Acharya & BM Reddy College of Pharmacy, Soldevanahalli, Achit Nagar Post, Bengaluru, Karnataka, India
Epilepsy hits a lot of people around the world, but for about one third of them, regular meds just do not stop the seizures completely. That leaves a bunch of folks looking for other ways to manage it, and thats where things like neuromodulation come in as a real option. I am focusing here on three main devices for this, vagus nerve stimulation, deep brain stimulation, and responsive neurostimulation. The idea is to compare how they work, if they actually help with seizures, and any risks involved. It seems like they all aim at messing with the brains signals to cut down on episodes. Take vagus nerve stimulation first. It targets the left vagus nerve, which somehow affects parts of the brain and brainstem. From what I have seen in the data, it cuts seizures by around 45 percent on average. Higher settings seem to make it work better, and a lot of patients say their mood gets a lift too. That part stands out, since its not just about the seizures. Then theres responsive neurostimulation, which is different because its like a smart system. It keeps watching the brains activity all the time and zaps it right when something weird starts up. Real life results look good over years, with reductions going up to 82 percent by the third year or so. I think that closed loop thing makes it feel more precise, kind of tailored. Deep brain stimulation is another one, sending steady pulses to break up the seizure rhythms. It usually hits the thalamus area. Studies over time show it gets better as you go, maybe down to 75 percent fewer seizures after seven years. Its continuous, which might explain the buildup. Overall, these devices help about half the people who try them by dropping seizure frequency around 50 percent. But its not perfect for everyone, and some do better than others. The field now is moving towards looking at the brain as a network, using stuff like live tracking of waves and detailed scans. Combining them, say VNS with RNS, could make treatments more custom. This part gets a bit messy to explain, but it feels like thats the direction.
One out of every hundred people across the planet lives with epilepsy, a brain-related health issue marked by repeated seizures. Third on the list of common nervous system disorders globally, it affects millions [1]. Though drugs that prevent seizures work well for about two-thirds of those diagnosed, others do not respond fully to these medicines. For this group, treatment shifts toward different paths - some turn to strict eating plans such as the ketogenic approach, while others explore operations targeting specific areas of the brain. These procedures may involve removing tissue, isolating neural pathways, or using implanted devices to regulate electrical activity [2,3]. Fewer than half of those who undergo surgery still face ongoing seizures, though most see meaningful improvement [4]. Even so, a notable portion - between 15% and 40% - with epilepsy remain affected by episodes disruptive to everyday life, regardless of current therapies [5].
One path forward lies in neuromodulation. First recognized by the FDA in 1997, vagus nerve stimulation became an option for adults and teens dealing with partial-onset seizures. By 2017, its use extended down to kids aged four. Before deep brain stimulation reached approval in 2018 - focused on the thalamus’ anterior nucleus - the RNS system had already cleared regulatory review back in 2014 [6].
2. Vagus Nerve Stimulation (VNS)
2.1 Clinical Mechanism and Background
Although small, the VNS setup includes a pulse generator implanted in the chest and a lead with three spiral-shaped electrodes. One of these coils secures the wire in place; the other two handle stimulation duties. Through a cut in the neck, surgeons access the left vagus nerve before linking it to the device. Targeting this particular nerve reduces heart-related concerns that might arise if the right-side nerve were used instead [7].
Though researchers continue exploring how it works, VNS likely influences brain function through connections between the brainstem and higher cortical regions carried by sensory branches of the vagus nerve. Starting at the nucleus tractus solitarius, signals travel into key brainstem structures - like the locus coeruleus, dorsal raphe, and parabrachial area - shaping neural responses along the way. From there, impulses extend toward central processing zones: the thalamus, parts of the somatosensory cortex, the anterior cingulate, and prefrontal areas included. These routes may help regulate communication across thalamocortical networks, reducing abnormal synchronization linked to seizure patterns, especially those seen in gamma frequency ranges [8].
2.2 Clinical Efficacy
FDA Approval Study (1997): VNS gained FDA approval in 1997 after results from an open-label trial allowed its use in children older than four who had drug-resistant focal seizures with impaired awareness. Improvement was seen in more than half of those treated - response rates reached 36.8% by year one, climbed to 43.2% by year two, then settled at 42.7% through year three following implant placement [9].
Meta- Analytical Data: Seizure rates dropped by an average of 45%, according to data pooled from 74 research trials. Those diagnosed with generalized epilepsy saw their episodes fall by nearly 58%. Notably, individuals affected by tuberous sclerosis showed improvement - seizures lessened by almost 68%. Even greater impact appeared among people recovering from brain trauma, where frequency declined close to 79%. These patterns emerged clearly when researchers examined specific patient clusters [10].
Paediatric Efficacy: More than half of young patients saw seizure frequency drop by 50% or more, according to a review published in 2021. Improvements in general health continued over time. Evidence comes from study number 11.
Stimulation Intensity: A single measure shows results improve when intensity rises. From the E03 trial, strong VNS led to a 24.5% drop in seizures - weak settings only managed 6.1%. Seizures stopped entirely for 31% on full power, yet just 14% under softer output [7]. Later evidence came from E05, where heavier pulses cut episodes by 28%, while lighter ones reached 15% [7].
2.3 Quality of Life and Adverse Effects
VNS therapy often links to better mood; one study using intense stimulation found clear drops in depression and anxiety after twelve weeks [12]. The benefits remain consistent through follow-up periods [13,14].
One year out, hoarseness shows up in about 28%, while tingling affects 12%. Into the second year, voice shifts remain noticeable in close to every fifth person, though headaches surface in just under five percent. After three years, trouble breathing appears rarely - fewer than three in a hundred. Right after placement, some face infections tied to the device [9]; others notice their vocal cords moving slower, which alters how they speak. A mild form of facial muscle weakness also turns up now and then below the face's midline [7].
Figure 1: Mechanism of VNS
3. Deep Brain Stimulation (DBS)
3.1 Overview and Targets
Electrical pulses from DBS run constantly, lacking real-time adjustments meant to curb seizures. Sitting where the cortex meets deeper regions, the thalamus becomes a key point for intervention [15,16]. Studies have mainly explored stimulation at three spots within it: the anterior nucleus (ANT), Centro median nucleus (CMT), along with the pulvinar [17].
3.2 Anterior Nucleus of the Thalamus (ANT) DBS
A third of participants showed meaningful improvement under stimulation, though outcomes differed by seizure location. Those with seizures starting in the temporal region responded more strongly than those with broader network involvement. The study included individuals unresponsive to standard medications. In randomized conditions, real treatment outperformed sham across multiple measures. Results emerged over several months without immediate effects. Response rates varied, but overall trends favoured intervention. Follow-up confirmed sustained patterns beyond initial phases. [18,19]
Years later, results showed seizures dropped by an average of 41% after twelve months, climbing to 69% over five years, then reaching 75% by year seven [20]. By the eleventh year, decline rates held steady anywhere from 60% up to 80% [21]. Improvements in thinking skills - like focus, choices, and mood control - remained clear through five and nine years of observation [22].
3.3 Centro median Nucleus (CMT) and Pulvinar DBS
One unexpected outcome stood out - eight out of nine people showed at least half as much abnormal brain wave activity after receiving deep brain stimulation through both sides of the thalamus. Focusing on broad forms of epilepsy, especially those seen in Lennox-Gastaut syndrome, researchers applied this method carefully. Results like these have popped up before; earlier work done by Velasco and colleagues [24], then later confirmed by Fisher's group [25], pointed in similar directions. What changed was how consistently strong the response appeared across participants.
Pulled from recent studies, the pulvinar nucleus shows tight links with both inner and surface regions of the temporal lobe. When seizures begin in the temporal area, scans have spotted slowed fluid movement specifically within the pulvinar region [27].
3.4 DBS Mechanisms and Safety
One idea suggests DBS works by breaking up rhythmic patterns in brain activity [29]. When people with temporal lobe seizures respond to treatment, their EEGs show less coordination in theta and alpha frequencies [30]. Because of this, signals across neural networks shift, altering how regions like the brainstem connect to the thalamus, movement areas, and spinal circuits [31]. After surgery, imaging reveals improved alignment in how different parts of the brain communicate [32].
Though rare, some patients reported tingling or pain near the device after five years in the SANTE study - roughly one in five affected. Infections at the implant location appeared less often, impacting nearly 13 out of every hundred. Misplaced leads turned up in just over eight percent. Mood dips were noted more frequently, seen in a third of participants.[20] When used in children, brain stimulation targeting CMT or ANT areas carried similar risks; infection stood out most, showing up around ten times per hundred procedures. [28]
Figure 2: Mechanism of DBS
4. Responsive Neurostimulation (RNS)
4.1 Closed-Loop Technology and Efficacy
When unusual brain signals appear, RNS responds instantly - measuring neural activity nonstop while applying focused electric pulses just when needed [33, 34, 35].
A key study led by Morrell and team placed RNS systems into 191 grown-ups struggling with tough-to-treat partial seizures. In the masked period lasting 12 weeks, those receiving active stimulation saw their seizure frequency drop by 41.5%, while placebo participants improved only 9.4% [36]. Over time, results kept improving - after twelve months, the middle patient experienced a 44% decline [37]; two years brought it to 53%. Real-life data revealed even stronger outcomes: 67% fewer episodes after one year, climbing toward 82% by the third.[39] After tracking individuals for nine years, researchers noticed most reached at least a 75% dip in attacks; close to one out of five stayed entirely seizure-free across an entire year [38].
One year later, more than half of the young patients saw their seizures drop by over fifty percent - this outcome appeared across fifteen kids in a group of twenty-seven [42]. Though still early, results hint that responsive neurostimulation may help beyond focal cases, including broader forms like Lennox-Gastaut Syndrome when applied via CMT-targeted setups [41].
4.2 Mechanisms of Action and Safety
Though first thought to block active seizure events straight away [43], findings now indicate RNS forms working barriers, isolating overactive neuron groups [44]. With continued use, such separation shifts how brain areas communicate based on rhythm patterns [45], fostering long-term reorganization - this weakens faulty links, causing seizures to split into briefer episodes [46]. The system fires often, delivering between 600 and 2,000 pulses each day, despite individuals noticing few visible attacks [39, 40].
Five percent of patients experience significant complications linked to the device after nine years. Though most issues are rare, infections remain a concern - 4.1% face general procedure-related infections. Implant-specific major infections appear more often, showing up in 12.1% across nearly two thousand patient-years. Bleeding not caused by seizures affects 2.7%. Seizures lasting longer than usual happen in 8.2%, even when devices work correctly. Memory stays stable; mood does not decline, nor does risk for suicidal thoughts rise with RNS use [38].
Figure 3: Mechansim of RNS
5. Comparative Efficacy and Emerging Trends
Change now favors a network view of brain function, replacing isolated spot treatments with methods that guide full circuits toward better activity states [48]. Because SEEG helps refine placement [54], and computer simulations mimic lesions to predict effects [56], fine-tuning stimulation becomes more precise [57, 58, 59]. While researchers map key connection points [55], they also track coordination within neural firing patterns using GPFA [49]; at the same time, focusing on exact parts of regions like ANT [51, 52] or CMT [53] improves results. Better outcomes emerge when targeting accounts for broader circuit behavior rather than fixed anatomical spots.
One out of every two people using neuromodulation sees seizure frequency drop by half, according to pooled study results [60, 61, 62]. When treatments like VNS are paired with RNS [63], outcomes shift in favor of tougher epilepsy profiles. Devices capable of sensing and delivering stimulation at once open new paths - especially where single approaches fall short [64]. Though different in design, they often act through similar routes: breaking up synchronized brain activity [65], adjusting how easily neurons fire [66], or reshaping connections across time [67].
Looking ahead, handling ethics in children's care sets one direction [68]. Stronger safeguards for gadgets streaming brain signals come next [69]. Better tools to foresee seizures shape another path forward [70]. Systems adjusting on their own using live input are now being put into practice [71]. Methods like rTMS, tDCS, or targeted sound waves offer alternatives without surgery - these too hold promise [72].
CONCLUSION
Half a lifetime of medical records shows that changing nervous system activity helps about thirty percent of people whose seizures do not respond to medication. Signals delivered via the vagus nerve, probes placed within the brain, or intelligent surface implants reduce seizure frequency by around fifty percent in almost half of users - each method works differently but reaches similar outcomes. Progress now accelerates as high-resolution scans, real-time brainwave tracking, and precise digital simulations merge into tailored treatments targeting neural networks with growing precision.
REFERENCES
Dr. T Haribabu, Sanilyne M Lyndem, Sahil A, Dr. Manjunatha PM, Dr. Uday Raj Sharma, Dr. Surendra Vada, Comparative Outcomes of Vagus Nerve Stimulation, Deep Brain Stimulation, and Responsive Neurostimulation in Epilepsy, Int. J. of Pharm. Sci., 2026, Vol 4, Issue 3, 3705-3714. https://doi.org/10.5281/zenodo.19271399
10.5281/zenodo.19271399
