standing in healthy subjects.

The vestibular system is essential to produce adequate postural responses enabling voluntary movement. However, how the vestibular system influences corticospinal output during postural tasks is still unknown. Here, we examined the modulation exerted by the vestibular system on corticospinal output during standing. Healthy subjects (n = 25) maintained quiet standing, head facing forward with eyes closed. Galvanic vestibular stimulation (GVS) was applied bipolarly and binaurally at different delays prior to transcranial magnetic stimulation (TMS) which triggered motor evoked potentials (MEPs). With the cathode right/anode left configuration, MEPs in right Soleus (SOL) muscle were significantly suppressed when GVS was applied at ISI = 40 and 130ms before TMS. With the anode right/cathode left configuration, no significant changes were observed. Changes in the MEP amplitude were then compared to changes in the ongoing EMG when GVS was applied alone. Only the decrease in MEP amplitude at ISI = 40ms occurred without change in the ongoing EMG, suggesting that modulation occurred at a premotoneuronal level. We further investigated whether vestibular modulation could occur at the motor cortex level by assessing changes in the direct corticospinal pathways using the short-latency facilitation of the SOL Hoffmann reflex (H-reflex) by TMS. None of the observed modulation occurred at the level of motor cortex. Finally, using the long-latency facilitation of the SOL H-reflex, we were able to confirm that the suppression of MEP at ISI = 40ms occurred at a premotoneuronal level. The data indicate that vestibular signals modulate corticospinal output to SOL at both premotoneuronal and motoneuronal levels during standing.

The effect of combined transcranial direct current stimulation and peripheral nerve electrical stimulation on corticospinal excitability.

Transcranial direct current stimulation (tDCS) and peripheral nerve electrical stimulation (PES) can change corticospinal excitability. tDCS can be used to non-invasively modulate the cerebral cortex’s excitability by applying weak current to an electrode attached to the head, and the effect varies with the electrode’s polarity. Previous studies have reported the effect of combined tDCS and PES on corticospinal excitability; when compared to single stimulation, combined stimulation increases cortical excitability. In contrast, another study reported that the effect of tDCS is attenuated by PES; hence, there is no consensus opinion on the effect on combined stimulation. Therefore, this study aimed to clarify the effect of combined tDCS and PES on corticospinal excitability. In Experiment 1, the combined stimulation of anodal tDCS and PES (anodal tDCS + PES) was performed, and in Experiment 2, a combined stimulation with PES, after cathodal tDCS (PES after cathodal tDCS), was performed using a homeostatic metaplasticity theoretical model. In Experiment 1, anodal tDCS produced a significant increase from baseline in motor-evoked potential (MEP) amplitude 10 min after stimulation, but no significant changes in MEP amplitude were observed with PES or the anodal tDCS + PES condition. Experiment 2 showed a significant decrease in MEP amplitude immediately after cathodal tDCS, and a significant increase in MEP amplitude 15 min after PES, but no significant change in MEP amplitude was observed with sequential PES following cathodal tDCS. In conclusion, our data indicate that PES with anodal tDCS suppressed the effect of tDCS. Also, PES after cathodal tDCS did not induce homeostatic metaplasticity and increase corticospinal excitability.

Alterations in Motor Cortical Excitability Induced by Peripheral Stimulation With Magnetic Stimulation

The conditioning of cortical excitability by transcranial magnetic stimulation (TMS) has become a valuable technique to promote recovery of motor function after stroke. As TMS is not used in all patients, we investigated the hypothesis that peripheral stimulation may have an adjustment effect on motor cortical excitability. Our experimental paradigm was divided into three phases. In the first phase, TMS was delivered to the left or right primary motor cortex to induce a motor evoked potential (MEP) from the contralateral first dorsal interosseous muscle. The measured MEPs in this phase were used to evaluate the effect of peripheral stimulation. In the second phase, 1 Hz magnetic stimulation was applied over the contralateral or ipsilateral forearm for motor cortex as peripheral stimulation. In the third phase, the MEP was evoked by TMS and recorded using the same setting as the first phase. We found that a decrease in MEP amplitude was observed in the left motor cortex following peripheral stimulation over the right forearm. By contrast, the MEP amplitude was not altered in the right motor cortex by peripheral stimulation over the left forearm. An increase in MEP amplitude was observed in the ipsilateral motor cortex induced by peripheral stimulation over the left or right forearm. We also found that by changing the MEP amplitude, the motor cortex excitability varied according to magnetic stimulation of the forearm. These data suggest that peripheral stimulation may have an adjustment effect on motor cortical excitability, via changes in the stimulus site.

Insights About the Neuroplasticity State on the Effect of Intramuscular Electrical Stimulation in Pain and Disability Associated With Chronic Myofascial Pain Syndrome (MPS): A Double-Blind, Randomized, Sham-Controlled Trial.

Background: There is limited evidence concerning the effect of intramuscular electrical stimulation (EIMS) on the neural mechanisms of pain and disability associated with chronic Myofascial Pain Syndrome (MPS).Objectives: To provide new insights into the EIMS long-term effect on pain and disability related to chronic MPS (primary outcomes). To assess if the neuroplasticity state at baseline could predict the long-term impact of EIMS on disability due to MPS we examined the relationship between the serum brain-derived-neurotrophic-factor (BDNF) and by motor evoked potential (MEP). Also, we evaluated if the EIMS could improve the descending pain modulatory system (DPMS) and the cortical excitability measured by transcranial magnetic stimulation (TMS) parameters.Methods: We included 24 right-handed female with chronic MPS, 19–65 years old. They were randomically allocated to receive ten sessions of EIMS, 2 Hz at the cervical paraspinal region or a sham intervention (n = 12).Results: A mixed model analysis of variance revealed that EIMS decreased daily pain scores by -73.02% [95% confidence interval (CI) = -95.28 to -52.30] and disability due to pain -43.19 (95%CI, -57.23 to -29.39) at 3 months of follow up. The relative risk for using analgesics was 2.95 (95% CI, 1.36 to 6.30) in the sham group. In the EIMS and sham, the change on the Numerical Pain Scale (NPS0-10) throughout CPM-task was -2.04 (0.79) vs. -0.94 (1.18), respectively, (P = 0.01). EIMS reduced the MEP -28.79 (-53.44 to -4.15), while improved DPMS and intracortical inhibition. The MEP amplitude before treatment [(Beta = -0.61, (-0.58 to -0.26)] and a more significant change from pre- to post-treatment on serum BDNF) (Beta = 0.67; CI95% = 0.07 to 1.26) were predictors to EIMS effect on pain and disability due to pain.Conclusion: These findings suggest that a bottom–up effect induced by the EIMS reduced the analgesic use, improved pain, and disability due to chronic MPS. This effect might be mediated by an enhancing of corticospinal inhibition as seen by an increase in IC and a decrease in MEP amplitude. Likewise, the MEP amplitude before treatment and the changes induced by the EIMS in the serum BDNF predicted it’s long-term clinical impact on pain and disability due MPS.The trial is recorded in ClinicalTrials.gov: NCT02381171.

Inhibitory and facilitatory connections from dorsolateral prefrontal to primary motor cortex in healthy humans at rest—An rTMS study

BackgroundThe human motor system consists of several divisions in the frontal lobes. The physiological function of projections from the dorsolateral prefrontal cortex (DLPFC) to the primary motor cortex (M1) remains elusive. Here, we introduce theta burst stimulation (TBS)-based protocols to target inhibitory and facilitatory connections in the DLPFC-M1 network. MethodsIntermittent and continuous TBS with 600 pulses (iTBS600/cTBS600) were applied to the left DLPFC. Resting motor threshold (RMT), motor-evoked potential (MEP), and short-interval intracortical inhibition (SICI) were measured with transcranial magnetic stimulation to the ipsilateral M1. ResultsiTBS600 to the DLPFC decreased MEP amplitude in M1. Conversely, cTBS600 to the DLPFC increased MEP amplitude in M1. The peak decrease in MEP amplitude after iTBS600 was negatively correlated with the peak increase in MEP amplitude after cTBS600. There were no significant effects in the control group with the sham stimulation. DiscussionThese results provide insight into the regulation of inhibitory and facilitatory balance from the local DLPFC to M1. TBS modulation in one brain region will induce interactions within other remote cortical areas. Our results enable better understanding of how cognitive resources are allocated to achieve optimal control of motor output.

Variability and Predictors of Response to Continuous Theta Burst Stimulation: A TMS-EEG Study.

Continuous theta-burst stimulation (cTBS) is a repetitive transcranial magnetic stimulation paradigm reported to decrease the excitability of the stimulated cortical area and which is thought to reflect a form of inhibitory synaptic plasticity. However, since its introduction, the effect of cTBS has shown a remarkable variability in its effects, which are often quantified by measuring the amplitude of motor evoked potentials (MEPs). Part of this inconsistency in experimental results might be due to an intrinsic variability of TMS effects caused by genetic or neurophysiologic factors. However, it is also possible that MEP only reflect the excitability of a sub-population of output neurons; resting EEG power and measures combining TMS and electroencephalography (TMS-EEG) might represent a more thorough reflection of cortical excitability. The aim of the present study was to verify the robustness of several predictors of cTBS response, such as I wave recruitment and baseline MEP amplitude, and to test cTBS after-effects on multiple neurophysiologic measurements such as MEP, resting EEG power, local mean field power (LMFP), TMS-related spectral perturbation (TRSP), and inter-trial phase clustering (ITPC). As a result, we were not able to confirm either the expected decrease of MEP amplitude after cTBS or the ability of I wave recruitment and MEP amplitude to predict the response to cTBS. Resting EEG power, LMFP, TRSP, and ITPC showed a more consistent trend toward a decrease after cTBS. Overall, our data suggest that the effect of cTBS on corticospinal excitability is variable and difficult to predict with common electrophysiologic markers, while its effect might be clearer when probed with combined TMS and EEG.

S147. Effect of 1 Hz and 5 Hz rTMS over supplementary motor area on motor cortical excitability

Recent clinical trial of repetitive transcranial magnetic stimulation (rTMS) in Parkinson’s disease (PD) showed that both 1 Hz and 5 Hz rTMS over supplementary motor cortex (SMA) are effective for motor symptoms in PD. Previous studies have also indicated 1 Hz rTMS over primary motor cortex (M1) induces an inhibition whereas 5 Hz rTMS produce facilitation in excitability. Our aim is to clarify why both 1 Hz and 5 Hz rTMS, which have the opposite effects in cortical excitability, show the similar beneficial effects for PD. Recent clinical trial of repe. Subjects are twelve right-handed healthy volunteers (10 men, mean age 30.9 ± 6.5 years). rTMS consists of total 1000 pulses of 1 Hz, 5 Hz rTMS and realistic sham stimulation over SMA at intensity of 110% active motor threshold for the tibialis anterior (TA). We recorded motor-evoked potentials (MEP) from the right first dorsal interosseous (FDI) muscle and measured MEPs, short-intercortical inhibition (SICI) and intercortical facilitation (ICF) before, immediately (0), 15 and 30 min after the end of each condition. A two-way repeated measures ANOVA demonstrated a significant main effect of ‘condition’ (1 Hz, 5 Hz and sham) on the mean MEP amplitude (F2,87 = 4.72, P = 0.0113), whereas no significant effect on ‘time’ (T0-T30) (F2,87 = 0.589, P = 0.56) and ‘time’ × ‘condition’ interaction (F2,87=0.79. P = 0.535). Post hoc t tests revealed that decrease in MEP amplitude lasted at least for 15 min after the end of stimulation (0 min P = 0.0048; 15 min P = 0.0047). SICI and ICF did not show significant changes after 1 Hz rTMS. There were no significant changes either in MEP, SICI and ICF after 5 Hz rTMS and sham stimulation. 1 Hz SMA-rTMS decreased the amplitude of MEP evoked by a single-pulse TMS, whereas 5 Hz SMA-rTMS did not show significant changes. We suggest that 1 Hz and 5 Hz SMA-rTMS show different physiological after-effects, even though both conditions have a similar therapeutic effect for PD. It is presumable that these two rTMS have different mechanism for improving motor symptoms of PD. Further investigation is required to clarify the precise physiological effects of SMA-rTMS.

Cerebellar Transcranial Direct Current Stimulation Modulates Corticospinal Excitability During Motor Training.

Background: Cerebellar activity can be modulated using cerebellar transcranial direct current stimulation (ctDCS) and, when applied concurrently with task training, has been shown to facilitate cognitive and motor performance. However, how ctDCS facilitates motor performance is not fully understood.Objective/Hypothesis: To assess the electrophysiological and motor performance effects of ctDCS applied during motor training.Methods: Fourteen healthy adults (age 28.8 ± 10.5 years) were randomly assigned to complete one session of finger tracking training with either simultaneous bilateral anodal or sham ctDCS. Training was completed in two 15 min epochs with a 5-min break (total 30 min stimulation, 2 mA). Tracking accuracy and corticospinal and intracortical excitability were measured immediately before and after the training period. Motor cortical excitability measures included resting motor threshold (RMT), motor evoked potential (MEP) amplitude, cortical silent period (CSP) and short interval intracortical inhibition (SICI).Results: There was a significant interaction of Group * Time for MEP amplitude and CSP duration (p < 0.01). Post hoc analysis revealed MEP amplitude was increased in the sham group (p < 0.01), indicating increased corticospinal excitability from baseline while the anodal group displayed a decrease in MEP amplitude (p = 0.023) and prolongation of CSP duration (p < 0.01). SICI and RMT remained unchanged following ctDCS and training. Task accuracy was improved in both groups at post-test with a significant effect of Time (p < 0.01); however, there was no effect of Group (p = 0.45) or interaction of Group * Time (p = 0.83). During training, there was a significant effect of Block (p < 0.01) but no significant effect of Group or interaction effect (p > 0.06).Conclusions: ctDCS applied during task training is capable of modulating or interfering with practice-related changes in corticospinal excitability without disrupting performance improvement.

Long-lasting effects of transcranial static magnetic field stimulation on motor cortex excitability

BackgroundTranscranial static magnetic field stimulation (tSMS) was recently added to the family of inhibitory non-invasive brain stimulation techniques. However, the application of tSMS for 10–20 min over the motor cortex (M1) induces only short-lasting effects that revert within few minutes. ObjectiveWe examined whether increasing the duration of tSMS to 30 min leads to long-lasting changes in cortical excitability, which is critical for translating tSMS toward clinical applications. MethodsThe study comprised 5 experiments in 45 healthy subjects. We assessed the impact of 30-min-tSMS over M1 on corticospinal excitability, as measured by the amplitude of motor evoked potentials (MEPs) and resting motor thresholds (RMTs) to single-pulse transcranial magnetic stimulation (TMS) (experiments 1–2). We then assessed the impact of 30-min-tSMS on intracortical excitability, as measured by short-interval intracortical facilitation (SICF) and short-interval intracortical inhibition (SICI) using paired-pulse TMS protocols (experiments 2–4). We finally assessed the impact of 10-min-tSMS on SICF and SICI (experiment 5). Results30-min-tSMS decreased MEP amplitude compared to sham for at least 30 min after the end of the stimulation. This long-lasting effect was associated with increased SICF and reduced SICI. 10-min-tSMS –previously reported to induce a short-lasting decrease in MEP amplitude– produced the opposite changes in intracortical excitability, decreasing SICF while increasing SICI. ConclusionsThese results suggest a dissociation of intracortical changes in the consolidation from short-lasting to long-lasting decrease of corticospinal excitability induced by tSMS. The long-lasting effects of 30-min-tSMS open the way to the translation of this simple, portable and low-cost technique toward clinical trials.

Anxiety-dependent modulation of motor responses to pain expectancy.

The relationship between pain expectancy and motor system plays a crucial role in the human defensive system. Here, we took advantage of the inhibitory modulation of the motor pathway to the muscle of the hand receiving painful stimuli, by recording motor-evoked potentials (MEPs) to Transcranial Magnetic Stimulation (TMS). We employed a classical conditioning paradigm in which neutral (visual and auditory) stimuli were conditioned by pairing either painful or not-painful stimuli (electric shocks) in separated groups. Only the Pain Group showed clear motor responses: i.e. a significant decrease in MEPs amplitude, with respect to the neutral condition, not only in conditioning stimuli, when actual shocks were paired with neutral stimuli, but also in conditioned stimuli, when shocks were only expected. Significant differences between the two groups suggest that the MEPs decrease is specific for pain expectancy and does not pertain to anticipation in general. Furthermore, in the Pain Group, a significant negative correlation between physiological responses to conditioned stimuli and the participants’ anxiety traits was found: the lower the MEPs amplitude, the higher the participants’ anxiety scores. The present findings suggest that, in order for defensive motor responses to occur, actual pain is not necessary; rather, anxiety-dependent pain expectancy can be sufficient.

Modulation of corticospinal output in agonist and antagonist proximal arm muscles during motor preparation.

Previous studies have shown modulation of corticospinal output of the agonist muscle when a known-movement is prepared but withheld until a response signal appearance, reflecting motor preparation processes. However, modulation in the antagonist muscles has not been described, despite the fact that reaching movements require precise coordination between the activation of agonist and antagonist muscles. In this study, participants performed an instructed-delay reaction time (RT) task, with randomized elbow flexion and extension movements. The aim was to assess the time course modulation of corticospinal output in two antagonist muscles, by simultaneously quantified the amplitude of motor evoked potentials (MEPs) in biceps brachii and triceps brachii, and the amplitude and direction of elbow movements evoked by transcranial magnetic stimulation (TMS). Depending on the prepared movement direction, a specific modulation of corticospinal output was observed, MEPs and TMS-evoked movements amplitude being relatively greater for extension compared to flexion. At the end of motor preparation, a decrease in MEPs amplitude was observed for both biceps brachii and triceps brachii, regardless of the prepared movement direction. In contrast, the probability of evoking movement in the flexion direction and the amplitude of TMS-evoked movement decreased at the end of preparation for flexion, but not for extension. Together, these results confirm the existence of inhibitory processes at the end of the motor preparation, probably to avoid a premature motor response. Moreover, they provide evidence of differences in the corticospinal control of elbow flexor and extensor muscles with patterns of modulation that are not necessarily reciprocal during motor preparation.

Electrophysiological influence of temporal occlusion of the parent artery during aneurysm surgery

Intraoperative monitoring of the motor evoked potential (MEP) during cerebral aneurysm surgery has been widely used to confirm surgical safety. In this study, we retrospectively analyzed the influence of the MEP amplitude resulting from temporal occlusion of the parent artery, and appropriate judgement in the surgery was discussed. Ten patients underwent temporal occlusion of the parent artery during aneurysm surgery, and five of these patients showed a decrease in the MEP amplitude following temporal arterial occlusion. Clinical factors in patients with and without MEP decrease were compared. The time gap between the surgical procedure and the MEP change and recovery was then investigated. A decrease in the MEP amplitude caused by temporal occlusion had a significantly higher occurrence compared with permanent clip failure. The time from the release procedure to MEP amplitude recovery was relatively longer than the time from the occlusion procedure to the decrease in MEP amplitude. The time from release procedure to MEP amplitude recovery showed a weak correlation with the parent artery occlusion time. There is a time gap between releasing the temporal arterial occlusion and MEP recovery that is similar to temporal parent arterial occlusion and the MEP decrease. The cause of MEP amplitude should be judged carefully, and influence of parent artery temporal occlusion should be taken into consideration during aneurysm clipping.

Real-Time Evaluation of Anterior Choroidal Artery Patency During Aneurysm Clipping.

Inadvertent occlusion of the anterior choroidal artery during aneurysm clipping can cause a disabling stroke in minutes. We evaluate the clinical utility of direct cortical motor evoked potential (MEP) monitoring during aneurysm clipping, as a real-time assessment of arterial patency, prior to performing indocyanine green videoangiography. Direct cortical MEPs were recorded in seven patients undergoing surgery for aneurysms that involved or abutted the anterior choroidal artery. The aneurysms clipped in those seven patients included four anterior choroidal artery aneurysms and six posterior communicating artery aneurysms. Serial MEP recordings were performed during the intradural dissection, aneurysm exposure, and clip placement. A significant change in MEPs after clip placement would prompt immediate inspection and removal or repositioning of the clip. If the clip placement appeared satisfactory and MEP recordings were stable, then an intraoperative indocyanine green videoangiogram was performed to confirm obliteration of the aneurysm and patency of the arteries. Seven patients underwent successful clipping of anterior choroidal artery aneurysms and posterior communicating artery aneurysms using direct cortical MEP monitoring, with good clinical and radiographic outcomes. In six patients, no changes in MEP amplitudes were observed following permanent clip placement. In one patient, a profound decrease in MEP amplitude occurred 220 seconds after placement of a permanent clip on a large posterior communicating aneurysm. An inspection revealed that the anterior choroidal artery was kinked. The clip was immediately removed, and the MEP signals returned to baseline shortly thereafter. A clip was then optimally placed, and the patient awoke without neurologic deficit. Direct cortical MEPs are a useful adjunct to standard electrophysiologic monitoring in aneurysm surgery, particularly when the anterior choroidal artery or lenticulostriate arteries are at risk. When these arteries are occluded, infarction may occur before the occlusion is detected by indocyanine green videoangiography or intraoperative angiography. The use of MEPs allows real-time detection of ischemia to subcortical motor pathways.

Effects of high frequency repetitive transcranial magnetic stimulation with physical healthy exercise in stroke

It has been recently demonstrated high frequency repetitive transcranial magnetic stimulation (HF-rTMS) can improve motor function after stroke. However, there is no study that tested the synergetic effects of physical therapy to HF-rTMS in clinical settings. We therefore investigated the effect of physical healthy exercise (PHE) on paretic arm combined with HF-rTMS in stroke patients. All patients underwent HF-rTMS on contralesional hemisphere for 15 minutes and PHE on paretic arm. The cortical excitability by the amplitude and latency of motor evoked potential (MEP) were measured. We also evaluated arm function using Box and Block, arm reach, 9-hole pegboard, and grip force tests. We found for the first time significant differences of MEP between pre- and post-intervention. HF-rTMS with PHE had a tendency to induce a decrease in MEP amplitude on the nonparetic hand whereas it led to an increment in MEP amplitude in the paretic hand. In particular, the Box and Block, power grip, and arm reach tests showed improvement through every session. Furthermore, motor function and MEP were correlated especially on paretic side. These results indicate PHE with HF-rTMS partially improves arm function after stroke which may support additional effect to rehabilitation in stroke patients.

Basic study on the influence of inhibition induced by the magnetic stimulation on the peripheral nerve

The purpose of this study is to analyze the inhibition mechanism of magnetic stimulation on motor function. A magnetic stimulator with a flat figure-eight coil was used to stimulate the peripheral nerve of the antebrachium. The intensity of magnetic stimulation was 0.8 T, and the stimulation frequency was 1 Hz. The amplitudes of the motor-evoked potentials (MEPs) at the abductor pollicis brevis muscle and first dorsal interosseous muscle were used to evaluate the effects of magnetic stimulation. The effects of magnetic stimulation were evaluated by analyzing the MEP amplitude before and after magnetic stimulation to the primary motor cortex. The results showed that MEP amplitude after magnetic stimulation compared with before magnetic stimulation decreased. Because there were individual differences in MEP amplitude induced by magnetic stimulation, the MEP amplitude after stimulation was normalized by the amplitude of each participant before stimulation. The MEP amplitude after stimulation decreased by approximately 58% (p &amp;lt; 0.01) on average compared with before stimulation. Previous studies suggested that magnetic stimulation to the primary motor cortex induced an increase or a decrease in MEP amplitude. Furthermore, previous studies have shown that the alteration in MEP amplitude was induced by cortical excitability based on magnetic stimulation. The results of this study showed that MEP amplitude decreased following magnetic stimulation to the peripheral nerve. We suggest that the decrease in MEP amplitude found in this study was obtained via the feedback from a peripheral nerve through an afferent nerve to the brain. This study suggests that peripheral excitement by magnetic stimulation of the peripheral nerve may control the central nervous system via afferent feedback.