Motor Evoked Potentials Responses Research Articles

43. Motor evoked potentials monitoring for the evaluation of reversal of profound rocuronium-induced neuromuscular blockade by sugammadex in vocalis muscle

Recovery of paralysis of the vocalis cords is one objective of reversal agents after neuromuscular block (NMB). Sugammadex is a novel cyclodextrin, the first in a new class of selective binding reversal agents that terminates NMB with the steroidal nondepolarizing agents, rocuronium and vecuronium. We designed this study to evaluate the efficacy of sugammadex in reversing profound rocuronium-induced NMB at the laryngeal adductor muscles using recording motor evoked potentials (MEPs) from vocal muscles after transcranial electrical stimulation (TES). 5 patients undergoing propofol-remifentanil anesthesia for the surgery of the thyroid gland were enrolled for reversal of profound NMB (sugammadex 16 mg/kg, 3 min after rocuronium 1.2 mg/kg). During surgical procedures, to prevent laryngeal nerve injury, all patients underwent neurophysiologic monitoring using MEPs from vocalis muscles. After injection of 16 mg/kg of sugammadex, the means of recovery time of the basal MEPs response at the laryngeal adductor muscles was less than 1 min. In the postoperative period, no lesion to the vocalis cords caused by the surface laryngeal electrode during electrophysiological monitoring was also noted. Recovery from profound rocuronium-induced block on the larynx is fast and complete with sugammadex.

Intracerebral Implantation of Autologous Peripheral Blood Stem Cells in Stroke Patients: A Randomized Phase II Study

In our previous study, intracerebral implantation of peripheral blood stem cells (PBSCs) improved functional outcome in rats with chronic cerebral infarction. Based on this finding, a randomized, single blind controlled study was conducted in 30 patients [PBSC group (n = 15) and control group (n = 15)] with middle cerebral artery infarction confirmed on a T2-weighted MRI 6 months to 5 years after a stroke. Only subjects with neurological deficits of intermediate severity based on the National Institute of Health Stroke Scale (NIHSS; range: 9-20) that had been stable for at least 3 months were enrolled. Those in the PBSC group received subcutaneous G-CSF injections (15 µg/kg/day) for 5 consecutive days, and then stereotaxic implantation of 3-8 × 10(6) CD34(+) immunosorted PBSCs. All 30 patients completed the 12-month follow-up. No serious adverse events were noted during study period. Improvements in stroke scales (NIHSS, ESS, and EMS) and functional outcomes (mRS) from baseline to the end of the 12-month follow-up period were significantly greater in the PBSC than the control group. The fiber numbers asymmetry (FNA) scores based on diffusion tensor image (DTI) tractography were reduced in every PBSC-treated subject, but not in the control group. Reduction in the FNA scores correlated well with the improvement in NIHSS. Furthermore, a positive motor-evoked potential (MEP) response by transcranial magnetic stimulation (TMS) appeared in 9 of the 15 subjects in the PBSC group. This phase II study demonstrated that implantation of autologous CD34(+) PBSC was safe, feasible, and effective in improving functional outcome.

Motor cortical function and the precision grip.

While task‐dependent changes in motor cortical outputs have been previously reported, the issue of whether such changes are specific for complex hand tasks remains unresolved. The aim of the present study was to determine whether cortical inhibitory tone and cortical output were greater during precision grip and power grip. Motor cortex excitability was undertaken by using the transcranial magnetic stimulation threshold tracking technique in 15 healthy subjects. The motor‐evoked potential (MEP) responses were recorded over the abductor pollicis brevis (APB), with the hand in the following positions: (1) rest, (2) precision grip and (3) power grip. The MEP amplitude (MEP amplitude REST 23.6 ± 3.3%; MEP amplitude PRECISION GRIP 35.2 ± 5.6%; MEP amplitude POWER GRIP 19.6 ± 3.4%, F = 2.4, P < 0.001) and stimulus‐response gradient (SLOPEREST 0.06 ± 0.01; SLOPEPRCISION GRIP 0.15 ± 0.04; SLOPE POWER GRIP 0.07 ± 0.01, P < 0.05) were significantly increased during precision grip. Short interval intracortical inhibition (SICI) was significantly reduced during the precision grip (SICI REST 15.0 ± 2.3%; SICI PRECISION GRIP 9.7 ± 1.5%, SICI POWER GRIP 15.9 ± 2.7%, F = 2.6, P < 0.05). The present study suggests that changes in motor cortex excitability are specific for precision grip, with functional coupling of descending corticospinal pathways controlling thumb and finger movements potentially forming the basis of these cortical changes.

P39. Fast versus slow charge cortical stimulation for motor evoked potential

Fast charge (FC) and slow charge (SC) stimulation protocols are both available on modern neuromonitoring machines in order to induce motor evoked potentials (MEP). In order to define the best strategy for MEP recording, we have compared the efficiency and the feasibility of both stimulation protocols for the induction of motor evoked potential in neurosurgical patients that present without myelopathy. Fifteen consecutive adult patients (13 arthrodesis and 2 kyphoplasties) without clinical motor deficit undergoing spine surgery under neuromonitoring were included in this study. Fast (50 μs) and slow (500 ms) charge biphasic cortical stimulation was applied between C3 and C4 electrodes in trains of 5 at 500 Hz. Muscular response was quantified as the area under the curve between the MEP start and end time. We were able to deliver FC and SC in all patients. SC induced always-measurable MEP response up to 140 V. On the contrary, in some patients FC induced large recording artefacts that precluded measurement. Current delivery saturated between 100 (129 ± 32 mA) and 140 (117 ± 62 mA) V for SC while this was not the case for FC up to 450 V (660 ± 123 mA). In the same way MEP area under the curve value reached a plateau between 120 and 140 V for SC (96% of maximal response) while FC induced MEP area under the curve varied linearly with stimulation current (R2 = 0.998). When both stimulations were directly compared, FC was able to induce a maximal response that was approximately 1.3 times larger than SC for the same muscle in the same patient. In our experience, FC cortical stimulation is more efficient and more potent than SC stimulation. The only drawback of FC compared to SC is the large stimulation artefact when the ground electrode is placed on the scalp. The value of displacing the ground electrode to the sternum or the coccyx to minimize stimulation artefacts needs to be studied in the future. The results of FC stimulation also needs to be verified in myelopathic patients.

Short-latency afferent inhibition is a poor predictor of individual susceptibility to rTMS-induced plasticity in the motor cortex of young and older adults.

Cortical plasticity, including long-term potentiation (LTP)-like plasticity, can be assessed non-invasively with repetitive transcranial magnetic stimulation (rTMS) protocols. In this study, we examined age differences in responses to intermittent theta burst stimulation (iTBS) in a group of 20 young and 18 healthy older adults. Because the cholinergic system plays a role in the neural processes underlying learning and memory, including LTP, we also investigated whether short latency afferent inhibition (SAI), a neurophysiological marker of central cholinergic activity, would be associated with age-related differences in LTP-like plasticity induced by iTBS.Methods: SAI was first assessed by examining the modulation of motor evoked potentials (MEPs) in response to median nerve conditioning 20 ms prior to TMS. Participants then underwent iTBS (3 pulses at 50 Hz every 200 ms for 2 s with 8 s between trains, repeated 20 times). MEP responses (120% resting motor threshold (RMT)) were assessed immediately after iTBS and 5, 10, and 20 min post-application.Results: Responses to iTBS were quite variable in both age groups, with only approximately 60% of the participants (n = 13 young and 10 older adults) showing the expected facilitation of MEP responses. There were no significant age group differences in MEP facilitation following iTBS. Although older adults exhibited reduced SAI, individual variations were not associated with susceptibility to express LTP-like induced plasticity after iTBS.Conclusion: Overall, these results are consistent with reports of high inter-individual variability in responses to iTBS. Although SAI was reduced in older adults, consistent with a deterioration of the cholinergic system with age, SAI levels were not associated with LTP-like plasticity as assessed with iTBS.

The effect of muscle vibration on short latency intracortical inhibition in humans.

The purpose of the present study was to investigate the effect of muscle vibration (MV) on short latency intracortical inhibition (SICI) and facilitation (ICF) assessed by paired-pulse transcranial magnetic stimulation (TMS). Nineteen right-handed healthy subjects were investigat ed without and with MV of the right extensor carpi radialis (ECR), using single- and paired-pulse TMS with interstimulus interval (ISI) of 3 and 13 ms. Intensities of the conditioning and test stimulus were 70 and 120 % of the motor threshold at rest. The motor-evoked potentials (MEPs) were recorded simultaneously from the vibrated ECR and its antagonist flexor carpi radialis (FCR). In all the subjects a SICI of similar strength could be observed at 3 ms, at rest and during MV both in the vibrated muscle as well as in its antagonist. The subjects were divided in two groups according to the changes in MEP response to paired-pulse TMS with 13 ms ISI observed during MV. In nine subjects SICI was evident also at 13 ms when vibration was applied, while in another ten subjects vibration induced ICF at 13 ms. The effect of MV is not just a facilitation of SICI, but a stronger prolongation of the effect of intracortical inhibition to an ISI at which ICF is well pronounced, when the intensity of the conditioning stimulus exceeds the threshold for intracortical facilitation.

Central Fatigue Assessed by Transcranial Magnetic Stimulation in Ultratrail Running

The well-established central deficit in ultraendurance running races is not understood. The use of transcranial magnetic stimulation (TMS) in parallel with peripheral nerve stimulation provides insight into the source of these central changes. The aims of this study were to determine the presence and magnitude of voluntary activation deficits, especially supraspinal deficits, after a mountain trail-running race and to determine whether this can be explained by simultaneous changes in corticospinal excitability and intracortical inhibition. Neuromuscular function (TMS and femoral nerve electrical stimulation) of the knee extensors was evaluated before and after a 110-km ultratrail in 25 experienced ultraendurance trail runners during maximal and submaximal voluntary contractions and in relaxed muscle. Voluntary activation assessed by both femoral nerve electrical stimulation (-26%) and TMS (-16%) decreased and were correlated (P < 0.01). Decreases in potentiated twitch and doublet amplitudes were correlated with decreased voluntary activation assessed by TMS (P < 0.05). There was increased motor-evoked potential (MEP) amplitude (P < 0.05) without change in cortical silent period (CSP) elicited by TMS at optimal stimulus intensity. Conversely, CSP at suboptimal TMS intensity increased (P < 0.05) without concurrent change in MEP amplitude. The present results demonstrate the development of a large central activation deficit assessed by TMS, indicating that cortical motoneurons are severely impaired in their ability to fire at optimal frequency or be fully recruited after an ultraendurance running race. MEP and CSP responses suggest a shift in the sigmoidal MEP-stimulus intensity relationship toward larger MEP at higher TMS intensity without change in inflection point of the curve and a left shift in the CSP-stimulus intensity relationship.

Effect of training on corticomotor excitability in clinical neck pain

Corticomotor excitability has been shown to correlate with motor learning and functional recovery. The aim of the present study was to monitor changes in excitability of the corticomotor pathways induced by neck training and to compare the effects in patients with neck or knee pain and pain-free participants. Corticomotor excitability was assessed using transcranial magnetic stimulation and electromyography at baseline, after 30 min and 1 h, and at a 1-week follow-up visit. The primary outcome measures were changes in amplitudes and latencies of motor evoked potentials (MEPs) at 1-week follow-up. MEP responses induced by neck training yielded significantly different outcomes in the three groups. In the group with neck pain and training, MEP amplitudes were significantly reduced between baseline and 30 min (p ≤ 0.05), but with no significant difference between baseline, 1 h (p = 0.178) and 1 week (p = 0.067). In the group with knee pain and training, MEP amplitudes significantly increased between baseline and 30 min (p ≤ 0.01) and 1 h (p < 0.001), but not after 1 week (p = 0.524) compared with baseline. In the pain-free group, there were no changes over time. Neck training reduced neuroplastic responsiveness of corticomotor pathways in neck pain patients in contrast to knee pain patients and pain-free participants. Increased attention to adaptive and maladaptive neuroplastic responses induced by training may prove valuable in the process of optimizing clinical outcomes.

Cyclical changes of cortical excitability and metaplasticity in migraine: Evidence from a repetitive transcranial magnetic stimulation study

The primary brain dysfunctions leading to the onset of a migraine attack remain largely unknown. Other important open questions concern the mechanisms of initiation, continuation, and termination of migraine pain, and the changes in brain function underlying migraine transformation. Brief trains of high-frequency repetitive transcranial magnetic stimulation (rTMS), when applied to the primary motor cortex at suprathreshold intensity (⩾120% of resting motor threshold [RMT]), elicit in healthy subjects a progressive, glutamate-dependent facilitation of the motor evoked potentials (MEP). Conversely, in conditions of increased cortical excitability, the rTMS trains induce inhibitory MEP responses likely mediated by cortical homeostatic mechanisms. We enrolled 66 migraine-without-aura patients, 48 migraine-with-aura patients, 14 patients affected by chronic migraine (CM), and 20 healthy controls. We assessed motor cortical response to 5-Hz rTMS trains of 10 stimuli given at 120% RMT. Patients with episodic migraine were studied in different phases of the migraine cycle: interictal, preictal, ictal, and postictal states. Results showed a facilitatory MEP response during the trains in patients evaluated in the preictal phase, whereas inhibitory responses were observed during and after a migraine attack, as well as in CM patients. In the interictal phase, different responses were observed, depending on attack frequency: facilitation in patients with low and inhibition in those with high attack recurrence. Our findings suggest that changes in cortical excitability and fluctuations in the threshold for inhibitory metaplasticity underlie the migraine attack recurrence, and could be involved in the process of migraine transformation.

Facial Motor Neuron Excitability in Hemifacial Spasm: A Facial MEP Study

Hemifacial spasm (HFS) may be due to peripheral axon ephapsis or central motor neuron hyperexcitability. Low facial motor evoked potential (MEP) thresholds or MEP responses to single pulse stimulation (normally multipulse stimulation is needed) may support the central hypothesis. We retrospectively compared response thresholds for facial MEPs in 65 patients undergoing surgical microvascular decompression (MVD) for HFS and 29 patients undergoing surgery for skull base tumors. Single pulse stimulation elicited facial Mep in up to 87% of HFS patients whereas only 10% of tumor patients responded to single pulse stimulation. When comparing facial MEP thresholds using multi-pulse stimulus trains the voltage required in the HFS group were significantly lower then in skull base tumor patients (p < 0.001). the MEP latencies and amplitudes at threshold stimulation were similar between the two groups. these results suggest the facial corticobulbar pathway demonstrates enhanced excitability in HFS.

Factors Affecting the Motor Evoked Potential Responsiveness and Parameters in Patients With Supratentorial Stroke

ObjectiveTo investigate the factors which affect the motor evoked potential (MEP) responsiveness and parameters and to find the correlation between the function of the upper extremities and the combined study of MEP with a diffusion tensor tractography (DTT) in patients with stroke.MethodsA retrospective study design was used by analyzing medical records and neuroimaging data of 70 stroke patients who underwent a MEP test between June 2011 and March 2013. MEP parameters which were recorded from the abductor pollicis brevis muscle were the resting motor threshold, latency, amplitude, and their ratios. Functional variables, Brunnstrom stage of hand, upper extremity subscore of Fugl-Meyer assessment, Manual Function Test, and the Korean version of Modified Barthel Index (K-MBI) were collected together with the biographical and neurological data. The DTT parameters were fiber number, fractional anisotropy value and their ratios of affected corticospinal tract. The data were compared between two groups, built up according to the presence (MEP-P) or absence (MEP-N) of MEP on the affected hand.ResultsFunctional and DTT variables were significantly different between MEP-P and MEP-N groups (p<0.001). Among the MEP-P group, the amplitude ratio (unaffected/affected) was significantly correlated with the Brunnstrom stage of hand (r=-0.427, p=0.013), K-MBI (r=-0.380, p=0.029) and the time post-onset (r=-0.401, p=0.021). The functional scores were significantly better when both MEP response and DTT were present and decreased if one or both of the two studies were absent.ConclusionThis study indicates MEP responsiveness and amplitude ratio are significantly associated with the upper extremity function and the activities of daily living performance, and the combined study of MEP and DTT provides useful information.

Usefulness of the Combined Motor Evoked and Somatosensory Evoked Potentials for the Predictive Index of Functional Recovery After Primary Pontine Hemorrhage

ObjectiveTo investigate the predictive index of functional recovery after primary pontine hemorrhage (PPH) using the combined motor evoked potential (MEP) and somatosensory evoked potential (SEP) in comparison to the hematoma volume and transverse diameter measured with computerized tomography.MethodsPatients (n=14) with PPH were divided into good- and poor-outcome groups according to the modified Rankin Score (mRS). We evaluated clinical manifestations, radiological characteristics, and the combined MEP and SEP responses. The summed MEP and SEP (EP sum) was compared to the hematoma volume and transverse diameter predictive index of global disability, gait ability, and trunk stability in sitting posture.ResultsAll measures of functional status and radiological parameters of the good-outcome group were significantly better than those of the poor-outcome group. The EP sum showed the highest value for the mRS and functional ambulatory category, and transverse diameter showed the highest value for "sitting-unsupported" of Berg Balance Scale.ConclusionThe combined MEP and SEP is a reliable and useful tool for functional recovery after PPH.

Motor empathy is a consequence of misattribution of sensory information in observers

Human behavior depends crucially on the ability to interact with others and empathy has a critical role in enabling this to occur effectively. This can be an unconscious process and based on natural instinct and inner imitation (Montag et al., 2008) responding to observed and executed actions (Newman-Norlund et al., 2007). Motor empathy relating to painful stimuli is argued to occur via the mirror system in motor areas (Rizzolatti and Luppino, 2001). Here we investigated the effects of the location of emotional information on the responses of this system. Motor evoked potential (MEP) amplitudes from the right first dorsal interosseus (FDI) muscle in the hand elicited by single pulses of transcranial magnetic stimulation (TMS) delivered over the left motor cortex were measured while participants observed a video of a needle entering a hand over the FDI muscle, representing a painful experience for others. To maintain subjects’ internal representation across different viewing distances, we used the same size of hand stimuli both in peripersonal and extrapersonal space. We found a reduced MEP response, indicative of inhibition of the corticospinal system, only for stimuli presented in peripersonal space and not in extrapersonal space. This empathy response only occurring for near space stimuli suggests that it may be a consequence of misidentification of sensory information as being directly related to the observer. A follow up experiment confirmed that the effect was not a consequence of the size of the stimuli presented, in agreement with the importance of the near space/far space boundary for misattribution of body related information. This is consistent with the idea that empathy is, at least partially, a consequence of misattribution of perceptual information relating to another to the observer and that pain perception is modulated by the nature of perception of the pain.

Rare True-Positive Isolated SSEP Loss With Preservation of MEPs Response During Scoliosis Correction

Case report. To report a case of a true-positive isolated somatosensory evoked potential (SSEP) loss with preservation of motor evoked potential (MEP) response during scoliosis correction. Combined intraoperative monitoring uses SSEPs and MEPs to decrease the probability of observing false-negative events. In combination, SSEPs and MEPs have become a standard of care for spinal deformity surgery. However, literature review reveals several cases of false-negative response with combined SSEPs and MEPs, raising the contention that intraoperative monitoring does not reliably identify all isolated selective spinal cord dysfunction. A 15-year-old female patient with a 65° right thoracic adolescent idiopathic scoliosis underwent correction and posterior spinal fusion with segmental pedicle screw instrumentation. After capture and derotation of the left concave rod, left-sided irreversible SSEP loss occurred whereas MEPs remained unchanged. After excluding systemic factors, anesthetic causes, or technical fault, deformity correction was released and instrumentation removed. No cortical breach was reported during pedicle screw removal. Postoperatively, no clinical sensory or motor deficit was present; computed tomography demonstrated a burst left pedicle at T10 with the medial pedicle wall fragment in direct contact with the dorsal spinal cord. Magnetic resonance imaging excluded cord edema or other evidence of injury. Three days after surgery, intraoperative monitoring showed delayed latencies and amplitudes of the left SSEP. An uneventful reinsertion of instrumentation and correction excluding the left T10 pedicle screw was performed 7 days after the initial surgery. This case report provides evidence of selective posterior spinal cord dysfunction with sparing of the anterior columns immediately after a correction maneuver and emphasizes the importance of simultaneous SSEP and MEP monitoring. To the authors' knowledge, there is no previous report of a true-positive isolated SSEP loss with preservation of MEP response during scoliosis correction. N/A.

Voluntary muscle and motor cortical activation during progressive exercise and passively induced hyperthermia

This study examined whether central fatigue was exacerbated by an increase in muscle contractile speed caused by passive hyperthermia (PaH) and whether exercise-induced hyperthermia (ExH) combined with related peripheral fatigue influenced this response. The ExH was induced by cycling at 60% of maximal oxygen uptake in 38°C conditions and the PaH by sitting in a 48°C climate chamber. Ten men performed brief (≈ 5 s) and sustained (30 s) maximal voluntary isometric contractions (MVCs) of the knee extensors at baseline (CON, ∼37.1°C) and during moderate (MOD, ≈ 38.5°C) and severe (SEV, ∼39.5°C) hyperthermia. Motor nerve and transcranial magnetic stimulation were used to assess voluntary muscle and cortical activation level, along with contractile properties. Brief MVC force decreased to a similar extent during SEV-ExH (-8%) and SEV-PaH (-6%; P < 0.05 versus CON). Sustained MVC force also decreased during MOD-ExH (-10%), SEV-ExH (-13%) and SEV-PaH (-7%; P < 0.01 versus CON). Motor nerve and cortical activation were reduced on reaching MOD (≈ 3%) and SEV (≈ 5%) ExH and PaH during the brief and sustained MVCs (P < 0.01 versus CON). Peak twitch force decreased on reaching SEV-ExH and SEV-PaH (P < 0.05 versus CON). Following transcranial magnetic stimulation, during the brief and sustained MVCs the peak muscle relaxation rate increased in ExH and PaH (P < 0.01 versus CON). The increase was greatest during the sustained contraction in SEV-PaH (P < 0.01), but this did not exacerbate central fatigue relative to ExH. These results indicate that during fatiguing cycling exercise in the heat, quadriceps peak relaxation rate increases. However, the centrally mediated rate of activation appears sufficient to overcome even the largest increase in muscle relaxation rate, seen during SEV-PaH.

Preserved corticospinal conduction without voluntary movement after spinal cord injury

Case report. To identify preserved corticomotor connection in chronic spinal cord injury (SCI) in the absence of clinically observable movement. Rehabilitation Hospital and Medical Research Institute, NY, USA. The motor-evoked potential (MEP) response to transcranial magnetic stimulation (TMS) was recorded using surface electromyography from the right biceps brachii, extersor carpi radialis (ECR), flexor carpi radialis (FCR) and abductor pollicis brevis (APB) muscles in a 31-year-old male traumatic SCI chronic patient-ASIA B, injury level C5. Motor power scores were additionally obtained from a clinician blinded to the results of TMS. TMS could consistently elicit MEPs of normal latency, phase and amplitude, in the severely affected ECR muscle but not the similarly affected FCR muscle. The response in proximal and unaffected biceps muscle was larger than the healthy subject, whereas no response was obtained in the distal APB muscle as expected. TMS can identify residual pathways not apparent from clinical assessment alone, which may have prescriptive value for rehabilitation.

Correlation between electrophysiological properties, morphological maturation, and olig gene changes during postnatal motor tract development

This study investigated electrophysiological and histological changes as well as alterations of myelin relevant proteins of descending motor tracts in rat pups. Motor-evoked potentials (MEPs) represent descending conducting responses following stimulation of the motor cortex to responses being elicited from the lower extremities. MEP responses were recorded biweekly from postnatal (PN) week 1 to week 9 (adult). MEP latencies in PN week 1 rats averaged 23.7 ms and became shorter during early maturation, stabilizing at 6.6 ms at PN week 4. During maturation, the conduction velocity (CV) increased from 2.8 ± 0.2 at PN week 1 to 35.2 ± 3.1 mm/ms at PN week 8. Histology of the spinal cord and sciatic nerves revealed progressive axonal myelination. Expression of the oligodendrocyte precursor markers PDGFRα and NG2 were downregulated in spinal cords, and myelin-relevant proteins such as GalC, CNP, and MBP increased during maturation. Oligodendrocyte-lineage markers Olig2 and MOG, expressed in myelinated oligodendrocytes, peaked at PN week 3 and were downregulated thereafter. A similar expression pattern was observed in neurofilament M/H subunits that were extensively phosphorylated in adult spinal cords but not in neonatal spinal cords, suggesting an increase in axon diameter and myelin formation. Ultrastructural morphology in the ventrolateral funiculus (VLF) showed axon myelination of the VLF axons (99.3%) at PN week 2, while 44.6% were sheathed at PN week 1. Increased axon diameter and myelin thickness in the VLF and sciatic nerves were highly correlated to the CV (rs > 0.95). This suggests that MEPs could be a predicator of morphological maturity of myelinated axons in descending motor tracts.

Effect of expectancy and personality on cortical excitability in Parkinson's disease

Our previous studies in Parkinson's disease have shown that both levodopa and expectancy of receiving levodopa reduce cortical excitability. We designed this study to evaluate how degree of expectancy and other individual factors modulate placebo response in Parkinson's patients. Twenty-six Parkinson's patients were randomized to 1 of 3 groups: 0%, 50%, and 100% expectancy of receiving levodopa. All subjects received placebo regardless of expectancy group. Subjects completed the NEO-Five Factor Inventory, General Perceived Self-Efficacy Scale, and Perceived Stress Scale. Cortical excitability was measured by the amplitude of motor-evoked potential (MEP) evoked by transcranial magnetic stimulation. Objective physical fatigue of extensor carpi radialis before and after placebo levodopa was also measured. Responders were defined as subjects who responded to the placebo levodopa with a decrease in MEP. Degree of expectancy had a significant effect on MEP response (P < .05). Subjects in the 50% and 100% expectancy groups responded with a decrease in MEP, whereas those in the 0% expectancy group responded with an increase in MEP (P < .05). Responders tended to be more open to experience than nonresponders. There were no significant changes in objective physical fatigue between the expectancy groups or between responders and nonresponders. Expectancy is associated with changes in cortical excitability. Further studies are needed to examine the relationship between personality and placebo effect in Parkinson's patients. © 2013 Movement Disorder Society.

Motor Evoked Potential Response Latencies Demonstrate Moderate Correlations with Height and Limb Length in Healthy Young Adults

ABSTRACT.The purposes of this study were to determine 1) if motor evoked potential (MEP) response latencies and central motor conduction time (CMCT) are significantly correlated with lower extremity (LE) length or height, and 2) determine if MEP response latencies and CMCT are different between sexes among healthy adults. A cross-sectional, descriptive laboratory design was used. MEPs were recorded from 106 subjects (60 females, 46 males; age 20.1±2.4 years) by applying transcranial magnetic stimulation over the primary motor cortex. MEP response latencies were recorded using electromyography (EMG) responses from the tibialis anterior; CMCT was calculated from cortical and spinal-evoked MEP latencies. MEP latencies were significantly different between males (29.53±3.02 msec) and females (27.69±2.81 msec). Height accounted for greater variability (η2=.369 or approximately 37%) between genders and demonstrated a good-to-moderate correlation with MEP latency (r=.595, p= <.0001). Accounting for height as a confounding variable in the analyses, no significant differences between genders was observed (F1,103=2.45, p=.21). MEP latency should be adjusted to each subjects' height to account for the unwanted variability associated with the varied heights of subjects being tested, thereby permitting an accurate comparison and meaningful interpretation of MEPs between subjects or patients.

The effect of acetaminophen ingestion on cortico-spinal excitability

Acetaminophen (ACT) facilitates the inhibition of voltage-gated calcium and sodium currents, which may effect cortico-spinal excitability. Twelve subjects ingested acetaminophen or a placebo and underwent transcranial magnetic stimulation to assess the motor evoked potential (MEP), and cortical silent period (CSP). ACT significantly increased MEP response (P > 0.05) but had no effect on CSP (P > 0.05). This indicates that ACT increases MEP and should be controlled for in studies where these measures are of interest.