White matter stimulation for the treatment of epilepsy

Adequate control of seizures in a case of lead migration and neuromodulation of the posterior Sylvian junction: A case report

Background

This report aims to describe the neuromodulation effect on seizure control in a patient with a left hippocampal migrated electrode to the Posterior Sylvian Junction (PSJ) during a follow-up of 17 years.

Case Description

We report a case of a female patient with drug-resistant epilepsy who initiated at seven years old and underwent a stereotactic frame-based insertion of a left hippocampal electrode for deep brain stimulation (DBS). Posterior migration of the electrode was identified at PSJ by postoperative magnetic resonance imaging one month after surgery. A consistent seizure reduction (Engel IC) was obtained with 2v-120 uS-145 Hz, contacts 0-3 negative, casing positive DBS parameters and maintained to this day. Patient data were collected from electronic medical records preceded by obtaining an informed consent for research and publication purposes. Stimulation parameter adjustments were confirmed with the digital records of the local device provider (Medtronic).

Results

PSJ is a connectivity confluence point of white matter pathways in the posterior quadrant of the hemispheres. White mater DBS could be considered for research as a potential complementary target for neuromodulation of refractory epilepsy.

Epilepsy Networks and Their Surgical Relevance

Surgical epilepsy is a rapidly evolved field. As the understanding and concepts of epilepsy shift towards a network disorder, surgical outcomes may shed light on numerous components of these systems. This review documents the evolution of the understanding of epilepsy networks and examines the data generated by resective, ablative, neuromodulation, and invasive monitoring surgeries in epilepsy patients. As these network tools are better integrated into epilepsy practice, they may eventually inform surgical decisions and improve clinical outcomes.

From basic sciences and engineering to epileptology: A translational approach

Collaborative efforts between basic scientists, engineers, and clinicians are enabling translational epileptology. In this article, we summarize the recent advances presented at the International Conference for Technology and Analysis of Seizures (ICTALS 2022): (1) novel developments of structural magnetic resonance imaging; (2) latest electroencephalography signal-processing applications; (3) big data for the development of clinical tools; (4) the emerging field of hyperdimensional computing; (5) the new generation of artificial intelligence (AI)-enabled neuroprostheses; and (6) the use of collaborative platforms to facilitate epilepsy research translation. We highlight the promise of AI reported in recent investigations and the need for multicenter data-sharing initiatives.

Medial Pulvinar Stimulation in Temporal Lobe Epilepsy: A Literature Review and a Hypothesis Based on Neuroanatomical Findings

While bilateral stimulation of the anterior thalamic nuclei remains the only approved deep brain stimulation (DBS) option for focal epilepsy, two additional thalamic targets have been proposed. Earlier work indicated the potential of centromedian thalamic nucleus stimulation with recent findings highlighting the medial pulvinar nucleus. The latter has been shown to exhibit electrophysiological and imaging alterations in patients with partial status epilepticus and temporal lobe epilepsy. On this basis, recent studies have begun assessing the feasibility and efficacy of pulvinar stimulation, with encouraging results on the reduction of seizure frequency and severity. Building on existing neuroanatomical knowledge, indicating that the medial pulvinar is connected to the temporal lobe via the temporopulvinar bundle of Arnold, we hypothesize that this is one of the routes through which medial pulvinar stimulation affects temporal lobe structures. We suggest that further anatomic, imaging, and electrophysiologic studies are warranted to deepen our understanding of the subject and guide future clinical applications.

Adding a single pulse into high-frequency pulse stimulations can substantially alter the following episode of neuronal firing in rat hippocampus

Background. High-frequency stimulation (HFS) sequences of electrical pulses are commonly utilized in many types of neuromodulation therapies. The temporal pattern of pulse sequences characterized by varying inter-pulse intervals (IPI) has emerged as an adjustable dimension to generate diverse effects of stimulations to meet the needs for developing the therapies.Objective:To explore the hypothesis that a simple manipulation of IPI by inserting a pulse in HFS with a constant IPI can substantially change the neuronal responses.Approach. Antidromic HFS (A-HFS) and orthodromic HFS (O-HFS) sequences were respectively applied at the alveus (the efferent axons) and the Schaffer collaterals (the afferent axons) of hippocampal CA1 region in anesthetized ratsin-vivo. The HFS sequences lasted 120 s with a pulse frequency of 100 Hz and an IPI of 10 ms. In the late steady period (60-120 s) of the HFS, additional pulses were inserted into the original pulse sequences to investigate the alterations of neuronal responses to the changes in IPI. The amplitudes and latencies of antidromic/orthodromic population spikes (APS/OPS) evoked by pulses were measured to evaluate the alterations of the evoked firing of CA1 pyramidal neurons caused by the pulse insertions.Main Results. During the steady period of A-HFS at efferent axons, the evoked APSs were suppressed due to intermittent axonal block. Under this situation, inserting a pulse to shorten an IPI was able to redistribute the following neuronal firing thereby generating an episode of oscillation in the evoked APS sequence including APSs with significantly increased and decreased amplitudes. Also, during the steady period of O-HFS without obvious OPS, a pulse insertion was able to generate a large OPS, indicating a synchronized firing of a large population of post-synaptic neurons induced by a putative redistribution of activations at the afferent axons under O-HFS.Significance. This study firstly showed that under the situation of HFS-induced axonal block, changing an IPI by a single-pulse insertion can substantially redistribute the evoked neuronal responses to increase synchronized firing of neuronal populations during both antidromic and O-HFS with a constant IPI originally. The finding provides a potential way to enhance the HFS action on neuronal networks without losing some other functions of HFS such as generating axonal block.

Deep Brain Stimulation in Epilepsy: A Role for Modulation of the Mammillothalamic Tract in Seizure Control?

BACKGROUND

Deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS) can improve seizure control for patients with drug-resistant epilepsy (DRE). Yet, one cannot overlook the high discrepancy in efficacy among patients, possibly resulting from differences in stimulation site.

OBJECTIVE

To test the hypothesis that stimulation at the junction of the ANT and mammillothalamic tract (ANT-MTT junction) increases seizure control.

METHODS

The relationship between seizure control and the location of the active contacts to the ANT-MTT junction was investigated in 20 patients treated with ANT-DBS for DRE. Coordinates and Euclidean distance of the active contacts relative to the ANT-MTT junction were calculated and related to seizure control. Stimulation sites were mapped by modelling the volume of tissue activation (VTA) and generating stimulation heat maps.

RESULTS

After 1 yr of stimulation, patients had a median 46% reduction in total seizure frequency, 50% were responders, and 20% of patients were seizure-free. The Euclidean distance of the active contacts to the ANT-MTT junction correlates to change in seizure frequency (r2 = 0.24, P = .01) and is ∼30% smaller (P = .015) in responders than in non-responders. VTA models and stimulation heat maps indicate a hot-spot at the ANT-MTT junction for responders, whereas non-responders had no evident hot-spot.

CONCLUSION

Stimulation at the ANT-MTT junction correlates to increased seizure control. Our findings suggest a relationship between the stimulation site and therapy response in ANT-DBS for epilepsy with a potential role for the MTT. DBS directed at white matter merits further exploration for the treatment of epilepsy.

Contributions of Imaging to Neuromodulatory Treatment of Drug-Refractory Epilepsy

Epilepsy affects about 1% of the world's population, and up to 30% of all patients will ultimately not achieve freedom from seizures with anticonvulsive medication alone. While surgical resection of a magnetic resonance imaging (MRI) -identifiable lesion remains the first-line treatment option for drug-refractory epilepsy, surgery cannot be offered to all. Neuromodulatory therapy targeting "seizures" instead of "epilepsy" has emerged as a valuable treatment option for these patients, including invasive procedures such as deep brain stimulation (DBS), responsive neurostimulation (RNS) and peripheral approaches such as vagus nerve stimulation (VNS). The purpose of this review is to provide in-depth information on current concepts and evidence on network-level aspects of drug-refractory epilepsy. We reviewed the current evidence gained from studies utilizing advanced imaging methodology, with a specific focus on their contributions to neuromodulatory therapy.

Acute modulation of the limbic network with low and high-frequency stimulation of the human fornix

Targeted stimulation of white matter has opened newer perspectives in the field of neuromodulation, towards an attempt to improve memory or as a therapy for epilepsy. Stimulation of the fornix, being a part of the Papez circuit, is likely to modulate the limbic network excitability. However, the stimulation-frequency dependent variability in network excitability is unknown. In the case study, which involved stereo electroencephalographic (SEEG) recording of field potentials in a 48-year old left-handed woman with suspected temporal lobe epilepsy, we demonstrated the network effects of acute low (1 and 10 Hz) and high (50 Hz) frequency electrical stimulation of fornix. Mapping the short-latency evoked responses to forniceal stimulation confirmed the SEEG target localization within the Papez circuit. Low and high-frequency stimulation of the fornix produced opposite effects in the post-stimuli excitability, with the latter causing increased excitability in the limbic network that culminated in a clinical seizure. A distinct spectral peak around 8 Hz confirmed that sensing field potentials from the forniceal white matter is feasible. This is the first case study that provided an insight into how the temporal patterning of forniceal stimulation altered the downstream limbic network excitability.

Selective modulation of neuronal firing by pulse stimulations with different frequencies in rat hippocampus

Background

Deep brain stimulation (DBS) has a good prospect for treating many brain diseases. Recent studies have shown that axonal activation induced by pulse stimulations may play an important role in DBS therapies through wide projections of axonal fibers. However, it is undetermined whether the downstream neurons are inhibited or excited by axonal stimulation. The present study addressed the question in rat hippocampus by in vivo experiments.

Methods

Pulse stimulations with different frequencies (10–400 Hz) were applied to the Schaffer collateral, the afferent fiber of hippocampal CA1 region in anaesthetized rats. Single-unit spikes of interneurons and pyramidal cells in the downstream region of stimulation were recorded and evaluated.

Results

Stimulations with a lower frequency (10 or 20 Hz) did not change the firing rates of interneurons but decreased the firing rates of pyramidal cells (the principal neurons) significantly. The phase-locked firing of interneurons during these stimulations might increase the efficacy of GABAergic inhibitions on the principal neurons. However, stimulations with a higher frequency (100–400 Hz) increased the firing rates of both types of the neurons significantly. In addition, the increases of interneurons’ firing were greater than the increases of pyramidal cells. Presumably, increase of direct excitation from afferent impulses together with failure of GABAergic inhibition might result in the increase of pyramidal cells’ firing by a higher stimulation frequency. Furthermore, silent periods appeared immediately following the cessation of stimulations, indicating a full control of the neuronal firing by the stimulation pulses during axonal stimulation. Furthermore longer silent periods were associated with higher stimulation frequencies.

Conclusions

Low-frequency (10–20 Hz) and high-frequency (100–400 Hz) stimulations of afferent axonal fibers exerted opposite effects on principal neurons in rat hippocampus CA1. These results provide new information for advancing deep brain stimulation to treat different brain disorders.

Small Changes in Inter-Pulse-Intervals Can Cause Synchronized Neuronal Firing During High-Frequency Stimulations in Rat Hippocampus

Deep brain stimulation (DBS) traditionally utilizes electrical pulse sequences with a constant frequency, i.e., constant inter-pulse-interval (IPI), to treat certain brain disorders in clinic. Stimulation sequences with varying frequency have been investigated recently to improve the efficacy of existing DBS therapy and to develop new treatments. However, the effects of such sequences are inconclusive. The present study tests the hypothesis that stimulations with varying IPI can generate neuronal activity markedly different from the activity induced by stimulations with constant IPI. And, the crucial factor causing the distinction is the relative differences in IPI lengths rather than the absolute lengths of IPI nor the average lengths of IPI. In rat experiments in vivo, responses of neuronal populations to applied stimulation sequences were collected during stimulations with both constant IPI (control) and random IPI. The stimulations were applied in the efferent fibers antidromically (in alveus) or in the afferent fibers orthodromically (in Schaffer collaterals) of pyramidal cells, the principal cells of hippocampal CA1 region. Amplitudes and areas of population spike (PS) waveforms were used to evaluate the neuronal responses induced by different stimulation paradigms. During the periods of both antidromic and orthodromic high-frequency stimulation (HFS), the HFS with random IPI induced synchronous neuronal firing with large PS even if the lengths of random IPI were limited to a small range of 5-10 ms, corresponding to a frequency range 100-200 Hz. The large PS events did not appear during control stimulations with a constant frequency at 100, 200, or 130 Hz (i.e., the mean frequency of HFS with random IPI uniformly distributed within 5-10 ms). Presumably, nonlinear dynamics in neuronal responses to random IPI might cause the generation of synchronous firing under the situation without any long pauses in HFS sequences. The results indicate that stimulations with random IPI can generate salient impulses to brain tissues and modulate the synchronization of neuronal activity, thereby providing potential stimulation paradigms for extending DBS therapy in treating more brain diseases, such as disorders of consciousness and vegetative states.

Axonal Stimulations With a Higher Frequency Generate More Randomness in Neuronal Firing Rather Than Increase Firing Rates in Rat Hippocampus

Deep brain stimulation (DBS) has been used for treating many brain disorders. Clinical applications of DBS commonly require high-frequency stimulations (HFS, ∼100 Hz) of electrical pulses to obtain therapeutic efficacy. It is not clear whether the electrical energy of HFS functions other than generating firing of action potentials in neuronal elements. To address the question, we investigated the reactions of downstream neurons to pulse sequences with a frequency in the range 50-200 Hz at afferent axon fibers in the hippocampal CA1 region of anesthetized rats. The results show that the mean rates of neuronal firing induced by axonal HFS were similar even for an up to fourfold difference (200:50) in the number and thereby in the energy of electrical pulses delivered. However, HFS with a higher pulse frequency (100 or 200 Hz) generated more randomness in the firing pattern of neurons than a lower pulse frequency (50 Hz), which were quantitatively evaluated by the significant changes of two indexes, namely, the peak coefficients and the duty ratios of excitatory phase of neuronal firing, induced by different frequencies (50-200 Hz). The findings indicate that a large portion of the HFS energy might function to generate a desynchronization effect through a possible mechanism of intermittent depolarization block of neuronal membranes. The present study addresses the demand of high frequency for generating HFS-induced desynchronization in neuronal activity, which may play important roles in DBS therapy.

Treatment options for posttraumatic epilepsy

PURPOSE OF REVIEW

Posttraumatic seizures (PTS) and posttraumatic epilepsy (PTE) are common and debilitating consequences of traumatic brain injury (TBI). Early PTS result in secondary brain injury by raising intracranial pressure and worsening cerebral edema and metabolic crisis. PTE is a localization-related epilepsy strongly associated with TBI severity, but risk factors for PTE and epileptogenesis are incompletely understood and are active areas of research. Medical management of PTS in adults and children is reviewed. Surgical options for posttraumatic drug-resistant epilepsy are also discussed.

RECENT FINDINGS

Continuous electroencephalography is indicated for children and adults with TBI and coma because of the high incidence of nonconvulsive seizures, periodic discharges, and associated secondary brain injury in this population. Neuroinflammation is a central component of secondary brain injury and appears to play a key role in epileptogenesis. Levetiracetam is increasingly used for seizure prophylaxis in adults and children, but variability remains.

SUMMARY

PTS occur commonly after TBI and are associated with secondary brain injury and worse outcomes in adults and children. Current medical and surgical management options for PTS and PTE are reviewed.

Proceedings of the Fourth Annual Deep Brain Stimulation Think Tank: A Review of Emerging Issues and Technologies

This paper provides an overview of current progress in the technological advances and the use of deep brain stimulation (DBS) to treat neurological and neuropsychiatric disorders, as presented by participants of the Fourth Annual DBS Think Tank, which was convened in March 2016 in conjunction with the Center for Movement Disorders and Neurorestoration at the University of Florida, Gainesveille FL, USA. The Think Tank discussions first focused on policy and advocacy in DBS research and clinical practice, formation of registries, and issues involving the use of DBS in the treatment of Tourette Syndrome. Next, advances in the use of neuroimaging and electrochemical markers to enhance DBS specificity were addressed. Updates on ongoing use and developments of DBS for the treatment of Parkinson's disease, essential tremor, Alzheimer's disease, depression, post-traumatic stress disorder, obesity, addiction were presented, and progress toward innovation(s) in closed-loop applications were discussed. Each section of these proceedings provides updates and highlights of new information as presented at this year's international Think Tank, with a view toward current and near future advancement of the field.