Cortical excitability and seizure control influence attention performance in patients with idiopathic generalized epilepsies (IGEs)

Drug-resistant juvenile myoclonic epilepsy: A literature review

The ILAE's Task Force on Nosology and Definitions revised in 2022 its definition of juvenile myoclonic epilepsy (JME), the most common idiopathic generalized epilepsy disorder, but this definition may well change again in the future. Although good drug response could almost be a diagnostic criterion for JME, drug resistance (DR) is observed in up to a third of patients. It is important to distinguish this from pseudoresistance, which is often linked to psychosocial problems or psychiatric comorbidities. After summarizing these aspects and the various definitions applied to JME, the present review lists the risk factors for DR-JME that have been identified in numerous studies and meta-analyses. The factors most often cited are absence seizures, young age at onset, and catamenial seizures. By contrast, photosensitivity seems to favor good treatment response, at least in female patients. Current hypotheses on DR mechanisms in JME are based on studies of either simple (e.g., cortical excitability) or more complex (e.g., anatomical and functional connectivity) neurophysiological markers, bearing in mind that JME is regarded as a neural network disease. This research has revealed correlations between the intensity of some markers and DR, and above all shed light on the role of these markers in associated neurocognitive and neuropsychiatric disorders in both patients and their siblings. Studies of neurotransmission have mainly pointed to impaired GABAergic inhibition. Genetic studies have generally been inconclusive. Increasing restrictions have been placed on the use of valproate, the standard antiseizure medication for this syndrome, owing to its teratogenic and developmental risks. Levetiracetam and lamotrigine are prescribed as alternatives, as is vagal nerve stimulation, and there are several other promising antiseizure drugs and neuromodulation methods. The development of better alternative treatments is continuing to take place alongside advances in our knowledge of JME, as we still have much to learn and understand.

The landscape of drug resistant absence seizures in adolescents and adults: Pathophysiology, electroclinical spectrum and treatment options

The persistence of typical absence seizures (AS) in adolescence and adulthood may reduce the quality of life of patients with genetic generalized epilepsies (GGEs). The prevalence of drug resistant AS is probably underestimated in this patient population, and treatment options are relatively scarce. Similarly, atypical absence seizures in developmental and epileptic encephalopathies (DEEs) may be unrecognized, and often persist into adulthood despite improvement of more severe seizures. These two seemingly distant conditions, represented by typical AS in GGE and atypical AS in DEE, share at least partially overlapping pathophysiological and genetic mechanisms, which may be the target of drug and neurostimulation therapies. In addition, some patients with drug-resistant typical AS may present electroclinical features that lie in between the two extremes represented by these generalized forms of epilepsy.

Neuromorphometric associations with mood, cognition, and self-reported exercise levels in epilepsy and healthy individuals

Regular physical activity may promote beneficial neuroplasticity, e.g., increased hippocampus volume. However, it is unclear whether self-reported physical exercise in leisure (PEL) levels are associated with the brain structure features demonstrated by exercise interventions. This pilot study investigated the relationship between PEL, mood, cognition, and neuromorphometry in patients with idiopathic generalized epilepsy (IGEs) compared to healthy controls (HCs). Seventeen IGEs and 19 age- and sex-matched HCs underwent magnetic resonance imaging (MRI) at 3T. The Baecke Questionnaire of Habitual Physical Activity, Profile of Mood States, and Montreal Cognitive Assessment (MoCA) assessed PEL, mood, and cognition, respectively. Structural MRI data were analyzed by voxel- and surface-based morphometry. IGEs had significantly lower PEL (p < 0.001), poorer mood (p = 0.029), and lower MoCA scores (p = 0.027) than HCs. These group differences were associated with reduced volume, decreased gyrification, and altered surface topology (IGEs < HCs) in frontal, temporal and cerebellar regions involved in executive function, memory retrieval, and emotional regulation, respectively. These preliminary results support the notion that increased PEL may promote neuroplasticity in IGEs, thus emphasizing the role of physical activity in promoting brain health in people with epilepsy.

Is cortical inhibition in primary motor cortex related to executive control?

Recent research using paired-pulse transcranial magnetic stimulation (TMS) has shown that the speed with which people can stop an action is linked to GABAergic inhibitory activity in the motor system. Specifically, a significant proportion of the variance in stop signal reaction time (SSRT; a widely used measure of inhibitory control) is accounted for by short-interval cortical inhibition (SICI). It is still unclear whether this relationship reflects a broader link between GABAergic processes and executive functions, or a specific link between GABAergic processes and motor stopping ability. The current study sought to replicate the correlation between SSRT and SICI while investigating whether this association generalises to other measures of inhibitory control and working memory, and to long-interval cortical inhibition (LICI). Participants completed a battery of inhibition (Stop-Signal, Stroop, Flanker) and working memory (n-back, Digit Span, and Operation Span) tasks. We replicated the correlation between SICI and SSRT but found no other correlations between behavioural measures of executive control and the two cortical measures of inhibition. These findings indicate that the relationship between SSRT and SICI is specific to a particular property of response inhibition and likely reflects the function of local inhibitory networks mediated by GABA_A.

Drug resistance in idiopathic generalized epilepsies: Evidence and concepts

Although approximately 10%-15% of patients with idiopathic generalized epilepsy (IGE)/genetic generalized epilepsy remain drug-resistant, there is no consensus or established concept regarding the underlying mechanisms and prevalence. This review summarizes the recent data and the current hypotheses on mechanisms that may contribute to drug-resistant IGE. A literature search was conducted in PubMed and Embase for studies on mechanisms of drug resistance published since 1980. The literature shows neither consensus on the definition nor a widely accepted model to explain drug resistance in IGE or one of its subsyndromes. Large-scale genetic studies have failed to identify distinct genetic causes or affected genes involved in pharmacokinetics. We found clinical and experimental evidence in support of four hypotheses: (1) "network hypothesis"-the degree of drug resistance in IGE reflects the severity of cortical network alterations, (2) "minor focal lesion in a predisposed brain hypothesis"-minor cortical lesions are important for drug resistance, (3) "interneuron hypothesis"-impaired functioning of γ-aminobutyric acidergic interneurons contributes to drug resistance, and (4) "changes in drug kinetics"-genetically impaired kinetics of antiseizure medication (ASM) reduce the effectiveness of available ASMs. In summary, the exact definition and cause of drug resistance in IGE is unknown. However, published evidence suggests four different mechanisms that may warrant further investigation.

Brainwaves beyond diagnosis: Wider applications of electroencephalography in idiopathic generalized epilepsy

Electroencephalography (EEG) has long been used as a versatile and noninvasive diagnostic tool in epilepsy. With the advent of digital EEG, more advanced applications of EEG have emerged. Compared with technologically advanced practice in focal epilepsies, the utilization of EEG in idiopathic generalized epilepsy (IGE) has been lagging, often restricted to a simple diagnostic tool. In this narrative review, we provide an overview of broader applications of EEG beyond this narrow scope, discussing how the current clinical and research applications of EEG may potentially be extended to IGE. The current literature, although limited, suggests that EEG can be used in syndromic classification, guiding antiseizure medication therapy, predicting prognosis, unraveling biorhythms, and investigating functional brain connectivity of IGE. We emphasize the need for longer recordings, particularly 24-h ambulatory EEG, to capture discharges reflecting circadian and sleep-wake cycle-associated variations for wider EEG applications in IGE. Finally, we highlight the challenges and limitations of the current body of literature and suggest future directions to encourage and enhance more extensive applications of this potent tool.

Relationships between cognitive function, seizure control, and self-reported leisure-time exercise in epilepsy

Exercise may be a strategy for improvement of cognitive deficits commonly present in people with idiopathic generalized epilepsies (IGE). We investigated the relationship between cognition and level of physical exercise in leisure (PEL) in people with IGE who have been seizurefree for at least 6 months (IGE-) as compared to those who have not been seizurefree (IGE+) and healthy controls (HCs). We hypothesized that higher level of physical exercise is associated with better cognitive functioning in patients with IGE and HCs, and that seizure control affects both PEL levels and cognitive functioning in patients with IGE. We recruited 75 participants aged 18-65: 31 people with IGE (17 IGE-, 14 IGE+) and 44 HCs. Participants completed assessments of quality of life (SF-36), physical activity levels (Baecke questionnaire and International Physical Activity Questionnaire (IPAQ)) and cognition (Montreal Cognitive Assessment (MoCA), Hopkins Verbal Learning Test - Revised (HVLT), and flanker task). Group differences (HCs vs. IGE; HCs vs. IGE+ vs. IGE-) were assessed. Pearson correlations examined linear relationships between PEL and cognitive performance. Groups were similar in age and sex. Compared to HCs, patients with IGE had higher body mass index, fewer years of education, and consistently scored worse on all measures except flanker task accuracy on incongruent trials. When examining IGE- and IGE+ subgroups, compared to HCs, both had higher body mass index, and fewer years of education. Healthy controls scored significantly better than one or both of the IGE groups on SF-36 scores, PEL levels, IPAQ activity level, MoCA scores, HVLT learning and long-delay free-recall scores, and flanker task accuracy on congruent trials. Among patients with IGE, there were no significant differences between age of epilepsy onset, duration of epilepsy, number of anti-seizure drugs (ASDs) currently being used, or the group distribution of type of IGE. In the combined sample (IGE+, IGE- and HCs), PEL positively correlated with MoCA scores (Pearson's r = 0.238; p = 0.0397) and with flanker task accuracy on congruent trials (Pearson's r = 0.295; p = 0.0132). Overall, patients with IGE performed worse than HCs on cognitive and physical activity measures, but the cognitive impairments were more pronounced for IGE+, while physical exercise levels were less for patients with IGE regardless of seizure control. While positive relationships between leisure-time PEL and cognitive performance are promising, further investigations into how exercise levels interact with cognitive functioning in epilepsy are needed.

A Systematic Review of Long-Interval Intracortical Inhibition as a Biomarker in Neuropsychiatric Disorders

Long-interval intracortical inhibition (LICI) is a paired-pulse transcranial magnetic stimulation (TMS) paradigm mediated in part by gamma-aminobutyric acid receptor B (GABA_B) inhibition. Prior work has examined LICI as a putative biomarker in an array of neuropsychiatric disorders. This review conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) sought to examine existing literature focused on LICI as a biomarker in neuropsychiatric disorders. There were 113 articles that met the inclusion criteria. Existing literature suggests that LICI may have utility as a biomarker of GABA_B functioning but more research with increased methodologic rigor is needed. The extant LICI literature has heterogenous methodology and inconsistencies in findings. Existing findings to date are also non-specific to disease. Future research should carefully consider existing methodological weaknesses and implement high-quality test-retest reliability studies.

Slow repetitive transcranial magnetic stimulation in refractory juvenile myoclonic epilepsies

OBJECTIVE

The objective of the study was to investigate the effects of slow repetitive transcranial magnetic stimulation (rTMS) on patients with refractory juvenile myoclonic epilepsy (JME).

METHODS

One thousand pulses with the intensity of 120% active motor threshold (AMT) at 0.2 Hz frequency were applied on 5 consecutive days in 10 patients with refractory JME. Sham rTMS was performed after 3 months. Electroencephalography (EEG) examinations were performed before rTMS, on the 5th day, and 1, 2, 4, and 8 weeks after rTMS. Resting motor threshold (RMT), AMT, and cortical silent periods (CSPs) were recorded before the application and at the end of day 5. The changes in the quality of life were evaluated using the Quality of Life in Epilepsy Inventory (QOLIE-31).

RESULTS

No adverse effects were observed. The number of seizures decreased by 29-50%, and interictal discharge durations decreased 2 weeks after the real rTMS. No significant difference was observed between the AMT and RMT values recorded before and after the stimulations. Statistically significant increases in CSP duration and quality of life scores were found following real rTMS. Repetitive transcranial magnetic stimulation may be considered as a safe treatment option in refractory JME.

CONCLUSION

This study provides some positive evidence that rTMS may be effective in resistant JME.

Cortical excitability in epilepsy and the impact of antiepileptic drugs: transcranial magnetic stimulation applications

INTRODUCTION

Epileptic conditions are characterized by impaired cortical excitation/inhibition balance and interneuronal disinhibition. Transcranial magnetic stimulation (TMS) is a neurophysiological method that assesses brain excitation/inhibition.

AREA COVERED

This review was written after a detailed search in PubMed, EMBASE, ISI web of science, SciELO, Scopus, and Cochrane Controlled Trials databases from 1990 to 2020. It summarizes TMS applications for diagnostic and therapeutic purposes in epilepsy. TMS studies help to distinguish different epilepsy conditions and explore the antiepileptic drugs' (AEDs') effects on neuronal microcircuits and plasticity mechanisms. Repetitive TMS studies showed that low-frequency rTMS (0.33-1 Hz) can reduce seizures' frequency in refractory epilepsy or pause ongoing seizures; however, there is no current approval for its use in such patients as adjunctive treatment to AEDs.

EXPERT OPINION

There are variable and conflicting TMS results which reflect the distinct pathogenic mechanisms of each epilepsy condition, the dynamic epileptogenic process over the long disease course resulting in the development of recurrent spontaneous seizures and/or progression of epilepsy after it is established, and the differential effect of AEDs on cortical excitability. Future epilepsy research should focus on combined TMS/functional connectivity studies that explore the complex cortical excitability circuits and networks using different TMS parameters and techniques.

Neuroimaging of memory in frontal lobe epilepsy

In a large percentage of epilepsies, seizures have focal onset. These epilepsies are associated with a wide range of behavioral and cognitive deficits sometimes limited to the functions encompassed within the ictal onset zone but, more frequently, expanding beyond it. The presence of impairments associated with neuroanatomical areas outside of the ictal onset zone suggests distal propagation of epileptic activity via brain networks and interconnected whole-brain neural circuitry. In patients with frontal lobe epilepsy (FLE), using functional magnetic resonance imaging (fMRI) to identify deficits in working, semantic, and episodic memory may provide a lens through which to understand typical and atypical network organization. A network approach to focal epilepsy is relevant in these patients because of the frequently noted early age of seizure onset. Early seizure-related disruption in healthy brain development may result in a significant brain reorganization, development of compensation-related mechanisms of dealing with function abnormalities and disruptions, and the propagation of epileptic activity from the focus to widespread brain areas (functional deficit zones). Benefits of a network approach in the study of focal epilepsy are discussed along with considerations for future neuroimaging studies of patients with FLE.

fMRI study of cannabidiol-induced changes in attention control in treatment-resistant epilepsy

Patients with treatment-resistant epilepsy (TRE) frequently exhibit memory and attention deficits that contribute to their poor personal and societal outcomes. We studied the effects of adjunct treatment with pharmaceutical grade cannabidiol (CBD) oral solution (Epidiolex®; Greenwich Biosciences, Inc.) on attention control processes related to stimulus conflict resolution in patients with TRE. Twenty-two patients with TRE underwent 3 T magnetic resonance imaging (MRI) before receiving (PRE) and after achieving a stable dose of CBD (ON). Functional MRI (fMRI) data were collected while patients performed 2 runs of a flanker task (FT). Patients were instructed to indicate via button press the congruent (CON) and incongruent (INC) conditions. We performed t-tests to examine with FT attention control processes at PRE and ON visits and to compare the 2 visits using derived general linear model (GLM) data (INC - CON). We performed generalized psychophysiological interaction (gPPI) analyses to assess changes in condition-based functional connectivity on FT. Median time between fMRI visits was 10 weeks, and median CBD dose at follow-up was 25 mg/kg/d. From PRE to ON, participants experienced improvements in seizure frequency (SF) (p = 0.0009), seizure severity (Chalfont Seizure Severity Scale (CSSS); p < 0.0001), and mood (Total Mood Disturbance (TMD) score from Profile of Mood States (POMS); p = 0.0026). Repeated measures analysis of variance showed nonsignificant improvements in executive function from 34.6 (23.5)% to 41.9 (22.4)% CON accuracy and from 34.2 (25.7)% to 37.6 (24.4)% INC accuracy (p = 0.199). Change in CON accuracy was associated with change in INC accuracy (r_S = 0.81, p = 0.0005). Participants exhibited CBD-induced increases in fMRI activation in the right superior frontal gyrus (SFG) and right insula/middle frontal gyrus (MFG) and decrease in activation for both regions at ON relative to PRE (corrected p = 0.05). The subset of patients who improved in FT accuracy with CBD showed a negative association between change in right insula/MFG activation and change in accuracy for the INC condition (r_S = -0.893, p = 0.0068). The gPPI analysis revealed a CBD-induced decrease in condition-based functional connectivity differences for the right SFG seed region (corrected p = 0.05). Whole-brain regression analysis documented a negative association of change in right insula/MFG condition-based connectivity with change in INC accuracy (corrected p = 0.005). Our results suggest that CBD modulates attention control processing in patients with TRE by reducing right SFG and right insula/MFG activation related to stimulus conflict resolution and by dampening differences in condition-based functional connectivity of the right SFG. Our study is the first to provide insight into how CBD affects the neural substrates involved in attention processing and how modulation of the activity and functional connectivity related to attentional control processes in the right insula/MFG may be working to improve cognitive performance in TRE.

Cortical excitability affects mood state in patients with idiopathic generalized epilepsies (IGEs)

Previously, we demonstrated an association between cortical hyperexcitability and mood disturbance in healthy adults. Studies have documented hyperexcitability in patients with idiopathic generalized epilepsies (IGEs; long-interval intracortical inhibition [LICI]) and high prevalence of mood comorbidities. This study aimed to investigate the influences of cortical excitability and seizure control on mood state in patients with IGEs. Single and paired-pulse transcranial magnetic stimulation (TMS) was applied to 30 patients with IGEs (16 controlled IGEs [cIGEs], 14 with treatment-resistant IGEs [trIGEs]), and 22 healthy controls (HCs) to assess cortical excitability with LICI. The Profile of Mood Sates (POMS) questionnaire was used to assess total mood disturbance (TMD), as well as, six mood domains: Depression, Confusion, Anger, Anxiety, Fatigue, and Vigor. To assess the effects of seizure control (HC vs. cIGEs vs. trIGEs) and LICI response (inhibitory vs. excitatory) on TMD, a two-way multivariate analysis of variance (MANOVA) was performed. Analyses revealed a significant main effect of long-interval intracortical inhibition (LICI) response on TMD (F(1, 46) = 4.69, p = 0.04), but not seizure control (F(2, 46) = 0.288, p = 0.75). Excitatory responders endorsed significantly higher TMD scores, indicating greater mood disturbance, than inhibitory responders (MD = -2.12; T (50) = -2.47, p = 0.04). Also, excitatory responders endorsed more items than inhibitory responders on the Depression (MD = -2.12; T (50) = -2.47, p = 0.04) and Fatigue (MD = -3.42; T (50) = -2.96, p = 0.03) subscales of the POMS. These findings provide further evidence of a relationship between hyperexcitability and mood disturbance, and indicate that cortical excitability may have greater influence on mood state than seizure control in patients with IGEs. Results also support theories for the underlying role of gamma-aminobutyric acid (GABA) network dysfunction in the etiology of depression. To better understand the clinical relevance and causal nature of these relationships, further investigation is warranted.