Synchronized finger exercise reduces surround inhibition

Objective

To investigate whether hand muscle repetitive use reduces surround inhibition (SI) as observed in patients with focal hand dystonia, we performed a transcranial magnetic stimulation (TMS) study in 15 healthy right-handed volunteers.

Methods

TMS was set to be triggered by self-initiated flexion of the index finger at 3 ms after movement onset. Motor evoked potentials (MEPs) of the abductor digiti minimi (ADM) were measured before and at 0, 10, 20 and 30 min after ‘single’ (little finger abduction) and ‘dual’ (both index finger flexion and little finger abduction) exercise at 0.5 Hz for 30 min. SI was calculated as (mean control MEP – mean self-triggered MEP) × 100/mean control MEP.

Results

Compared to single exercise, dual exercise produced significantly larger and longer-lasting enhancements of self-triggered MEPs, and greater reduction in calculated SIs.

Conclusions

This result demonstrates that synchronized finger exercise can reduce SI between the involved muscles possibly due either to the strengthening of the excitatory connections or to the weakening of the inhibitory connections between them, and may illustrate the association between hand muscle repetitive use and disturbed SI observed in FHD.

Significance

The operation of surround inhibition can be reduced by practicing synchronous movements.     

Distinct neural mechanisms of tonal processing between musicians and non-musicians

ObjectiveBoth behavioral and neural responses to deviant melody endings can be enhanced through musical training. Yet it is unknown whether there are any differences in the neural responses of musicians and non-musicians given no difference in their behavioral responses. It is also unknown whether the melody preceding the fixed final tone influences the sense of completion.MethodsWe recorded neuromagnetic responses in ten musicians and ten non-musicians while they were evaluating the sense of completion associated with melodies.ResultsThe sense of a melody’s completion was influenced by the combination of the preceding melody and the ending tones. The N1 had shorter latency in musicians, while the sustained field had larger amplitudes in non-musicians.ConclusionsMusicians and non-musicians rated the sense of completion similarly, yet neural responses differed between the groups.SignificanceThese findings suggest that neural processes in musicians and non-musicians may be distinct even when the sense of completion is assessed similarly in both groups. In other words, there might be specific tonal processing available to non-musicians which can compensate for their lack of musical training.     

Longitudinal changes of motor cortical excitability and transcallosal inhibition after subcortical stroke

Objective

A general lack of longitudinal studies on interhemispheric interactions following stroke led us to use transcranial magnetic stimulation (TMS) to examine changes in corticospinal/intracortical excitability and transcallosal inhibition over a 1-year period following subcortical stroke.

Methods

We measured TMS parameters such as motor threshold (MT), short-interval intracortical inhibition (SICI), and ipsilateral silent period (iSP) and evaluated clinical scores at three time-points (T1, T2, and T3) in 24 patients and 25 age-matched healthy subjects.

Results

At T1, we observed reduced MTs and SICIs with prolonged iSPs in the unaffected hemisphere (UH). In contrast, increased MTs and reduced SICIs were observed in the affected hemisphere (AH). These abnormalities gradually reduced and no MEP response to TMS at T1 predicted a worse prognosis. The prolonged iSP at T1 was associated with more severe impairments, but it did not necessarily predict a worse prognosis after 1 year.

Conclusions

UH excitability was increased at the post-acute time-period, which may have resulted in enhanced transcallosal inhibition to the AH. However, it is unclear whether there was a causal relationship between the enhanced transcallosal inhibition and the extent of clinical recovery.

Significance

This is the first study to demonstrate changes in transcallosal inhibition over a longitudinal period following stroke.     

Prognostic value of somatosensory- and motor-evoked potentials in patients with a non-traumatic coma

Summary A total of 28 patients with non-traumatic coma were studied both with somatosensory- and motor-evoked potentials. While somatosensory-evoked potentials (SEP) have proved to be useful in predicting the outcome in patients with severe brain damage, the aim of this study was to find out whether the additional evaluation of motor-evoked potentials (MEP) could contribute to a better prediction of the outcome than SEP alone. Our results clearly indicate that in terms of prognostic value, SEP are superior to MEP. Nine patients with bilaterally preserved MEP died, while all of the patients with bilaterally preserved SEP and a central conduction time 6.5 ms survived, with a Glasgow outcome score of 1 to 3. Therefore, we cannot recommend the inclusion of MEP in the prognostic evaluation of patients with non-traumatic coma.     

Abnormality of motor cortex excitability in peripherally induced dystonia.

It is widely accepted that peripheral trauma such as soft tissue injuries can trigger dystonia, although little is known about the underlying mechanism. Because peripheral injury only rarely appears to elicit dystonia, a predisposing vulnerability in cortical motor areas might play a role. Using single and paired-pulse pulse transcranial magnetic stimulation, we evaluated motor cortex excitability of a hand muscle in a patient with peripherally induced foot dystonia, in her brother with craniocervical dystonia, and in her unaffected sister, and compared their results to those from a group of normal subjects. In the patient with peripherally induced dystonia, we found a paradoxical intracortical facilitation at short interstimulus intervals of 3 and 5 milliseconds, at which regular intracortical inhibition (ICI) occurred in healthy subjects. These findings suggest that the foot dystonia may have been precipitated as the result of a preexisting abnormality of motor cortex excitability. Furthermore, the abnormality of ICI in her brother and sister indicates that altered motor excitability may be a hereditary predisposition. The study demonstrates that the paired-pulse technique is a useful tool to assess individual vulnerability, which can be particularly relevant when the causal association between trauma and dystonia is less evident.     

Motor-evoked potentials in response to fatiguing grip exercise in multiple sclerosis patients.

OBJECTIVE: This study examined central and peripheral effects of fatiguing exercise (3 min maximal grip) in healthy controls (n=10) and multiple sclerosis (MS) subjects with weakness, MS-W (n=16) and normal motor function, MS-NM (n=16) in the studied extremity.Method: Transcranial magnetic stimulation (TMS) was used to assess resting and facilitated motor-evoked potentials (MEPs) of abductor pollicus brevis (APB) and flexor carpi radialis (FCR) muscles before and after fatiguing exercise. Exercise-induced depletion and recovery of phosphocreatine (PCr) were measured using (31)P magnetic resonance spectroscopy ((31)PMRS) in FCR. RESULTS AND CONCLUSION: MS subjects demonstrated significantly lower peak force and a faster decline in force than controls. Contralateral muscle activation (hand grip) before the fatigue protocol resulted in significantly increased MEP amplitudes in all groups. Contralateral hand grip following fatiguing exercise resulted in significantly higher MEP amplitudes in controls and MS-NM subjects, but not MS-W subjects. Fatiguing exercise resulted in prolonged central motor conduction time (CMCT) in MS subjects, but not controls. No group differences in PCr depletion or resynthesis were observed. All groups demonstrated significant post-exercise depression (PED) of MEP amplitude that persisted beyond the time course of PCr recovery, indicating fatigue was central in origin. MS subjects were less able than controls to increase cortical excitability using contralateral muscle activation following fatiguing exercise, possibly indicating impaired conduction in the corpus callosum.     

电刺激运动诱发电位监护在脊柱脊髓手术中的应用

目的观察运动诱发电位在脊柱脊髓手术监护中的应用效果。方法对30例脊柱脊髓手术患者采用经颅电刺激-四肢肌记录肌活动电位，行术中脊髓机能监测，其中对采用经颅电刺激-四肢肌记录无效者，配合经脊髓硬膜外刺激-四肢肌记录肌活动电位。结果30例采用经颅电刺激-四肢肌记录方法，其中26例于术中和术后都记录到了正常的运动诱发电位波形。其余4例改为使用经脊髓硬膜外刺激-四肢肌记录方法后，共29例患者的运动诱发电位获得记录。结论采用经颅电刺激，并配合经脊髓硬膜外刺激-四肢肌记录肌活动电位，使术中对脊髓内部运动传导通路机能监测的有效率得到了提高。     

The effect of direct current field polarity on recovery after acute experimental spinal cord injury

Recent evidence indicates that direct current (DC) fields promote recovery of acutely injured central and peripheral nervous system axons. The polarity of the applied DC field may play an important role in modulating these effects. In the present study, the effect of DC field polarity on recovery of injured spinal cord axons was examined anatomically, electrophysiologically and behaviourly in a rat model. After a 53 g clip compression injury of the cord at T1, 30 adult rats were randomly and blindly allocated to one of three groups (n = 10 each): one group received implantation of a DC stimulator (14 microA) with the cathode caudal to the injury site; the second group received implantation of a similar stimulator with the cathode rostral to the injury site; and the third group received a sham (O microA) stimulator. Clinical neurological function was assessed by the inclined plane technique and axonal function was assessed by motor- and somatosensory-evoked potentials (MEP and SSEP). A quantitative assessment of axonal integrity was performed by counting neurons in the brain retrogradely labelled by the axonal tracer horseradish peroxidase (HRP) and by counting axons at the injury site. The inclined plane scores (P less than 0.0001), MEP amplitude (P less than 0.02), counts of neurons retrogradely labelled by HRP (P less than 0.0001), and axon counts at the injury site (P less than 0.01) were significantly greater in the group treated with a DC field with the cathode caudal to the lesion than in the other two groups. Conversely, the cathode rostral DC field caused a decrease in the number of neurons retrogradely labelled by HRP (P less than 0.05) compared to the sham and cathode caudal groups. These data confirm our previous finding that DC fields promote recovery of acutely injured spinal cord axons. Furthermore, the polarity of the applied field is of critical importance to this effect.     

Awake far lateral craniotomy for resection of foramen magnum meningioma in a patient with tenuous motor and somatosensory evoked potentials

We report a patient with an infratentorial lesion resected under a far-lateral approach during awake craniotomy to optimize intraoperative monitoring. A 72-year-old man presented with falls, difficulty walking, and lower extremity weakness. MRI revealed a 2.2 by 2.3 by 2.8 cm mass at the right cervicomedullary junction, with mass effect on the adjacent spinal cord. During two attempts during surgical positioning under general anesthesia, motor evoked potentials were lost. Each time the operation was aborted. During the third operation, the patient underwent monitored, light anaesthesia and was awakened periodically to confirm conscious motor function. The operation proceeded without complication, and postoperatively there was no further decrease in motor function. This is, to our knowledge, the first use of an awake operation for an infratentorial meningioma via the far-lateral approach, demonstrating the technique may be used safely and can be useful in optimizing motor function monitoring.     

Reduced plastic brain responses to repetitive transcranial magnetic stimulation in severe obstructive sleep apnea syndrome

ObjectivesAbnormalities in cortical excitability have been proposed to underlie the pathophysiology of various neurocognitive manifestations of obstructive sleep apnea syndrome (OSAS). Transcranial magnetic stimulation (TMS) provides a noninvasive method for study and modulation of cortical excitability in the human brain, and repetitive TMS (rTMS) has been proven useful for neurophysiologic investigation in various neurologic conditions. We aimed to investigate cortical excitability in patients with OSAS during wakefulness and to determine if rTMS would change the abnormal excitability patterns.MethodsMeasures of motor cortical and corticospinal excitability (resting motor threshold [RMT], motor-evoked potential [MEP] amplitude, and cortical silent period [CSP]) were taken before and after a session of 10-Hz rTMS applied to the motor cortex in 13 individuals with untreated severe OSAS (apnea–hypopnea index [AHI] > 30) and 12 age- and sex-matched healthy controls (HC).ResultsOSAS subjects had a significantly higher RMT (P < .003) and a longer CSP duration (P < .002) compared to HC. No difference was observed between MEP values of OSAS subjects and HC (P > .05). In response to rTMS, the HC group had a significant increase in CSP and MEP values from baseline, which were absent in OSAS subjects.ConclusionsIndividuals with OSAS demonstrated increased motor cortex inhibition, which did not respond to 10-Hz rTMS. As rTMS-induced changes in MEP and CSP involve a separate neurotransmitter system (N-methyl-d-aspartate [NMDA] and gamma-aminobutyric acid [GABA], respectively), these findings suggest a widespread alteration in cortical neurophysiology in severe OSAS subjects that requires clarification with further exploration.     

Bladder filling inhibits somatic spinal motoneurones

OBJECTIVES: Despite evidence that the activation of visceral afferents modulates spinal motoneurone activity in humans the responsible circuits remain unclear. We investigated changes in spinal motoneurone excitability during bladder filling in 8 healthy subjects and in 8 patients with spinal cord lesions and 5 patients with multi-infarct encephalopathy. METHODS: Spinal motoneurone excitability was studied by analysing changes in H-reflex, F-wave and motor-evoked potential (MEP) size recorded from the calf muscles under different bladder filling conditions. RESULT: In normal subjects, maximal bladder filling significantly suppressed the H-reflex, F-wave and MEPs; after bladder voiding these responses returned to normal. In patients with encephalopathy maximal bladder filling strongly reduced H-reflex size; similarly to normal subjects H-reflex returned to control value after bladder voiding. In patients with spinal cord lesions, activation of bladder afferents left the H-reflex unchanged. CONCLUSIONS: These findings indicate that bladder distension induces post-synaptic inhibition of spinal motoneurones through a suprasegmental pathway, which is interrupted by rostral spinal cord lesions. This vesical-induced inhibition is probably mediated by the propriospinal system rather than by the diffuse noxious inhibitory control circuit.     

Cognitive deficits during status epilepticus and time course of recovery: a case report

We describe a young woman with progressive cognitive and neurological deficits during a parietal lobe status epilepticus (SE). Ictal FDG-PET showed left parietal lobe hypermetabolism and frontal lobe hypometabolism with concomitant EEG slowing. Cognitive and neurological deficits fully reversed more than 1 year after seizure remission, and were associated with normalization of FDG-PET and EEG. Our findings suggest that ictal hypometabolism and EEG delta activity at a distance from the epileptic focus were seizure-related phenomena, possibly representing inhibition in seizure propagation pathways, which could be responsible for the epileptic encephalopathy.     

Inhibitory connections between motor neurons modify a centrally generated motor pattern in the leech nervous system

Both excitatory and inhibitory motor neurons innervate longitudinal body wall muscles in the leech Hirudo medicinalis. Each inhibitory motor neuron also centrally inhibits the excitatory motor neurons that innervate its same muscle field. This central inhibition is strong, probably monosynaptic, and largely a function of graded membrane potential changes in the inhibitory motor neurons. During leech swimming, both the excitatory and inhibitory motor neurons are rhythmically active. Here, we present evidence that the inhibitory motor neurons phasically inhibit the excitatory motor neurons during swimming, thereby augmenting the amplitude of membrane potential oscillations and the burst intensity of the excitors.     

Ipsilesional motor-evoked potential absence in pediatric hemiparesis impacts tracking accuracy of the less affected hand

This study analyzed the relationship between electrophysiological responses to transcranial magnetic stimulation (TMS), finger tracking accuracy, and volume of neural substrate in children with congenital hemiparesis. Nineteen participants demonstrating an ipsilesional motor-evoked potential (MEP) were compared with eleven participants showing an absent ipsilesional MEP response. Comparisons of finger tracking accuracy from the affected and less affected hands and ipsilesional/contralesional (I/C) volume ratio for the primary motor cortex (M1) and posterior limb of internal capsule (PLIC) were done using two-sample t-tests. Participants showing an ipsilesional MEP response demonstrated superior tracking performance from the less affected hand (p = 0.016) and significantly higher I/C volume ratios for M1 (p = 0.028) and PLIC (p = 0.005) compared to participants without an ipsilesional MEP response. Group differences in finger tracking accuracy from the affected hand were not significant. These results highlight differentiating factors amongst children with congenital hemiparesis showing contrasting MEP responses: less affected hand performance and preserved M1 and PLIC volume. Along with MEP status, these factors pose important clinical implications in pediatric stroke rehabilitation. These findings may also reflect competitive developmental processes associated with the preservation of affected hand function at the expense of some function in the less affected hand.     

Differential motor and electrophysiological outcome in rats with mid-thoracic or high lumbar incomplete spinal cord injuries

We have investigated the motor changes in rats subjected to a moderate photochemical injury on mid-thoracic (T8) or high lumbar (L2) spinal cord segments. Fourteen days after surgery, L2 injured animals presented gross locomotor deficits (scored 10+/-2.8 in the BBB scale), decreased amplitude of motor-evoked potentials (MEPs) recorded on tibialis anterior (TA) and plantar (PL) muscles (24% and 6% of the preoperative mean values, respectively), reduced M wave amplitudes (75%, 62%), and also facilitated monosynaptic reflexes evidenced by an increase of the H/M amplitude ratio (158% and 563%). On the other hand, T8 injured animals had only slight deficits in locomotion (18+/-0.6 in the BBB scale), a minimal reduction in MEP amplitudes (78% and 71% in TA and PL muscles), normal M wave amplitudes, and a milder increase of the H/M ratio in the TA muscle (191%) but less pronounced in the PL muscle (172%). The percentage of spared tissue at the site of injury was similar in both experimental groups (L2: 79% and T8: 82%). Taken together, these results indicate that lumbar spinal injuries have more severe consequences on hindlimb motor output than injuries exerted on thoracic segments. The causes of this anatomical difference may be attributed to damage inflicted on the central pattern generator of locomotion resulting in dysfunction of lumbar motoneurons and altered spinal reflexes modulation.     

The detection of sensitivity of proprioception by a new clinical test: The dual joint position test

Objectives

To date, very few studies have paid attention to the joint sense (proprioception) of toes other than the big toe. We evaluated the sensitivity of joint position sense at the joint of the great toe in comparison to other digits, and with that determined by the dual digit stimulation test, in a sample of healthy normal controls and patients with clinical diagnosis of the lemniscal system dysfunction.

Material and methods

Seventy-two patients with lemniscal system dysfunction (55 clinically definitive multiple sclerosis, 17 vasculitis) and 110 healthy volunteers participated in the study. All subjects underwent the joint position sense test of all digits of upper and lower extremities. The position sense resulting from the combined operation of the joints of the second and the fourth digits (simultaneous two digits position sense) was also measured and subsequently compared with the results of the great toe position sense.

Results

Upper extremities: no difference was found in recognition of the position sense in the single digits of the upper extremities between patients and healthy volunteers. There was a significant difference in the dual joint position test of the right upper extremity between patients and the case group (p < 0.05) but not in the left upper extremity. Lower extremities: there was no significant difference in proprioception of the great toe neither in the right and nor in the left side between patients and normal subjects. However, the joint position sense of other single digits was deteriorated in the patients, a difference that was significant compared to normal controls (p < 0.05). Additionally, patients and normal controls displayed a difference in dual digit position sense of the right and left lower extremities (p < 0.05).

Conclusions

We show in this paper that the proprioception of simultaneous dual digits is diminished in patients when compared to a single digit position sense. Moreover, the great toe proprioception is less sensitive than other digits. Taken together, these observations lend evidence for a new clinical method which we named as dual joint position test. We suggest this novel method offers clinical utility to demonstrate lemniscal system dysfunction.     

Novel TMS-EEG indexes to investigate interhemispheric dynamics in humans

ObjectiveTo validate two indexes of interhemispheric signal propagation (ISP) and balance (IHB) by combining transcranial magnetic stimulation (TMS) and electroencephalography (EEG).MethodsWe used TMS-EEG to non-invasively stimulate the two hemispheres of 50 healthy volunteers and measured interhemispheric dynamics in terms of ISP and IHB. We repeated our evaluation after three weeks to assess the reliability of our indexes. We also tested whether our TMS-EEG measures were correlated with traditional interhemispheric inhibition (IHI), as measured with motor-evoked potentials (MEPs).ResultsOur main results showed that ISP and IHB (1) have a high reproducibility among all the participants tested; (2) have a high test-retest reliability (3) are linearly correlated with IHI, as measured with MEPs.ConclusionsThe main contribution of this study lies in the proposal of new TMS-EEG cortical measures of interhemispheric dynamics and in their validation in terms of intra- and inter-subject reliability. We also provide the first demonstration of the correlation between ISP and IHI.SignificanceOur results are relevant for the investigation of interhemispheric dynamics in clinical populations where MEPs are not reliable.     

Afferent and efferent synaptic connections of somatostatin-immunoreactive neurons in the rat fascia dentata

The aim of this study was to determine whether somatostatin (SS)-immunoreactive neurons of the rat fascia dentata are involved in specific excitatory circuitries that may result in their selective damage in models of epilepsy. Synaptic connections of SS-immunoreactive neurons were determined at the electron microscopic level by using normal and colchicine pretreated rats. Vibratome sections prepared from both fascia dentata of control animals and from rats that had received an ipsilateral lesion of the entorhinal cortex 30-36 hours before sacrifice were immunostained for SS by using a monoclonal antibody (SS8). Correlated light and electron microscopic analysis demonstrated that many SS-immunoreactive neurons in the hilus send dendritic processes into the outer molecular layer of the fascia dentata, and dendrites of the same neurons occupy broad areas in the dentate hilar area. The majority of SS-immunoreactive axon terminals form symmetric synapses with the granule cell dendrites in the outer molecular layer and also innervate deep hilar neurons. Via their dendrites in the outer molecular layer, the SS-immunoreactive neurons receive synaptic inputs from perforant pathway axons which were identified by their anterograde degeneration following entorhinal lesions. The axons from the entorhinal cortex are the first segment of the main hippocampal excitatory loop. The hilar dendrites of the same SS-immunoreactive cells establish synapses with the mossy axon collaterals which represent the second member in this excitatory neuronal chain. These observations suggest that SS-immunoreactive neurons in the dentate hilar area may be driven directly by their perforant path synapses and via the granule cells which are known to receive a dense innervation from the entorhinal cortex. These observations demonstrate that SS-immunoreactive neurons in the hilar region are integrated in the main excitatory impulse flow of the hippocampal formation.     

Usefulness of motor-evoked potential monitoring during coil embolization of anterior choroidal artery aneurysms: technical reports

Abstract

Objectives: To determine whether transcranial motor-evoked potential (TCMEP) monitoring is useful for detecting blood flow insufficiency in the anterior choroidal artery (AChA) and reflects motor function during coil embolization of AChA aneurysms.

Methods: We analysed MEP findings in seven patients who underwent coil embolization for AChA aneurysms. Corkscrew electrodes positioned at C3 and C4 were used to deliver supra-maximal stimuli (230-550 V). TCMEPs were recorded from the brachioradialis, abductor pollicis brevis, anterior tibialis, and abductor hallucis muscles during all endovascular surgery procedures.

Results: Three of seven patients showed transient decreases in TCMEP amplitudes obtained from the lower extremities after coil insertion into the aneurysms, although digital subtraction angiography (DSA) showed no blood flow insufficiency in the AChAs. In two of these three patients, extraction of the coils resulted in recovery of TCMEP amplitudes. In the other patient, the amplitude recovered gradually during repeated TCMEP recordings. One of the three patients experienced transient hemiparesis and aphasia 3 hours after treatment. No patients experienced permanent morbidity post-operatively.

Discussion: Decreases in TCMEP amplitude during endovascular treatment for AChA aneurysms are likely to reflect motor dysfunction due to a subtle blood flow insufficiency in the AChA, not detectable by DSA. TCMEP monitoring is a simple and safe monitoring method during coil embolization of AChA aneurysms.     

Cerebellar Transcranial Magnetic Stimulation: The Role of Coil Geometry and Tissue Depth

BackgroundWhile transcranial magnetic stimulation (TMS) coil geometry has important effects on the evoked magnetic field, no study has systematically examined how different coil designs affect the effectiveness of cerebellar stimulation.HypothesisThe depth of the cerebellar targets will limit efficiency. Angled coils designed to stimulate deeper tissue are more effective in eliciting cerebellar stimulation.MethodsExperiment 1 examined basic input–output properties of the figure-of-eight, batwing and double-cone coils, assessed with stimulation of motor cortex. Experiment 2 assessed the ability of each coil to activate cerebellum, using cerebellar-brain inhibition (CBI). Experiment 3 mapped distances from the scalp to cerebellar and motor cortical targets in a sample of 100 subjects' structural magnetic resonance images.ResultsExperiment 1 showed batwing and double-cone coils have significantly lower resting motor thresholds, and recruitment curves with steeper slopes than the figure-of-eight coil. Experiment 2 showed the double-cone coil was the most efficient for eliciting CBI. The batwing coil induced CBI only at higher stimulus intensities. The figure-of-eight coil did not elicit reliable CBI. Experiment 3 confirmed that cerebellar tissue is significantly deeper than primary motor cortex tissue, and we provide a map of scalp-to-target distances.ConclusionsThe double-cone and batwing coils designed to stimulate deeper tissue can effectively stimulate cerebellar targets. The double-cone coil was found to be most effective. The depth map provides a guide to the accessible regions of the cerebellar volume. These results can guide coil selection and stimulation parameters when designing cerebellar TMS studies.