The Combination of rTMS and Pharmacotherapy on In Vitro Models: A Mini-Review

BACKGROUND

Repetitive Transcranial Magnetic Stimulation (rTMS) is a non-invasive brain stimulation technique that is being actively explored as a potential therapeutic modality in various neuropsychiatric disorders, such as depression, neuropathic pain, epilepsy, multiple sclerosis, and neurodegenerative disorders, including the Parkinson's and Alzheimer's disease. The Food and Drug Administration (FDA) approved rTMS for the treatment of major depression, migraine-associated headaches, and Obsessive Compulsive Disorder (OCD). The fact that a significant proportion of patients suffering from these disorders fail to respond to current pharmacological interventions indicates the need for alternative therapies like rTMS.

OBJECTIVE

The objective was to find and summarize all studies combining the use of rTMS and pharmacological interference in vitro, in order to facilitate future studies.

METHODS

The results of studies combining the use of rTMS with pharmacological interference in vitro were focused on. The PubMed database was searched using the terms "rTMS", "repetitive", "transcranial", "magnetic", "stimulation", "in vitro", "in vivo", "cell cultures" untilMarch 2019 and 7 eligible studies were found.

RESULTS

Overall results show a synergistic effect of rTMS and pharmacotherapy in vitro with additive effectiveness, better prognosis, and superior potential management.

CONCLUSION

The limited amount of knowledge denotes the need for additional in vitro studies on the combination of rTMS and pharmacotherapy, which could be extended to in vivo studies and ultimately help design clinical trials so as to improve the therapeutic management of patients with a wide array of neuropsychiatric disorders.

Web-Based Intervention Effects on Mild Cognitive Impairment Based on Apolipoprotein E Genotype: Quasi-Experimental Study

BACKGROUND

Apolipoprotein E (APOE) ε4 allele is a major genetic risk factor for Alzheimer disease and mild cognitive impairment (MCI). Computer-based training programs can improve cognitive performance in elderly populations. However, the effects of computer-based interventions on MCI APOE ε4 carriers have never been studied before.

OBJECTIVE

The effects of different web-based interventions and the APOE isoform-specific differences in training outcomes are investigated.

METHODS

Using a quasi-experimental study design, 202 participants with MCI aged 60 years and older took part in three different intervention programs (physical and cognitive [Long-Lasting Memories, or LLM], cognitive [Active Control, or AC], or physical intervention [Physical Training Control, or PTC]) via an innovative information and communication technologies exergaming platform. Participants in each interventional group were subdivided into APOE ε4 carriers and non-APOE ε4 carriers. All participants underwent an extensive neuropsychological evaluation before and after the training, blood tests, and brain imaging.

RESULTS

All interventions resulted in multiple statistically significant cognitive benefits after the intervention. Verbal learning (California Verbal Learning Test: immediate recall test score-LLM: P=.04; AC: P<.001), working memory (digit span forward and backward test scores-AC: P=.03; PTC: P=.02 and P=.006, respectively), and long-term memory (California Verbal Learning Test: delayed recall test score-LLM: P=.02; AC: P=.002; and PTC: P=.02) were improved. There was no statistically significant difference among the intervention effects. APOE ε4 presence moderates intervention effects as the LLM intervention improved only their task-switching processing speed (Trail Making Test, Part B: P=.03) and the PTC intervention improved only the working memory (digit span backward: P=.03). No significant performance alteration was noted for the APOE ε4+ cognitive AC training group.

CONCLUSIONS

None of the applied interventions could be identified as the optimal one; it is suggested, however, that combined cognitive and physical training and physical training via exergaming may be more effective for the high-risk MCI ΑPOE ε4+ subgroup.

EEG in fitness to drive evaluations in people with epilepsy - Considerable variations across Europe

PURPOSE

Epilepsy patients consider driving issues to be one of their most serious concerns. Ideally, decisions regarding fitness to drive should be based upon thorough evaluations by specialists in epilepsy care. In 2009, an EU directive was published aiming to harmonize evaluation practices within European countries, but, despite these recommendations, whether all epileptologists use the same criteria is unclear. We therefore conducted this study to investigate routine practices on how epileptologists at European epilepsy centers evaluate fitness to drive.

METHODS

A questionnaire was sent to 63 contact persons identified through the European Epi-Care and the E-pilepsy network. The questionnaire addressed how fitness-to-drive evaluations were conducted, the involvement of different professionals, the use and interpretation of EEG, and opinions on existing regulations and guidelines.

RESULTS

The questionnaire was completed by 35 participants (56 % response rate). Results showed considerable variation regarding test routines and the emphasis placed on the occurrence and extent of epileptiform discharges revealed by EEG. 82 % of the responders agreed that there was a need for more research on how to better evaluate fitness-to-drive in people with epilepsy, and 89 % agreed that regulations on fitness to drive evaluations should be internationally coordinated.

CONCLUSION

Our survey showed considerable variations among European epileptologists regarding use of EEG and how findings of EEG pathology should be assessed in fitness-to-drive evaluations. There is a clear need for more research on this issue and international guidelines on how such evaluations should be carried out would be of value.

Working memory profiles of patients with multiple sclerosis: Where does the impairment lie?

Introduction: Previous studies have mostly provided general estimations regarding Working Memory impairment in patients with Multiple Sclerosis. The aim of the present study was to investigate the relative degree of impairment in the four Working Memory components in Multiple Sclerosis. Method: Thirty-eight patients diagnosed with MS and 27 matched controls were assessed using 12 different cognitive tasks of the four components, i.e. phonological loop, visuospatial sketchpad, central executive and episodic buffer. More precisely, Greek translated and adapted versions of the following tasks were administered: Digit recall, Word recall, Non-word recall, Block recall, Mazes recall, Visual Patterns recall, Backward Digit recall, Backward Block recall, Listening recall, Logical Memory I-Immediate Story recall and Greek Verbal Learning Test, which is based on the California Verbal Learning Test. Results: The phonological loop, the central executive and the spatial subcomponent of the visuospatial sketchpad were found to be equally disrupted in MS patients. The episodic buffer was found to be more heavily affected. On the other hand, the visual subcomponent of the visuospatial sketchpad proved to be preserved. Conclusions: WM subcomponents are differentially affected in patients with MS. This novel finding is discussed within the framework of existing knowledge regarding WM impairment in MS.

Identification of Hidden Sources by Estimating Instantaneous Causality in High-Dimensional Biomedical Time Series

The study of connectivity patterns of a system’s variables, such as multi-channel electroencephalograms (EEG), is of utmost importance towards a better understanding of its internal evolutionary mechanisms. Here, the problem of estimating the connectivity network from multivariate time series in the presence of prominent unobserved variables is addressed. The causality measure of partial mutual information from mixed embedding (PMIME), designed to estimate direct lag-causal effects in the presence of many observed variables, is adapted to estimate also zero-lag effects, the so-called instantaneous causality. We term the proposed advanced method, PMIME0. The estimation of instantaneous causality by PMIME0 is a signature of the presence of hidden source in the observed system, as demonstrated analytically in a toy model. It is further demonstrated that the PMIME0 identifies the true instantaneous with great accuracy in a variety of high-dimensional dynamical systems. The method is applied to EEG data with epileptiform discharges (EDs), and the results imply a strong impact of unobserved confounders during the EDs. This finding comes as a possible explanation for the increased levels of causality during epileptic seizures estimated by some measures affected by the presence of a common source.

Central motor pathways in tropical spastic paraparesis: a combined transcranial magnetic stimulation and diffusion tensor imaging study

BACKGROUND

Previous transcranial magnetic stimulation (TMS) studies in patients with tropical spastic paraparesis (TSP) have focused on central motor conduction time measurements while other TMS parameters remained unexplored. From a neuroradiological point of view, pyramidal tract involvement with magnetic resonance imaging and diffusion tensor imaging (DTI) has been rarely reported in TSP.  Accordingly, the present study investigated the mean threshold (MT) and silent period (SP) as well as DTI measurements in TSP.

CASE DESCRIPTION

A 35-year-old female patient presented with a 15-year history of spastic paraparesis with minimal upper-limb involvement. Serum and cerebrospinal fluid samples were positive for HTLV-I. TMS was performed with a figure-of-eight coil (recording, abductor hallucis and first dorsal interosseous muscles). Thr was measured at 1 % steps. SPs were elicited at 5 % increments from 0 to 100 % maximum stimulus intensity (SI), and data were used to construct a stimulus/response (S/R) curve of SI vs SP. The resulting S/R curves were fitted to a Boltzmann equation and statistically compared to control data. Voxel-based DTI analysis was performed with SPM 99. Corticospinal tractography was based on diffusion tensor data. The TMS examination disclosed that MT was significantly increased (54.5 ± 6.36 % vs 41.08 ± 7.85 % in a group of 82 controls, p=0.019). The patient's SP S/R curve had significantly reduced Max values compared to 13 age-matched controls (160.4 ± 0.91 ms vs 228.36 ± 38.69 ms, p <0.001). Fractional anisotropy was decreased in a cluster of voxels corresponding to the area of the pyramidal tract (0.388 ± 0.015 vs 0.506 ± 0.02 in 20 age-matched controls, p <0.001).

CONCLUSION

The described results provide novel neurophysiological and imaging evidence for central motor pathways malfunctioning in TSP. HIPPOKRATIA 2017, 21(4): 191-193.

Dynamics of Epileptiform Discharges Induced by Transcranial Magnetic Stimulation in Genetic Generalized Epilepsy

Objective: In patients with Genetic Generalized Epilepsy (GGE), transcranial magnetic stimulation (TMS) can induce epileptiform discharges (EDs) of varying duration. We hypothesized that (a) the ED duration is determined by the dynamic states of critical network nodes (brain areas) at the early post-TMS period, and (b) brain connectivity changes before, during and after the ED, as well as within the ED. Methods: EEG recordings from two GGE patients were analyzed. For hypothesis (a), the characteristics of the brain dynamics at the early ED stage are measured with univariate and multivariate EEG measures and the dependence of the ED duration on these measures is evaluated. For hypothesis (b), effective connectivity measures are combined with network indices so as to quantify the brain network characteristics and identify changes in brain connectivity. Results: A number of measures combined with specific channels computed on the first EEG segment post-TMS correlate with the ED duration. In addition, brain connectivity is altered from pre-ED to ED and post-ED and statistically significant changes were also detected across stages within the ED. Conclusion: ED duration is not purely stochastic, but depends on the dynamics of the post-TMS brain state. The brain network dynamics is significantly altered in the course of EDs.

Investigation of the motor system in two siblings with Canavan's disease: a combined transcranial magnetic stimulation (TMS) - diffusion tensor imaging (DTI) study

Canavan's disease (CD) is a hereditary leukodystrophy caused by mutations in the aspartoacylase gene (ASPA), leading to spongiform degeneration of the white matter and severe impairment of psychomotor development. We present the cases of two non-Jewish sisters with CD that have a milder and protracted clinical course compared to typical CD. MRI imaging revealed bilateral high-signal-intensity areas in the thalami and the internal capsule and MR spectroscopy showed typical findings for CD (a marked increase in N-acetylaspartate (NAA) levels). FA values of the right and left corticospinal tracts at the level of the posterior limb of the internal capsule, and the centrum semiovale were found to be significantly reduced compared to healthy controls. From a neurophysiological point of view, the peripheral motor system was normal. In contrast, cortical stimulation at maximal intensity failed to elicit facilitated or resting MEPs and silent periods (SPs) in upper and lower limbs, providing evidence for significant upper motor pathway dysfunction.

The Hemiconvulsions-Hemiplegia-Epilepsy (HHE) syndrome: a transcranial magnetic stimulation-EEG study

BACKGROUND

The Hemiconvulsions-Hemiplegia-Epilepsy (HHE) syndrome is currently regarded as an extremely rare condition. The etiological and pathophysiological mechanisms underlying this medical rarity as well as the optimal therapeutic approaches remain poorly defined and understood. We present the clinical, radiological and electroencephalography (EEG) findings of a patient with the HHE syndrome and describe the response of the continuously present epileptiform abnormalities to transcranial magnetic stimulation (TMS).

CASE DESCRIPTION

A 33-year old male patient was referred to our department for investigation and management of intractable epilepsy. His seizures began at the age of three months when, during the course of a common febrile illness, he developed repetitive clonic seizures involving the left upper and lower limbs, followed by permanent left hemiplegia. After extensive investigations, he was diagnosed with "idiopathic" HHE syndrome. Currently, he suffers from left hemiplegia, severe intellectual impairment [Intelligence Quotient (IQ) <30] and asymmetric, bilateral tonic seizures occurring 1-3 times daily despite treatment with valproate, topiramate, lamotrigine, rufinamide, and perampanel. Brain magnetic resonance imaging revealed atrophy of the right hemisphere and serial EEGs disclosed continuous sharp waves, the generators of which were localized by electrical source imaging (ESI) to two distinct sources within the right hemisphere. Repetitive TMS [210 stimuli of 1 Hz at 100 % corticomotor threshold applied with a circular coil over the generators of epileptic discharges (EDs)] resulted in a statistically significant decrease of ED counts compared to sham stimulation and the post-verum TMS period.

CONCLUSION

We present the clinical-laboratory profile and the long-term follow up of a patient with the HHE syndrome. Further, we describe the effects of TMS on EDs. The latter observation raises the possibility that TMS-EEG may be used in select cases with intractable epilepsy as a surrogate marker of responsiveness to more invasive modalities (i.e., cortical stimulation). HIPPOKRATIA 2017, 21(2): 101-104.

Current standards of neuropsychological assessment in epilepsy surgery centers across Europe

We explored the current practice with respect to the neuropsychological assessment of surgical epilepsy patients in European epilepsy centers, with the aim of harmonizing and establishing common standards. Twenty-six epilepsy centers and members of "E-PILEPSY" (a European pilot network of reference centers in refractory epilepsy and epilepsy surgery), were asked to report the status of neuropsychological assessment in adults and children via two different surveys. There was a consensus among these centers regarding the role of neuropsychology in the presurgical workup. Strong agreement was found on indications (localization, epileptic dysfunctions, adverse drugs effects, and postoperative monitoring) and the domains to be evaluated (memory, attention, executive functions, language, visuospatial skills, intelligence, depression, anxiety, and quality of life). Although 186 different tests are in use throughout these European centers, a core group of tests reflecting a moderate level of agreement could be discerned. Variability exists with regard to indications, protocols, and paradigms for the assessment of hemispheric language dominance. For the tests in use, little published evidence of clinical validity in epilepsy was provided. Participants in the survey reported a need for improvement concerning the validity of the tests, tools for the assessment of everyday functioning and accelerated forgetting, national norms, and test co-normalization. Based on the present survey, we documented a consensus regarding the indications and principles of neuropsychological testing. Despite the variety of tests in use, the survey indicated that there may be a core set of tests chosen based on experience, as well as on published evidence. By combining these findings with the results of an ongoing systematic literature review, we aim for a battery that can be recommended for the use across epilepsy surgical centers in Europe.

Dysfibrinogenemia and multiple sclerosis: spuriously associated or causally linked?

BACKGROUND

The inherited dysfibrinogenemias comprise rare congenital coagulation disorders which are clinically characterized by bleeding diathesis and, in occasional patients, by thrombotic tendency or combined bleeding-thrombotic events. In recent years, accumulating evidence suggested that fibrinogen has a critical role in the pathogenesis of neuroinflammatory disorders, including multiple sclerosis. We describe the presentation and long-term follow-up of a patient with inherited dysfibrinogenemia and concomitant clinical and laboratory evidence of demyelinating disease.   Case description:  A 16-year-old male patient presented in 2003 with bilateral sensory symptomatology preceded by an episode of epistaxis. His past medical history included episodes of spontaneous nosebleeds as well as Duane syndrome and mild atrophy of the right upper limb. Coagulation testing of the patient and his asymptomatic father revealed in both the presence of a clotting defect, consistent with inherited dysfibrinogenemia (named Fibrinogen Thessaloniki). Within seven months, the patient presented with a new episode of motor semiology whereas serial brain magnetic resonance imaging (MRI) scans revealed T2 lesions with bilateral distribution, some of which with gadolinium enhancement. The cerebrospinal fluid examination disclosed the presence of oligoclonal bands in the central nervous system compartment. The patient was started on azathioprine (2.5 mg/kg/24h) which led to clinical and radiological stabilization for nine years. In 2013, the dose of azathioprine was reduced, due to an elevation of his amylase levels, resulting in radiological deterioration with an increased T2 lesion load. The reinstitution of azathioprine at therapeutic doses led to radiological improvement and clinical stability as of today.

CONCLUSION

The described case of inherited dysfibrinogenemia and concomitant multiple sclerosis provides speculative evidence for a causal link, rather than a chance association, between these two entities. Further studies are warranted to corroborate this hypothesis in experimental and clinical settings. HIPPOKRATIA 2017, 21(1): 49-51.

The impact of paclitaxel and carboplatin chemotherapy on the autonomous nervous system of patients with ovarian cancer

Background

Paclitaxel-based regimens are frequently associated with the development of peripheral neuropathy. The autonomous nervous system (ANS) effects, however, of this chemotherapeutic agent remain unexplored.

Methods

We investigated a group of 31 female patients with ovarian cancer receiving treatment with paclitaxel and carboplatin, as well as a group of 16 healthy age- and gender-matched healthy volunteers. All study participants completed a questionnaire and were assessed neurophysiologically at three time points (baseline, 3–4 months and 6–8 months following the onset of chemotherapy). The evaluation of the ANS included assessment of the adrenergic cardiovascular function (orthostatic hypotension-OH), parasympathetic heart innervation (30/15 ratio) and sympathetic skin response (SSR).

Results

At the 3–4 months ANS assessment, 19.2 % of the patients had systolic OH and the same percentage had diastolic OH, but at the 6–8 months evaluation no patient had systolic OH and only 13.8 % had diastolic OH. The values of the 30/15 ratio were significantly reduced at both time points, whereas the SSR was not affected.

Conclusions

Combined paclitaxel and carboplatin chemotherapy is associated with significant effects on the parasympathetic heart innervation and occasionally with effects on the adrenergic cardiovascular reaction. The SSR remained unaffected. Physicians should be alert to the possibility of these treatment-emergent side effects, so as to monitor ANS parameters and introduce treatment modifications accordingly. Our findings however, should be validated in larger cohorts.

Electronic supplementary material

The online version of this article (doi:10.1186/s12883-016-0710-4) contains supplementary material, which is available to authorized users.

Cortico-cortical and motor evoked potentials to single and paired-pulse stimuli: An exploratory transcranial magnetic and intracranial electric brain stimulation study

BACKGROUND

Paired-pulse (PP) paradigms are commonly employed to assess in vivo cortical excitability using transcranial magnetic stimulation (TMS) to stimulate the primary motor cortex and modulate the induced motor evoked potential (MEP). Single-pulse cortical direct electrical stimulation (DES) during intracerebral EEG monitoring allows the investigation of brain connectivity by eliciting cortico-cortical evoked potentials (CCEPs). However, PP paradigm using intracerebral DES has rarely been reported and has never been previously compared with TMS.

OBJECTIVE

The work was intended (i) to verify that the well-established modulations of MEPs following PP TMS remain similar using DES in the motor cortex, and (ii) to evaluate if a similar pattern could be observed in distant cortico-cortical connections through modulations of CCEP.

METHODS

Three patients undergoing intracerebral EEG monitoring with electrodes implanted in the central region were studied. Single-pulse DES (1-3 mA, 1 ms, 0.2 Hz) and PP DES using six interstimulus intervals (5, 15, 30, 50, 100, and 200 ms) in the motor cortex with concomitant recording of CCEPs and MEPs in contralateral muscles were performed. Finally, a navigated PP TMS session targeted the intracranial stimulation site to record TMS-induced MEPs in two patients.

RESULTS

MEP modulations elicited by PP intracerebral DES proved similar among the three patients and to those obtained by PP TMS. CCEP modulations elicited by PP intracerebral DES usually showed a pattern comparable to that of MEP, although a different pattern could be observed occasionally.

CONCLUSION

PP intracerebral DES seems to involve excitatory and inhibitory mechanisms similar to PP TMS and allows the recording of intracortical inhibition and facilitation modulation on cortico-cortical connections. Hum Brain Mapp 37:3767-3778, 2016. © 2016 Wiley Periodicals, Inc.

Current practices in long-term video-EEG monitoring services: A survey among partners of the E-PILEPSY pilot network of reference for refractory epilepsy and epilepsy surgery

PURPOSE

The European Union-funded E-PILEPSY network aims to improve awareness of, and accessibility to, epilepsy surgery across Europe. In this study we assessed current clinical practices in epilepsy monitoring units (EMUs) in the participating centers.

METHOD

A 60-item web-based survey was distributed to 25 centers (27 EMUs) of the E-PILEPSY network across 22 European countries. The questionnaire was designed to evaluate the characteristics of EMUs, including organizational aspects, admission, and observation of patients, procedures performed, safety issues, cost, and reimbursement.

RESULTS

Complete responses were received from all (100%) EMUs surveyed. Continuous observation of patients was performed in 22 (81%) EMUs during regular working hours, and in 17 EMUs (63%) outside of regular working hours. Fifteen (56%) EMUs requested a signed informed consent before admission. All EMUs performed tapering/withdrawal of antiepileptic drugs, 14 (52%) prior to admission to an EMU. Specific protocols on antiepileptic drugs (AED) tapering were available in four (15%) EMUs. Standardized Operating Procedures (SOP) for the treatment of seizure clusters and status epilepticus were available in 16 (59%). Safety measures implemented by EMUs were: alarm seizure buttons in 21 (78%), restricted patient's ambulation in 19 (70%), guard rails in 16 (59%), and specially designated bathrooms in 7 (26%). Average costs for one inpatient day in EMU ranged between 100 and 2200 Euros.

CONCLUSION

This study shows a considerable diversity in the organization and practice patterns across European epilepsy monitoring units. The collected data may contribute to the development and implementation of evidence-based recommended practices in LTM services across Europe.

Causality networks from multivariate time series and application to epilepsy

Granger causality and variants of this concept allow the study of complex dynamical systems as networks constructed from multivariate time series. In this work, a large number of Granger causality measures used to form causality networks from multivariate time series are assessed. For this, realizations on high dimensional coupled dynamical systems are considered and the performance of the Granger causality measures is evaluated, seeking for the measures that form networks closest to the true network of the dynamical system. In particular, the comparison focuses on Granger causality measures that reduce the state space dimension when many variables are observed. Further, the linear and nonlinear Granger causality measures of dimension reduction are compared to a standard Granger causality measure on electroencephalographic (EEG) recordings containing episodes of epileptiform discharges.

Direct Causal Networks for the Study of Transcranial Magnetic Stimulation Effects on Focal Epileptiform Discharges

Background: Transcranial magnetic stimulation (TMS) can have inhibitory effects on epileptiform discharges (EDs) of patients with focal seizures. However, the brain connectivity before, during and after EDs, with or without the administration of TMS, has not been extensively explored. Objective: To investigate the brain network of effective connectivity during ED with and without TMS in patients with focal seizures. Methods: For the effective connectivity a direct causality measure is applied termed partial mutual information from mixed embedding (PMIME). TMS-EEG data from two patients with focal seizures were analyzed. Each EEG record contained a number of EDs in the majority of which TMS was administered over the epileptic focus. As a control condition, sham stimulation over the epileptogenic zone or real TMS at a distance from the epileptic focus was also performed. The change in brain connectivity structure was investigated from the causal networks formed at each sliding window. Conclusion: The PMIME could detect distinct changes in the network structure before, within, and after ED. The administration of real TMS over the epileptic focus, in contrast to sham stimulation, terminated the ED prematurely in a node-specific manner and regained the network structure as if it would have terminated spontaneously.

Transcranial Magnetic Stimulation Combined with EEG Reveals Covert States of Elevated Excitability in the Human Epileptic Brain

BACKGROUND

Transcranial magnetic stimulation combined with electroencephalogram (TMS-EEG) can be used to explore the dynamical state of neuronal networks. In patients with epilepsy, TMS can induce epileptiform discharges (EDs) with a stochastic occurrence despite constant stimulation parameters. This observation raises the possibility that the pre-stimulation period contains multiple covert states of brain excitability some of which are associated with the generation of EDs.

OBJECTIVE

To investigate whether the interictal period contains "high excitability" states that upon brain stimulation produce EDs and can be differentiated from "low excitability" states producing normal appearing TMS-EEG responses.

METHODS

In a cohort of 25 patients with Genetic Generalized Epilepsies (GGE) we identified two subjects characterized by the intermittent development of TMS-induced EDs. The high-excitability in the pre-stimulation period was assessed using multiple measures of univariate time series analysis. Measures providing optimal discrimination were identified by feature selection techniques. The "high excitability" states emerged in multiple loci (indicating diffuse cortical hyperexcitability) and were clearly differentiated on the basis of 14 measures from "low excitability" states (accuracy = 0.7).

CONCLUSION

In GGE, the interictal period contains multiple, quasi-stable covert states of excitability a class of which is associated with the generation of TMS-induced EDs. The relevance of these findings to theoretical models of ictogenesis is discussed.