Quadriceps cortical adaptations in individuals with an anterior cruciate ligament injury

BACKGROUND

Altered quadriceps corticomotor excitability has been demonstrated following anterior cruciate ligament (ACL) injury and reconstruction, however only the single joint vasti muscles have been assessed. There is no current data on rectus femoris corticomotor excitability following ACL injury, the biarticular quadriceps muscle also critical for force attenuation and locomotion. The purpose of this study was to examine rectus femoris corticomotor excitability, intracortical inhibition and cortical motor representation in individuals with and without an ACL injury.

METHODS

A cross-sectional design was used to evaluate corticomotor excitability bilaterally in individuals with a physician confirmed ACL injury (12 males, six females; mean±SD age: 29.6±8.4years; BMI: 24.8±2.3kg·m(2); 69.5±42.5days post-injury) compared to a healthy control group (12 males, six females; age: 29.2±6.8years; BMI: 24.6±2.3kg·m(2)). Single-pulse transcranial magnetic stimulation (TMS) was used to assess corticomotor excitability and cortical motor representation, and paired-pulse TMS used to assess intracortical inhibition for rectus femoris while participants maintained a knee extension force at 10% of body weight.

RESULTS

The cortical silent period (cSP) duration was longer in the injured limb of the ACL group compared to the uninjured limb (P=0.004). No significant differences were found for corticomotor excitability, intracortical inhibition or cortical motor representation center position and size (P>0.05).

CONCLUSIONS

There is preliminary evidence that the cSP is longer, but changes in rectus femoris corticomotor excitability and cortical motor representation are not present following ACL injury.

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

BACKGROUND

Antiepileptic 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.

HYPOTHESIS

The 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).

METHODS

Fifteen 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.

RESULTS

The 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).

CONCLUSION

A 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.

Intra-Subject Consistency and Reliability of Response Following 2 mA Transcranial Direct Current Stimulation

BACKGROUND

Transcranial direct current stimulation (tDCS) is a popular non-invasive brain stimulation technique that has been shown to influence cortical excitability. While polarity specific effects have often been reported, this is not always the case, and variability in both the magnitude and direction of the effects have been observed.

OBJECTIVE/HYPOTHESIS

We aimed to explore the consistency and reliability of the effects of tDCS by investigating changes in cortical excitability across multiple testing sessions in the same individuals. A within subjects design was used to investigate the effects of anodal and cathodal tDCS applied to the motor cortex. Four experimental sessions were tested for each polarity in addition to two sham sessions.

METHODS

Transcranial magnetic stimulation (TMS) was used to measure cortical excitability (TMS recruitment curves). Changes in excitability were measured by comparing baseline measures and those taken immediately following 20 minutes of 2 mA stimulation or sham stimulation.

RESULTS

Anodal tDCS significantly increased cortical excitability at a group level, whereas cathodal tDCS failed to have any significant effects. The sham condition also failed to show any significant changes. Analysis of intra-subject responses to anodal stimulation across four sessions suggest that the amount of change in excitability across sessions was only weakly associated, and was found to have poor reliability across sessions (ICC = 0.276). The effects of cathodal stimulation show even poorer reliability across sessions (ICC = 0.137). In contrast ICC analysis for the two sessions of sham stimulation reflect a moderate level of reliability (ICC = .424).

CONCLUSIONS

Our findings indicate that although 2 mA anodal tDCS is effective at increasing cortical excitability at group level, the effects are unreliable across repeated testing sessions within individual participants. Our results suggest that 2 mA cathodal tDCS does not significantly alter cortical excitability immediately following stimulation and that there is poor reliability of the effect within the same individual across different testing sessions.

A meta-analysis of the effects of aging on motor cortex neurophysiology assessed by transcranial magnetic stimulation

OBJECTIVE

Transcranial magnetic stimulation (TMS) is a non-invasive tool used for studying cortical excitability and plasticity in the human brain. This review aims to quantitatively synthesize the literature on age-related differences in cortical excitability and plasticity, examined by TMS.

METHODS

A literature search was conducted using MEDLINE, Embase, and PsycINFO from 1980 to December 2015. We extracted studies with healthy old (50-89years) versus young (16-49years) individuals that utilized the following TMS measures: resting motor threshold (RMT), short-interval cortical inhibition (SICI), short-latency afferent inhibition (SAI), cortical silent period (CSP), intracortical facilitation (ICF), and paired associative stimulation (PAS).

RESULTS

We found a significant increase in RMT (g=0.414, 95% confidence interval (CI) [0.284, 0.544], p<0.001), a significant decrease in SAI (g=0.778, 95% CI [0.478, 1.078], p<0.001), and a trending decrease in LTP-like plasticity (g=-0.528, 95% CI [-1.157, 0.100] p<0.1) with age.

CONCLUSIONS

Our findings suggest an age-dependent reduction in cortical excitability and sensorimotor integration within the human motor cortex.

SIGNIFICANCE

Alterations in the ability to regulate cortical excitability, sensorimotor integration and plasticity may underlie several age-related motor deficits.

Motor cortical excitability in obsessive-compulsive disorder: Transcranial magnetic stimulation study

OBJECTIVES

Transcranial magnetic stimulation is a non-invasive method of stimulating the brain that is increasingly being used in neuropsychiatric research. Previous work has suggested that the pathophysiology of obsessive-compulsive disorder (OCD) may involve dysfunction of excitatory and/or inhibitory brain function. This study aimed to extend those findings.

METHODS

The study included 45 OCD patients and 15 age- and sex-matched healthy volunteers. Clinical evaluation was conducted using the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), Hamilton Anxiety Rating Scale (HAM-A), and Clinical Global Impression rating scale (CGI). Physiological measures were resting and active motor thresholds (RMT and AMT), motor evoked potential (MEP) amplitude, cortical silent period (CSP) and transcallosal inhibition (TCI) durations, short-interval intracortical inhibition (SICI), and intracortical facilitation.

RESULTS

RMT and AMT were significantly lower in patients than in the control group. The mean duration of the CSP and TCI were also significantly shorter. Obsessive trait was associated with significant reduction of TCI duration compared to compulsive trait. There was significant reduction in SICI in OCD patients compared to controls. There were no significant correlations between the Y-BOCS, HAM-A and CGI scores and the cortical excitability parameters.

CONCLUSION

These results provide further evidence for inhibitory deficits or increased facilitation in cortical circuits of patients with OCD.

A GABBR2 gene variant modifies pathophysiology in Huntington's disease

Striatal degeneration in Huntington's disease (HD) causes changes in cortico-subcortical pathways. Transcranial magnetic stimulation (TMS) is a valuable tool for assessing pathophysiology within these pathways, yet has had limited application in HD. As cortico-subcortical pathways are largely mediated by GABA and dopamine receptor genes, understanding how these genes modulate neurophysiology in HD may provide new insights into how underlying pathology maps onto clinical phenotype. Twenty-nine participants with HD underwent motor cortex stimulation, while corticospinal excitability, cortical inhibition and intracortical facilitation were indexed via peripheral electromyography. Single-nucleotide polymorphism mapping was performed across six genes that are known to modulate cortico-subcortical pathways (GABRA2, GABBR1, GABBR2, DRD1, DRD2, DRD4). Genetic associations with six TMS measures and age at onset were investigated. Our hierarchical multiple regression analysis, controlling for CAG and age, revealed that a GABBR2 variant, predicted to be disease-causative, was significantly associated with corticospinal excitability at corrected levels. A subsequent uncorrected exploratory analysis revealed associations between GABBR2, GABRA2 and DRD2 variants with TMS measures of corticospinal excitability and cortical inhibition in HD, as well as with age at onset. Our findings support the notion that uncovering genetic associations with pathophysiological measures and age at onset is an important way forward in terms of generating meaningful biomarkers with diagnostic and prognostic sensitivity, and identifying novel human-validated targets for future clinical trials.

Single and paired-pulse electrical stimulation during invasive EEG recordings

Invasive EEG recordings are frequently required during the presurgical exploration of patients with drug-resistant focal epilepsy in order to clarify the epileptic zone location. Intracranial direct electrical stimulations (DES) induce EEG and/or clinical responses that participate in this evaluation. Clinical DES protocols (1Hz and/or 50Hz) trigger massive cortical activation that can elicit seizures, after-discharges or complex clinical signs. In contrast, low-energy (<1Hz) protocols activate more localized cortical regions using single-pulse electrical stimulations (SPES). SPES can elicit two main types of responses. Cortico-cortical evoked potentials (CCEPs) correspond to highly consistent early responses, appearing before 100ms after stimulation, with fixed latency; they are considered physiological and assess the effective connectivity between the recorded regions. Late responses appear after 100ms; they are rare, inconsistent with variable latency and are suggestive of an underlying epileptogenic cortex. Paired-pulse stimulation paradigm associates a conditioning and a test stimulation to induce intracortical inhibition or facilitation by modifying the response amplitude. Largely used in transcranial magnetic stimulation, it has rarely been applied to CCEP although the mechanisms put in place seem highly similar. Low frequency intracerebral stimulations allow analysing brain connectivity and cortical excitability with a high temporal and spatial resolution. The development of new stimulation protocols and the combination with imaging or statistical techniques recently offered promising results.

Neurophysiological measurements of affected and unaffected motor cortex from a cross-sectional, multi-center individual stroke patient data analysis study

OBJECTIVES

Transcranial magnetic stimulation (TMS) has been used to measure cortical excitability as a functional measurement of corticomotor pathways. Given its potential application as an assessment tool in stroke, we aimed to analyze the correlation of TMS parameters with clinical features in stroke using data from 10 different centers.

METHODS

Data of 341 patients with a clinical diagnosis of stroke were collected from studies assessing cortical excitability using TMS. We used a multivariate regression model in which the baseline cortical excitability parameter "resting Motor Threshold (rMT)" was the main outcome and the demographic, anatomic and clinical characteristics were included as independent variables.

RESULTS

The variable "severity of motor deficit" consistently remained significant in predicting rMT in the affected hemisphere, with a positive β coefficient, in the multivariate models after sensitive analyses and adjusting for important confounders such as site center. Additionally, we found that the correlations between "age" or "time since stroke" and the rMT in the affected hemisphere were significant, as well as the interaction between "time since stroke" and "severity of motor deficit".

CONCLUSIONS

We have shown that severity of motor deficit is an important predictor for rMT in the affected hemisphere. Additionally, time since stroke seems to be an effect modifier for the correlation between motor deficit and rMT. In the unaffected motor cortex, these correlations were not significant. We discuss these findings in the context of stroke rehabilitation.

Cholinergic circuitry functioning in patients with vascular cognitive impairment--no dementia

BACKGROUND

An impairment of central cholinergic activity, as evaluated non-invasively by the short-latency afferent inhibition (SAI) of motor responses evoked by transcranial magnetic stimulation (TMS), was observed in patients with Alzheimer's disease (AD) and amnestic Mild Cognitive Impairment. Conversely, the involvement of central cholinergic neurotransmission in vascular dementia (VaD) is still under debate and data on Vascular Cognitive Impairment--No Dementia (VCI-ND) at risk for future VaD are lacking.

OBJECTIVE

To test for the first time SAI in patients with VCI-ND.

METHODS

Single-pulse TMS measures of cortical excitability and SAI were evaluated in 25 VCI-ND patients with subcortical ischemic lesions and 20 age-matched healthy controls. Functional status, neuropsychological tests evaluating frontal lobe abilities, and white matter lesions (WMLs) load were assessed.

RESULTS

A significant difference was found between patients and controls for the mean SAI, although this result did not resist after the Bonferroni correction. In the whole group of patients and controls, SAI showed a correlation with worse scores at the Montreal Cognitive Assessment (r = 0.376, p < 0.01). SAI also positively correlated with the total vascular burden (r = 0.345, p < 0.05) but not with the WML severity.

CONCLUSIONS

Central cholinergic pathway does not seem to be involved in VCI-ND, and the current results differ from those reported in primary cholinergic forms of dementia, such as AD. SAI might represent a valuable additional tool in the differential diagnosis of the dementing processes and in identifying potential responders to cholinergic agents.

Use of theta-burst stimulation in changing excitability of motor cortex: A systematic review and meta-analysis

Noninvasive brain stimulation has been demonstrated to modulate cortical activity in humans. In particular, theta burst stimulation (TBS) has gained notable attention due to its ability to induce lasting physiological changes after short stimulation durations. The present study aimed to provide a comprehensive meta-analytic review of the efficacy of two TBS paradigms; intermittent (iTBS) and continuous (cTBS), on corticospinal excitability in healthy individuals. Literature searches yielded a total of 87 studies adhering to the inclusion criteria. iTBS yielded moderately large MEP increases lasting up to 30 min with a pooled SMD of 0.71 (p<0.00001). cTBS produced a reduction in MEP amplitudes lasting up to 60 min, with the largest effect size seen at 5 min post stimulation (SMD=-0.9, P<0.00001). The collected studies were of heterogeneous nature, and a series of tests conducted indicated a degree of publication bias. No significant change in SICI and ICF was observed, with exception to decrease in SICI with cTBS at the early time point (SMD=0.42, P=0.00036). The results also highlight several factors contributing to TBS efficacy, including the number of pulses, frequency of stimulation and BDNF polymorphisms. Further research investigating optimal TBS stimulation parameters, particularly for iTBS, is needed in order for these paradigms to be successfully translated into clinical settings.

Whole body heat stress increases motor cortical excitability and skill acquisition in humans

OBJECTIVE

Vigorous systemic exercise stimulates a cascade of molecular and cellular processes that enhance central nervous system (CNS) plasticity and performance. The influence of heat stress on CNS performance and learning is novel. We designed two experiments to determine whether passive heat stress (1) facilitated motor cortex excitability and (2) improved motor task acquisition compared to no heat stress.

METHODS

Motor evoked potentials (MEPs) from the first dorsal interosseus (FDI) were collected before and after 30 min of heat stress at 73 °C. A second cohort of subjects performed a motor learning task using the FDI either following heat or the no heat condition.

RESULTS

Heat stress increased heart rate to 65% of age-predicted maximum. After heat, mean resting MEP amplitude increased 48% (p<0.05). MEP stimulus-response amplitudes did not differ according to stimulus intensity. In the second experiment, heat stress caused a significant decrease in absolute and variable error (p<0.05) during a novel movement task using the FDI.

CONCLUSIONS

Passive environmental heat stress (1) increases motor cortical excitability, and (2) enhances performance in a motor skill acquisition task.

SIGNIFICANCE

Controlled heat stress may prime the CNS to enhance motor skill acquisition during rehabilitation.

Visual evoked potentials in subgroups of migraine with aura patients

Background

Patients suffering from migraine with aura can have either pure visual auras or complex auras with sensory disturbances and dysphasia, or both. Few studies have searched for possible pathophysiological differences between these two subgroups of patients.

Methods

Methods - Forty-seven migraine with aura patients were subdivided in a subgroup with exclusively visual auras (MA, N = 27) and another with complex neurological auras (MA+, N = 20). We recorded pattern-reversal visual evoked potentials (VEP: 15 min of arc cheques, 3.1 reversal per second, 600 sweeps) and measured amplitude and habituation (slope of the linear regression line of amplitude changes from the 1st to 6th block of 100 sweeps) for the N1-P1 and P1-N2 components in patients and, for comparison, in 30 healthy volunteers (HV) of similar age and gender distribution.

Results

VEP N1-P1 habituation, i.e. amplitude decrement between 1st and 6th block, which was obvious in most HV (mean slope −0.50), was deficient in both MA (slope +0.01, p = 0.0001) and MA+ (−0.0049, p = 0.001) patients. However, VEP N1-P1 amplitudes across blocks were normal in MA patients, while they were significantly greater in MA+ patients than in HVs.

Conclusions

Our findings suggest that in migraine with aura patients different aura phenotypes may be underpinned by different pathophysiological mechanisms. Pre-activation cortical excitability could be higher in patients with complex neurological auras than in those having pure visual auras or in healthy volunteers.

Cholinergic circuitry functioning in patients with vascular cognitive impairment--no dementia

BACKGROUND

An impairment of central cholinergic activity, as evaluated non-invasively by the short-latency afferent inhibition (SAI) of motor responses evoked by transcranial magnetic stimulation (TMS), was observed in patients with Alzheimer's disease (AD) and amnestic Mild Cognitive Impairment. Conversely, the involvement of central cholinergic neurotransmission in vascular dementia (VaD) is still under debate and data on Vascular Cognitive Impairment--No Dementia (VCI-ND) at risk for future VaD are lacking.

OBJECTIVE

To test for the first time SAI in patients with VCI-ND.

METHODS

Single-pulse TMS measures of cortical excitability and SAI were evaluated in 25 VCI-ND patients with subcortical ischemic lesions and 20 age-matched healthy controls. Functional status, neuropsychological tests evaluating frontal lobe abilities, and white matter lesions (WMLs) load were assessed.

RESULTS

A significant difference was found between patients and controls for the mean SAI, although this result did not resist after the Bonferroni correction. In the whole group of patients and controls, SAI showed a correlation with worse scores at the Montreal Cognitive Assessment (r = 0.376, p < 0.01). SAI also positively correlated with the total vascular burden (r = 0.345, p < 0.05) but not with the WML severity.

CONCLUSIONS

Central cholinergic pathway does not seem to be involved in VCI-ND, and the current results differ from those reported in primary cholinergic forms of dementia, such as AD. SAI might represent a valuable additional tool in the differential diagnosis of the dementing processes and in identifying potential responders to cholinergic agents.

The Effect of Transcranial Direct Current Stimulation (tDCS) Electrode Size and Current Intensity on Motor Cortical Excitability: Evidence From Single and Repeated Sessions

BACKGROUND

Current density is considered an important factor in determining the outcomes of tDCS, and is determined by the current intensity and electrode size. Previous studies examining the effect of these parameters on motor cortical excitability with small sample sizes reported mixed results.

OBJECTIVE/HYPOTHESIS

This study examined the effect of current intensity (1 mA, 2 mA) and electrode size (16 cm(2), 35 cm(2)) on motor cortical excitability over single and repeated tDCS sessions.

METHODS

Data from seven studies in 89 healthy participants were pooled for analysis. Single-session data were analyzed using mixed effects models and repeated-session data were analyzed using mixed design analyses of variance. Computational modeling was used to examine the electric field generated.

RESULTS

The magnitude of increases in excitability after anodal tDCS was modest. For single-session tDCS, the 35 cm(2) electrodes produced greater increases in cortical excitability compared to the 16 cm(2) electrodes. There were no differences in the magnitude of cortical excitation produced by 1 mA and 2 mA tDCS. The repeated-sessions data also showed that there were greater increases in excitability with the 35 cm(2) electrodes. Further, repeated sessions of tDCS with the 35 cm(2) electrodes resulted in a cumulative increase in cortical excitability. Computational modeling predicted higher electric field at the motor hotspot for the 35 cm(2) electrodes.

CONCLUSIONS

2 mA tDCS does not necessarily produce larger effects than 1 mA tDCS in healthy participants. Careful consideration should be given to the exact positioning, size and orientation of tDCS electrodes relative to cortical regions.

Resting-state fMRI reveals enhanced functional connectivity in spatial navigation networks after transcranial direct current stimulation

A number of studies have established that transcranial direct current stimulation (tDCS) modulates cortical excitability. We previously demonstrated polarity dependent changes in parietal lobe blood oxygen level dependent (BOLD) fMRI in a group of young adults during a spatial navigation task [15]. Here we used resting state functional connectivity (rsFC) to examine whether analogous changes were also evident during the resting state. Participants were randomized to either a parietal-anodal, frontal-cathodal (P+F-) or the opposite montage (P-F+) and received 20min of tDCS (2mA) before undergoing resting-state fMRI. rsFC was evaluated between the groups by placing a seed in the medial superior parietal lobule (mSPL), which was under the target electrode. rsFC between the mSPL and a number of other areas involved in spatial navigation, scene processing, and sensorimotor processing was significantly higher in the P+F- than the P-F+ group. Thus, the modulatory effects of tDCS were evident during rest and suggest that stimulation primes not just the underlying neocortex but an extended network that can be recruited as necessary during active task performance.

Efficacy and Time Course of Theta Burst Stimulation in Healthy Humans

BACKGROUND

In the past decade research has shown that continuous (cTBS) and intermittent theta burst stimulation (iTBS) alter neuronal excitability levels in the primary motor cortex.

OBJECTIVE

Quantitatively review the magnitude and time course on cortical excitability of cTBS and iTBS.

METHODS

Sixty-four TBS studies published between January 2005 and October 2014 were retrieved from the scientific search engine PubMED and included for analyses. The main inclusion criteria involved stimulation of the primary motor cortex in healthy volunteers with no motor practice prior to intervention and motor evoked potentials as primary outcome measure.

RESULTS

ITBS applied for 190 s significantly increases cortical excitability up to 60 min with a mean maximum potentiation of 35.54 ± 3.32%. CTBS applied for 40 s decreases cortical excitability up to 50 min with a mean maximum depression of -22.81 ± 2.86%, while cTBS applied for 20 s decreases cortical excitability (mean maximum -27.84 ± 4.15%) for 20 min.

CONCLUSION

The present findings offer normative insights into the magnitude and time course of TBS-induced changes in cortical excitability levels.

Distinctive patterns of cortical excitability to transcranial magnetic stimulation in obstructive sleep apnea syndrome, restless legs syndrome, insomnia, and sleep deprivation

Altered responses to transcranial magnetic stimulation (TMS) in obstructive sleep apnea syndrome (OSAS), restless legs syndrome (RLS), insomnia, and sleep-deprived healthy subjects have been reported. We have reviewed the relevant literature in order to identify eventual distinctive electrocortical profiles based on single and paired-pulse TMS, sensorimotor modulation, plasticity-related and repetitive TMS measures. Although obtained from heterogeneous studies, the detected changes might be the result of the different pathophysiological substrates underlying OSAS, RLS, insomnia and sleep deprivation rather than reflect the general effect of non-specific sleep loss and instability. OSAS tends to exhibit an increased motor cortex inhibition, which is reduced in RLS; intracortical excitability seems to be in favor of an "activating" profile in chronic insomnia and in sleep-deprived healthy individuals. Abnormal plasticity-related TMS phenomena have been demonstrated in OSAS and RLS. This review provides a perspective of TMS techniques by further understanding the role of neurotransmission pathways and plastic remodeling of neuronal networks involved in common sleep disorders. TMS might be considered a valuable tool in the assessment of sleep disorders, the evaluation of the effect of therapy and the design of non-pharmacological approaches.

Investigations of motor-cortex cortical plasticity following facilitatory and inhibitory transcranial theta-burst stimulation in schizophrenia: a proof-of-concept study

Impaired neural plasticity has been proposed as an important pathophysiological feature underlying the neurobiology and symptomatology of schizophrenia. In this proof-of-concept study, we aimed to explore cortical plasticity in schizophrenia patients with two different transcranial theta-burst (TBS) paradigms. TBS induces Ca(2+)-dependent long-term-potentiation (LTP)-like and long-term-depression (LTP)-like plasticity in the human motor cortex. A total of 10 schizophrenia patients and 10 healthy controls were included in this study. Cortical excitability was investigated using transcranial magnetic stimulation in each study participant before and after TBS applied to the left primary motor-cortex on two different days. cTBS600 was used to induce LTD-like and cTBS300 was used to induce LTP-like plasticity in the absence of any prior motor-cortex activation. Repeated measures ANOVAs showed a significant interaction between the timecourse, the study group and the stimulation paradigm (cTBS600 vs. cTBS300) for the left, but not for the right hemisphere. Healthy controls showed an MEP amplitude decrease at a trend level following cTBS600 and a numeric, but not significant, increase in MEP amplitudes following cTBS300. Schizophrenia patients did not show an MEP amplitude decrease following cTBS600, but surprisingly a significant MEP decrease following cTBS300. The proportion of subjects showing the expected changes in motor-cortex excitability following both cTBS paradigms was higher in healthy controls. These preliminary results indicate differences in cortical plasticity following two different cTBS protocols in schizophrenia patients compared to healthy controls. However, the incomplete plasticity response in the healthy controls and the proof-of-concept nature of this study need to be considered as important limitations.

Evidence for an excitatory GABAA response in human motor cortex in idiopathic generalised epilepsy

PURPOSE

Impaired GABAergic inhibition has been implicated in the pathophysiology of epilepsy. The possibility of a paradoxical excitatory effect of GABA in epilepsy has been suggested, but has not been investigated in vivo. We investigated pre- and post-synaptic GABAergic mechanisms in patients with idiopathic generalised epilepsy (IGE).

METHOD

In 10 patients and 12 control subjects we explored short- and long-interval intracortical inhibition (SICI, LICI; post-synaptic GABAA and GABAB-mediated respectively) and long-interval intracortical facilitation (LICF; pre-synaptic disinhibition) using transcranial magnetic stimulation.

RESULTS

While post-synaptic GABAB-mediated inhibition was unchanged in IGE (p=0.09), LICF was reduced compared to controls (controls: 141±17% of baseline; untreated patients: 107±12%, p=0.2; treated patients: 79±10%, p=0.003). GABAA-mediated inhibition was reduced in untreated patients (response amplitude 56±4% of baseline vs. 26±6% in controls, p=0.004) and normalised with treatment (37±12%, p=0.5 vs. controls). When measured during LICI, GABAA-mediated inhibition became excitatory in untreated IGE (response amplitude 120±10% of baseline, p=0.017), but not in treated patients.

CONCLUSION

Pre- and post-synaptic GABA-mediated inhibitory mechanisms are altered in IGE. The findings lend in vivo support to evidence from experimental models and in vitro studies of human epileptic brain tissue that GABA may have a paradoxical excitatory role in ictogenesis.

Direct comparison of cortical excitability to transcranial magnetic stimulation in obstructive sleep apnea syndrome and restless legs syndrome

OBJECTIVE

Changes to transcranial magnetic stimulation (TMS) have been reported in obstructive sleep apnea syndrome (OSAS) and restless legs syndrome (RLS), although no direct comparison study is available. The aim of this new investigation is to assess and compare cortical excitability of OSAS and RLS patients using the same methodology and under the same experimental conditions.

METHODS

Fourteen patients with OSAS and 12 with RLS were compared to 14 age-matched controls. All patients were untreated and had a severe degree of disease. Resting motor threshold (rMT), cortical silent period (CSP) and motor evoked potentials MEPs, as well as intracortical inhibition (ICI) and facilitation at interstimulus interval (ISI) of 3 and 10 ms, respectively, were explored from the right first dorsal interosseous muscle, during wakefulness.

RESULTS

rMT was higher in OSAS than in RLS and controls. CSP was shorter in RLS only when compared to apneic patients, whereas it was similar between OSAS and controls. OSAS subjects exhibited slightly prolonged central motor conductivity, whereas MEP amplitude was smaller in both patient groups. The ICI ratio at ISI of 3 ms was decreased in RLS patients only.

CONCLUSIONS

Distinct changes of responses at TMS were found, probably connected with the different neurophysiological substrates underlying OSAS and RLS and could not be interpreted as a mere reflection of the effects of sleep architecture alteration. TMS can be considered an additional tool for the understanding of clinical and pathophysiological aspects of sleep disorders, and possibly for the evaluation of the effect of therapy.

Repetitive transcranial magnetic stimulation in patients with drug-resistant major depression: A six-month clinical follow-up study

OBJECTIVE

In this study we aimed to assess the long-term efficacy of repetitive Transcranial Magnetic Stimulation (rTMS) on depressive symptoms and cognitive performance in patients with drug-resistant major depressive disorder (MDD).

METHODS

Fifteen drug-resistant depressed outpatients completed an acute trial with augmentative high-frequency rTMS over the left dorsolateral prefrontal cortex (DLPFC) and were compared with 15 drug-resistant MDD patients who underwent sham procedure. Depressive symptoms were evaluated with the Hamilton Depression Rating Scale and Montgomery-Asberg Depression Rating Scale. The Frontal Assessment Battery and the Stroop Color-Word Test Interference (Stroop T) were used to probe executive functions. Outcome measures were obtained at baseline, 4 weeks after the rTMS, as well as 3 months and 6 months after the end of the stimulation protocol.

RESULTS

After the active rTMS, patients showed a significant decrease in the scores at the depression rating scales that lasted for 6 months. A transient improvement was also observed at the Stroop T, although it did not persist in time.

CONCLUSIONS

High-frequency rTMS over the left DLPFC may have long-term antidepressant effect in drug-resistant MDD. TMS is a valuable tool for the add-on treatment of mood disorders and for the design of customized stimulation protocols.

Direct comparison of cortical excitability to transcranial magnetic stimulation in obstructive sleep apnea syndrome and restless legs syndrome

OBJECTIVE

Changes to transcranial magnetic stimulation (TMS) have been reported in obstructive sleep apnea syndrome (OSAS) and restless legs syndrome (RLS), although no direct comparison study is available. The aim of this new investigation is to assess and compare cortical excitability of OSAS and RLS patients using the same methodology and under the same experimental conditions.

METHODS

Fourteen patients with OSAS and 12 with RLS were compared to 14 age-matched controls. All patients were untreated and had a severe degree of disease. Resting motor threshold (rMT), cortical silent period (CSP) and motor evoked potentials MEPs, as well as intracortical inhibition (ICI) and facilitation at interstimulus interval (ISI) of 3 and 10 ms, respectively, were explored from the right first dorsal interosseous muscle, during wakefulness.

RESULTS

rMT was higher in OSAS than in RLS and controls. CSP was shorter in RLS only when compared to apneic patients, whereas it was similar between OSAS and controls. OSAS subjects exhibited slightly prolonged central motor conductivity, whereas MEP amplitude was smaller in both patient groups. The ICI ratio at ISI of 3 ms was decreased in RLS patients only.

CONCLUSIONS

Distinct changes of responses at TMS were found, probably connected with the different neurophysiological substrates underlying OSAS and RLS and could not be interpreted as a mere reflection of the effects of sleep architecture alteration. TMS can be considered an additional tool for the understanding of clinical and pathophysiological aspects of sleep disorders, and possibly for the evaluation of the effect of therapy.

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 _{PRECISIONGRIP} 35.2 ± 5.6%; MEP amplitude _POWERGRIP 19.6 ± 3.4%, F = 2.4, P < 0.001) and stimulus‐response gradient (SLOPE_REST 0.06 ± 0.01; SLOPE_PRCISIONGRIP 0.15 ± 0.04; SLOPE _POWERGRIP 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 _{PRECISIONGRIP} 9.7 ± 1.5%, SICI _POWERGRIP 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.

This manuscript establishes that specific cortical mechanisms underlie the maintenance of the precision grip. The mechanisms appear distinct to the processes maintaining the power grip.

Stimulation intensities of transcranial direct current stimulation have to be adjusted in children and adolescents

OBJECTIVE

The aim of the present study was to investigate the effect of the transcranial direct current stimulation (tDCS) on motor cortex excitability in healthy children and adolescents.

METHODS

We applied 1mA anodal or cathodal tDCS for 10min on the left primary motor cortex of 19 healthy children and adolescents (mean age 13.9±0.4years). In order to prove whether the effects of tDCS may be attributed to the stimulation intensity, 10 children and adolescents were studied again using 0.5mA anodal and cathodal tDCS. Sham stimulation was used as a control.

RESULTS

Compared with sham stimulation, both 1mA anodal and cathodal tDCS resulted in a significant increase of Motor evoked potentials (MEP) amplitudes which remained to be prominent even one hour after the end of stimulation. Interestingly, the 0.5mA cathodal tDCS decreased cortico-spinal excitability whereas the 0.5mA anodal stimulation did not result in any effect.

CONCLUSION

For the first time, the study demonstrates age-specific influences of tDCS on cortical excitability of the primary motor cortex.

SIGNIFICANCE

Thus, the stimulation protocols of the tDCS have to be optimized according to age by planning studies in pediatric population.

Poor Tolerance of Motor Cortex rTMS in Chronic Migraine

BACKGROUND

Two small studies had evaluated the efficacy of rTMS in migraine. One tested high frequency rTMS over the dorsolateral prefrontal cortex while the other evaluated 1 Hz rTMS over the vertex.

AIM

To test the feasibility of 10 Hz rTMS of motor cortex as an adjunctive therapy in patients with chronic migraine Materials and Methods: We randomized (2:1 ratio) chronic migraine patients on medical preventive treatment to receive either rTMS or sham therapy for 10 sessions. rTMS (80% resting motor threshold, 10Hz, 20 trains, 5 secs/train, inter-train interval 1 min, total 1000 stimuli/session) was applied over the right motor cortex.

RESULT

Nine patients were randomized. Six received rTMS and three had sham therapy. Three patients in the rTMS arm withdrew from the study due to increased headache frequency and discomfort from the treatment. The remaining six cases (3 rTMS, 3 sham) completed the study. The study was prematurely stopped due to the significant worsening of headache from rTMS. No significant differences in outcome measures were found between real and sham rTMS.

CONCLUSION

Although the study was terminated prematurely, the high dropout rate (50%) due to worsening headaches suggested that rTMS over the motor cortex is poorly tolerated in chronic migraine.