Laryngeal Muscle-Evoked Potential Recording as an Indicator of Vagal Nerve Fiber Activation.

BACKGROUND: Vagus nerve stimulation (VNS) is an adjunctive therapy for drug-resistant epilepsy. Noninvasive evoked potential recordings in laryngeal muscles (LMEPs) innervated by vagal branches may provide a marker to assess effective vagal nerve fiber activation. We investigated VNS-induced LMEPs in patients with epilepsy in acute and chronic settings. MATERIALS AND METHODS: A total of 17 of 25 patients underwent LMEP recordings at initiation of therapy (acute group); 15 of 25 patients after one year of VNS (chronic group); and 7 of 25 patients were tested at both time points (acute + chronic group). VNS-induced LMEPs were recorded following different pulse widths and output currents using six surface laryngeal EMG electrodes to calculate input/output curves and estimate LMEP latency, threshold current for minimal (Ithreshold), half-maximal (I50), and 95% of maximal (I95) response induction and amplitude of maximal response (Vmax). These were compared with the acute + chronic group and between responders and nonresponders in the acute and chronic group. RESULTS: VNS-induced LMEPs were present in all patients. Ithreshold and I95 values ranged from 0.25 to 1.00 mA and from 0.42 to 1.77 mA, respectively. Estimated mean LMEP latencies were 10 ± 0.1 milliseconds. No significant differences between responders and nonresponders were observed. In the acute + chronic group, Ithreshold values remained stable over time. However, at the individual level in this group, Vmax was lower in all patients after one year compared with baseline. CONCLUSIONS: Noninvasive VNS-induced LMEP recording is feasible both at initiation of VNS therapy and after one year. Low output currents (0.25-1.00 mA) may be sufficient to activate vagal Aα-motor fibers. Maximal LMEP amplitudes seemed to decrease after chronic VNS therapy in patients.

Long-term chemogenetic suppression of seizures in a multifocal rat model of temporal lobe epilepsy.

OBJECTIVE: One third of epilepsy patients do not become seizure-free using conventional medication. Therefore, there is a need for alternative treatments. Preclinical research using designer receptors exclusively activated by designer drugs (DREADDs) has demonstrated initial success in suppressing epileptic activity. Here, we evaluated whether long-term chemogenetic seizure suppression could be obtained in the intraperitoneal kainic acid rat model of temporal lobe epilepsy, when DREADDs were selectively expressed in excitatory hippocampal neurons. METHODS: Epileptic male Sprague Dawley rats received unilateral hippocampal injections of adeno-associated viral vector encoding the inhibitory DREADD hM4D(Gi), preceded by a cell-specific promotor targeting excitatory neurons. The effect of clozapine-mediated DREADD activation on dentate gyrus evoked potentials and spontaneous electrographic seizures was evaluated. Animals were systemically treated with single (.1 mg/kg/24 h) or repeated (.1 mg/kg/6 h) injections of clozapine. In addition, long-term continuous release of clozapine and olanzapine (2.8 mg/kg/7 days) using implantable minipumps was evaluated. All treatments were administered during the chronic epileptic phase and between 1.5 and 13.5 months after viral transduction. RESULTS: In the DREADD group, dentate gyrus evoked potentials were inhibited after clozapine treatment. Only in DREADD-expressing animals, clozapine reduced seizure frequency during the first 6 h postinjection. When administered repeatedly, seizures were suppressed during the entire day. Long-term treatment with clozapine and olanzapine both resulted in significant seizure-suppressing effects for multiple days. Histological analysis revealed DREADD expression in both hippocampi and some cortical regions. However, lesions were also detected at the site of vector injection. SIGNIFICANCE: This study shows that inhibition of the hippocampus using chemogenetics results in potent seizure-suppressing effects in the intraperitoneal kainic acid rat model, even 1 year after viral transduction. Despite a need for further optimization, chemogenetic neuromodulation represents a promising treatment prospect for temporal lobe epilepsy.

Localization of deep brain activity with scalp and subdural EEG.

To what extent electrocorticography (ECoG) and electroencephalography (scalp EEG) differ in their capability to locate sources of deep brain activity is far from evident. Compared to EEG, the spatial resolution and signal-to-noise ratio of ECoG is superior but its spatial coverage is more restricted, as is arguably the volume of tissue activity effectively measured from. Moreover, scalp EEG studies are providing evidence of locating activity from deep sources such as the hippocampus using high-density setups during quiet wakefulness. To address this question, we recorded a multimodal dataset from 4 patients with refractory epilepsy during quiet wakefulness. This data comprises simultaneous scalp, subdural and depth EEG electrode recordings. The latter was located in the hippocampus or insula and provided us with our "ground truth" for source localization of deep activity. We applied independent component analysis (ICA) for the purpose of separating the independent sources in theta, alpha and beta frequency band activity. In all patients subdural- and scalp EEG components were observed which had a significant zero-lag correlation with one or more contacts of the depth electrodes. Subsequent dipole modeling of the correlating components revealed dipole locations that were significantly closer to the depth electrodes compared to the dipole location of non-correlating components. These findings support the idea that components found in both recording modalities originate from neural activity in close proximity to the depth electrodes. Sources localized with subdural electrodes were ~70% closer to the depth electrode than sources localized with EEG with an absolute improvement of around ~2cm. In our opinion, this is not a considerable improvement in source localization accuracy given that, for clinical purposes, ECoG electrodes were implanted in close proximity to the depth electrodes. Furthermore, the ECoG grid attenuates the scalp EEG, due to the electrically isolating silastic sheets in which the ECoG electrodes are embedded. Our results on dipole modeling show that the deep source localization accuracy of scalp EEG is comparable to that of ECoG. SIGNIFICANCE STATEMENT: Deep and subcortical regions play an important role in brain function. However, as joint recordings at multiple spatial scales to study brain function in humans are still scarce, it is still unresolved to what extent ECoG and EEG differ in their capability to locate sources of deep brain activity. To the best of our knowledge, this is the first study presenting a dataset of simultaneously recorded EEG, ECoG and depth electrodes in the hippocampus or insula, with a focus on non-epileptiform activity (quiet wakefulness). Furthermore, we are the first study to provide experimental findings on the comparison of source localization of deep cortical structures between invasive and non-invasive brain activity measured from the cortical surface.

High-gamma oscillations precede visual steady-state responses: A human electrocorticography study.

The robust steady-state cortical activation elicited by flickering visual stimulation has been exploited by a wide range of scientific studies. As the fundamental neural response inherits the spectral properties of the gazed flickering, the paradigm has been used to chart cortical characteristics and their relation to pathologies. However, despite its widespread adoption, the underlying neural mechanisms are not well understood. Here, we show that the fundamental response is preceded by high-gamma (55-125 Hz) oscillations which are also synchronised to the gazed frequency. Using a subdural recording of the primary and associative visual cortices of one human subject, we demonstrate that the latencies of the high-gamma and fundamental components are highly correlated on a single-trial basis albeit that the latter is consistently delayed by approximately 55 ms. These results corroborate previous reports that top-down feedback projections are involved in the generation of the fundamental response, but, in addition, we show that trial-to-trial variability in fundamental latency is paralleled by a highly similar variability in high-gamma latency. Pathology- or paradigm-induced alterations in steady-state responses could thus originate either from deviating visual gamma responses or from aberrations in the neural feedback mechanism. Experiments designed to tease apart the two processes are expected to provide deeper insights into the studied paradigm.

Semantic and perceptual priming activate partially overlapping brain networks as revealed by direct cortical recordings in humans.

Facilitation of object processing in the brain due to a related context (priming) can be influenced by both semantic connections and perceptual similarity. It is thus important to discern these two when evaluating the spatio-temporal dynamics of primed object processing. The repetition-priming paradigm frequently used to study perceptual priming is, however, unable to differentiate between the mentioned priming effects, possibly leading to confounded results. In the current study, we recorded brain signals from the scalp and cerebral convexity of nine patients with refractory epilepsy in response to related and unrelated image-pairs, all of which shared perceptual features while only related ones had a semantic connection. While previous studies employing a repetition-priming paradigm observed largely overlapping networks between semantic and perceptual priming effects, our results suggest that this overlap is only partial (both temporally and spatially). These findings stress the importance of controlling for perceptual features when studying semantic priming.

Long-term chemogenetic suppression of spontaneous seizures in a mouse model for temporal lobe epilepsy.

OBJECTIVE: More than one-third of patients with temporal lobe epilepsy (TLE) continue to have seizures despite treatment with antiepileptic drugs, and many experience severe drug-related side effects, illustrating the need for novel therapies. Selective expression of inhibitory Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) allows cell-type-specific reduction of neuronal excitability. In this study, we evaluated the effect of chemogenetic suppression of excitatory pyramidal and granule cell neurons of the sclerotic hippocampus in the intrahippocampal mouse model (IHKA) for temporal lobe epilepsy. METHODS: Intrahippocampal IHKA mice were injected with an adeno-associated viral vector carrying the genes for an inhibitory DREADD hM4Di in the sclerotic hippocampus or control vector. Next, animals were treated systemically with different single doses of clozapine-N-oxide (CNO) (1, 3, and 10 mg/kg) and clozapine (0.03 and 0.1 mg/kg) and the effect on spontaneous hippocampal seizures, hippocampal electroencephalography (EEG) power, fast ripples (FRs) and behavior in the open field test was evaluated. Finally, animals received prolonged treatment with clozapine for 3 days and the effect on seizures was monitored. RESULTS: Treatment with both CNO and clozapine resulted in a robust suppression of hippocampal seizures for at least 15 hours only in DREADD-expressing animals. Moreover, total EEG power and the number of FRs were significantly reduced. CNO and/or clozapine had no effects on interictal hippocampal EEG, seizures, or locomotion/anxiety in the open field test in non-DREADD epileptic IHKA mice. Repeated clozapine treatment every 8 hours for 3 days resulted in almost complete seizure suppression in DREADD animals. SIGNIFICANCE: This study shows the potency of chemogenetics to robustly and sustainably suppress spontaneous epileptic seizures and pave the way for an epilepsy therapy in which a systemically administered exogenous drug selectively modulates specific cell types in a seizure network, leading to a potent seizure suppression devoid of the typical drug-related side effects.

Representation of steady-state visual evoked potentials elicited by luminance flicker in human occipital cortex: An electrocorticography study.

Despite the widespread use of steady-state visual evoked potentials (SSVEPs) elicited by luminance flicker in clinical and research settings, their spatial and temporal representation in the occipital cortex largely remain elusive. We performed intracranial-EEG recordings in response to targets flickering at frequencies from 11 to 15 Hz using a subdural electrode grid covering the entire right occipital cortex of a human subject, and we were able to consistently locate the gazed stimulus frequency at the posterior side of the primary visual cortex (V1). Peripheral flickering, undetectable in scalp-EEG, elicited activations in the interhemispheric fissure at locations consistent with retinotopic maps. Both foveal and peripheral activations spatially coincided with activations in the high gamma band. We detected localized alpha synchronization at the lateral edge of V2 during stimulation and transient post-stimulation theta band activations at the posterior part of the occipital cortex. Scalp-EEG exhibited only a minor occipital post-stimulation theta activation, but a strong transient frontal activation.

Involvement of GATOR complex genes in familial focal epilepsies and focal cortical dysplasia.

OBJECTIVE: The discovery of mutations in DEPDC5 in familial focal epilepsies has introduced a novel pathomechanism to a field so far dominated by ion channelopathies. DEPDC5 is part of a complex named GAP activity toward RAGs (GATOR) complex 1 (GATOR1), together with the proteins NPRL2 and NPRL3, and acts to inhibit the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) pathway. GATOR1 is in turn inhibited by the GATOR2 complex. The mTORC1 pathway is a major signaling cascade regulating cell growth, proliferation, and migration. We aimed to study the contribution of GATOR complex genes to the etiology of focal epilepsies and to describe the associated phenotypical spectrum. METHODS: We performed targeted sequencing of the genes encoding the components of the GATOR1 (DEPDC5, NPRL2, and NPRL3) and GATOR2 (MIOS, SEC13, SEH1L, WDR24, and WDR59) complex in 93 European probands with focal epilepsy with or without focal cortical dysplasia. Phospho-S6 immunoreactivity was used as evidence of mTORC1 pathway activation in resected brain tissue of patients carrying pathogenic variants. RESULTS: We identified four pathogenic variants in DEPDC5, two in NPRL2, and one in NPRL3. We showed hyperactivation of the mTORC1 pathway in brain tissue from patients with NPRL2 and NPRL3 mutations. Collectively, inactivating mutations in GATOR1 complex genes explained 11% of cases of focal epilepsy, whereas no pathogenic mutations were found in GATOR2 complex genes. GATOR1-related focal epilepsies differ clinically from focal epilepsies due to mutations in ion channel genes by their association with focal cortical dysplasia and seizures emerging from variable foci, and might confer an increased risk of sudden unexplained death in epilepsy (SUDEP). SIGNIFICANCE: GATOR1 complex gene mutations leading to mTORC1 pathway upregulation is an important cause of focal epilepsy with cortical malformations and represents a potential target for novel therapeutic approaches.

Early occurrence of red blood cell alloimmunization in patients with sickle cell disease.

Red blood cell (RBC) alloimmunization is a major complication of transfusion therapy in sickle cell disease (SCD). Identification of high-risk patients is hampered by lack of studies that take the cumulative transfusion exposure into account. In this retrospective cohort study among previously non-transfused SCD patients in the Netherlands, we aimed to elucidate the association between the cumulative transfusion exposure, first alloimmunization and independent risk factors. A total of 245 patients received 11 952 RBC units. Alloimmunization occurred in 43 patients (18%), half of them formed their first alloantibody before the 8th unit. In patients with exposure to non-extended matched transfusions (ABO and RhD) the cumulative alloimmunization risk increased up to 35% after 60 transfused units. This was significantly higher compared to a general transfused population (HR 6.6, CI 4.2-10.6). Receiving the first transfusion after the age of 5 was an independent risk factor for alloimmunization (HR 2.3, CI 1.0-5.1). Incidental, episodic transfusions in comparison to chronic scheme transfusions (HR 2.3, CI 0.9-6.0), and exposure to non-extended matched units in comparison to extended matching (HR 2.0, CI 0.9-4.6) seemed to confer a higher alloimmunization risk. The majority of first alloantibodies are formed after minor transfusion exposure, substantiating suggestions of a responder phenotype in SCD and stressing the need for risk factor identification. In this study, older age at first transfusion, episodic transfusions and non-extended matched transfusions appeared to be risk factors for alloimmunization. Am. J. Hematol. 91:763-769, 2016. © 2016 Wiley Periodicals, Inc.

Neuropeptide FF and prolactin-releasing peptide decrease cortical excitability through activation of NPFF receptors.

OBJECTIVE: Drugs with a novel mechanism of action are needed to reduce the number of people with epilepsy that are refractory to treatment. Increasing attention is paid to neuropeptide systems and several anticonvulsant neuropeptides have already been described, such as galanin, ghrelin, and neuropeptide Y (NPY). Many others, however, have not been investigated for their ability to affect epileptic seizures. In this study, the potential anticonvulsant activities of three members of the RF-amide neuropeptide family, neuropeptide FF (NPFF), prolactin-releasing peptide (PrRP), and kisspeptin (Kp) and other receptor ligands (NPFF1/2 R, GPR10, and GRP54, respectively) were tested in the motor cortex stimulation model. METHODS: A train of pulses with increasing intensity (0-10 mA over 150 s, 50 Hz, pulse width 2 msec) was delivered to the motor cortex of rats. The threshold intensity for eliciting a motor response (i.e., motor threshold) was determined through behavioral observation and used as a measure for cortical excitability. The threshold was determined before, during, and after the intracerebroventricular (i.c.v.) administration of various NPFF1/2 R, GPR10, and GPR54 receptor ligands. RESULTS: NPFF and PrRP significantly increased the motor threshold by a maximum of 143 ± 27 and 83 ± 13 µA, respectively, for the doses of 1 nmol/h (p < 0.05). The increase of motor threshold by NPFF and PrRP was prevented by pretreatment and co-treatment with the NPFF1/2 R antagonist RF9. Pretreatment with a selective NPFF1 R antagonist also prevented the threshold increase induced by NPFF. Kp did not increase motor threshold. SIGNIFICANCE: Intracerebroventricular infusion of NPFF or PrRP decreases cortical excitability in rats through activation of NPFFRs. Furthermore, the NPFF1 R is required for the NPFF-induced decrease in cortical excitability.

Chronic subthreshold cortical stimulation: A promising therapy for motor cortex seizures.

Chronic subthreshold cortical stimulation (CSCS) is a form of neurostimulation consisting of continuous or cyclic, open-loop, subthreshold electrical stimulation of a well-defined epileptogenic zone (EZ). CSCS has seen limited clinical use but could be a safe and effective long-term treatment of focal drug resistant epilepsy, in particular when the EZ is located in the motor cortex. We present a case of a 49-year-old woman suffering from debilitating focal motor seizures. Treatment with CSCS resulted in significant clinical improvement, enabling her to walk unaided for the first time in years.

Ictal-onset localization through connectivity analysis of intracranial EEG signals in patients with refractory epilepsy.

PURPOSE: Fifteen percent to 25% of patients with refractory epilepsy require invasive video-electroencephalography (EEG) monitoring (IVEM) to precisely delineate the ictal-onset zone. This delineation based on the recorded intracranial EEG (iEEG) signals occurs visually by the epileptologist and is therefore prone to human mistakes. The purpose of this study is to investigate whether effective connectivity analysis of intracranially recorded EEG during seizures provides an objective method to localize the ictal-onset zone. METHODS: In this study data were analyzed from eight patients who underwent IVEM at Ghent University Hospital in Belgium. All patients had a focal ictal onset and were seizure-free following resective surgery. The effective connectivity pattern was calculated during the first 20 s of ictal rhythmic iEEG activity. The out-degree, which is reflective of the number of outgoing connections, was calculated for each electrode contact for every single seizure during these 20 s. The seizure specific out-degrees were summed per patient to obtain the total out-degree. The electrode contact with the highest total out-degree was considered indicative of localization of the ictal-onset zone. This result was compared to the conclusion of the visual analysis of the epileptologist and the resected brain region segmented from postoperative magnetic resonance imaging (MRI). KEY FINDINGS: In all eight patients the electrode contact with the highest total out-degree was among the contacts identified by the epileptologist as the ictal onset. This contact, that we named "the driver," always laid within the resected brain region. Furthermore, the patient-specific connectivity patterns were consistent over the majority of seizures. SIGNIFICANCE: In this study we demonstrated the feasibility of correctly localizing the ictal-onset zone from iEEG recordings by using effective connectivity analysis during the first 20 s of ictal rhythmic iEEG activity.

In vivo inhibition of epileptiform afterdischarges in rat hippocampus by light-activated chloride channel, stGtACR2.

AIMS: The blue light-sensitive chloride-conducting opsin, stGtACR2, provides potent optogenetic silencing of neurons. The present study investigated whether activation of stGtACR2 in granule cells of the dentate gyrus (DG) inhibits epileptic afterdischarges in a rat model. METHODS: Rats were bilaterally injected with 0.9 µl of AAV2/7-CaMKIIα-stGtACR2-fusionred in the DG. Three weeks later, afterdischarges were recorded from the DG by placing an optrode at the injection site and a stimulation electrode in the perforant path (PP). Afterdischarges were evoked every 10 min by unilateral electrical stimulation of the PP (20 Hz, 10 s). During every other afterdischarge, the DG was illuminated for 5 or 30 s, first ipsilaterally and then bilaterally to the PP stimulation. The line length metric of the afterdischarges was compared between illumination conditions. RESULTS: Ipsilateral stGtACR2 activation during afterdischarges decreased the local field potential line length only during illumination and specifically at the illuminated site but did not reduce afterdischarge duration. Bilateral illumination did not terminate the afterdischarges. CONCLUSION: Optogenetic inhibition of excitatory neurons using the blue-light sensitive chloride channel stGtACR2 reduced the amplitude of electrically induced afterdischarges in the DG at the site of illumination, but this local inhibitory effect was insufficient to reduce the duration of the afterdischarge.

Clinical added value of magnetic source imaging in the presurgical evaluation of refractory focal epilepsy.

OBJECTIVE: This prospective, bicentre, blinded, intention to treat study assessed the clinical added value of magnetic source imaging (MSI) in the presurgical evaluation of patients with refractory focal epilepsy (RFE). METHODS: 70 consecutive patients with RFE (42 men; mean age 31.5 years, range 3-63) from two Belgian centres were prospectively included. All patients underwent conventional non-invasive presurgical evaluation (CNIPE) and a whole head magnetoencephalography recording (Elekta Neuromag). Equivalent current dipoles corresponding to interictal epileptiform discharges (IED) were fitted in the patients' spherical head model and coregistered on their MRI to produce MSI results. Results of CNIPE were first discussed blinded to the MSI results in respective multidisciplinary epilepsy surgery meetings to determine the presumed localisation of the epileptogenic zone and to set surgical or additional presurgical plans. MSI results were then discussed multidisciplinarily. MSI influence on the initial management plan was assessed. RESULTS: Based on CNIPE, 21 patients had presumed extratemporal epilepsy, 38 had presumed temporal epilepsy and 11 had undetermined localisation epilepsy. MSI showed IED in 52 patients (74.5%) and changed the initial management in 15 patients (21%). MSI related changes were significantly more frequent in patients with presumed extratemporal or undetermined localisation epilepsy compared with patients with presumed temporal epilepsy (p≤0.001). These changes had a clear impact on clinical management in 13% of all patients. CONCLUSION: MSI is a clinically relevant, non-invasive neuroimaging technique for the presurgical evaluation of patients with refractory focal epilepsy and, particularly, in patients with presumed extratemporal and undetermined localisation epilepsy.

The Manchester triage system: improvements for paediatric emergency care.

OBJECTIVE: To improve the Manchester Triage System (MTS) in paediatric emergency care. METHODS: The authors performed a prospective observational study at the emergency departments of a university and teaching hospital in The Netherlands and included children attending in 2007 and 2008. The authors developed and implemented specific age-dependent modifications for the MTS, based on patient groups where the system's performance was low. Nurses applied the modified system in 11,481 (84%) patients. The reference standard for urgency defined five levels based on a combination of vital signs at presentation, potentially life-threatening conditions, diagnostic resources, therapeutic interventions and follow-up. The reference standard for urgency was previously defined and available in 11,260/11,481 (96%) patients. RESULTS: Compared with the original MTS specificity improved from 79% (95% CI 79% to 80%) to 87% (95% CI 86% to 87%) while sensitivity remained similar ((63%, 95% CI 59% to 66%) vs (64%, 95% CI 60% to 68%)). The diagnostic OR increased (4.1 vs 11). CONCLUSIONS: Modifications of the MTS for paediatric emergency care resulted in an improved specificity while sensitivity remained unchanged. Further research should focus on the improvement of sensitivity.

Parallel roles of neuroinflammation in feline and human epilepsies.

Autoimmune encephalitis refers to a group of disorders characterised by a non-infectious encephalitis, often with prominent seizures and surface neuronal autoantibodies. AE is an important cause of new-onset refractory status epilepticus in humans and is frequently responsive to immunotherapies including corticosteroids, plasma exchange, intravenous immunoglobulin G and rituximab. Recent research suggests that parallel autoantibodies can be detected in non-human mammalian species. The best documented example is leucine-rich glioma-inactivated 1 (LGI1)-antibodies in domestic cats with limbic encephalitis (LE). In this review, we discuss the role of neuroinflammation and autoantibodies in human and feline epilepsy and LE.

The potential of invasive and non-invasive vagus nerve stimulation to improve verbal memory performance in epilepsy patients.

It has been demonstrated that acute vagus nerve stimulation (VNS) improves word recognition memory in epilepsy patients. Transcutaneous auricular vagus nerve stimulation (taVNS) has gained interest as a non-invasive alternative to improve cognition. In this prospective randomized cross-over study, we investigated the effect of both invasive VNS and taVNS on verbal memory performance in 15 patients with drug-resistant epilepsy. All patients conducted a word recognition memory paradigm in 3 conditions: VNS ON, VNS OFF and taVNS (3-period 3-treatment cross-over study design). For each condition, patients memorized 21 highlighted words from text paragraphs. Afterwards, the intervention was delivered for 30 s. Immediate recall and delayed recognition scores were obtained for each condition. This memory paradigm was repeated after 6 weeks of VNS therapy in 2 conditions: VNS ON and VNS OFF (2-period 2-treatment cross-over study design). Acute VNS and taVNS did not improve verbal memory performance. Immediate recall and delayed recognition scores were significantly improved after 6 weeks of VNS treatment irrespective of the acute intervention. We can conclude that the previously described positive effects of invasive VNS on verbal memory performance could not be replicated with invasive VNS and taVNS. An improved verbal memory performance was seen after 6 weeks of VNS treatment, suggesting that longer and more repetitive stimulation of the vagal pathway is required to modulate verbal memory performance.Clinical trial registration number: NCT05031208.

Cognitive tasks propagate the neural entrainment in response to a visual 40 Hz stimulation in humans.

Introduction: Alzheimer's disease is one of the great challenges in the coming decades, and despite great efforts, a widely effective disease-modifying therapy in humans remains elusive. One particular promising non-pharmacological therapy that has received increased attention in recent years is based on the Gamma ENtrainment Using Sensory stimulation (GENUS), a high-frequency neural response elicited by a visual and/or auditory stimulus at 40 Hz. While this has shown to be effective in animal models, studies on human participants have reported varying success. The current work hypothesizes that the varying success in humans is due to differences in cognitive workload during the GENUS sessions. Methods: We recruited a cohort of 15 participants who underwent a scalp-EEG recording as well as one epilepsy patient who was implanted with 50 subdural surface electrodes over temporo-occipital and temporo-basal cortex and 14 depth contacts that targeted the hippocampus and insula. All participants completed several GENUS sessions, in each of which a different cognitive task was performed. Results: We found that the inclusion of a cognitive task during the GENUS session not only has a positive effect on the strength and extent of the gamma entrainment, but also promotes the propagation of gamma entrainment to additional neural areas including deep ones such as hippocampus which were not recruited when no cognitive task was required from the participants. The latter is of particular interest given that the hippocampal complex is considered to be one of the primary targets for AD therapies. Discussion: This work introduces a possible improvement strategy for GENUS therapy that might contribute to increasing the efficacy of the therapy or shortening the time needed for the positive outcome.