Finding the Sweet Spot: Fine-Tuning DBS Parameters to Cure Seizures While Avoiding Psychiatric Complications

Septal stimulation attenuates hippocampal seizure with subregion specificity

OBJECTIVE

Deep brain stimulation (DBS) is a promising approach for the treatment of epilepsy. However, the optimal target for DBS and underlying mechanisms are still not clear. Here, we compared the therapeutic effects of DBS on distinct septal subregions, aimed to find the precise targets of septal DBS and related mechanisms for the clinical treatment.

METHODS

Assisted by behavioral test, electroencephalography (EEG) recording and analyzing, selectively neuronal manipulation and immunohistochemistry, we assessed the effects of DBS on the three septal subregions in kainic acid (KA)-induced mouse seizure model.

RESULTS

DBS in the medial septum (MS) not only delayed generalized seizure (GS) development, but reduced the severity; DBS in the vertical diagonal band of Broca (VDB) only reduced the severity of GS, while DBS in the horizontal diagonal band of Broca (HDB) subregion showed no anti-seizure effect. Notably, DBS in the MS much more efficiently decreased abnormal activation of hippocampal neurons. EEG spectrum analysis indicated that DBS in the MS and VDB subregions mainly increased the basal hippocampal low-frequency (delta and theta) rhythm. Furthermore, ablation of cholinergic neurons in the MS and VDB subregions blocked the anti-seizure and EEG-modulating effects of septal DBS, suggesting the seizure-alleviating effect of DBS was dependent on local cholinergic neurons.

SIGNIFICANCE

DBS in the MS and VDB, rather than HDB, attenuates hippocampal seizure by activation of cholinergic neurons-augmented hippocampal delta/theta rhythm. This may be of great therapeutic significance for the clinical treatment of epilepsy with septal DBS.

PLAIN LANGUAGE SUMMARY

The optical target of deep brain stimulation in the septum is still not clear. This study demonstrated that stimulation in the medial septum and vertical diagonal band of Broca subregions, but not the horizontal diagonal band of Broca, could alleviate hippocampal seizure through cholinergic neurons-augmented hippocampal delta/theta rhythm. This study may shed light on the importance of precise regulation of deep brain stimulation therapy in treating epileptic seizures.

High and low frequency anterior nucleus of thalamus deep brain stimulation: Impact on memory and mood in five patients with treatment resistant temporal lobe epilepsy

High frequency anterior nucleus of the thalamus deep brain stimulation (ANT DBS) is an established therapy for treatment resistant focal epilepsies. Although high frequency-ANT DBS is well tolerated, patients are rarely seizure free and the efficacy of other DBS parameters and their impact on comorbidities of epilepsy such as depression and memory dysfunction remain unclear. The purpose of this study was to assess the impact of low vs high frequency ANT DBS on verbal memory and self-reported anxiety and depression symptoms. Five patients with treatment resistant temporal lobe epilepsy were implanted with an investigational brain stimulation and sensing device capable of ANT DBS and ambulatory intracranial electroencephalographic (iEEG) monitoring, enabling long-term detection of electrographic seizures. While patients received therapeutic high frequency (100 and 145 Hz continuous and cycling) and low frequency (2 and 7 Hz continuous) stimulation, they completed weekly free recall verbal memory tasks and thrice weekly self-reports of anxiety and depression symptom severity. Mixed effects models were then used to evaluate associations between memory scores, anxiety and depression self-reports, seizure counts, and stimulation frequency. Memory score was significantly associated with stimulation frequency, with higher free recall verbal memory scores during low frequency ANT DBS. Self-reported anxiety and depression symptom severity was not significantly associated with stimulation frequency. These findings suggest the choice of ANT DBS stimulation parameter may impact patients' cognitive function, independently of its impact on seizure rates.

Spatial and amplitude dynamics of neurostimulation: Insights from the acute intrahippocampal kainate seizure mouse model

OBJECTIVE

Neurostimulation is an emerging treatment for patients with drug-resistant epilepsy, which is used to suppress, prevent, and terminate seizure activity. Unfortunately, after implantation and despite best clinical practice, most patients continue to have persistent seizures even after years of empirical optimization. The objective of this study is to determine optimal spatial and amplitude properties of neurostimulation in inhibiting epileptiform activity in an acute hippocampal seizure model.

METHODS

We performed high-throughput testing of high-frequency focal brain stimulation in the acute intrahippocampal kainic acid mouse model of status epilepticus. We evaluated combinations of six anatomic targets and three stimulus amplitudes.

RESULTS

We found that the spike-suppressive effects of high-frequency neurostimulation are highly dependent on the stimulation amplitude and location, with higher amplitude stimulation being significantly more effective. Epileptiform spiking activity was significantly reduced with ipsilateral 250 μA stimulation of the CA1 and CA3 hippocampal regions with 21.5% and 22.2% reductions, respectively. In contrast, we found that spiking frequency and amplitude significantly increased with stimulation of the ventral hippocampal commissure. We further found spatial differences with broader effects from CA1 versus CA3 stimulation.

SIGNIFICANCE

These findings demonstrate that the effects of therapeutic neurostimulation in an acute hippocampal seizure model are highly dependent on the location of stimulation and stimulus amplitude. We provide a platform to optimize the anti-seizure effects of neurostimulation, and demonstrate that an exploration of the large electrical parameter and location space can improve current modalities for treating epilepsy.

PLAIN LANGUAGE SUMMARY

In this study, we tested how electrical pulses in the brain can help control seizures in mice. We found that the electrode's placement and the stimulation amplitude had a large effect on outcomes. Some brain regions, notably nearby CA1 and CA3, responded positively with reduced seizure-like activities, while others showed increased activity. These findings emphasize that choosing the right spot for the electrode and adjusting the strength of electrical pulses are both crucial when considering neurostimulation treatments for epilepsy.

The thalamus is the causal hub of intervention in patients with major depressive disorder: Evidence from the Granger causality analysis

Major depressive disorder (MDD) is the leading mental disorder and afflicts more than 350 million people worldwide. The underlying neural mechanisms of MDD remain unclear, hindering the accurate treatment. Recent brain imaging studies have observed functional abnormalities in multiple brain regions in patients with MDD, identifying core brain regions is the key to locating potential therapeutic targets for MDD. The Granger causality analysis (GCA) measures directional effects between brain regions and, therefore, can track causal hubs as potential intervention targets for MDD. We reviewed literature employing GCA to investigate abnormal brain connections in patients with MDD. The total degree of effective connections in the thalamus (THA) is more than twice that in traditional targets such as the superior frontal gyrus and anterior cingulate cortex. Altered causal connections in patients with MDD mainly included enhanced bottom-up connections from the thalamus to various cortical and subcortical regions and reduced top-down connections from these regions to the THA, indicating excessive uplink sensory information and insufficient downlink suppression information for negative emotions. We suggest that the thalamus is the most crucial causal hub for MDD, which may serve as the downstream target for non-invasive brain stimulation and medication approaches in MDD treatment.

The effects of electric fields on the mechanical properties and microstructure of ex vivo porcine brain tissues

As a popular tool for regulating the physiological conditions of the brain and treating brain diseases, electrotherapy has become increasingly mature in clinical applications. However, the mechanical properties and microstructure of the brain that change with weak electric fields are often overlooked. Thus, the mechanical behaviors of the brain tissue, which play a critical role in modulating the brain form and brain function, need to be taken into account. Herein, the direct current electric fields were combined with a customized indentation device and simultaneously focused on the changes in the mechanical properties and microstructure of ex vivo porcine brain tissues under electric fields. The experimental results showed that the electric fields reduced the shear modulus and viscosity and increased the relaxation rate of ex vivo porcine brain tissues. Moreover, electric fields polarized the cell bodies and reduced proteoglycan content in the cortex. The TEM observation confirmed that the electric fields deepened the degree of endoplasmic reticulum expansion and decreased the structural integrity of the cell membrane and myelin sheath. This study confirmed the effect of electric fields on ex vivo brain tissues; concurrently, it created comparable space in microscopic structure/compositions and mechanical parameters for future deeper brain experiments under stress-electric field coupling.

Improving the effectiveness of ANT DBS therapy for epilepsy with optimal current targeting

OBJECTIVE

Deep brain stimulation of the ANT is a novel treatment option in refractory epilepsy with an established efficacy at the group level. However, data on the effect of individualized programming are currently lacking. We report the effect of programming changes on outcome in deep brain stimulation of anterior nucleus of thalamus (ANT DBS). Secondly, we investigated whether the effect differs between seizure types. Thirdly, we compared the response status between patients with stimulation contacts verified inside the ANT with patients with contacts located outside of ANT.

METHODS

The participants were 27 consecutive patients with ANT DBS implantation with at least two-year follow-up. Seizures were subdivided into focal aware (FAS), focal impaired awareness (FIAS), and focal to bilateral tonic-clonic seizures (FBTCS). The patients' seizure diaries were analyzed retrospectively to assess changes in different seizure types. Active contact locations for each patient were verified from preoperative MRI and postoperative CT fusion images using SureTune III (Medtronic Inc, Minneapolis, MN) software.

RESULTS

A significant reduction in monthly mean seizure frequency occurred in FIAS: 56% at two-year and 65% at five-year follow-up. The effects on FAS and FBTCS were less pronounced. Patients with contacts inside the ANT or on the anterolateral border of ANT experienced a greater reduction in seizure frequency than patients with outside-ANT contacts. Ultimately, seven patients became responders due to changes in DBS programming or repositioning of contacts, increasing our responder rate from 44% to 70% as measured by a seizure reduction of at least 50%.

SIGNIFICANCE

ANT DBS appears to be especially effective in reducing FIAS, when the appropriately chosen contacts are activated.