Intraoperative neurophysiological responses in epileptic patients submitted to hippocampal and thalamic deep brain stimulation

Functional network dynamics between the anterior thalamus and the cortex in deep brain stimulation for epilepsy

Owing to its unique connectivity profile with cortical brain regions, and its suggested role in the subcortical propagation of seizures, the anterior nucleus of the thalamus (ANT) has been proposed as a key deep brain stimulation (DBS) target in drug-resistant epilepsy. However, the spatio-temporal interaction dynamics of this brain structure, and the functional mechanisms underlying ANT DBS in epilepsy remain unknown. Here, we study how the ANT interacts with the neocortex in vivo in humans and provide a detailed neurofunctional characterization of mechanisms underlying the effectiveness of ANT DBS, aiming at defining intraoperative neural biomarkers of responsiveness to therapy, assessed at 6 months post-implantation as the reduction in seizure frequency. A cohort of 15 patients with drug-resistant epilepsy (n = 6 males, age = 41.6 ± 13.79 years) underwent bilateral ANT DBS implantation. Using intraoperative cortical and ANT simultaneous electrophysiological recordings, we found that the ANT is characterized by high amplitude θ (4-8 Hz) oscillations, mostly in its superior part. The strongest functional connectivity between the ANT and the scalp EEG was also found in the θ band in ipsilateral centro-frontal regions. Upon intraoperative stimulation in the ANT, we found a decrease in higher EEG frequencies (20-70 Hz) and a generalized increase in scalp-to-scalp connectivity. Crucially, we observed that responders to ANT DBS treatment were characterized by higher EEG θ oscillations, higher θ power in the ANT, and stronger ANT-to-scalp θ connectivity, highlighting the crucial role of θ oscillations in the dynamical network characterization of these structures. Our study provides a comprehensive characterization of the interaction dynamic between the ANT and the cortex, delivering crucial information to optimize and predict clinical DBS response in patients with drug-resistant epilepsy.

Deep learning for automated detection of generalized paroxysmal fast activity in Lennox-Gastaut syndrome

OBJECTIVES

Generalized paroxysmal fast activity (GPFA) is a key electroencephalographic (EEG) feature of Lennox-Gastaut Syndrome (LGS). Automated analysis of scalp EEG has been successful in detecting more typical abnormalities. Automatic detection of GPFA has been more challenging, due to its variability from patient to patient and similarity to normal brain rhythms. In this work, a deep learning model is investigated for detection of GPFA events and estimating their overall burden from scalp EEG.

METHODS

Data from 10 patients recorded during four ambulatory EEG monitoring sessions are used to generate and validate the model. All patients had confirmed LGS and were recruited into a trial for thalamic deep-brain stimulation therapy (ESTEL Trial).

RESULTS

The correlation coefficient between manual and model estimates of event counts was r2 = 0.87, and for total burden was r2 = 0.91. The average GPFA detection sensitivity was 0.876, with an average false-positive rate of 3.35 per minute. There was no significant difference found between patients with early or delayed deep brain stimulation (DBS) treatment, or those with active vagal nerve stimulation (VNS).

CONCLUSIONS

Overall, the deep learning model was able to accurately detect GPFA and provide accurate estimates of the overall GPFA burden and electrographic event counts, albeit with a high false-positive rate.

SIGNIFICANCE

Automated GPFA detection may enable automated calculation of EEG biomarkers of burden of disease in LGS.

Deep brain stimulation of the anterior nuclei of the thalamus in focal epilepsy

OBJECTIVE

To review the therapeutic effects of deep brain stimulation of the anterior nuclei of the thalamus (ANT-DBS) and the predictors of its effectiveness, safety, and adverse effects.

METHODS

A comprehensive search of the medical literature (PubMed) was conducted to identify relevant articles investigating ANT-DBS therapy for epilepsy. Out of 332 references, 77 focused on focal epilepsies were reviewed.

RESULTS

The DBS effect is probably due to decreased synchronization of epileptic activity in the cortex. The potential mechanisms from cellular to brain network levels are presented. The ANT might participate actively in the network elaborating focal seizures. The effects of ANT-DBS differed in various studies; ANT-DBS was linked with a 41% seizure frequency reduction at 1 year, 69% at 5 years, and 75% at 7 years. The most frequently reported adverse effects, depression and memory impairment, were considered non-serious in the long-term follow-up view. ANT-DBS also has been used in a few cases to treat status epilepticus.

CONCLUSIONS

We reviewed the clinical literature and identified several factors that may predict seizure outcome following DBS therapy. More large-scale trials are required since there is a need to explore stimulation settings, apply patient-tailored therapy, and identify the presurgical predictors of patient response.

SIGNIFICANCE

A critical review of the published literature on ANT-DBS in focal epilepsy is presented. ANT-DBS mechanisms are not fully understood; possible explanations are provided. Biomarkers of ANT-DBS effectiveness may lead to patient-tailored therapy.

Short-term changes in cortical physiological arousal measured by electroencephalography during thalamic centromedian deep brain stimulation

OBJECTIVE

The intralaminar thalamus is well implicated in the processes of arousal and attention. Stimulation of the intralaminar thalamus has been used therapeutically to improve level of alertness in minimally conscious individuals and to reduce seizures in refractory epilepsy, both presumably through modulation of thalamocortical function. Little work exists that directly measures the effects of intralaminar thalamic stimulation on cortical physiological arousal in humans. Therefore, our goal was to quantify cortical physiological arousal in individuals with epilepsy receiving thalamic intralaminar deep brain stimulation.

METHODS

We recorded scalp electroencephalogram (EEG) during thalamic intralaminar centromedian (CM) nucleus stimulation in 11 patients with medically refractory epilepsy. Participants underwent stimulation at 130 Hz and 300 µs for periods of 5 min alternating with 5 min of rest while stimulus voltage was titrated upward from 1 to 5 V. EEG signal power was analyzed in different frequency ranges in relation to stimulus strength and time.

RESULTS

We found a progressive increase in broadband gamma (25-100 Hz) cortical EEG power (F = 7.64, p < .05) and decrease in alpha (8-13 Hz) power (F = 4.37, p < .05) with thalamic CM stimulation. Topographic maps showed these changes to be widely distributed across the cortical surface rather than localized to one region.

SIGNIFICANCE

Previous work has shown that broadband increases in gamma frequency power and decreases in alpha frequency power are generally associated with states of cortical activation and increased arousal/attention. Our observed changes therefore support the possible role of cortical activation and increased physiological arousal in therapeutic effects of intralaminar thalamic stimulation for improving both epilepsy and attention. Further investigations with this approach may lead to methods for determining optimal deep brain stimulation parameters to improve clinical outcome in these disorders.

UltraHigh Field MR Imaging in Epilepsy

More than one million people in the United States suffer from seizures that are not controlled with antiseizure medications. Targeted interventions such as surgery and deep brain stimulation can confer seizure reduction or even freedom in many of these patients with drug-resistant epilepsy, but success critically depends on identification of epileptogenic zones through MR imaging. Ultrahigh field imaging facilitates improved sensitivity and resolution across many imaging modalities and may facilitate better detection of epileptic markers than is achieved at lower field strengths. The increasing availability and clinical adoption of ultrahigh field scanners play an important role in characterizing drug-resistant epilepsy and planning for its treatment.

Long-term seizure outcome during continuous bipolar hippocampal deep brain stimulation in patients with temporal lobe epilepsy with or without mesial temporal sclerosis: An observational, open-label study

OBJECTIVE

We present the findings related to seizure outcome during hippocampal deep brain stimulation (Hip-DBS) in patients with refractory temporal lobe epilepsy.

METHODS

Twenty-five patients submitted to Hip-DBS were studied. All patients were evaluated with interictal and ictal electroencephalography (EEG) and high-resolution 1.5 T magnetic resonance imaging (MRI). The hippocampus was targeted directly on MRI using a posterior occipital burr hole approach. Bipolar continuous stimulation was ramped up until 3.0 V (300 µs, 130 Hz). Patients were considered responders if at least 50% seizure frequency reduction was obtained.

RESULTS

Median age was 39 years; median follow-up time was 57 months (16 women). All patients had focal with impaired awareness seizure (FIAS) and 23 patients had focal aware seizure (FAS). Baseline median FAS and FIAS frequency was 8. Ictal EEG showed unilateral (n = 10) or bilateral (n = 15) seizure onset. MRI showed unilateral (n = 11) or bilateral (n = 8) mesial temporal sclerosis (MTS) and was normal in six6 patients. Fifteen patients were submitted to bilateral and 10 patients to unilateral Hip-DBS. Median reduction in FAS frequency was 66%. Eighteen patients with FAS were considered responders and five (21%) were free of FAS. Median FIAS frequency (n = 25) reduction was 91%. Twenty-two patients were considered responders and eight (32%) were free of FIAS. FIAS were significantly more reduced then FAS (P = .017). There was no relation between any contact's position within the hippocampus and outcome for either FAS (P = .727) or FIAS (P = .410). There was no difference in outcome in patients submitted to either unilateral or bilateral Hip-DBS regarding FAS (P = .978) or FIAS (P = .693).

SIGNIFICANCE

Hip-DBS significantly reduced the frequency of both FAS and FIAS in this cohort of patients with refractory temporal lobe epilepsy. Hip-DBS might represent a good therapeutic option in such patients not amenable to resective surgery.

Seizure outcome during bilateral, continuous, thalamic centromedian nuclei deep brain stimulation in patients with generalized epilepsy: a prospective, open-label study

OBJECTIVE

We report on the seizure frequency and attention outcome during thalamic centromedian stimulation (CM-DBS) in patients with refractory generalized epilepsy (GE).

METHODS

Twenty consecutive patients with GE who were submitted to CM-DBS and had at least one year of follow-up were prospectively studied. The CM was targeted bilaterally. Stimulation intensity was ramped up (bipolar, continuous, 130 Hz; 300μsec) until 4.5 V or until side effects developed. Contacts` position was determined on postoperative volumetric MRI scans. Attention was qualitatively evaluated using the SNAP-IV (Swanson, Nolan, and Pelham) questionnaire. Patients were considered responders during CM-DBS if an at least 50% seizure frequency reduction was obtained compared to baseline.

RESULTS

Median age was 15.5 years (13 males). Median follow-up time was 2.55 years. EEG disclosed generalized spike-and wave discharges in all patients. MRI was normal in 10 patients, showed diffuse atrophy in 6 patients, and showed abnormalities in 4 patients (3 patients had bilateral cortical development abnormalities and one had unilateral hemispheric atrophy). Patients presented with daily multiple seizure types (8 to 66 per day; median: 37), including tonic, atonic, myoclonic, atypical absence and generalized tonic-clonic seizures. Mean DBS intensity was 4.3 V. An insertional effect was noted in 14 patients. CM-DBS was able to significantly reduce the frequency of tonic (p < 0.001), atypical absence seizures (p < 0.001), atonic seizures (p = 0.001) and bilateral generalized tonic-clonic seizures (p = 0.004). One patient became seizure-free. Ninety percent of the patients were considered responders (>50% seizure frequency reduction). All patients showed some improvement in attention. The mean number of items in which improvement was noted in the SNAP-IV questionnaire was 4.8. There was a significant relationship between overall seizure frequency reduction and improvement of attention (p = 0.033).

DISCUSSION

This prospective, open label study included a large, homogeneous cohort and provided evidence on the efficacy of CM-DBS in reducing the seizure burden and increasing attention in patients with refractory generalized epilepsy.

The Appearance Order of Varying Intervals Introduces Extra Modulation Effects on Neuronal Firing Through Non-linear Dynamics of Sodium Channels During High-Frequency Stimulations

Electrical pulse stimulation in the brain has shown success in treating several brain disorders with constant pulse frequency or constant inter-pulse interval (IPI). Varying IPI may offer a variety of novel stimulation paradigms and may extend the clinical applications. However, a lack of understanding of neuronal responses to varying IPI limits its informed applications. In this study, to investigate the effects of varying IPI, we performed both rat experiments and computational modeling by applying high-frequency stimulation (HFS) to efferent axon fibers of hippocampal pyramidal cells. Antidromically evoked population spikes (PSs) were used to evaluate the neuronal responses to pulse stimulations with different IPI patterns including constant IPI, gradually varying IPI, and randomly varying IPI. All the varying IPI sequences were uniformly distributed in the same interval range of 10 to 5 ms (i.e., 100 to 200 Hz). The experimental results showed that the mean correlation coefficient of PS amplitudes to the lengths of preceding IPI during HFS with random IPI (0.72 ± 0.04, n = 7 rats) was significantly smaller than the corresponding correlation coefficient during HFS with gradual IPI (0.92 ± 0.03, n = 7 rats, P < 0.001, t-test). The PS amplitudes induced by the random IPI covered a wider range, over twice as much as that induced by the gradual IPI, indicating additional effects induced by merely changing the appearance order of IPI. The computational modeling reproduced these experimental results and provided insights into these modulatory effects through the mechanism of non-linear dynamics of sodium channels and potassium accumulation in the narrow peri-axonal space. The simulation results showed that the HFS-induced increase of extracellular potassium ([K⁺] _o ) elevated the membrane potential of axons, delayed the recovery course of sodium channels that were repeatedly activated and inactivated during HFS, and resulted in intermittent neuronal firing. Because of non-linear membrane dynamics, random IPI recruited more neurons to fire together following specific sub-sequences of pulses than gradual IPI, thereby widening the range of PS amplitudes. In conclusion, the study demonstrated novel HFS effects of neuronal modulation induced by merely changing the appearance order of the same group of IPI of pulses, which may inform the development of new stimulation patterns to meet different demands for treating various brain diseases.

How technology is driving the landscape of epilepsy surgery

This article emphasizes the role of the technological progress in changing the landscape of epilepsy surgery and provides a critical appraisal of robotic applications, laser interstitial thermal therapy, intraoperative imaging, wireless recording, new neuromodulation techniques, and high-intensity focused ultrasound. Specifically, (a) it relativizes the current hype in using robots for stereo-electroencephalography (SEEG) to increase the accuracy of depth electrode placement and save operating time; (b) discusses the drawback of laser interstitial thermal therapy (LITT) when it comes to the need for adequate histopathologic specimen and the fact that the concept of stereotactic disconnection is not new; (c) addresses the ratio between the benefits and expenditure of using intraoperative magnetic resonance imaging (MRI), that is, the high technical and personnel expertise needed that might restrict its use to centers with a high case load, including those unrelated to epilepsy; (d) soberly reviews the advantages, disadvantages, and future potentials of neuromodulation techniques with special emphasis on the differences between closed and open-loop systems; and (e) provides a critical outlook on the clinical implications of focused ultrasound, wireless recording, and multipurpose electrodes that are already on the horizon. This outlook shows that although current ultrasonic systems do have some limitations in delivering the acoustic energy, further advance of this technique may lead to novel treatment paradigms. Furthermore, it highlights that new data streams from multipurpose electrodes and wireless transmission of intracranial recordings will become available soon once some critical developments will be achieved such as electrode fidelity, data processing and storage, heat conduction as well as rechargeable technology. A better understanding of modern epilepsy surgery will help to demystify epilepsy surgery for the patients and the treating physicians and thereby reduce the surgical treatment gap.

Variability Between Direct and Indirect Targeting of the Anterior Nucleus of the Thalamus

BACKGROUND

Preoperative thalamic targeting methods have historically relied on indirect targeting techniques that do not fully account for variances in anatomy or for thalamic atrophy in epilepsy. We aimed to address variability noted between traditional indirect targeting and direct targeting methods for the anterior nucleus of the thalamus (ANT).

METHODS

Fifteen consecutive patients undergoing ANT deep brain stimulator placement were evaluated (30 thalamic nuclei). Direct ANT targeting was performed using a fast gray matter acquisition T1 inversion recovery sequence and compared with standard stereotactic coordinates. Thalamic volumes were calculated for each patient, and degree of thalamic volume loss was assessed compared with matched control subjects. Vertex analysis was performed to assess shape changes in the thalamus compared with age- and sex-matched subjects.

RESULTS

There was significant variation between direct and indirect targets in the y-axis and z-axis on both sides. On the left, the direct target was located at y = 2 ± 1.3 mm and z = 9.3 ± 1.8 mm (both P = 0.02). On the right, the direct target was located at y = 2.9 ± 1.8 mm and z = 9.2 ± 2 mm (both P ≤ 0.0003). There was no significant difference in the x-coordinate on either side (P > 0.5). Additionally, there was a correlation between thalamic volume and difference between direct and indirect targets in the y-axis and the z-axis.

CONCLUSIONS

We showed a significant difference in direct and indirect targeting in the y-axis and z-axis when targeting the ANT for deep brain stimulation for epilepsy. This difference is correlated to thalamic volume, with a larger difference noted in patients with thalamic atrophy.

Cerebrospinal Fluid Egress from the Quadripolar Deep Brain Stimulation Electrode for Anterior Nucleus of the Thalamus for Refractory Epilepsy

Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) is an effective treatment for refractory epilepsy. Due to the unique location of ANT in the thalamus facing the lateral and third ventricles, transventricular DBS lead placement is an essential part of ANT DBS. However, there is no report regarding hardware problems including impedance variability in transventricular ANT DBS due to limited experience. A 45-year-old male patient with previously effective, bilateral ANT DBS presented with increasing seizure frequency and a shortened battery longevity within 2 years. Magnetic resonance imaging showed that the left-sided DBS lead was in the third ventricle leaning on the medial wall of ANT. Electrode revision was performed. Upon disconnecting the proximal lead from the extension connection, cerebrospinal fluid egress through fine gaps between the metallic electrode contacts, and electrode spacing was observed. This case raises a concern about the transventricular approach for ANT lead placement because the currently available DBS electrode lead is not waterproofed. A careful, longitudinal follow-up of DBS impedance for ANT DBS is warranted.

Epilepsy and Neuromodulation-Randomized Controlled Trials

Neuromodulation is a treatment strategy that is increasingly being utilized in those suffering from drug-resistant epilepsy who are not appropriate for resective surgery. The number of double-blinded RCTs demonstrating the efficacy of neurostimulation in persons with epilepsy is increasing. Although reductions in seizure frequency is common in these trials, obtaining seizure freedom is rare. Invasive neuromodulation procedures (DBS, VNS, and RNS) have been approved as therapeutic measures. However, further investigations are necessary to delineate effective targeting, minimize side effects that are related to chronic implantation and to improve the cost effectiveness of these devices. The RCTs of non-invasive modes of neuromodulation whilst showing much promise (tDCS, eTNS, rTMS), require larger powered studies as well as studies that focus at better targeting techniques. We provide a review of double-blinded randomized clinical trials that have been conducted for neuromodulation in epilepsy.

Deep brain stimulation for refractory temporal lobe epilepsy: a systematic review and meta-analysis with an emphasis on alleviation of seizure frequency outcome

OBJECTIVE

Conflicting conclusions have been reported regarding predictors of deep brain stimulation (DBS) outcome in patients with refractory temporal lobe epilepsy (TLE). The main goal of this meta-analysis study was to identify possible predictors of remarkable seizure reduction (RSR).

METHODS

We conducted a comprehensive search of English-language literature published since 1990 and indexed in PubMed, Embase, and the Cochrane Library that addressed seizure outcomes in patients who underwent DBS for refractory TLE. A pooled RSR rate was determined for eight included studies. RSR rates were analyzed relative to potential prognostic variables. Random- or fixed-effects models were used depending on the presence or absence of heterogeneity.

RESULTS

The pooled RSR rate among 61 DBS-treated patients with TLE from 8 studies was 59%. Higher likelihood of RSR was found to be associated with lateralization of stimulation, lateralized ictal EEG findings, and a longer follow-up period. Seizure semiology, MRI abnormalities, and patient sex were not predictive of RSR rate. The best electrode type for RSR was the Medtronic 3389. Hippocampal and anterior thalamic nuclei (ATN) sites of stimulation had similar odds of producing RSR.

CONCLUSIONS

DBS is an effective therapeutic modality for intractable TLE, particularly in patients with lateralized EEG abnormalities and in patients treated on the ictal side. This meta-analysis provides evidence-based information for determining DBS suitability in presurgical counseling and for explaining seizure outcomes.

Neurostimulation as a promising epilepsy therapy

The revolution in theory, swift technological developments, and invention of new devices have driven tremendous progress in neurostimulation as a third‐line treatment for epilepsy. Over the past decades, neurostimulation took its place in the field of epilepsy as an advanced treatment technique and opened up a new world. Numerous animal studies have proven the physical efficacy of stimulation of the brain and peripheral nerves. Based on this optimistic fundamental research, new advanced techniques are being explored in clinical practice. Over the past century, drawing on the benefits brought about by vagus nerve stimulation for the treatment of epilepsy, various new neurostimulation modalities have been developed to control seizures. Clinical studies including case reports, case series, and clinical trials have been booming in the past several years. This article gives a comprehensive review of most of these clinical studies. In addition to highlighting the advantages of neurostimulation for the treatment of epilepsy, concerns with this modality and future development directions are also discussed. The biggest advantage of neurostimulation over pharmacological treatments for epilepsy is the modulation of the epilepsy network by delivering stimuli at a specific target or the “hub.” Conversely, however, a lack of knowledge of epilepsy networks and the mechanisms of neurostimulation may hinder further development. Therefore, theoretical research on the mechanism of epileptogenesis and epilepsy networks is needed in the future. Within the multiple modalities of neuromodulation, the final choice should be made after full discussion with a multidisciplinary team at a presurgical conference. Furthermore, the establishment of a neurostimulation system with standardized parameters and rigorous guidelines is another important issue. To achieve this goal, a worldwide collaboration of epilepsy centers is also suggested in the future.

Seizure outcome after hippocampal deep brain stimulation in patients with refractory temporal lobe epilepsy: A prospective, controlled, randomized, double-blind study

OBJECTIVE

We designed a prospective, randomized, controlled, double-blind study to evaluate the efficacy of hippocampal deep brain stimulation (Hip-DBS) in patients with refractory temporary lobe epilepsy (TLE).

METHODS

Sixteen adult patients with refractory TLE were studied. Patient's workup included medical history, interictal and ictal electroencephalography (EEG), and high-resolution 1.5T magnetic resonance imaging (MRI). Patients were randomized on a 1:1 proportion to an active (stimulation on) or to a control (no stimulation) arm. After implantation, patients were allowed to recover for 1 month, which was followed by a 1-month titration (or sham) period. The 6-month blinded phase started immediately afterward. A postoperative MRI confirmed the electrode's position in all patients. All patients received bipolar continuous stimulation. Stimulus duration was 300 μs and frequency was 130 Hz; final intensity was 2 V. Patients were considered responders when they had at least 50% seizure frequency reduction.

RESULTS

All patients had focal impaired awareness seizures (FIAS, complex partial seizures), and 87% had focal aware seizures (FAS, simple partial seizures). Mean preoperative seizure frequency was 12.5 ± 9.4 (mean ± standard deviation) per month. MRI findings were normal in two patients, disclosed bilateral mesial temporal sclerosis (MTS) in three, left MTS in five, and right MTS in six patients. An insertional effect could be noted in both control and active patients. In the active group (n = 8), four patients became seizure-free; seven of eight were considered responders and one was a nonresponder. There was a significant difference regarding FIAS frequency between the two groups from the first month of full stimulation (p < 0.001) until the end of the blinded phase (p < 0.001). This was also true for FAS, except for the third month of the blinded phase.

SIGNIFICANCE

Hip-DBS was effective in significantly reducing seizure frequency in patients with refractory TLE in the active group, as compared to the control group. Fifty-percent of the patients in the active group became seizure-free. The present study is the larger prospective, controlled, double-blind study to evaluate the effects of Hip-DBS published to date.

Relationship between Postoperative EEG Driving Response and Lead Location in Deep Brain Stimulation of the Anterior Nucleus of the Thalamus for Refractory Epilepsy

OBJECTIVES

Interpreting the postoperative electroencephalographic (EEG) driving response (DR) as an indicator of electrode placement within the thalamic nucleus in deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) for refractory epilepsy is controversial.

MATERIALS AND METHODS

We retrospectively investigated the relationship between postoperative EEG DR and the location of 11 electrodes in 6 patients who underwent ANT DBS for refractory epilepsy.

RESULTS

Cerebral synchronizing EEG DR was observed in 10 electrodes. However, 9 of the 11 electrodes were located within the ANT. For the 2 electrodes that missed the ANT, DR was observed in 1 misplaced electrode facing the anterior surface of the ANT within the third ventricle. The other misplaced electrode without DR elicitation showed a DR after electrode repositioning.

CONCLUSIONS

The diagnostic significance of DR as indirect evidence of electrodes being within thalamic nuclei is limited. If DR is not elicited, it should be regarded as a misplacement. Even if DR is elicited, it may not be interpreted as a sound indicator of proper electrode placement within the thalamus. A sophisticated, postoperative imaging study is warranted in every case of ANT DBS.

Anterior nuclear deep brain stimulation guided by concordant hippocampal recording

OBJECT

Anterior nuclear (AN) stimulation has been reported to reduce the frequency of seizures, in some cases dramatically; however, it has not been approved by the US Food and Drug Administration. The anterior nucleus is difficult to target because of its sequestered location, partially surrounded by the ventricle. It has traditionally been targeted by using transventricular or lateral transcortical routes. Here, the authors report a novel approach to targeting the anterior nucleus and neurophysiologically confirming effective stimulation of the target, namely evoked potentials in the hippocampus.

METHODS

Bilateral AN 3389 electrodes were placed in a novel trajectory followed by bilateral hippocampal 3391 electrodes from a posterior trajectory. Each patient was implanted bilaterally with a Medtronic Activa PC+S device under an investigational device exemption approval. Placement was confirmed with CT. AN stimulation-induced hippocampal evoked potentials were measured to functionally confirm placement in the anterior nucleus.

RESULTS

Two patients had implantations by way of a novel AN trajectory with concomitant hippocampal electrodes. There were no lead misplacements. Postoperative stimulation of the anterior nucleus with a PC+S device elicited evoked potentials in the hippocampus. Thus far, both patients have reported a > 50% improvement in seizure frequency.

CONCLUSIONS

Placing AN electrodes posteriorly may provide a safer trajectory than that used for traditionally placed AN electrodes. In addition, with a novel battery that is capable of electroencephalographic recording, evoked potentials can be used to functionally assess the Papez circuit. This treatment paradigm may offer increased AN stimulation efficacy for medically intractable epilepsy by assessing functional placement more effectively and thus far has proven safe.

Seizure Outcome After Battery Depletion in Epileptic Patients Submitted to Deep Brain Stimulation

OBJECTIVE

We studied patients treated with chronic DBS in whom there was depletion of the generator's battery, in order to get insight on the modulatory potential of chronic DBS in refractory epilepsy.

MATERIAL

Nine adult patients with refractory epilepsy treated with at least three years of deep brain stimulation (DBS), and who were followed up for at least six months after battery depletion were studied. One patient was treated with hippocampal DBS (Hip-DBS), two to centro-median DBS (CM-DBS) and six to anterior nucleus stimulation (AN-DBS).

RESULTS

Two patients did not have seizure's frequency modification after battery depletion; the other seven patients had seizure frequency increase, including those three patients that were seizure-free. Five of those seven patients who had seizure frequency increase after battery's depletion had seizure's frequency lower than their pre-DBS baseline seizure frequency; two of such patients returned to their pre-DBS baseline seizure frequency.

CONCLUSIONS

In the majority of the patients, three years of chronic DBS did not show a permanent effect on epileptogenesis. On the other hand, the post-battery depletion seizure's frequency was usually much lower than the baseline (pre-DBS) seizure's frequency, suggesting that there was actual network neuromodulation.

Deep brain stimulation for the treatment of epilepsy: circuits, targets, and trials

Deep brain stimulation (DBS) has proven remarkably safe and effective in the treatment of movement disorders. As a result, it is being increasingly applied to a range of neurologic and psychiatric disorders, including medically refractory epilepsy. This review will examine the use of DBS in epilepsy, including known targets, mechanisms of neuromodulation and seizure control, published clinical evidence, and novel technologies. Cortical and deep neuromodulation for epilepsy has a long experimental history, but only recently have better understanding of epileptogenic networks, precise stereotactic techniques, and rigorous trial design combined to improve the quality of available evidence and make DBS a viable treatment option. Nonetheless, underlying mechanisms, anatomical targets, and stimulation parameters remain areas of active investigation.

c-FOS expression after hippocampal deep brain stimulation in normal rats

OBJECTIVES

We studied the effects of Hip-deep brain stimulation (DBS) on the expression of the inducible transcription factor c-FOS in the brain of normal rats.

MATERIALS AND METHODS

Ten Wistar rats were anesthetized, and nine were implanted with epidural and hippocampal electrodes for brain activity recording; one animal was used as sham. Bipolar stimulating electrodes were implanted in the left hippocampus. Three animals were used as control (implanted but not stimulated), one as sham (not implanted, not stimulated), and six as the study group. Stimulation was carried out using square wave pulses with 0.8V, 300 μsec, and 130 Hz (∼25μC/cm2) on the left hippocampus through the implanted bipolar hippocampal lead. Three animals were submitted to a one-hour and three to a six-hour stimulation session. Immunohistochemistry was employed to visualize c-FOS distribution in the rat's brain. The presence of seizures and electrocorticographic findings also were observed.

RESULTS

In animals submitted to both one-hour or six-hour unilateral hippocampal stimulation sessions, there was a significant bilateral overexpression of c-FOS in the hippocampus proper, dentate gyrus, and hylus. In the CA1 and CA3 regions, although activation was bilateral, c-FOS hyperexpression prevailed at the stimulated side over time; this was not true for the hilar and dentate gyrus regions where a more symmetric activation occurred over time. A significant c-FOS activation occurred after one hour of Hip-DBS in the ipsilateral amygdala; there was no contralateral amygdala activation, and by six hours, no amygdala activation was noted. No c-FOS activation was noted in other brain areas.

DISCUSSION

Our data showed that unilateral Hip-DBS was able to cause widespread and persistent bilateral activation of the normal rat limbic system, although in some, nuclei activation prevailed over the stimulated side. Cortical activation outside the limbic system was not noted. Our data represent a first approach to study the mechanistic paradigm involved in Hip-DBS.

Transient global amnesia associated with accidental high-frequency stimulation of the right hippocampus in deep brain stimulation for segmental dystonia

We report on a 66-year-old woman with segmental dystonia treated with chronic bilateral deep brain stimulation of the globus pallidus internus, in whom accidental high-voltage, high-frequency stimulation induced an episode of transient global amnesia (TGA) via an electrode contact which was misplaced in the right hippocampus. A possible mechanism underlying this TGA episode may have been the inhibition of local neuronal activity or fiber activation by high current density via direct electrical stimulation of hippocampal structures. While a unifying etiology of TGA has not been proven so far, our case demonstrates a possible link between focal electrical stimulation of hippocampal structures and the full clinical picture of the syndrome.

Seizure outcome after hippocampal deep brain stimulation in a prospective cohort of patients with refractory temporal lobe epilepsy

PURPOSE

In this study, we present the results obtained from a series of patients with refractory temporal lobe epilepsy (r-TLE) who underwent hippocampal deep brain stimulation (Hip-DBS).

METHODS

Nine consecutive adult patients were studied. Low-frequency and high-frequency stimulation was carried out immediately after the insertion of each electrode. Chronic continuous high-frequency stimulation was used during treatment. The mean follow-up time was 30.1 months. The mean age of the patients was 37.2 years. The MRI scan was normal in three patients; four patients had bilateral mesial temporal sclerosis (MTS), and two had unilateral MTS.

RESULTS

The patients with unilateral MTS received unilateral implantation and experienced a 76% and an 80% reduction in seizure frequency after Hip-DBS. All patients with normal MRI scans were implanted bilaterally. Two of these patients received unilateral activation of the electrodes and experienced a 97% and an 80% reduction in seizure frequency; the third patient had bilateral activation of the device and was a non-responder. All patients with bilateral MTS were implanted bilaterally. Three of these patients received unilateral activation of the device and experienced a 66%, a 66% and a 100% reduction in seizure frequency after Hip-DBS; one patient had bilateral electrode activation, and was a non-responder. Whenever present, generalised tonic-clonic seizures disappeared completely after Hip-DBS.

CONCLUSIONS

Although performed on a relatively small number of patients, Hip-DBS was safe and effective in our patients with r-TLE. Seven of the nine patients were considered responders. Hip-DBS might represent a useful therapeutic option in patients with refractory temporal lobe epilepsy who were not candidates for resective surgery or have had previous failed procedures.

Chronic evaluation of a clinical system for deep brain stimulation and recording of neural network activity

BACKGROUND/AIMS

In conjunction with therapeutic stimulation, next-generation deep brain stimulation (DBS) devices may offer the ability to record and analyze neural signals, providing for unprecedented insight into DBS effects on neural networks. This work was conducted to evaluate an implantable, clinical-grade system that permits concurrent stimulation and recording using a large animal (ovine) model recently developed to study DBS for epilepsy.

METHODS

Following anesthesia and 1.5-tesla MRI acquisition, unilateral anterior thalamic and hippocampal DBS leads were implanted (n = 3) using a frameless stereotactic system. Chronic, awake recordings of evoked potentials (EPs) and local field potentials were collected with the implanted device and analyzed off-line.

RESULTS

Hippocampal EPs were stable over long-term (>1 year) recording and consistent in morphology and latency with prior acute results. Thalamic and hippocampal DBS produced both excitatory and inhibitory network effects that were stimulation site and parameter dependent. Free roaming recordings illustrated periods of highly correlated activity between these two structures within the circuit of Papez.

CONCLUSIONS

These results provide further insight into mechanisms of DBS therapy for epilepsy and an encouraging demonstration of the capabilities of this new technology, which in the future, may afford unique opportunities to study human brain function and neuromodulation mechanism of action.

Deep brain stimulation for epilepsy

Deep brain stimulation for seizures has been applied to cerebellum, caudate, locus coeruleus, subthalamic nucleus, mammillary bodies, centromedian thalamus, anterior nucleus of thalamus, hippocampus and amygdala, hippocampal commissure, corpus callosum, neocortex, and occasionally to other sites. Animal and clinical studies have primarily investigated seizure prevention and, to a lessersmaller extent, seizure interruption. No studies have yet shown stimulation able to cure epilepsy. A wide variety of stimulation parameters have been employed in multiple different combinations of frequencies, amplitudes, and durations. Literature review identifies at least 52 clinical studies of brain stimulation for epilepsy in 817 patients. Two studies were large, randomized, and controlled, one in the anterior nucleus of thalamus and another at the cortical or hippocampal seizure focus; both of these studies showed efficacy and tolerability of stimulation. Many questions remain. We do not know the mechanisms, the best stimulation parameters, the best patient population, or how to predict benefit in advance. We do not know why benefit of neurostimulation for epilepsy seems to increase over time or whether there are long-term deleterious effects. All of these questions may be answerable with a combination of laboratory research and clinical experience.

Deep brain stimulation for refractory epilepsy

Deep brain stimulation (DBS) is a method of treatment utilized to control medically refractory epilepsy (RE). Patients with medically refractory epilepsy who do not achieve satisfactory control of seizures with pharmacological treatment or surgical resection of the epileptic focus and those who do not qualify for surgery could benefit from DBS. The most frequently used stereotactic targets for DBS are the anterior thalamic nucleus, subthalamic nucleus, central-medial thalamic nucleus, hippocampus, amygdala and cerebellum. The DBS is believed to be an effective method of treatment for various types of epilepsy among adults and adolescents. Side effects may be associated with implantation of electrodes and with the stimulation itself. An increasing number of publications and growing interest in DBS application for RE may result in standardization of the qualification and treatment protocol for RE with DBS.