Transcranial direct current stimulation for refractory major depressive disorder temporal lobe epilepsy: A quantitative electroencephalography study

Transcranial Direct Current Stimulation Reduces Anxiety, Depression and Plasmatic Corticosterone in a Rat Model of Atypical Generalized Epilepsy

Affective disorders (i.e. anxiety and depression) are commonly observed in patients with epilepsy and induce seizure aggravation. Animal models of epilepsy that exhibit affective disorder features are essential in developing new neuromodulatory treatments. GEAS-W rats (Generalized Epilepsy with Absence Seizures, Wistar background) are an inbred model of generalized epilepsy showing spontaneous spike-wave discharges concomitant with immobility. Transcranial Direct Current Stimulation (tDCS) is a safe non-invasive neuromodulatory therapy used to modulate dysfunctional circuitries frequently and successfully applied in affective disorders for symptom alleviation. Here we investigated anxiolytic and antidepressant effects of tDCS in GEAS-W rats and the role of corticosterone as a possible mechanism of action. GEAS-W and Wistar rats were randomly divided into control, sham-tDCS and active-tDCS groups. Both tDCS groups received 15 sessions of sham or active-tDCS (1 mA, cathode). Behavioural tests included the Open Field and Forced Swimming tests followed by corticosterone analysis. We observed a main effect of treatment and a significant treatment by strain interaction on anxiety-like and depressive-like behaviours, with active-tDCS GEAS-W rats entering the center of the open field more often and showing less immobility in the forced swimming test. Furthermore, there was a main effect of treatment on corticosterone with active-tDCS animals showing marked reduction in plasmatic levels. This study described preclinical evidence to support tDCS treatment of affective disorders in epilepsy and highlights corticosterone as a possible mechanism of action.

Transcranial direct current stimulation (tDCS) in the management of epilepsy: A systematic review

PURPOSE

Current therapies for the management of epilepsy are still suboptimal for several patients due to inefficacy, major adverse events, and unavailability. Transcranial direct current stimulation (tDCS), an emergent non-invasive neuromodulation technique, has been tested in epilepsy samples over the past two decades to reduce either seizure frequency or electroencephalogram (EEG) epileptiform discharges.

METHODS

A systematic review was performed in accordance with PRISMA guidelines (PROSPERO record CRD42020160292). A thorough electronic search was completed in MEDLINE, EMBASE, CENTRAL and Scopus databases for trials that applied tDCS interventions to children and adults with epilepsy of any cause, from inception to April 30, 2020.

RESULTS

Twenty-seven studies fulfilled eligibility criteria, including nine sham-controlled and 18 uncontrolled trials or case reports/series. Samples consisted mainly of drug-resistant focal epilepsy patients that received cathodal tDCS stimulation targeted at the site with maximal EEG abnormalities. At follow-up, 84 % (21/25) of the included studies reported a reduction in seizure frequency and in 43 % (6/14) a decline in EEG epileptiform discharge rate was observed. No serious adverse events were reported.

CONCLUSIONS

Cathodal tDCS is both a safe and probably effective technique for seizure control in patients with drug-resistant focal epilepsy. However, published trials are heterogeneous regarding samples and methodology. More and larger sham-controlled randomized trials are needed, preferably with mechanistic informed stimulation protocols, to further advance tDCS therapy in the management of epilepsy.

The utility and application of electrophysiological methods in the study of visual hallucinations

Visual hallucinations (VH) are a common symptom in multiple clinical and non-clinical populations. Although structural and functional neuroimaging has informed the understanding of VH, temporal resolution is limited. Electrophysiological techniques provide a complementary perspective on dynamic and temporal aspects of neural functioning, offering greater insight into the mechanisms underlying their formation. In this review we examine and critically evaluate the emerging evidence base utilising electrophysiological approaches in the study of VH. Overall, increased visual system excitability, dysfunctional visual processing and network connectivity, and cholinergic dysfunction have been consistently observed in VH-prone pathologies. However, a major limitation is in the lack of robust experimental studies and the reliance on single case reports. We conclude that electrophysiology provides tentative evidence for the contribution of bottom-up, top-down, and network dysfunction in the aetiology of VH, supporting several existing VH models. Furthermore, we discuss how electrophysiology has been directly utilised in specific clinical interventions for VH. Further exploration utilising electrophysiology in combination with, for example, neuroimaging will help better understand VH aetiology while aiding in the development of novel therapeutic interventions for this difficult to treat symptom.