Mean Resting Motor Threshold Research Articles

Differences in neurometabolites and transcranial magnetic stimulation motor maps in children with attention-deficit/hyperactivity disorder.

Background:Although much is known about cognitive dysfunction in attention-deficit/hyperactivity disorder (ADHD), few studies have examined the pathophysiology of disordered motor circuitry. We explored differences in neurometabolite levels and transcranial magnetic stimulation (TMS)–derived corticomotor representations among children with ADHD and typically developing children.Methods:We used magnetic resonance spectroscopy (MRS) protocols to measure excitatory (glutamate + glutamine [Glx]) and inhibitory (γ-aminobutyric acid [GABA]) neurometabolite levels in the dominant primary motor cortex (M1) and the supplementary motor area (SMA) in children with ADHD and typically developing children. We used robotic neuronavigated TMS to measure corticospinal excitability and create corticomotor maps.Results:We collected data from 26 medication-free children with ADHD (aged 7–16 years) and 25 typically developing children (11–16 years). Children with ADHD had lower M1 Glx (p = 0.044, d = 0.6); their mean resting motor threshold was lower (p = 0.029, d = 0.8); their map area was smaller (p = 0.044, d = 0.7); and their hotspot density was higher (p = 0.008, d = 0.9). M1 GABA levels were associated with motor map area (p = 0.036).Limitations: Some TMS data were lost because the threshold of some children exceeded 100% of the machine output. The relatively large MRS voxel required to obtain sufficient signal-to-noise ratio and reliably measure GABA levels encompassed tissue beyond the M1, making this measure less anatomically specific.Conclusion:The neurochemistry and neurophysiology of key nodes in the motor network may be altered in children with ADHD, and the differences appear to be related to each other. These findings suggest potentially novel neuropharmacological and neuromodulatory targets for ADHD.

Effect of racial background on motor cortical function as measured by threshold tracking transcranial magnetic stimulation.

A previous study using traditional paired-pulse TMS methods (amplitude-tracking) has reported differences in resting motor threshold (RMT) and short-interval intracortical inhibition (SICI) between healthy subjects of Caucasian and Han Chinese backgrounds, probably due to differences in the skull shape. The amplitude-tracking method delivers stimuli with constant intensity and causes substantial variabilities in motor-evoked potential amplitudes. To overcome this variability, threshold tracking transcranial magnetic stimulation (TT-TMS) has been developed. The present study aimed to investigate whether racial differences in motor cortical function exist, using TT-TMS. A total of 83 healthy volunteers (30 Caucasians, 25 Han Chinese, and 28 Japanese) were included in the present series. In TT-TMS and nerve conduction studies, electrodes were placed on the dominant limb, with measures recorded from the abductor pollicis brevis muscle. Stimulations were delivered with a circular coil, directly above the primary motor cortex. There were no significant differences at all the SICI intervals between races. Similarly, there were no significant differences in other measures of excitability including mean RMT, intracortical facilitation, and cortical silent period. Contrary to traditional amplitude-tracking TMS, motor cortical excitability and thereby motor cortical function is minimally influenced by racial differences when measured by TT-TMS. Recent studies have disclosed that SICI measured by TT-TMS differentiates amyotrophic lateral sclerosis (ALS) from ALS mimic disorders, with high sensitivity and specificity, in Caucasians. This study suggested that TT-TMS can be applied for the ALS diagnosis in Asian patients, as well as Caucasians.NEW & NOTEWORTHY Threshold tracking transcranial magnetic stimulation (TT-TMS) was applied for Caucasians, Han Chinese, and Japanese. No significant differences were found in TMS excitability indexes among races. Recent studies have disclosed that TT-TMS indexes differentiate amyotrophic lateral sclerosis (ALS) from ALS mimic disorders, with high sensitivity and specificity, in Caucasians. This study suggested that TT-TMS can be applied for the ALS diagnosis in Asian patients, as well as Caucasians.

Distilling the essence of TMS-evoked EEG potentials (TEPs): A call for securing mechanistic specificity and experimental rigor

Distilling the essence of TMS-evoked EEG potentials (TEPs): A call for securing mechanistic specificity and experimental rigor

F147. Absolute and relative reliability of short-interval intracortical inhibition measured by threshold tracking transcranial magnetic stimulation

Introduction Paired-pulse transcranial magnetic stimulation (TMS) is a useful tool to examine brain function. The technique relies on measuring the size of the motor evoked potential (MEP) generated using a fixed test stimulus, although MEP amplitude can vary by up to twofold per trial. TMS measures have shown significant within- and between-subject variability in ‘constant stimulus’ paired-pulse paradigms, raising concerns about reliability and potentially limiting clinical utility. As such, the present study was undertaken to assess whether threshold tracking TMS (TT-TMS) may overcome problems due to the variability of MEP amplitude. The aim of this study is to describe the absolute and relative reliability of short-interval intracortical inhibition (SICI) using TT-TMS. Methods TT-TMS studies were performed on twenty-six healthy subjects over three sessions (two recordings on the same day and one seven days apart), with MEPs recorded over abductor pollicis brevis. Absolute and relative reliability was established by calculating the standard error of the measurements (SEM), minimal detectable change (MDC) and intraclass correlation coefficient (ICC). Results No significant differences in mean resting motor threshold (RMT), SICI at 1 ms, SICI at 3 ms, and averaged SICI were observed between sessions. Averaged SICI presented the lowest SEM and highest ICCs for both within-day and between-day comparisons. Specifically, averaged SICI presented an excellent within-day (ICC = 0.88) and between-days (ICC = 0.95) reproducibility. SEM and MDC were large in all paired-pulse TT-TMS variables, setting a limit to the ability to track small changes in longitudinal studies. Additionally, SICI at 1 ms showed a higher SEM than SICI at 3 ms, suggesting different physiological processes between these two periods. The absolute and relative reliability was higher for tests undertaken seven days apart compared to tests performed on the same day. Conclusion Averaged SICI is the most reproducible variable across paired-pulse TT-TMS measures, showing an excellent ICC. TT-TMS measures demonstrated reduced variability when repeat tests were undertaken at the same time over different days compared to repeated testing at different times on the same day. It is recommended that changes in cortical excitability should be measured and averaged over a number of interstimulus intervals to further reduce variability.

Additive effects of sequential excitatory and inhibitory theta burst stimulation in improving cortical excitability following ischaemic stroke

ABSTRACTPurpose: To study the effects of sequential excitatory and inhibitory theta burst stimulation (TBS) on cortical excitability in patients with subacute ischaemic stroke.Methods: Fifteen patients with first-ever middle cerebral artery ischaemic stroke within last three months were subjected to intermittent TBS over the hand area (M1) of the stroke hemisphere (iTBSSH) followed by continuous TBS over the intact hemisphere M1 (cTBSIH). The study measured motor evoked potential (MEP) amplitude, resting motor threshold (RMT) and contralateral cortical silent period (cCSP) at baseline and after 7 minutes of each TBS session.Results: The mean age of the patients was 62.4 ± 8.0 years. The absolute changes in baseline motor physiological parameters were significantly greater after cTBSIH than after iTBSSH (p = 0.001). Following iTBSSH, there was a significant decrease in mean RMT (7.4%; p < 0.001). Following cTBSIH, there was further 18.3% increase in mean MEP amplitude and decrease in mean RMT (4.7%; p < 0.001) and cCSP (5.6%; p < 0.001) of the stroke hemisphere. Similar changes of smaller magnitude were noted in 12 age-matched controls.Conclusions: The results indicate that combining iTBSSH and cTBSIH can have additive effect in increasing cortical excitability in subacute ischaemic patients with stroke.

P157 Reliability of threshold tracking technique for short interval intracortical inhibition

Introduction In threshold-tracking TMS, stimulation intensity is adjusted online to maintain a predefined target MEP response, thus allowing monitoring and controlling for the naturally occurring fluctuations in corticospinal excitability as well as technical errors. Although it is emerging as a useful clinical tool, little is known about its reliability and comparability with conventional techniques. Objectives To evaluate the reproducibility of the threshold-tracking (constant response ) TMS technique for short interval intracortical inhibition (SICI) and compare it with standard (constant stimulus ) measurements. Methods SICI was measured in 12 healthy volunteers (6 males, 31 ± 7.6 years) from the right FDI muscle using an automated stimulation protocol incorporating (i) conventional, fixed-intensity (A-SICI) and (ii) threshold tracking (T-SICI) methods at conditioning stimuli (CS) of 50–80% resting motor threshold (RMT) and interstimulus interval of 2.5 ms. RMT was defined as a stimulation intensity required to evoke a response of 0.2 mV and was determined by threshold tracking. Measurements were repeated on the same day and at least a week later by a single operator. Results No significant differences in mean RMT, A-SICI and T-SICI were observed between sessions. RMT and TS, measured by threshold-tracking technique, showed excellent intra- and adequate interday reproducibility. At 50% RMT CS both types of SICI had poor reproducibility. At all other CS intensities, T-SICI had excellent intraday (intraclass correlation coefficient, ICC 0.81–0.92) and adequate-to-excellent interday (ICC 0.61–0.88) reproducibility, while A-SICI showed poor intraday and poor-to-adequate interday reproducibility (ICC 0.29–0.37 and 0.37–0.51, respectively). Conclusion SICI measured by threshold tracking shows good intra- and interday reproducibility. Automation of the procedure and allowance for naturally occurring fluctuations in cortical excitability by threshold tracking may increase the reproducibility of SICI.

Excitability of the motor cortex in patients with migraine changes with the time elapsed from the last attack

BackgroundMotor-evoked potentials (MEPs) produced by single-pulse transcranial magnetic stimulation (TMS) of the motor cortex can be an objective measure of cortical excitability. Previously, MEP thresholds were found to be normal, increased, or even reduced in patients with migraine. In the present study, we determined whether the level of cortical excitability changes with the time interval from the last migraine attack, thereby accounting for the inconsistencies in previous reports.MethodsTwenty-six patients with untreated migraine without aura (MO) underwent a MEP study between attacks. Their data were then compared to the MEP data collected from a group of 24 healthy volunteers (HVs). During the experiment, the TMS figure-of-eight coil was positioned over the left motor area. After identifying the resting motor threshold (RMT), we delivered 10 single TMS pulses (rate: 0.1 Hz, intensity: 120% of the RMT) and averaged the resulting MEP amplitudes.ResultsThe mean RMTs and MEP amplitudes were not significantly different between the MO and HV groups. In patients with MO, the RMTs were negatively correlated with the number of days elapsed since the last migraine attack (rho = -0.404, p = 0.04).ConclusionOur results suggest that the threshold for evoking MEPs is influenced by the proximity of an attack; specifically, the threshold is lower when a long time interval has passed after an attack, and is higher (within the range of normative values) when measured close to an attack. These dynamic RMT variations resemble those we reported previously for visual and somatosensory evoked potentials and may represent time-dependent plastic changes in brain excitability in relation to the migraine cycle.

4. The degree of motor cortex excitability in migraine depends on the days elapsed since the last attack

Here, we investigated whether level of cortical excitability changes with the distance from the last migraine attack could explain previous inconsistent results. Twenty-six patients with untreated migraine without aura (MO) underwent MEP study between attacks and were compared to a group of 24 healthy volunteers (HV). The TMS figure-of-eight coil was positioned over the left motor area. We first identified the resting motor threshold (RMT) and then amplitude of MEP was evaluated by delivering and averaging 10 single pulses of TMS using a stimulus intensity of 120% RMT at a rate of 0.1 Hz. Mean RMTs (54.2 in MO vs. 55.8 in HV) and MEP amplitudes (3057 microV in MO vs. 3675 microV in HV) were not significantly different between MO and HV. In MO, the RMT negatively correlated with days elapsed since the last migraine attack ( r = −0.426, p = 0.03), i.e. RMT was minimal at a long time interval after an attack while it was greater and within the range of normative values approaching to an attack. The dynamic RMT variations found here resemble those we have previously reported for visual and somatosensory evoked potentials, and may represent time-dependent plastic changes in brain excitability in relation with the migraine cycle.

Effect of a single dose of retigabine in cortical excitability parameters: A cross-over, double-blind placebo-controlled TMS study

BackgroundAntiepileptic drugs (AEDs) decrease the occurrence of epileptic seizures and modulate cortical excitability through several mechanisms that likely interact. The modulation of brain excitability by AEDs is believed to reflect their antiepileptic action(s) and could be used as a surrogate marker of their efficacy. Transcranial magnetic stimulation (TMS) is one of the best noninvasive methods to study cortical excitability in human subjects. Specific TMS parameters can be used to quantify the various mechanisms of action of AEDs. A new AED called retigabine increases potassium efflux by changing the conformation of KCNQ 2–5 potassium channels, which leads to neuronal hyperpolarisation and a decrease in excitability. HypothesisThe purpose of this study is to investigate the effect of retigabine on cortical excitability. Based on the known mechanisms of action of retigabine, we hypothesized that the oral intake of retigabine would increase the resting motor threshold (RMT). MethodsFifteen healthy individuals participated in a placebo-controlled, double-blind, randomised, clinical trial (RCT). The primary outcome measure was the RMT quantified before and after oral intake of retigabine. Several secondary TMS outcome measures were acquired. ResultsThe mean RMT, active motor threshold (AMT) and intensity to obtain a 1mV peak-to-peak amplitude potential (SI1mV) were significantly increased after retigabine intake compared to placebo (RMT: P=0.039; AMT: P=0.014; SI1mV: P=0.019). No significant differences were found for short-interval intracortical inhibition/intracortical facilitation (SICI/ICF), long-interval intracortical inhibition (LICI) or short-interval intracortical facilitation (SICF). ConclusionA single dose of retigabine increased the RMT, AMT and S1mV in healthy individuals. No modulating intracortical facilitation or inhibition was observed. This study provides the first in vivo demonstration of the modulating effects of retigabine on the excitability of the human brain, and the results are consistent with the data showing that retigabine hyperpolarizes neurons mainly by increasing potassium conductance

Alterations of cortical excitability and central motor conduction time in Wilson's disease

Wilson's disease (WD) leads to widespread structural alterations of central nervous system and our objectives were to determine the cortical excitability changes in WD by using transcranial magnetic stimulation (TMS). Thirteen patients with WD, diagnosed by the presence of Kayser–Fleischer ring and biochemical tests, were studied. TMS was performed using a figure-of-eight coil attached to Magstim 200 stimulator. Motor evoked potentials (MEP) were recorded from right first dorsal interosseous at rest. Resting motor threshold (RMT) was determined using standard techniques and central motor conduction time (CMCT) by ‘F’ wave method. Comparison was made with control data of our laboratory. Dysarthria was the presenting symptom in 5 patients (38.5%) and chorea, tremors, dystonia and abnormal gait in 2 patients each (15.4%). RMT was recordable in 10 patients and not recordable in 3. Compared to controls, patients in whom RMT was recordable, had significantly higher mean RMT (80.9±14.8 vs. 41.1±7, p<0.0001) and CMCT (6.7±0.5ms vs. 4.8±0.6ms; p<0.0001). In 2 of the 3 patients with non-recordable RMT, MEP could be obtained with active contraction. CMCT in these 2 patients was also prolonged. Patients with WD have reduced cortical excitability and prolonged CMCT which may be due to the intracortical presynaptic motor dysfunction.

Alterations in cortical excitability and central motor conduction time in spinocerebellar ataxias 1, 2 and 3: A comparative study

IntroductionSpinocerebellar ataxias 1, 2 and 3 (SCA1, SCA2 and SCA3) are CAG repeat disorders. The prevalence of changes in the cortical excitability and central motor conduction time (CMCT) in these disorders is largely unknown, and there are few studies which have compared these findings in the subtypes of SCA. The objectives of this study were to measure the cortical resting motor threshold (RMT) and CMCT using transcranial magnetic stimulation in patients with SCA1, SCA2, and SCA3. MethodsThe subjects of this study were 32 genetically confirmed patients with SCA (SCA1 = 15, SCA2 = 11, SCA3 = 6). Transcranial magnetic stimulation (TMS) was performed using a figure-of-eight coil attached to Magstim 200 stimulator. Motor evoked potentials were recorded from first dorsal interosseous at rest. RMT was determined using standard techniques and the CMCT by ‘F’ wave method. Comparison was made with data from 32 healthy controls. ResultsCompared to controls, the patients with SCA had significantly higher mean RMT as well as CMCT (RMT: 49.9 ± 9.1 vs. 41.5 ± 6.6, p < 0.0001; CMCT: 7.7 ± 2.3 ms vs. 4.8 ± 0.6 ms; p < 0.0001). When compared separately with the controls, while all the three subtypes of SCAs had significantly prolonged CMCT, only SCA1 and SCA3, but not SCA2 had significantly greater RMT. RMT and CMCT between patients with SCA2 and SCA3, and between SCA1 and SCA3 did not differ significantly, while SCA1 had significantly higher RMT and CMCT than SCA2. ConclusionsPatients with SCA have reduced cortical excitability and prolonged central motor conduction time, which was most evident in SCA1 and least in SCA2.

Can transcranial magnetic stimulation be used to evaluate patients with narcolepsy?

Narcolepsy is a rare, chronic sleep disorder characterized by excessive daytime sleepiness, cataplexy and other manifestations of dissociated rapid eye movement in sleep. We assessed the utility of transcranial magnetic stimulation (TMS) as an objective tool to elucidate the cortical excitability changes and also to analyze its role in assessing the treatment efficacy in narcolepsy. Eight patients with narcolepsy under our regular follow-up from 2000 to 2009 at our Sleep disorder clinic were chosen. All of them underwent polysomnography, multiple sleep latency tests and TMS. Resting motor threshold (RMT), cortical silent period (CSP) and central motor conduction time (CMCT) were assessed using TMS in both drug-naïve and post-treatment states. Eight controls were also subjected to all the three investigations. Appropriate statistical methods were used. The mean RMT (%) pre-treatment was higher in narcolepsy patients than that in controls, and it normalized following treatment. CSP and CMCT were unaffected in narcolepsy patients as compared to controls. This study shows that the cortical excitability is significantly low in narcolepsy patients. This motor cortex hypoexcitability becomes normal with the institution of treatment, pari passu with the control of symptoms. In future, TMS may be considered as an effective tool for documenting the treatment efficacy in patients with narcolepsy.

Zonisamide Changes Unilateral Cortical Excitability in Focal Epilepsy Patients

Background and PurposeTo evaluate changes in cortical excitability induced by zonisamide (ZNS) in focal epilepsy patients.MethodsTwenty-four drug-naїve focal epilepsy patients (15 males; overall mean age 29.8 years) were enrolled. The transcranial magnetic stimulation parameters obtained using two Magstim 200 stimulators were the resting motor threshold, amplitude of the motor-evoked potential (MEP), cortical silent period, short intracortical inhibition, and intracortical facilitation. These five transcranial magnetic stimulation parameters were measured before and after ZNS, and the findings were compared.ResultsAll 24 patients were treated with ZNS monotherapy (200-300 mg/day) for 8-12 weeks. After ZNS, MEP amplitudes decreased (-36.9%) significantly in epileptic hemispheres (paired t-test with Bonferroni's correction for multiple comparisons, p<0.05), whereas the mean resting motor threshold, cortical silent period, short intracortical inhibition, and intracortical facilitation were unchanged (p>0.05). ZNS did not affect cortical excitability in nonepileptic hemispheres.ConclusionsThese findings suggest that ZNS decreases cortical excitability only in the epileptic hemispheres of focal epilepsy patients. MEP amplitudes may be useful for evaluating ZNS-induced changes in cortical excitability.

Functional involvement of central nervous system at high altitude

Acute mountain sickness is a common discomfort experienced by unacclimatized persons on ascent to high altitude. We tested the hypothesis that exposure to high altitude affects cortical excitability using transcranial magnetic stimulation. We specifically analyzed the motor cortex excitability in normal subjects at high altitude and in a control condition near sea level. Mean resting motor threshold (RMT) was significantly higher at high altitude than at sea level (69.3 +/- 10.4 versus 56.3 +/- 10.9%; P = 0.042). Mean short intracortical inhibition (SICI) was significantly lower at high altitude than at sea level (percentage of test motor-evoked potential = 79.3 +/- 19.8 versus 28.7 +/- 17.5%; P = 0.0004). Symptoms of acute mountain sickness correlated with resting motor threshold changes induced by high altitude (R 2 = 0.53, P = 0.037). SaO2 correlated with SICI changes induced by high altitude (R 2 = 0.45, P = 0.036). We suggest that high altitude deeply changes cortical excitability by affecting both inhibitory and excitatory circuits and that this is reflected in acute mountain sickness symptoms.

Zonisamide decreases cortical excitability in patients with idiopathic generalized epilepsy

Objective To evaluate changes in cortical excitability after long-term zonisamide (ZNS) administration. Methods Fifteen drug-naïve idiopathic generalized epilepsy (IGE) patients (8 male, mean age 24.9 years) were enrolled. The transcranial magnetic stimulation (TMS) parameters obtained using two Magstim 200 stimulators were resting motor threshold (RMT), motor evoked potential (MEP) amplitudes, cortical silent period (CSP), intracortical inhibition (ICI), and intracortical facilitation (ICF). TMS parameters were compared before and after ZNS administration. Results All patients were administered ZNS monotherapy (200 mg/day) for 8 weeks. No patient reported seizures during the study period. After ZNS treatment MEP amplitudes were significantly reduced in right (−34.2%) and left hemispheres (−37.0%) (Wilcoxon’s signed rank test after Bonferroni’s correction for multiple comparisons, P < 0.05). Mean RMT, CSP, and ICI/ICF were not changed by ZNS ( P > 0.05). Conclusions These findings suggest that ZNS decreases cortical excitability in patients with IGE and a MEP amplitude is a useful TMS parameter for evaluating changes in cortical excitability induced by ZNS. Significance The findings in this study are helpful to understand how ZNS affects the excitability of the motor cortex in patients with IGE.

Motor cortex cholinergic dysfunction in CADASIL: A transcranial magnetic demonstration

Objective Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) is a hereditary small vessel disease responsible for an early onset cognitive impairment. Aim of our study was to test the cortical cholinergic innervation in CADASIL by short latency afferent inhibition (SAI) technique. Methods We applied SAI in ten CADASIL patients and in ten age-matched normal controls. SAI is a phenomenon observed on motor evoked potential when transcranial magnetic stimulation is delivered after a time ranging from 2 to 8 ms longer than the time needed by the peripheral nerve afferent input to reach the somatosensory cortex. Results The amount of short latency afferent inhibition was significantly smaller in CADASIL patients than in controls (79.5 ± 21.7% Vs 42.7 ± 14.1% of test size; p < 0.001, two tailed Mann–Whitney test). The mean resting motor threshold (RMT) was significantly lower in CADASIL patients than in controls (49.4 ± 14.4% Vs 65.6 ± 15.4%; p = 0.02). Conclusions We demonstrated by SAI technique a central cholinergic impairment in CADASIL. Significance SAI could be used to evaluate the cholinergic dysfunction and potentially the efficacy of cholinomimetic therapy in CADASIL.

Interhemispheric Inhibition in Distal and Proximal Arm Representations in the Primary Motor Cortex

Interhemispheric inhibitory interactions (IHI) operate between homologous distal hand representations in primary motor cortex (M1). It is not known whether proximal arm representations exhibit comparable effects on their homologous counterparts. We studied IHI in different arm representations, targeting triceps brachii (TB, n = 13), first dorsal interosseous (FDI, n = 13), and biceps brachii (BB, n = 7) muscles in healthy volunteers. Transcranial magnetic stimulation test stimuli (TS) were delivered to M1 contralateral to the target muscle preceded 10 ms by a conditioning stimulus (CS) to the opposite M1 at 110-150% resting motor threshold (RMT). IHI was calculated as the ratio between motor-evoked potential (MEP) amplitudes in conditioned relative to unconditioned trials. Mean RMTs were 38.9, 46.9, and 46.0% of stimulator output in FDI, TB, and BB muscles, respectively. IHI was 0.45 +/- 0.41 (FDI), 0.78 +/- 0.38 (TB), and 0.52 +/- 0.32 (BB, P < 0.01) when test MEP amplitudes were matched and 0.28 +/- 0.17 (FDI) and 0.85 +/- 0.31 (TB, P < 0.05) when TS intensities expressed as percentage RMT were matched. Significant IHI (P < 0.05) was identified with minimal CS intensities (expressed as percentage stimulator output) in the 30 s for FDI, 60 s for TB, and 40 s for BB. Additionally, a CS of roughly 120% RMT suppressed the test MEP but not a test H-reflex in BB, suggesting IHI observed in BB is likely mediated by a supraspinal mechanism. We conclude that IHI differs between different arm muscle representations, comparable between BB and FDI but lesser for TB. This finding suggests the amount of IHI between different arm representations does not strictly follow a proximal-to-distal gradient, but may be related to the role of each muscle in functional movement synergies.

Triple stimulation technique in patients with spinocerebellar ataxia type 6

Objective To establish further evidence that SCA6 may not be a pure cerebellar syndrome. Methods Seven patients with genetically confirmed SCA6 and 9 age-matched normal controls were studied. Recordings of the CMAP were obtained from the right first dorsal interosseus muscle. Transcranial magnetic stimulation of the left motor cortex was applied to the contralateral scalp with a plane figure-of-8 coil. Conventional transcranial magnetic stimulation (TMS), central motor conduction time (CMCT) by F-wave method and the triple stimulation technique (TST) amplitude ratio (TST test/TST control) were investigated. Results The mean resting motor threshold and mean CMCT did not show significant differences between normal controls and patients, but the mean TST amplitude ratio was significantly smaller in patients than in controls. Conclusions An abnormal TST represents upper motor neuron loss, central axon lesions or conduction blocks, or inexcitability in response to TMS. The lack of pathological changes in the corticospinal tract of patients with SCA6 indicates that this abnormality may be caused by crossed cerebellar diaschisis, or a functional disorder in the brain resulting from CACNA1A mutations. Significance TST is a useful method for quantifying corticospinal tract dysfunction.

Further evidence of corticospinal tract dysfunction in spinocerebellar ataxia type 6

Triple stimulation technique (TST) was performed with seven patients with genetically confirmed spinocerebellar ataxia type 6 (SCA6) and nine age-matched normal controls. Recordings of the CMAP were obtained from the right first dorsal interosseus (FDI) muscle. Transcranial magnetic stimulation (TMS) of the left motor cortex was applied to the contralateral scalp. Conventional TMS, central motor conduction time (CMCT) by F-wave method and the TST amplitude ratio (TST test/TST cond.) were investigated. The mean resting motor threshold and mean CMCT did not show significant differences between normal controls and patients, whereas the mean TST amplitude ratio was significantly smaller than in controls. An abnormal TST represents upper motor neuron loss, central axon lesions or conduction blocks or inexitability to TMS. Lack of any pathological change in corticospinal tract in SCA6 indicates that this abnormality may be caused by crossed cerebellar diaschisis (CCD) or a functional disorder in the brain caused by CACNA1A mutations.

Motor cortex hyperexcitability to transcranial magnetic stimulation in Alzheimer’s disease

Objectives: Recent transcranial magnetic stimulation (TMS) studies demonstrate that motor cortex excitability is increased in Alzheimer’s disease (AD) and that intracortical inhibitory phenomena are impaired. The aim of the present...