Transcranial magnetic stimulation and epilepsy

Slow Repetitive TMS for Drug-resistant Epilepsy: Clinical and EEG Findings of a Placebo-controlled Trial

PURPOSE

To assess the effectiveness of slow repetitive transcranial magnetic stimulation (rTMS) as an adjunctive treatment for drug-resistant epilepsy.

METHODS

Forty-three patients with drug-resistant epilepsy from eight Italian Centers underwent a randomized, double-blind, sham-controlled, crossover study on the clinical and EEG effects of slow rTMS. The stimulus frequency was 0.3 Hz. One thousand stimuli per day were given at the resting motor threshold intensity for 5 consecutive days, with a round coil at the vertex.

RESULTS

"Active" rTMS was no better than placebo for seizure reduction. However, it decreased interictal EEG epileptiform abnormalities significantly (p < 0.05) in one-third of the patients, which supports a detectable biologic effect. No correlation linked the rTMS effects on seizure frequency to syndrome or anatomic classification, seizure type, EEG changes, or resting motor threshold (an index of motor cortex excitability).

CONCLUSIONS

Although the antiepileptic action was not significant (p > 0.05), the individual EEG reactivity to "active" rTMS may be encouraging for the development of more-powerful, noninvasive neuromodulatory strategies.

rTMS Reveals Premotor Cortex Dysfunction in Frontal Lobe Epilepsy

PURPOSE

Studies of motor cortex excitability provided evidence that focal epilepsies may alter the excitability of cortical areas distant from the epileptogenic zone. In order to explore this hypothesis we studied the functional connectivity between premotor and motor cortex in seven patients with frontal lobe epilepsy and seizure onset zone outside the premotor or motor cortex.

METHODS

Low-frequency subthreshold repetitive transcranial magnetic stimulation was applied to the premotor cortex and its impact on motor cortex excitability was measured by the amplitude of motor-evoked potentials in response to direct suprathreshold stimulation of the motor cortex.

RESULTS

Stimulation of the premotor cortex of the non-epileptogenic hemisphere resulted in a progressive and significant inhibition of the motor cortex as evidenced by a reduction of motor evoked potential amplitude. On the other hand, stimulation of the premotor cortex of the epileptogenic hemisphere failed to inhibit the motor cortex. The reduced inhibition of the motor cortex by remote areas was additionally supported by the significantly shorter cortical silent periods obtained after stimulation of the motor cortex of the epileptogenic hemisphere.

CONCLUSION

These results show that the functional connectivity between premotor and motor cortex or motor cortex interneuronal excitability is impaired in the epileptogenic hemisphere in frontal lobe epilepsy while it is normal in the nonepileptogenic hemisphere.

Effects of repetitive transcranial magnetic stimulation on spike-and-wave discharges

Aim of this study was to evaluate the effect of 5Hz-suprathreshold repetitive transcranial magnetic stimulation (rTMS) on the duration of the spike-and-wave discharges (SWDs) in a patient presenting idiopathic absence seizures. At the moment of the study the patient presented a mild blunting of consciousness due to the high frequency of absences and EEG recordings showed sub-continuous, generalized, symmetrical and synchronous 3c/s SWDs, petit mal status. Trains of 10 stimuli (120% resting motor threshold) were delivered at 5Hz frequency at the beginning of the SWDs. 5Hz-rTMS trains significantly changed the EEG activity by reducing the duration of SWDs without changing the intervals between two consecutive discharges. rTMS had not significant after-effects on the epileptic activity and patient's clinical status. Despite the limitations of a single case report, our neurophysiological findings suggest that 5Hz-suprathreshold rTMS delivered in short trains induces a transitory interference of the ongoing epileptic activity.

Anatomical and physiological basis and mechanism of action of neurostimulation for epilepsy

Neurostimulation is an emerging treatment for neurological diseases. Different types of neurostimulation exist mainly depending of the part of the nervous system that is being affected and the way this stimulation is being administered. Vagus nerve stimulation (VNS) is a neurophysiological treatment for patients with medically or surgically refractory epilepsy. Over 30,000 patients have been treated with VNS. No clear predictive factors for responders have been identified. To date, the precise mechanism of action remains to be elucidated. Better insight in the mechanism of action may identify seizure types or syndromes that respond better to VNS and may guide the search for optimal stimulation parameters and finally improve clinical efficacy. Deep brain stimulation (DBS) has been used extensively as a treatment for movement disorders. Several new indications such as obsessive compulsive behaviour and cluster headache are being investigated with promising results. The vast progress in biotechnology along with the experience in other neurological diseases in the past ten years has led to a renewed interest in intracerebral stimulation for epilepsy. Epilepsy centers around the world have recently reinitiated trials with deep brain stimulation in different intracerebral structures such as the thalamus, the hippocampus and the subthalamic nucleus.

Brain plasticity: From pathophysiological mechanisms to therapeutic applications

Cerebral plasticity, which is the dynamic potential of the brain to reorganize itself during ontogeny, learning, or following damage, has been widely studied in the last decade, in vitro, in animals, and also in humans since the development of functional neuroimaging. In the first part of this review, the main hypotheses about the pathophysiological mechanisms underlying plasticity are presented. At a microscopic level, modulations of synaptic efficacy, unmasking of latent connections, phenotypic modifications and neurogenesis have been identified. At a macroscopic level, diaschisis, functional redundancies, sensory substitution and morphological changes have been described. In the second part, the behavioral consequences of such cerebral phenomena in physiology, namely the "natural" plasticity, are analyzed in humans. The review concludes on the therapeutic implications provided by a better understanding of these mechanisms of brain reshaping. Indeed, this plastic potential might be 'guided' in neurological diseases, using rehabilitation, pharmacological drugs, transcranial magnetic stimulation, neurosurgical methods, and even new techniques of brain-computer interface - in order to improve the quality of life of patients with damaged nervous systems.

Myoclonus and transcranial magnetic stimulation

The neural dysfunction at the origin of myoclonus may locate at various anatomical levels within the central nervous system, including the motor cortices. Transcranial magnetic stimulation (TMS) can be used to assess the balance between inhibitory and excitatory processes involved in the regulation of motor cortex activity and thereby, may be of value to determine the pathophysiological mechanisms of myoclonus. Using paired-pulse paradigms with various interstimulus intervals, TMS studies showed that intracortical inhibition (ICI) was reduced in progressive myoclonic epilepsy (PME). In contrast, ICI was decreased only for short interstimulus intervals in patients with juvenile myoclonic epilepsy (JME). Transcallosal inhibition and sensorimotor integration were also both altered in PME but not in JME. Actually, the loss of inhibitory regulation within the central nervous system might represent an intrinsic mechanism of myoclonus, whether of epileptic origin or not. Finally, the other TMS parameters of excitability (motor threshold, silent period, intracortical facilitation) were found normal in most cases of myoclonus. According to these observations, it was quite conceivable that the application of repetitive trains of TMS (rTMS) at inhibitory low-frequency (around 1 Hz) might be able to relieve myoclonus by restoring ICI. A few reported cases illustrate the efficacy of low-frequency rTMS to alleviate myoclonic symptoms. Therapeutic-like perspectives are opened for rTMS in these forms of myoclonus that are related to motor cortical hyperexcitability secondary to the loss of ICI.

Selective and nonselective benzodiazepine agonists have different effects on motor cortex excitability

Transcranial magnetic stimulation (TMS) is a useful method to study pharmacological effects on motor cortex excitability. Zolpidem is a selective agonist of the benzodiazepine receptor subtype BZ1 and has a distinct pharmacological profile compared to diazepam. To study the different effects of these two drugs on the cortical inhibitory system, TMS was performed before and after administration of a single oral dose of zolpidem (10 mg) and diazepam (5 mg) in six healthy volunteers. TMS tests included the determination of resting and active motor threshold (MT) and measurements of the amplitudes of motor evoked potentials, intracortical facilitation (ICF), short-latency intracortical inhibition (SICI), and long-latency intracortical inhibition (LICI), and determination of the cortical silent period (CSP). Both drugs were without effect on the active or resting MT and decreased the ICF. Prolongation of the CSP and enhancement of LICI only in the presence of zolpidem point to a specific BZ1-related mechanism underlying the long-lasting component of cortical inhibition. This selective modulation of the CSP and the LICI points to a specific role of BZ1 receptors in the control of inhibitory neuronal loops within the primary motor cortex.

From the left to the right: How the brain compensates progressive loss of language function

In normal right-handed subjects language production usually is a function oft the left brain hemisphere. Patients with aphasia following brain damage to the left hemisphere have a considerable potential to compensate for the loss of this function. Sometimes, but not always, areas of the right hemisphere which are homologous to language areas of the left hemisphere in normal subjects are successfully employed for compensation but this integration process may need time to develop. We investigated right-handed patients with left hemisphere brain tumors as a model of continuously progressive brain damage to left hemisphere language areas using functional neuroimaging and transcranial magnetic stimulation (TMS) to identify factors which determine successful compensation of lost language function. Only patients with slowly progressing brain lesions recovered right-sided language function as detected by TMS. In patients with rapidly progressive lesions no right-sided language function was found and language performance was linearly correlated with the lateralization of language related brain activation to the left hemisphere. It can thus be concluded that time is the factor which determines successful integration of the right hemisphere into the language network for compensation of lost left hemisphere language function.

Excitability of the human epileptic cortex after chronic valproate: A reappraisal

We explored the action of chronic valproic acid (VPA) on the human epileptic cortex by means of transcranial magnetic stimulation (TMS). TMS is an emerging biomarker for neurotropic drugs. We had 15 drug-naive patients with different epileptic syndromes. Interictally, we measured several TMS indexes of cortical excitability before commencing VPA and 3 months later. At that time, all patients were clinical responders to the drug, whose plasma levels were in the "therapeutic range". We then compared the two conditions, while 18 healthy subjects, of whom 12 were retested at a similar delay, acted as controls. In the pooled patients, the baseline resting motor threshold to TMS was similar to that of controls, but it increased significantly (P < 0.05) after VPA. Intracortical facilitation, another index of cortical excitability, was abnormally enhanced at baseline but decreased significantly after VPA (P < 0.05). On splitting patients according to their diagnosis, the threshold increase was significant (P < 0.05) among partial, but not generalized epilepsies. The reverse was true for changes in intracortical facilitation. TMS phenomena had no linear relation to VPA serum levels. Based on the known pharmacology of TMS effects, VPA reduced the intrinsic membrane excitability of motor cortical neurons, possibly through changes in Na+ channel activity. Then, VPA corrected a transmitter-mediated interneuronal hyper-excitability of the primary motor cortex. The former effect was best seen in partial, and the latter in generalized epilepsy patients.

Effects of repetitive transcranial magnetic stimulation in a patient with fixation-off sensitivity

Aim of the present study was to evaluate the acute and long-term effects of low-frequency repetitive transcranial magnetic stimulation (rTMS) on focal epileptiform interictal EEG activity in a patient with fixation-off sensitivity and partial epilepsy. Real and sham rTMS were delivered over the vertex. Two trains of 500 stimuli per day were delivered at 0.33 Hz frequency and threshold intensity for five consecutive days. The number of posterior EEG spikes and spike-and-wave complexes/min before and after the application of rTMS were compared in a blinded manner. In our patient, real-rTMS induced a long-lasting decrease in the number of posterior EEG spikes and spike-and-wave complexes/min. Despite the limitations of a single case report, our study confirms that low-frequency rTMS significantly reduces interictal focal epileptic activity over time.

Functional connectivity networks are disrupted in left temporal lobe epilepsy

OBJECTIVE

Functional connectivity maps the distributed network of brain regions fluctuating synchronously during a continuous brain state. This study sought to investigate whether patients with left temporal lobe epilepsy (TLE) differ from controls in their resting-state functional connectivity between typical language regions.

METHODS

We studied 17 patients with left TLE, together with eight healthy controls, using seeded functional connectivity. Seed regions were defined using the regions of maximal activation and deactivation during a language functional magnetic resonance imaging (fMRI) task in a separate cohort of 30 controls.

RESULTS

Language fMRI produced the expected activation pattern, which was not different between patients and controls. However, functional connectivity between language areas during rest was markedly different; whereas controls showed connectivity between each of the seed areas and the majority of the language areas, patients showed connectivity only with a few areas, particularly the seed area itself. This difference was significant in the direct comparison of patients and control connectivity maps.

INTERPRETATION

We suggest that this reduced connectivity in left temporal lobe epilepsy may reflect a disturbance of the language network during resting state in patients and may be related to subtle language difficulties in this patient population.

Improving the lives of patients with medically refractory epilepsy by electrical stimulation of the nervous system

Vagal nerve stimulation proved effective in animal models of epilepsy, and in open and double-blinded trials, in over 450 patients. Seizure reduction improved for at least 2 years. Almost 50% of treated patients achieve at least a 50% reduction in seizure frequency. Other advantages include termination of a seizure and improved alertness. Benefits were demonstrated in children, partial and generalized epilepsies, and in specific neurologic syndromes.

Effects of sleep deprivation on cortical excitability in patients affected by juvenile myoclonic epilepsy: a combined transcranial magnetic stimulation and EEG study

OBJECTIVE

To investigate the effect of sleep deprivation on corticospinal excitability in patients affected by juvenile myoclonic epilepsy (JME) using different transcranial magnetic stimulation (TMS) parameters.

METHODS

Ten patients with JME and 10 normal subjects underwent partial sleep deprivation. Motor threshold (MT), motor evoked potential amplitude (MEP), and silent period (SP) were recorded from the thenar eminence (TE) muscles. Short latency intracortical inhibition (SICI) and short latency intracortical facilitation (SICF) were studied using paired magnetic stimulation. TMS was performed before and after sleep deprivation; EEG and TMS were performed simultaneously.

RESULTS

In patients with JME, sleep deprivation induced a significant decrease in SICI and an increase in SICF, which was associated with increased paroxysmal activity. A significant decrease in the MT was observed. No significant changes in any TMS parameters were noted in normal subjects after sleep deprivation. The F wave was unchanged by sleep deprivation in both control subjects and in patients with JME.

CONCLUSIONS

In patients with JME, sleep deprivation produces increases in corticospinal excitability in motor areas as measured by different TMS parameters.

Transcranial magnetic stimulation in treatment-resistant depressed patients: a double-blind, placebo-controlled trial

This 5-week, randomized, double-blind, placebo-controlled trial investigated the efficacy and tolerability of high frequency repetitive transcranial magnetic stimulation (rTMS) directed to the left prefrontal cortex in drug-resistant depressed patients. Fifty-four patients were randomly assigned to receive 10 daily applications of either real or sham rTMS. Subjects assigned to receive active stimulation were divided into two further subgroups according to the intensity of stimulation: 80% vs. 100% of motor threshold (MT). At study completion, the response rates were 61.1% (n=11), 27.8% (n=5) and 6.2% (n=1) for the 100% MT group, 80% MT group and sham group, respectively. A significant difference (Pearson chi(2) test) was found between the 100% MT and sham groups, while the 80% MT group did not differ significantly from the sham group. Between the two active groups, a marginally significant difference was observed. Analysis of variance with repeated measures on Hamilton Depression Rating Scale scores revealed a significantly different decrease over time of depressive symptomatology among the three treatment groups. Treatment response appeared to be unrelated to the demographic and clinical characteristics recorded, and on the whole the technique was well tolerated. The results of this double-blind trial showed that rTMS may be a useful and safe adjunctive treatment for drug-resistant depressed patients.

Negative myoclonus induced by cortical electrical stimulation in epileptic patients

Negative myoclonus (NM) is a motor disorder characterized by a sudden and abrupt interruption of muscular activity. The EMG correlate of NM is a brief (<500 ms) silent period (SP) not preceded by any enhancement of EMG activity (i.e. myoclonus). This study investigated the role of premotor cortex (PMC), primary motor cortex (MI), primary somatosensory area (SI) and supplementary motor area (SMA) in the pathophysiology of cortical NM by means of intracerebral low frequency (1 Hz) electrical stimulation. In three drug-resistant epileptic patients undergoing presurgical evaluation, we delivered single electric pulses (stimulus duration: 3 ms; stimulus intensity ranging from 0.4 to 3 mA) to PMC (2 patients), MI (1 patient), SI and SMA through stereo-EEG electrodes; surface EMG was collected from both deltoids. The results showed that (i) the stimulation of PMC or MI could evoke a motor evoked potential (MEP) either at rest or during contraction, in this latter case followed by an SP; however, in two patients, at the lowest stimulus intensities (0.4 mA), 50% of stimuli could induce a pure SP, i.e. not preceded by an MEP; raising the intensity of stimulation (0.6 mA), the SPs showed an antecedent MEP in >80% of stimuli; (ii) the stimulation of SI at low stimulus intensities (from 0.4 to 0.8 mA) induced in two patients only SPs, never associated with an antecedent MEP, whereas in the third subject the SPs could be inconstantly preceded by an MEP; by incrementing the stimulus intensity (up to 3 mA), in all three patients the SPs tended to be preceded, although not constantly, by an MEP; stimulus intensity affected SP duration (i.e. the higher the intensity, the longer the SP), without influencing the latency of onset of the SPs; (iii) the stimulation of SMA induced only pure SPs, at all stimulus intensities up to 3 mA; as for SI, increment of stimulus intensity was paralleled by an increase in SP duration, without influencing the onset latency of SPs. We conclude that single electric pulse stimulation of PMC, MI, SI and SMA through stereo-EEG electrodes can induce pure SPs, not preceded by an MEP, which clinically appear as NM, suggesting therefore that these cortical areas may be involved in the genesis of this motor phenomenon. However, it must be pointed out that SMA stimulation induced only pure SPs, regardless of the stimulus intensity, whereas occurrence of pure SPs following stimulation of PMC, MI, and SI depended mainly on the intensity of stimulation.

La stimulation magnétique transcrânienne : applications en Neurologie

INTRODUCTION

Transcranial magnetic stimulation (TMS) was first applied to assess conduction time along the corticospinal tract, namely by recording motor evoked potentials.

STATE OF ART

At present, TMS techniques include cortical excitability and mapping studies using single or paired-pulse paradigms on the one hand, and repetitive TMS to induce cortical plasticity and to modify brain function on the other hand. TMS is a valuable, non-invasive tool in the diagnosis and the pathophysiological assessment of cortical dysfunction involved in various neurological diseases (multiple sclerosis, myelopathy, amyotrophic lateral sclerosis, movement disorders, epilepsy, stroke).

PERSPECTIVES AND CONCLUSION

In the near future, repetitive TMS could have therapeutic applications in neurology (epilepsy, stroke rehabilitation program) as is already the case in some psychiatric diseases. However, most of the new indications for treatment with cortical stimulation will be based on surgically-implanted neuromodulation procedures.

In Vivo Epileptogenicity of Focal Cortical Dysplasia: A Direct Cortical Paired Stimulation Study

PURPOSE

Alternation of the intracortical inhibitory and excitatory mechanisms in focal cortical dysplasia (FCD) has not been well elucidated in vivo in humans. We investigated in vivo alternation of these mechanisms in epileptogenesis of FCD by means of paired-pulse direct cortical electrical stimulation.

METHODS

A 31-year-old man with FCD at the left foot primary somatosensory (SI) and motor areas who underwent invasive monitoring with subdural electrodes was studied. By means of subdural electrodes, paired-pulse electrical stimulation was performed at the epileptic focus (foot SI) and control cortex (hand SI) with interstimulus interval (ISI) of 1-100 ms. Instead of using motor evoked potentials to investigate the degree of cortical excitability in response to motor cortex stimulation, we evaluated the size change of corticocortical evoked potentials (CCEPs), which are elicited at the adjacent cortex by direct cortical stimulation via fiber projection and thus reflect direct and indirect excitation of corticocortical projection neurons at the site of stimulation.

RESULTS

During the interictal state, paired-pulse stimulation of the focus revealed abnormally enhanced intracortical inhibition at ISI of 1-10 ms (maximum, 22%) compared with control stimulation of the hand SI (ISI of 1-2 ms; maximum, 18%) (p < 0.01). While the patient was having the somatosensory aura that later evolved into the left-leg clonic seizure, single and paired stimulation at the focus showed increased cortical excitability (enlarged CCEP) and decreased intracortical inhibition, respectively.

CONCLUSIONS

During the aura, interictally enhanced intracortical inhibition at the focus was replaced by increased cortical excitability and decreased intracortical inhibition, suggesting increased net intrinsic epileptogenicity during seizure generation in this patient with FCD.

A lack of effect from transcranial magnetic stimulation (TMS) on the vagus nerve stimulator (VNS)

OBJECTIVE

The effects of transcranial magnetic stimulation (TMS) on vagus nerve stimulation (VNS) are unknown. Understanding these effects is important before exposing individuals with an implanted VNS to TMS, as could occur in epilepsy or depression TMS research. To explore this issue, the TMS-induced current in VNS leads and whether TMS has an effect on the VNS pulse generator was assessed.

METHODS

Ex vivo measurement of current in VNS leads during single-pulse TMS and pulse generator function before, during, and after single-pulse TMS was assessed.

RESULTS

At the highest intensity and with the TMS coil held approximately 5 mm from the VNS wires, a 200 nA, 1.0 ms current was induced by TMS. This translates to an induced charge density of 3.3 nC/cm2/phase. The function of the pulse generator was unaffected by single-pulse TMS, even when its case was directly stimulated by the coil.

CONCLUSIONS

TMS-induced current in VNS electrodes was not only well outside of the range known to be injurious to peripheral nerve, but also below the activation threshold of nerve fibers.

SIGNIFICANCE

Using single-pulse TMS in individuals with VNS should not result in nerve stimulation or damage. Furthermore, single-pulse TMS does not affect the VNS pulse generator's function.

Role of the Contralateral Inferior Frontal Gyrus in Recovery of Language Function in Poststroke Aphasia

Background and Purpose— Functional neuroimaging studies have demonstrated right inferior frontal gyrus (IFG) activation in poststroke aphasia. It remains unclear whether this activation is essential for language performance. We tested this hypothesis in a positron emission tomography (PET) activation study during a semantic task with repetitive transcranial magnetic stimulation (rTMS) on right-handed patients experiencing poststroke aphasia and examined whether rTMS stimulation over the right and left IFG would interfere with language performance.

Methods— Eleven patients with left-sided middle cerebral arterial infarction, 50 to 75 years of age, were tested with the Aachen Aphasia Test Battery and underwent 15 O-H 2 O PET activation during a semantic task within 2 weeks after stroke. PET activation images were coregistered to T1-weighted MRIs. Stimulation sites were determined on renderings of head and brain over the maximum activation within left and right IFG. rTMS was performed with 20% maximum output (2.1 T), 10-s train duration, at 4Hz frequency. A positive rTMS effect was defined as an increased reaction time latency or error rate in the semantic task.

Results— PET activations of the IFG were observed on the left (3 patients) and bilaterally (8 patients). Right IFG stimulation was positive in 5 patients with right IFG activation, indicating essential language function. In a verbal fluency task, these patients had a lower performance than patients without right-sided TMS effect.

Conclusions— In some poststroke aphasics, right IFG activation is essential for residual language function. However, its compensatory potential seems to be less effective than in patients who recover left IFG function. These results suggest a hierarchy in recovery from poststroke aphasia and a (limited) compensatory potential of the nondominant hemisphere.

Hemodynamic and metabolic responses to activation, deactivation and epileptic discharges

To investigate the coupling between the hemodynamic and metabolic changes following functional brain activation as well as interictal epileptiform discharges (IEDs), blood oxygenation level dependent (BOLD), perfusion and oxygen consumption responses to a unilateral distal motor task and interictal epileptiform discharges (IEDs) were examined via continuous EEG-fMRI. Seven epilepsy patients performed a periodic (1 Hz) right-hand pinch grip using approximately 8% of their maximum voluntary contraction, a paradigm previously shown to produce contralateral MI neuronal excitation and ipsilateral MI neuronal inhibition. A multi-slice interleaved pulsed arterial spin labeling and T(2)*-weighted gradient echo sequence was employed to quantify cerebral blood flow (CBF) and BOLD changes. EEG was recorded throughout the imaging session and reviewed to identify the IEDs. During the motor task, BOLD, CBF and cerebral metabolic rate of oxygen consumption (CMR(O(2))) signals increased in the contra- and decreased in the ipsilateral primary motor cortex. The relative changes in CMR(O(2)) and CBF were linearly related, with a slope of 0.46 +/- 0.05. The ratio of contra- to ipsilateral CBF changes was smaller in the present group of epilepsy patients than in the healthy subjects examined previously. IEDs produced both increases and decreases in BOLD and CBF signals. In the two case studies for which the estimation criteria were met, the coupling ratio between IED-induced CMR(O(2)) and CBF changes was estimated at 0.48 +/- 0.17. These findings provide evidence for a preserved coupling between hemodynamic and metabolic changes in response to both functional activation and, for the two case studies available, in response to interictal epileptiform activity.

Experimental Electrical Stimulation Therapy for Epilepsy

Electrical stimulation of the nervous system is an attractive possible therapy for intractable epilepsy, but only stimulation of the vagus nerve has been subjected to large, controlled, and completed clinical trials. Controlled trials are in progress for intermittent cycling stimulation of the anterior nuclei of the thalamus, and for cortical stimulation at a seizure focus, responsive to detection of seizure onset. Anecdotal experience has been gathered with stimulation of cerebellum, centromedian thalamus, subthalamus, caudate, hippocampus, and brainstem. All stimulation of the central nervous system for epilepsy must be considered experimental.

Low-frequency transcranial magnetic stimulation for epilepsia partialis continua due to cortical dysplasia

The potential therapeutic role of repetitive transcranial magnetic stimulation (rTMS) in epilepsy has been increasingly recognized. We investigated the effects of low-frequency rTMS in a patient with epilepsia partialis continua (EPC) due to cortical dysplasia. A 31-year-old female patient experienced EPC in the right upper and lower extremities, which had lasted for 15 years without generalized seizures. MRI showed focal megaencephaly around the motor cortex suggestive of cortical dysplasia. A figure of eight magnetic coil was placed over the hand motor area, and 100 stimuli with an intensity at 90% of motor threshold were given at 0.5 Hz. Immediately after rTMS, EPC was nearly abolished. The effects had continued approximately for 2 months, and the second trial resulted in the similar effects and time-course. Low-frequency rTMS was safe and well tolerated in this patient. These findings support the concept that rTMS decreases cortical excitability, and may be an effective treatment for focal partial seizures.

Essential language function of the right hemisphere in brain tumor patients

Neuroimaging studies of language networks in patients with brain lesions of the left language-dominant hemisphere have shown activation in the right inferior frontal gyrus (IFG). We tested the functional relevance of right IFG activation using neuroimaging-guided repetitive transcranial magnetic stimulation (rTMS) to disturb language function over bilateral IFG in right-handed patients with brain tumors and controls. All subjects were susceptible to TMS over the left IFG. In patients, this susceptibility correlated with left-sided the degree of language lateralization to the left. Those patients with lowest dominance were also susceptible to right-sided TMS proving relevant language function of the right IFG.

Cortical silent period in a patient with focal epilepsy and Parry-Romberg syndrome

Progressive facial hemiatrophy (PFH), Parry-Romberg syndrome, is a rare disorder frequently associated with epilepsy. We describe a 28-year-old man who had PFH and partial epilepsy that was easily controlled with antiepileptic drugs. In accordance with this patient's benign course of seizures, the cortical silent period was prolonged in the symptomatic hemisphere. This finding may represent compensatory interictal mechanisms in epilepsy.

TMS in cognitive plasticity and the potential for rehabilitation

Cognitive neuroscientists use transcranial magnetic stimulation (TMS) in several ways, from aiming to increase understanding of brain-behavior relationships to transiently improving performance, both in normals and in patients with neurological and neuropsychological deficits. Different types of TMS (single-pulse, paired-pulse, repetitive) are able to interfere with higher brain functions that require the cooperation of different brain areas and complex neuronal networks. Currently, behavioral TMS effects on the brain are usually short-lived and their underlying mechanisms not yet wholly understood. However, the aim of using TMS to develop rehabilitative strategies for motor, perceptive and cognitive functions represents an intriguing challenge.

rTMS reduces focal brain hyperperfusion in two patients with EPC

OBJECTIVE

This study was performed to evaluate the acute effect of a single repetitive transcranial magnetic stimulation (rTMS) session in a focal hyperperfusion epileptogenic region to induce a transitory decrease of epileptiform activity.

CASE REPORT

Two epilepsia partialis continua (EPC)-diagnosed patients, received one session with 15 trains of rTMS (20 Hz; 2 s train, inter-train of 58 s). Before rTMS session, a brain ictal single photon emission computed tomography (SPECT) was performed to localize the focal frontal hyperperfusion region to establish the stimulation site. Immediately after the rTMS session another ictal SPECT was performed. Both patients showed a decrease of perfusion in the stimulated regions. For patient 1 epileptic seizures became intermittent until they stopped in the following 24 h. Patient 2 showed only a minimal improvement with a frequency decrease of epileptic spikes.

CONCLUSIONS

Our findings suggest that a single rTMS session reduces focal epileptogenic activity and could be an alternative approach for epileptic-resistant patients, but efficacy should be confirmed in a larger series.

Reduction of cortical myoclonus-related epileptic activity following slow-frequency rTMS. A case study

In a drug-resistant epilepsy patient with continuous forearm/hand positive myoclonia due to a focal cortical dysplasia of the right motor cortex, cortical jerk-related and electromyographic activity were recorded for 15 min before and after 1 Hz rTMS (15 min, 10% below the resting excitability threshold) of the right motor cortex. A stable negative cortical spike, time-locked with contralateral muscle jerks (60 > 100 microV), was detected only at perirolandic electrodes (maximal amplitudes: block 1 = 21.3 microV, block 2 = 22 microV, block 3 = 25.9 microV). After rTMS, only 20 muscle jerks accomplished the criterion of > 100 microV; blind back-averaging of these disclosed a topographically similar cortical spike, but with amplitude reduced by at least 50% (11.2 microV). This represents in vivo evidence of the possibility to selectively modulate the activity of an epileptic focus by intervening with local low-frequency rTMS.

Suprathreshold 0.3 Hz repetitive TMS prolongs the cortical silent period: potential implications for therapeutic trials in epilepsy

OBJECTIVE

To investigate the after-effects of 0.3 Hz repetitive transcranial magnetic stimulation (rTMS) on excitatory and inhibitory mechanisms at the primary motor cortex level, as tested by single-pulse TMS variables.

METHODS

In 9 healthy subjects, we studied a wide set of neurophysiological and behavioral variables from the first dorsal interosseous before (Baseline), immediately after (Post 1), and 90 min after (Post 2) the end of a 30 min long train of 0.3 Hz rTMS delivered at an intensity of 115% resting motor threshold (RMT). Variables under investigation were: maximal M wave, F wave, and peripheral silent period after ulnar nerve stimulation; RMT, amplitude and stimulus-response curve of the motor evoked potential (MEP), and cortical silent period (CSP) following TMS; finger-tapping speed.

RESULTS

The CSP was consistently lengthened at both Post 1 and Post 2 compared with Baseline. The other variables did not change significantly.

CONCLUSIONS

These findings suggest that suprathreshold 0.3 Hz rTMS produces a relatively long-lasting enhancement of the inhibitory mechanisms responsible for the CSP. These effects differ from those, previously reported, of 0.9-1 Hz rTMS, which reduces the excitability of the circuits underlying the MEP and does not affect the CSP. This provides rationale for sham-controlled trials aiming to assess the therapeutic potential of 0.3 Hz rTMS in epilepsy.