Increase In Motor Cortex Excitability Research Articles

Time course of neuromuscular responses to acute hypoxia during voluntary contractions.

What is the central question of this study? How does acute hypoxia alter central and peripheral fatigue during brief and sustained maximal voluntary muscle contractions? What is the main finding and its importance? Perception of fatigue during muscle contractions was increased progressively for 2 h after hypoxic exposure. However, an increase in motor cortex excitability and a decrease in voluntary activation of skeletal muscle were observed across the entire protocol when performing brief (3 s) maximal contractions. These adaptations were abolished if the brief contraction was held for a duration of 20 s, which was presumably attributable to a successful redistribution of blood to overcome the reduced oxygen content. Few studies have examined the time course of changes in the motor system after acute exposure to hypoxia. Thus, the purpose of this study was to examine how acute hypoxia affects corticospinal excitability, voluntary activation (VA) and the perception of fatigue during brief (3s) and sustained (20s) maximal voluntary contractions (MVCs). Fourteen healthy individuals (23±2.2years of age; four female) were exposed to hypoxia and sham conditions. During hypoxia, peripheral blood oxygen saturation was titrated over a 15min period and remained at 80% during testing. Corticospinal excitability and VA were assessed before titration (Pre), 0, 1 and 2 h after. At each time point, the brief and sustained elbow flexion MVCs were performed. Motor evoked potentials (MEPs) were obtained using transcranial magnetic stimulation. Superimposed and resting twitches were obtained from motor point stimulation of biceps brachii to calculate the level of VA, and ratings of perceived fatigue were obtained with a modified CR-10 Borg scale. A condition-by-time interaction was detected for the CR-10 Borg scale, whereby perception of fatigue increased progressively throughout the hypoxia protocol. However, main effects of MEP area and VA indicated that corticospinal excitability increased, and VA of the biceps brachii decreased, throughout the hypoxia protocol. Given that these changes in MEP area and VA were seen only when performing the brief MVCs (and not during the sustained MVCs), performing longer contractions might overcome reduced oxygen content by redirecting blood flow to active areas of the motor system.

Increased Motor Cortex Excitability for Concealed Visual Information

Abstract. Deceptive behavior involves complex neural processes involving the primary motor cortex. The dynamics of this motor cortex excitability prior to lying are still not well understood. We sought to examine whether corticospinal excitability can be used to suggest the presence of deliberately concealed information in a modified version of the guilty knowledge test (GKT). Participants pressed keys to either truthfully or deceitfully indicate their familiarity with a series of faces. Motor-evoked potentials (MEPs) were recorded during response preparation to measure muscle-specific neural excitability. We hypothesized that MEPs would increase during the deceptive condition not only in the lie-telling finger but also in the suppressed truth-telling finger. We report a group-level increase in overall corticospinal excitability 300 ms following stimulus onset during the deceptive condition, without specific activation of the neural representation of the truth-telling finger. We discuss cognitive processes, particularly response conflict and/or automated responses to familiar stimuli, which may drive the observed nonspecific increase of motor excitability in deception.

The Effect of Unihemispheric Concurrent Dual-Site Transcranial Direct Current Stimulation of Primary Motor and Dorsolateral Prefrontal Cortices on Motor Function in Patients With Sub-Acute Stroke.

It is believed that unihemispheric concurrent dual-site transcranial direct current stimulation (tDCSUHCDS) of the primary motor cortex (M1) and the dorsolateral prefrontal cortex (DLPFC) causes an increase in motor cortex excitability. However, the clinical effect of this type of stimulation on patients with neurological conditions is not yet known. The aim of the present study was to assess the effect of anodal-tDCSUHCDS (a-tDCSUHCDS) on upper limb motor function in subacute stroke patients. Fifteen patients participated in this sham-controlled crossover study. The main outcome measures were the reaction time (RT) to visual stimuli, completion time of a nine-pin pegboard (9-PPB), and the scores from the Fugl–Meyer assessment (FMA) for the upper limb of the involved side before and after three brain stimulation conditions. For a-tDCSUHCDS, the anodal electrodes were placed on the M1 and the DLPFC, while for a-tDCS, the anodal electrode was placed on the M1. For the sham stimulation, the tDCS was turned off after 30 s. For brain stimulation, the selected current was 1 mA for 20 min. After a-tDCSUHCDS, there was a significant reduction in the RT and completion time of the 9-PPB compared with the times after a-tDCS and the sham stimulation: p = 0.013 and p = 0.022, respectively). However, there was no significant difference in the FMA scores after the three types of stimulations (p = 0.085). Compared with a-tDCS, a-tDCSUHCDS temporarily improved the RT and dexterity of the involved hand in subacute stroke patients.Clinical Trial Registration: Iranian Registry of Clinical Trials (IRCT), identifier IRCT2015012520787N1.

Modulation of motor cortical excitability with auditory stimulation.

Loud sounds have been demonstrated to increase motor cortex excitability when transcranial magnetic stimulation (TMS) is synchronized with auditory evoked N100 potential measured from electroencephalography (EEG). The N100 potential is generated by an afferent response to sound onset and feature analysis, and upon novel sound it is also related to the arousal reaction. The arousal reaction is known to originate from the ascending reticular activating system of the brain stem and to modulate neuronal activity throughout the central nervous system. In this study we investigated the difference in motor evoked potentials (MEPs) when deviant and novelty stimuli were randomly interspersed in a train of standard tones. Twelve healthy subjects participated in this study. Three types of sound stimuli were used: 1) standard stimuli (800 Hz), 2) deviant stimuli (560 Hz), and 3) novelty stimuli (12 different sounds). In each stimulus sequence 600 stimuli were given. Of these, 90 were deviant stimuli randomly placed between the standard stimuli. Each of 12 novel sounds was presented once in pseudorandomized order. TMS was randomly mixed with the sound stimuli so that it was either synchronized with the individual N100 or trailed the sound onset by 200 ms. All sounds elicited an increase in motor cortex excitability. The type of sound had no significant effect. We also demonstrated that TMS timed at 200-ms intervals caused a significant increment of MEPs. This contradicted our hypothesis that MEP amplitudes to TMS synchronized with N100 would be greater than those to TMS at 200 ms after a sound and remains unexplained. NEW & NOTEWORTHY We demonstrated modulation of motor cortical excitability with parallel auditory stimulus by combining navigated transcranial magnetic stimulation (TMS) with auditory stimuli. TMS was synchronized with auditory evoked potentials considered to be generated by the unconscious attention call process in the auditory system.

Motor facilitation during observation of implied motion: Evidence for a role of the left dorsolateral prefrontal cortex

The phenomenon of motor resonance (the increase in motor cortex excitability during observation of actions) has been previously described. Transcranial magnetic stimulation (TMS) studies have demonstrated a similar effect during perception of implied motion (IM). The left dorsolateral prefrontal cortex (DLPFC) seems to be activated during action observation. Furthermore, the role of this brain area in motor resonance to IM is yet to be investigated. Fourteen healthy volunteers were enrolled into the study. We used transcranial direct current stimulation (tDCS) to stimulate DLPFC aiming to investigate whether stimulation with different polarities would affect the amplitude of motor evoked potential collected during observation of images with and without IM. The results of our experiment indicated that Cathodal tDCS over the left DLPFC prevented motor resonance during observation of IM. On the contrary, anodal and sham tDCS did not significantly modulate motor resonance to IM. The current study expands the understanding of the neural circuits engaged during observation of IM. Our results are consistent with the hypothesis that action understanding requires the interaction of large networks and that the left DLPFC plays a crucial role in generating motor resonance to IM.

S15-4. How to use NIBS in rehabilitation

Non-invasive brain stimulation (NIBS) can induce neural plasticity and modify functional recovery among patients with central nervous system (CNS) lesion. The improvement of motor function is task specific. Task specific training is gold standard of rehabilitation training. NIBS is, therefore, often used as pre-conditioning tool for rehabilitation training. Functional motor recovery may based on the increased motor cortex excitability and unmasking of pre-existed pathways with disinhibition of inhibitory interneuron. Reduced interhemispheric inhibition from unaffected hemisphere to affected hemisphere may be one of the mechanism in some limited patients. We review the effect of NIBS in rehabilitation for patients with CNS lesion and show our experience of applying transcranial direct current stimulation (tDCS) combined with electrical stimulation and rTMS, in especially, quadri pulse stimulation. It was supposed that NIBS is effective tool for rehabilitation. It is important to apply NIBS with task specific-rehabilitation training to improve motor function.

Translating novel findings of perceptual-motor codes into the neuro-rehabilitation of movement disorders

The bidirectional flow of perceptual and motor information has recently proven useful as rehabilitative tool for re-building motor memories. We analyzed how the visual-motor approach has been successfully applied in neurorehabilitation, leading to surprisingly rapid and effective improvements in action execution. We proposed that the contribution of multiple sensory channels during treatment enables individuals to predict and optimize motor behavior, having a greater effect than visual input alone. We explored how the state-of-the-art neuroscience techniques show direct evidence that employment of visual-motor approach leads to increased motor cortex excitability and synaptic and cortical map plasticity. This super-additive response to multimodal stimulation may maximize neural plasticity, potentiating the effect of conventional treatment, and will be a valuable approach when it comes to advances in innovative methodologies.

Delineating the Role of Cerebral Blood Flow and Hypocapnia on Neuromuscular Function

Neuromuscular fatigue, defined as the inability of a muscle to maintain a given level of force regardless of whether or not a task can be sustained, has been attributed, in part, to central mechanisms. Although reductions in cerebral blood flow (CBF) may be implicated in the development of central fatigue, the contribution from hypocapnic-reductions (i.e., PETCO2) in CBF versus reductions in CBF per se has yet to be isolated. PURPOSE: To examine the hypothesis that hypocapnia, independent of concomitant reductions in CBF, cause impairments in neuromuscular function. METHODS: Neuromuscular function, as indicated by motor evoked potentials (MEP), M-waves and cortical voluntary activation (cVA) of the flexor carpal radialis muscle during isometric wrist flexion, was assessed in 8 males (31±12 y) during 3 separate conditions: 1) cyclooxygenase inhibition using Indomethacin (Indo) to selectively reduce CBF; 2) controlled hyperventilation-induced hypocapnia (Hypocapnia); and 3) isocapnic hyperventilation (Isocapnia). CBF was estimated using transcranial Doppler ultrasound velocity measurements of the middle cerebral artery. Change from baseline and comparison of the 3 conditions was assessed using two-way repeated measures ANOVA. Relationships between variables were assessed using Pearson‘s correlations. RESULTS: The experimental conditions successfully isolated CBF and PETCO2. MEP amplitude (% M-wave amplitude) increased in hypocapnia (14.6±9.5%, p < 0.01) in comparison to Indo (-2.0±2.8%) and Isocapnia (0.6±1.8%); however, no significant changes were observed in M wave (p = 0.666) or cVA (p = 0.117). Correlation analysis revealed that MEP amplitude was inversely associated with PETCO2 (r = -0.54, p < 0.01) and cVA was weakly associated with CBF (r = 0.30, p < 0.05). CONCLUSIONS: Increased motor cortex excitability appears to be exclusive to hypocapnia but not reductions in CBF per se. However, a weak relationship between reductions in CBF and cVA exists, such that further research is required to confirm this finding and explore the potential implications. Supported by NSERC Discovery 227912-2012.

Speech dynamics are coded in the left motor cortex in fluent speakers but not in adults who stutter.

The precise excitability regulation of neuronal circuits in the primary motor cortex is central to the successful and fluent production of speech. Our question was whether the involuntary execution of undesirable movements, e.g. stuttering, is linked to an insufficient excitability tuning of neural populations in the orofacial region of the primary motor cortex. We determined the speech-related time course of excitability modulation in the left and right primary motor tongue representation. Thirteen fluent speakers (four females, nine males; aged 23-44) and 13 adults who stutter (four females, nine males, aged 21-55) were asked to build verbs with the verbal prefix 'auf'. Single-pulse transcranial magnetic stimulation was applied over the primary motor cortex during the transition phase between a fixed labiodental articulatory configuration and immediately following articulatory configurations, at different latencies after transition onset. Bilateral electromyography was recorded from self-adhesive electrodes placed on the surface of the tongue. Off-line, we extracted the motor evoked potential amplitudes and normalized these amplitudes to the individual baseline excitability during the fixed configuration. Fluent speakers demonstrated a prominent left hemisphere increase of motor cortex excitability in the transition phase (P = 0.009). In contrast, the excitability of the right primary motor tongue representation was unchanged. Interestingly, adults afflicted with stuttering revealed a lack of left-hemisphere facilitation. Moreover, the magnitude of facilitation was negatively correlated with stuttering frequency. Although orofacial midline muscles are bilaterally innervated from corticobulbar projections of both hemispheres, our results indicate that speech motor plans are controlled primarily in the left primary speech motor cortex. This speech motor planning-related asymmetry towards the left orofacial motor cortex is missing in stuttering. Moreover, a negative correlation between the amount of facilitation and stuttering severity suggests that we discovered a main physiological principle of fluent speech production and its role in stuttering.

Enhanced motor cortex excitability after spinal cord injury.

Enhanced motor cortex excitability after spinal cord injury.

P 160. The “dormant potential” of the non-dominant hemisphere: In teremispheric a symmetry of cortial plasticity

Introduction Lateralization of manual dexterity is a striking example of interemispheric asymmetry in cortical organization. Transcranial magnetic stimulation (TMS) studies have documented handedness related functional asymmetries in corticomotor excitability. Particularly, TMS has been used to analyze movement related cortical plasticity. Motor evoked potentials (MEP) amplitude increases immediately after brief periods of exercise (post-exercise facilitation) and then increases again after a rest period of 15 min following a defined motor task (delayed facilitation). The post-exercise facilitation seems to be due to transient increase of motor cortex excitability. Objective The delayed facilitation seems to reflect an intra-cortical synaptic reorganization consequent to motor tasks. In the present study, we compared changes in cortical excitability from respectively dominant (DH) and non dominant hemisphere (NDH) in both right-handed and left-handed subjects in function of a bimanual non-fatiguing motor task. We evaluated handedness related asymmetries. Material and methods As primary screening, the 24 enrolled subjects were classified as right or left handed by according to their description of the hand used for writing. Then, each subject completed the Edinburgh Handedness Inventory and was reclassified as a function of the handedness score. For each subject, the experimental protocol was repeated twice so that the cortical excitability could be separately assessed in each hemisphere. By mean of TMS, MEP amplitude, motor threshold, and silent period were assessed. Then subjects performed a bimanual motor task (regular repetitive opening-closing bilateral movements of the index finger onto the thumb). MEPs of the first dorsal interosseus were recorded before exercise (baseline condition), immediately after each exercise periods of 30, 60, 90 s (exercise conditions), and after 15 min of rest (rest condition). MEP amplitude elicited in each exercise conditions, and then in rest condition was compared with baseline, to evaluate the presence of post-exercise facilitation and delayed facilitation. Hemispheric differences of MEP amplitude after the rest period were related to the handedness score. Results Mean threshold intensity of TMS was significantly lower for DH compared to NDH. MEP amplitude was significantly increased in exercise conditions, independently of the hemisphere stimulated. However, in rest condition, only the NDH presented increased MEP amplitude, showing delayed-facilitation. Handedness scores and MEP asymmetry in rest condition were positively correlated. Conclusion Delayed facilitation asymmetry was lateralized to NDH and varied as a linear function of handedness. These results suggest that cortical plasticity changes in the two hemispheres. Our data provide evidence that DH and NDH answer differently to motor requests and they differently recover after exercise. Bimanual motor task induces changes in cortical excitability differently in the two hemispheres, in favor of the non-dominant site. We speculate that NDH has a “dormant potential” that can be activated if necessary. The examination of the effects of a bimanual motor task on cortical excitability may be relevant to better understanding cortical plasticity processes and may provide new tools to study neurological disorders characterized by central fatigue and less capacity to recovery.

P 41. Motor evoked potentials as biomarker for sexual urge

Introduction Previous work documents that motor cortex excitability is modulated by emotional states-induced by music for example. Recently, motivation and reward anticipation-operationalized by the viewing of food or money stimuli and by the use of a slot machine respectively-increased motor evoked potentials (MEPs). Motivational besides emotional, cognitive, and physiological processing is one component of a four component model of sexual arousal. Activity in limbic (emotional) areas is considered to spill over to motor cortex via the basal ganglia (motivation) with top-down control of frontal (cognitive) areas. Objectives Here, we aim to investigate the influence of sexual urge on motor evoked potentials. Materials and methods 24 heterosexual healthy men viewed single stimuli of naked women or men genitals covered with black bars. Control stimuli were generated by Fourier transformation of these stimuli. Each stimulus category was shown 60 times without repetition of one stimulus. Subjects had to judge if they want to see the person naked. Subjects received a transcranial magnetic resonance pulse during the motor preparation phase. Ratings with respect to emotional palatableness, sexual arousal, and sexual motivation were done after the MEP paradigm on a five-point scale. Results Heterosexual men showed increased motor evoked potentials for viewing female in contrast to male sexual stimuli. There were no significant correlations of the ratings with motor evoked potentials. Conclusion Increased motor cortex excitability might be not only related to the attractiveness of the female pictures but also to the aversiveness of the male pictures. Data with respect to homosexual subjects might add further hints for motor cortex excitability as biomarker for sexual urge.

Cathodal Transcranial Direct Current Stimulation in Children With Dystonia

Increased motor cortex excitability is a common finding in dystonia, and transcranial direct current stimulation can reduce motor cortex excitability. In an earlier study, we found that cathodal direct-current stimulation decreased motor overflow for some children with dystonia. To investigate this observation further, we performed a sham-controlled, double-blind, crossover study of 14 children with dystonia. We found a significant reduction in overflow following real stimulation, when participants performed the experimental task with the hand contralateral to the cathode. While these results suggest that cathodal stimulation may help some children to reduce involuntary overflow, the size of the effect is small. Further research will need to investigate ways to increase the magnitude of the effect of cathodal transcranial direct current stimulation.

Increased motor cortex excitability during motor imagery in brain-computer interface trained subjects

Background: Motor imagery (MI) is the mental performance of movement without muscle activity. It is generally accepted that MI and motor performance have similar physiological mechanisms.Purpose: To investigate the activity and excitability of cortical motor areas during MI in subjects who were previously trained with an MI-based brain-computer interface (BCI).Subjects and Methods: Eleven healthy volunteers without neurological impairments (mean age, 36 years; range: 24–68 years) were either trained with an MI-based BCI (BCI-trained, n = 5) or received no BCI training (n = 6, controls). Subjects imagined grasping in a blocked paradigm task with alternating rest and task periods. For evaluating the activity and excitability of cortical motor areas we used functional MRI and navigated transcranial magnetic stimulation (nTMS).Results: fMRI revealed activation in Brodmann areas 3 and 6, the cerebellum, and the thalamus during MI in all subjects. The primary motor cortex was activated only in BCI-trained subjects. The associative zones of activation were larger in non-trained subjects. During MI, motor evoked potentials recorded from two of the three targeted muscles were significantly higher only in BCI-trained subjects. The motor threshold decreased (median = 17%) during MI, which was also observed only in BCI-trained subjects.Conclusion: Previous BCI training increased motor cortex excitability during MI. These data may help to improve BCI applications, including rehabilitation of patients with cerebral palsy.

Dissociation of motor task-induced cortical excitability and pain perception changes in healthy volunteers.

BackgroundThere is evidence that interventions aiming at modulation of the motor cortex activity lead to pain reduction. In order to understand further the role of the motor cortex on pain modulation, we aimed to compare the behavioral (pressure pain threshold) and neurophysiological effects (transcranial magnetic stimulation (TMS) induced cortical excitability) across three different motor tasks.Methodology/Principal FindingsFifteen healthy male subjects were enrolled in this randomized, controlled, blinded, cross-over designed study. Three different tasks were tested including motor learning with and without visual feedback, and simple hand movements. Cortical excitability was assessed using single and paired-pulse TMS measures such as resting motor threshold (RMT), motor-evoked potential (MEP), intracortical facilitation (ICF), short intracortical inhibition (SICI), and cortical silent period (CSP). All tasks showed significant reduction in pain perception represented by an increase in pressure pain threshold compared to the control condition (untrained hand). ANOVA indicated a difference among the three tasks regarding motor cortex excitability change. There was a significant increase in motor cortex excitability (as indexed by MEP increase and CSP shortening) for the simple hand movements.Conclusions/SignificanceAlthough different motor tasks involving motor learning with and without visual feedback and simple hand movements appear to change pain perception similarly, it is likely that the neural mechanisms might not be the same as evidenced by differential effects in motor cortex excitability induced by these tasks. In addition, TMS-indexed motor excitability measures are not likely good markers to index the effects of motor-based tasks on pain perception in healthy subjects as other neural networks besides primary motor cortex might be involved with pain modulation during motor training.

Tendon vibration does not alter decreased responsiveness of motoneurones in the absence of motor cortical input during fatigue

Tendon vibration does not alter decreased responsiveness of motoneurones in the absence of motor cortical input during fatigue

Inter-session repeatability of cortical excitability measurements in patients with epilepsy

Previous studies have evaluated the inter-session variability of motor thresholds (MT), short intracortical inhibition and intracortical facilitation using paired pulse transcranial magnetic stimulation (TMS) in normal individuals. Here we evaluate the reproducibility of a range of measures of cortical excitability in patients with epilepsy. Twenty-four drug naïve patients with newly diagnosed epilepsy (13 idiopathic generalised epilepsy [IGE], 11 focal epilepsy) and seventeen non-epilepsy controls were studied. Motor threshold (MT) at rest and recovery curves constructed using paired pulse stimulation at short (2-15 ms) and long (50-400 ms) interstimulus intervals (ISIs) were analysed on two separate occasions, 4-20 weeks apart. The Lin's concordance correlation coefficient test was used to measure agreement between the two sessions. Significant levels of agreement between the two sessions were observed at MT and all the ISIs measured. This was highest in non-epilepsy controls. Cortical excitability measures are repeatable over time in both patients with epilepsy and healthy controls. Increased motor cortex excitability is a stable feature in epilepsy without significant inter-session variability.

Effects of Different Vibration Exercises on Bench Press

This study was undertaken to analyze the effects of different vibration recovery strategies via feet or hands on the number of repetitions performed and on mean velocity, peak velocity and blood lactate concentration during consecutive bench-press sets. 9 elite judo athletes performed 3 sets of bench press at 60% of one-repetition maximum (1RM), leading to failure and allowing a 180 s rest period between sets. During the rest period, 1 of the 3 following procedures was performed: 150 s rest plus 30 s push-up vibration exercise (Push-up), 150 s rest plus 30 s squat vibration exercise (Squat) or 180 s only rest (Passive). Statistical analysis revealed that the Squat condition resulted in a significant increase in the number of repetitions achieved, in comparison with all other rest strategies. However, kinematic parameters and blood lactate concentration were not affected by vibration. These data suggest that a vibration stimulus applied to the feet, between sets, can result in positive improvements in upper body resistance exercise performance. Although the mechanisms are not fully understood, this positive effect of vibration could be due to an increased motor cortex excitability and voluntary drive.

The dynamic regulation of cortical excitability is altered in episodic ataxia type 2

Episodic ataxia type 2 and familial hemiplegic migraine are two rare hereditary disorders that are linked to dysfunctional ion channels and are characterized clinically by paroxysmal neurological symptoms. Impaired regulation of cerebral excitability is thought to play a role in the occurrence of these paroxysms, but the underlying mechanisms are poorly understood. Normal ion channels are crucial for coordinating neuronal firing in response to facilitatory input. Thus, we hypothesized that channel dysfunction in episodic ataxia type 2 and familial hemiplegic migraine may impair the ability to adjust cerebral excitability after facilitatory events. We tested this hypothesis in patients with episodic ataxia type 2 (n = 6), patients with familial hemiplegic migraine (n = 7) and healthy controls (n = 13). All subjects received a high-frequency burst (10 pulses at 20 Hz) of transcranial magnetic stimulation to transiently increase the excitability of the motor cortex. Acute burst-induced excitability changes were probed at 50, 250, 500 and 1000 ms after the end of the burst. This was done using single-pulse transcranial magnetic stimulation to assess corticospinal excitability, and paired-pulse transcranial magnetic stimulation at an interstimulus interval of 2 and 10 ms to assess intracortical inhibition and facilitation, respectively. The time course of burst-induced excitability changes differed between groups. Healthy controls showed a short-lived increase in excitability that was only present 50 ms after the burst. In contrast, patients with episodic ataxia type 2 showed an abnormally prolonged increase in corticospinal excitability that was still present 250 ms after the transcranial magnetic stimulation burst. Furthermore, while controls showed a decrease in intracortical facilitation during the 1 s period following the transcranial magnetic stimulation burst, patients with episodic ataxia type 2 had increased intracortical facilitation 1000 ms after the burst. Intracortical inhibition was unaltered between groups. Patients with familial hemiplegic migraine were not significantly different from either controls or patients with episodic ataxia type 2. Together, these findings indicate that patients with episodic ataxia type 2 have an excessive increase in motor cortex excitability following a strong facilitatory input. We argue that this deficient control of cortical excitability may set the stage for the emergence of paroxysmal neural dysfunction in this disorder.

The peri-ictal state: cortical excitability changes within 24 h of a seizure

In this study, transcranial magnetic stimulation was used to investigate motor cortical excitability changes in the peri-ictal period, in drug-naive new-onset epilepsy patients. Eighty-seven studies were performed on 58 patients (23 with idiopathic generalized epilepsy and 35 with focal epilepsy) within 72 h before or after a seizure. Fifty studies in 35 patients were within 24 h of a seizure. In all 58 patients, an interictal baseline study was performed, at least 14 days from a seizure. Motor threshold and paired pulse recovery curve results obtained at short (2-15 ms) and long (50-400 ms) interstimulus intervals in each hemisphere (at <24 h pre- or post-seizure and 24-72 h pre- and post-seizure) were compared against the interictal results and normal control values obtained from 32 subjects. The nature of the seizure (generalized, focal or focal with secondary generalization) was also recorded. Increased motor cortex excitability, measured by decreased motor threshold, increased intracortical facilitation and decreased intracortical inhibition at short and long interstimulus intervals was seen in the 24 h before a seizure. Conversely, decreased excitability occurred in the 24 h after a seizure. These effects were bilateral in tonic-clonic seizures in idiopathic generalized epilepsy and also in secondarily generalized seizures in patients with focal epilepsy. Similar changes were seen in the hemisphere ipsilateral to the seizure focus in focal seizures that did not secondarily generalize, accompanied by complex excitability changes in the contralateral hemisphere. These effects were not apparent in the 24-72 h window. These results show that there are major and prolonged changes in motor cortex excitability in the pre and the postictal 24 h. Increased excitation precedes the seizure by hours and there is a similar period of decreased excitability following a seizure.