Subcutaneous deuterated substrate administration in mice: An alternative to tail vein infusion.

PURPOSE: Tail-vein catheterization and subsequent in-magnet infusion is a common route of administration of deuterium (2 H)-labeled substrates in small-animal deuterium (D) MR studies. With mice, because of the tail vein's small diameter, this procedure is challenging. It requires considerable personnel training and practice, is prone to failure, and may preclude serial studies. Motivated by the need for an alternative, the time courses for common small-molecule deuterated substrates and downstream metabolites in brain following subcutaneous infusion were determined in mice and are presented herein. METHODS: Three 2 H-labeled substrates-[6,6-2 H2 ]glucose, [2 H3 ]acetate, and [3,4,4,4-2 H4 ]beta-hydroxybutyrate-and 2 H2 O were administered to mice in-magnet via subcutaneous catheter. Brain time courses of the substrates and downstream metabolites (and semi-heavy water) were determined via single-voxel DMRS. RESULTS: Subcutaneous catheter placement and substrate administration was readily accomplished with limited personnel training. Substrates reached pseudo-steady state in brain within ∼30-40 min of bolus infusion. Time constants characterizing the appearance in brain of deuterated substrates or semi-heavy water following 2 H2 O administration were similar (∼15 min). CONCLUSION: Administration of deuterated substrates via subcutaneous catheter for in vivo DMRS experiments with mice is robust, requires limited personnel training, and enables substantial dosing. It is suitable for metabolic studies where pseudo-steady state substrate administration/accumulation is sufficient. It is particularly advantageous for serial longitudinal studies over an extended period because it avoids inevitable damage to the tail vein following multiple catheterizations.

Epilepsy Milestones 2.0: An updated framework for assessing epilepsy fellowships and fellows.

OBJECTIVE: Accreditation Council for Graduate Medical Education (ACGME)-accredited epilepsy fellowships, like other ACGME accredited training programs, use Milestones to establish learning objectives and to evaluate how well trainees are achieving these goals. The ACGME began developing the second iteration of the Milestones 6 years ago, and these are now being adapted to all specialties. Here, we describe the process by which Epilepsy Milestones 2.0 were developed and summarize them. METHODS: A work group of nine board-certified, adult and pediatric epileptologists reviewed Epilepsy Milestones 1.0 and revised them using a modified Delphi approach. RESULTS: The new Milestones share structural changes with all other specialties, including a clearer stepwise progression in professional development and the harmonized Milestones that address competencies common to all medical fields. Much of the epilepsy-specific content remains the same, although a major addition is a set of Milestones focused on reading and interpreting electroencephalograms (EEGs), which the old Milestones lacked. Epilepsy Milestones 2.0 includes a Supplemental Guide to help program directors implement the new Milestones. Together, Epilepsy Milestones 2.0 and the Supplemental Guide recognize advances in epilepsy, including stereo-EEG, neurostimulation, genetics, and safety in epilepsy monitoring units. SIGNIFICANCE: Epilepsy Milestones 2.0 address the shortcomings of the old Milestones and should facilitate the assessment of epilepsy fellowships and fellows by program directors, faculty, and fellows themselves.

Visually sensitive seizures: An updated review by the Epilepsy Foundation.

Light flashes, patterns, or color changes can provoke seizures in up to 1 in 4000 persons. Prevalence may be higher because of selection bias. The Epilepsy Foundation reviewed light-induced seizures in 2005. Since then, images on social media, virtual reality, three-dimensional (3D) movies, and the Internet have proliferated. Hundreds of studies have explored the mechanisms and presentations of photosensitive seizures, justifying an updated review. This literature summary derives from a nonsystematic literature review via PubMed using the terms "photosensitive" and "epilepsy." The photoparoxysmal response (PPR) is an electroencephalography (EEG) phenomenon, and photosensitive seizures (PS) are seizures provoked by visual stimulation. Photosensitivity is more common in the young and in specific forms of generalized epilepsy. PS can coexist with spontaneous seizures. PS are hereditable and linked to recently identified genes. Brain imaging usually is normal, but special studies imaging white matter tracts demonstrate abnormal connectivity. Occipital cortex and connected regions are hyperexcitable in subjects with light-provoked seizures. Mechanisms remain unclear. Video games, social media clips, occasional movies, and natural stimuli can provoke PS. Virtual reality and 3D images so far appear benign unless they contain specific provocative content, for example, flashes. Images with flashes brighter than 20 candelas/m2 at 3-60 (particularly 15-20) Hz occupying at least 10 to 25% of the visual field are a risk, as are red color flashes or oscillating stripes. Equipment to assay for these characteristics is probably underutilized. Prevention of seizures includes avoiding provocative stimuli, covering one eye, wearing dark glasses, sitting at least two meters from screens, reducing contrast, and taking certain antiseizure drugs. Measurement of PPR suppression in a photosensitivity model can screen putative antiseizure drugs. Some countries regulate media to reduce risk. Visually-induced seizures remain significant public health hazards so they warrant ongoing scientific and regulatory efforts and public education.

Gain-of-function HCN2 variants in genetic epilepsy.

Genetic generalized epilepsy (GGE) is a common epilepsy syndrome that encompasses seizure disorders characterized by spike-and-wave discharges (SWDs). Pacemaker hyperpolarization-activated cyclic nucleotide-gated channels (HCN) are considered integral to SWD genesis, making them an ideal gene candidate for GGE. We identified HCN2 missense variants from a large cohort of 585 GGE patients, recruited by the Epilepsy Phenome-Genome Project (EPGP), and performed functional analysis using two-electrode voltage clamp recordings from Xenopus oocytes. The p.S632W variant was identified in a patient with idiopathic photosensitive occipital epilepsy and segregated in the family. This variant was also independently identified in an unrelated patient with childhood absence seizures from a European cohort of 238 familial GGE cases. The p.V246M variant was identified in a patient with photo-sensitive GGE and his father diagnosed with juvenile myoclonic epilepsy. Functional studies revealed that both p.S632W and p.V246M had an identical functional impact including a depolarizing shift in the voltage dependence of activation that is consistent with a gain-of-function. In contrast, no biophysical changes resulted from the introduction of common population variants, p.E280K and p.A705T, and the p.R756C variant from EPGP that did not segregate with disease. Our data suggest that HCN2 variants can confer susceptibility to GGE via a gain-of-function mechanism.

Population pharmacokinetics of oral baclofen in pediatric patients with cerebral palsy.

OBJECTIVE: To characterize the population pharmacokinetics (PK) of oral baclofen and assess impact of patient-specific covariates in children with cerebral palsy (CP) in order to support its clinical use. SUBJECTS DESIGN: Children (2-17 years of age) with CP received a dose of titrated oral baclofen from 2.5 mg 3 times a day to a maximum tolerated dose of up to 20 mg 4 times a day. PK sampling followed titration of 10-12 weeks. Serial R- and S-baclofen plasma concentrations were measured for up to 16 hours in 49 subjects. Population PK modeling was performed using NONMEM 7.1 (ICON PLC; Ellicott City, Maryland). RESULTS: R- and S-baclofen showed identical concentration-time profiles. Both baclofen enantiomers exhibited linear and dose/kg-proportional PK, and no sex differences were observed. Average baclofen terminal half-life was 4.5 hours. A 2-compartment PK model with linear elimination and transit absorption steps adequately described concentration-time profiles of both baclofen enantiomers. The mean population estimate of apparent clearance/F was 0.273 L/h/kg with 33.4% inter-individual variability (IIV), and the apparent volume of distribution (Vss/F) was 1.16 L/kg with 43.9% IIV. Delayed absorption was expressed by a mean transit time of 0.389 hours with 83.7% IIV. Body weight, a possible genetic factor, and age were determinants of apparent clearance in these children. CONCLUSION: The PK of oral baclofen exhibited dose-proportionality and were adequately described by a 2-compartment model. Our population PK findings suggest that baclofen dosage can be based on body weight (2 mg/kg per day) and the current baclofen dose escalation strategy is appropriate in the treatment of children with CP older than 2 years of age.

Prevalence of Suicidality in Adolescents With Newly Diagnosed Focal Epilepsy at Diagnosis and Over the Following 36 Months.

BACKGROUND AND OBJECTIVES: Individuals with epilepsy have increased risk of suicidal ideation (SI) and behaviors when compared with the general population. This relationship has remained largely unexplored in adolescents. We investigated the prevalence of suicidality in adolescents with newly diagnosed focal epilepsy within 4 months of treatment initiation and over the following 36 months. METHODS: This was a post hoc analysis of the enrollment and follow-up data from the Human Epilepsy Project, an international, multi-institutional study that enrolled participants between 2012 and 2017. Participants enrolled were 11-17 years of age within 4 months of treatment initiation for focal epilepsy. We used data from the Columbia Suicide Severity Rating Scale (C-SSRS), administered at enrollment and over the 36-month follow-up period, along with data from medical records. RESULTS: A total of 66 adolescent participants were enrolled and completed the C-SSRS. At enrollment, 14 (21%) had any lifetime SI and 5 (8%) had any lifetime suicidal behaviors (SBs). Over the following 36 months, 6 adolescents reported new onset SI and 5 adolescents reported new onset SB. Thus, the lifetime prevalence of SI within this population increased from 21% to 30% (14-20 adolescents), and the lifetime prevalence of SB increased from 8% to 15% (5-10). DISCUSSION: The prevalence of suicidality in adolescents with newly diagnosed focal epilepsy reported in our study is consistent with previous findings of significant suicidality observed in epilepsy. We identify adolescents as an at-risk population at the time of epilepsy diagnosis and in the following years.

Unrecognized Focal Nonmotor Seizures in Adolescents Presenting to Emergency Departments.

BACKGROUND AND OBJECTIVES: Many adolescents with undiagnosed focal epilepsy seek evaluation in emergency departments (EDs). Accurate history-taking is essential to prompt diagnosis and treatment. In this study, we investigated ED recognition of motor vs nonmotor seizures and its effect on management and treatment of focal epilepsy in adolescents. METHODS: This was a retrospective analysis of enrollment data from the Human Epilepsy Project (HEP), an international multi-institutional study that collected data from 34 sites between 2012 and 2017. Participants were 12 years or older, neurotypical, and within 4 months of treatment initiation for focal epilepsy. We used HEP enrollment medical records to review participants' initial diagnosis and management. RESULTS: A total of 83 adolescents were enrolled between 12 and 18 years. Fifty-eight (70%) presented to an ED before diagnosis of epilepsy. Although most ED presentations were for motor seizures (n = 52; 90%), many patients had a history of nonmotor seizures (20/52 or 38%). Adolescents with initial nonmotor seizures were less likely to present to EDs (26/44 or 59% vs 32/39 or 82%, p = 0.02), and nonmotor seizures were less likely to be correctly identified (2/6 or 33% vs 42/52 or 81%, p = 0.008). A history of initial nonmotor seizures was not recognized in any adolescent who presented for a first-lifetime motor seizure. As a result, initiation of treatment and admission from the ED was not more likely for these adolescents who met the definition of epilepsy compared with those with no seizure history. This lack of nonmotor seizure history recognition in the ED was greater than that observed in the adult group (0% vs 23%, p = 0.03) and occurred in both pediatric and nonpediatric ED settings. DISCUSSION: Our study supports growing evidence that nonmotor seizures are often undiagnosed, with many individuals coming to attention only after conversion to motor seizures. We found this treatment gap is exacerbated in the adolescent population. Our study highlights a critical need for physicians to inquire about the symptoms of nonmotor seizures, even when the presenting seizure is motor. Future interventions should focus on improving nonmotor seizure recognition for this population in EDs.

Health-related quality of life before and after pediatric epilepsy surgery: the influence of seizure outcome on changes in physical functioning and social functioning.

Health-related quality of life (HRQOL) is an important outcome in pediatric epilepsy surgery, but there are few studies that utilize presurgical ratings to assess the effect of surgery on HRQOL. We collected parental ratings on the Quality of Life in Childhood Epilepsy (QOLCE) questionnaire for 28 children who participated in neuropsychological assessment before and after epilepsy surgery. Our results revealed significant improvements in overall HRQOL after surgery, especially in physical and social activities. These changes were apparent despite generally unchanged intellectual and psychological functioning. Children with better seizure outcome had more improvement in HRQOL; however, improvements were not statistically different among children with Engel class I, II, and III outcomes. Our results suggest that children can experience significant improvements in HRQOL following epilepsy surgery even when neuropsychological functioning remains unchanged. Moreover, improvements in HRQOL appear evident in children who experience any worthwhile improvement in seizure control (Engel class III or better).

Leptin inhibits 4-aminopyridine- and pentylenetetrazole-induced seizures and AMPAR-mediated synaptic transmission in rodents.

Leptin is a hormone that reduces excitability in some hypothalamic neurons via leptin receptor activation of the JAK2 and PI3K intracellular signaling pathways. We hypothesized that leptin receptor activation in other neuronal subtypes would have anticonvulsant activity and that intranasal leptin delivery would be an effective route of administration. We tested leptin's anticonvulsant action in 2 rodent seizure models by directly injecting it into the cortex or by administering it intranasally. Focal seizures in rats were induced by neocortical injections of 4-aminopyridine, an inhibitor of voltage-gated K+ channels. These seizures were briefer and less frequent upon coinjection of 4-aminopyridine and leptin. In mice, intranasal administration of leptin produced elevated brain and serum leptin levels and delayed the onset of chemical convulsant pentylenetetrazole-induced generalized convulsive seizures. Leptin also reduced neuronal spiking in an in vitro seizure model. Leptin inhibited alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) receptor-mediated synaptic transmission in mouse hippocampal slices but failed to inhibit synaptic responses in slices from leptin receptor-deficient db/db mice. JAK2 and PI3K antagonists prevented leptin inhibition of AMPAergic synaptic transmission. We conclude that leptin receptor activation and JAK2/PI3K signaling may be novel targets for anticonvulsant treatments. Intranasal leptin administration may have potential as an acute abortive treatment for convulsive seizures in emergency situations.

The ketogenic diet inhibits the mammalian target of rapamycin (mTOR) pathway.

The ketogenic diet (KD) is an effective treatment for epilepsy, but its mechanisms of action are poorly understood. We investigated the hypothesis that the KD inhibits mammalian target of rapamycin (mTOR) pathway signaling. The expression of pS6 and pAkt, markers of mTOR pathway activation, was reduced in hippocampus and liver of rats fed KD. In the kainate model of epilepsy, KD blocked the hippocampal pS6 elevation that occurs after status epilepticus. Because mTOR signaling has been implicated in epileptogenesis, these results suggest that the KD may have anticonvulsant or antiepileptogenic actions via mTOR pathway inhibition.

A ketogenic diet does not impair rat behavior or long-term potentiation.

The effect of the ketogenic diet on behavior and cognition is unclear. We addressed this issue in rats behaviorally and electrophysiologically.We fed postnatal day 21 rats a standard diet (SD), ketogenic diet (KD), or calorie-restricted diet (CR) for 2­3 weeks. CR controlled for the slower weight gain experienced by KD-fed rats. We assessed behavioral performance with a locomotor activity and a conditioned fear test. To evaluate possible parallel effects of diet on synaptic function, we examined paired-pulse modulation (PPM) and long-term potentiation (LTP) in the medial perforant path in vivo. KD-fed rats performed similarly to SD-fed rats on the behavioral tests and electrophysiologic assays. These data suggest that the KD does not alter behavioral performance or synaptic plasticity.

Concern of Photosensitive Seizures Evoked by 3D Video Displays or Virtual Reality Headsets in Children: Current Perspective.

This review assesses the risk of a photic-induced seizure in a child during viewing of 3D (binocular 3 dimensional, stereoscopic) movies or games, either on standard video displays or when wearing a virtual reality (VR) headset. Studies published by pediatric epilepsy experts emphasize the low risk of 3D viewing even for children with known photosensitive epilepsy (PSE). The low incidence of PSE is noteworthy because the number of hours devoted to 2D or 3D screen viewing and/or VR headset use by children worldwide has increased markedly over the last decade. The medical literature does not support the notion that VR headset use poses a risk for PSE.

Familial aggregation of status epilepticus in generalized and focal epilepsies.

OBJECTIVE: To determine whether familial aggregation of status epilepticus (SE) occurs in a large cohort of familial common epilepsies. METHODS: We used the Epilepsy Phenome/Genome Project dataset, which consisted of 2,197 participants in 1,043 family units with ≥2 members having a common generalized or nonacquired focal epilepsy (NAFE). We identified participants with a history of traditionally defined SE (TSE) (seizures ≥30 minutes) and operationally defined SE (OSE) (seizures ≥10 minutes) by chart review. We assessed familial aggregation of TSE and OSE using χ2 analysis and generalized estimating equations (GEE). RESULTS: One hundred fifty-five (7%) participants in 1,043 families had ≥1 episodes of TSE. Two hundred fifty (11%) had ≥1 episodes of OSE. In a χ2 analysis, the number of family units with ≥2 members having TSE (odds ratio [OR] 4.79, 95% confidence interval [CI] 2.56-8.97) or OSE (OR 4.23, 95% CI 2.67-6.70) was greater than expected by chance. In GEE models adjusted for sex, broad epilepsy class (GE or NAFE), age at onset, and duration of epilepsy, TSE in a proband predicted TSE in a first-degree relative (OR 2.79, 95% CI 1.24-6.22), and OSE in a proband predicted OSE in a first-degree relative (OR 2.91, 95% CI 1.65-5.15). The results remained significant in models addressing epilepsy severity by incorporating the number of antiseizure medications used or epilepsy surgery. CONCLUSIONS: TSE and OSE showed robust familial aggregation in a cohort of familial epilepsy independently of epilepsy severity or class, suggesting that genetic factors contribute to SE independently of the genetic cause of these epilepsies. CLINICALTRIALSGOV IDENTIFIER: NCT00552045.

The glycine transport inhibitor sarcosine is an NMDA receptor co-agonist that differs from glycine.

Sarcosine is an amino acid involved in one-carbon metabolism and a promising therapy for schizophrenia because it enhances NMDA receptor (NMDAR) function by inhibiting glycine uptake. The structural similarity between sarcosine and glycine led us to hypothesize that sarcosine is also an agonist like glycine. We examined this possibility using whole-cell recordings from cultured embryonic mouse hippocampal neurons. We found that sarcosine is an NMDAR co-agonist at the glycine binding site. However, sarcosine differed from glycine because less NMDAR desensitization occurred with sarcosine than with glycine as the co-agonist. This finding led us to examine whether the physiological effects of NMDAR activation with these two co-agonists are the same. The difference in desensitization probably accounts for rises in intracellular Ca(2+), as assessed by the fluorescent indicator fura-FF, being larger when NMDAR activation occurred with sarcosine than with glycine. In addition, Ca(2+)-activated K(+) currents following NMDAR activation were larger with sarcosine than with glycine. Compared to glycine, NMDAR-mediated autaptic currents decayed faster with sarcosine suggesting that NMDAR deactivation also differs with these two co-agonists. Despite these differences, NMDAR-dependent neuronal death as assessed by propidium iodide was similar with both co-agonists. The same was true for neuronal bursting. Thus, sarcosine may enhance NMDAR function by more than one mechanism and may have different effects from other NMDAR co-agonists.

Increased severity of pentylenetetrazol induced seizures in leptin deficient ob/ob mice.

Leptin modulates multiple ion channels making its net effect on brain excitability difficult to predict. One method of determining leptin's net effect on brain excitability is to examine brain excitability during chronic leptin deficiency. We compared the susceptibility of leptin deficient ob/ob and wild type mice to pentylenetetrazol (PTZ) induced seizures using continuous video electroencephalogram (EEG) recordings. We found that ob/ob mice were more likely to die and were more susceptible to generalized clonic and clonic-tonic seizures than wild type mice at submaximal PTZ doses. These findings suggest that chronic leptin deficiency in vivo increases seizure susceptibility.

Pharmacogenomic Variability of Oral Baclofen Clearance and Clinical Response in Children With Cerebral Palsy.

BACKGROUND: Pharmacogenomic variability can contribute to differences in pharmacokinetics and clinical responses. Pediatric patients with cerebral palsy with genetic variations have not been studied for these potential differences. OBJECTIVE: To determine the genetic sources of variation in oral baclofen clearance and clinical responses. DESIGN: Pharmacogenomic add-on study to determine variability in oral baclofen clearance and clinical responses. SETTING: Multicenter study based in academic pediatric cerebral palsy clinics. PARTICIPANTS: A total of 49 patients with cerebral palsy who had participated in an oral baclofen pharmacokinetic/pharmacodynamic study. METHODS OR INTERVENTIONS: Of 53 participants in a pharmacokinetic/pharmacodynamic trial, 49 underwent genetic analysis of 307 key genes and 4535 single-nucleotide polymorphisms involved in drug absorption, distribution, metabolism, and excretion. Associations between genotypes and phenotypes of baclofen disposition (weight-corrected and allometrically scaled clearance) and clinical endpoints (improvement from baseline in mean hamstring Modified Tardieu Scale scores from baseline for improvement of R1 spastic catch) were determined by univariate analysis with correction for multiple testing by false discovery rate. MAIN OUTCOME MEASUREMENTS: Primary outcome measures were the genotypic and phenotypic variability of oral baclofen in allometrically scaled clearance and change in the Modified Tardieu Scale angle compared to baseline. RESULTS: After univariate analysis of the data, the SNP of ABCC9 (rs11046232, heterozygous AT versus the reference TT genotype) was associated with a 2-fold increase in oral baclofen clearance (mean 0.51 ± standard deviation 0.05 L/h/kg for the AT genotype versus 0.25 ± 0.07 L/h/kg for the TT genotype, adjusted P < .001). Clinical responses were associated with decreased spasticity by Modified Tardieu Scale in allelic variants with SNPs ABCC12, SLC28A1, and PPARD. CONCLUSIONS: Genetic variation in ABCC9 affecting oral baclofen clearance highlights the need for continued studies of genetic polymorphisms to better characterize variable drug response in children with cerebral palsy. Single-nucleotide polymorphisms in ABCC12, SLC28A1, and PPARD were associated with varied responses, which warrants further investigation to determine their effect on spasticity. LEVEL OF EVIDENCE: II.

Ketogenic diet reduces hypoglycemia-induced neuronal death in young rats.

Hypoglycemia is an important complication of insulin treatment in diabetic children and may contribute to lasting cognitive impairment. Previous studies demonstrated that 21-day-old rats (P21) subjected to brief, repetitive episodes of hypoglycemia sustain cortical neuronal death. The developing brain is capable of utilizing alternative energy substrates acetoacetate and beta-hydroxybutyrate. In these studies we tested the hypothesis that the developing brain adapted to ketone utilization and provided with ketones during hypoglycemia by eating a ketogenic diet would sustain less brain injury compared to littermates fed a standard diet. Supporting this hypothesis, P21 rats weaned to a ketogenic diet and subjected to insulin-induced hypoglycemia at P25 had significantly less neuronal death than rats on a standard diet. This animal model may provide insight into the determinants influencing the brain's susceptibility to hypoglycemic injury.

Differential presynaptic modulation of excitatory and inhibitory autaptic currents in cultured hippocampal neurons.

Short-term synaptic plasticity has an important role in higher cortical function. Hyperpolarization may effect a form of short-term plasticity by promoting recovery from sodium channel inactivation or by activating axonal A-type potassium channels. To determine whether one or both processes occur, we examined the effect of hyperpolarizing prepulses on autaptic currents in cultured postnatal rat hippocampal neurons. As expected of enhanced recovery from sodium channel inactivation, hyperpolarizing prepulses reversibly increased fast excitatory autaptic currents (eacs) mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), slow eacs mediated by N-methyl-D-aspartate receptors (NMDARs), and inhibitory autaptic currents (iacs) mediated by gamma-aminobutyric acidA receptors (GABAARs). Hyperpolarizing prepulses augmented nearly all fast and slow eacs but only half of the iacs. This change occurred without a change in autaptic current kinetics. Of note, hyperpolarizing prepulses did not significantly reduce autaptic currents in any neuron studied. The rapidly dissociating competitive antagonists kynurenate and L-2-amino-5-phosphonovaleric acid (LAPV) inhibited fast and slow eacs, respectively, to the same extent with and without a hyperpolarizing prepulse. In addition, hyperpolarizing prepulses revealed a slow eac even after the slow eac evoked without a prepulse was completely blocked by the open channel blocker, (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801). Finally, hyperpolarizing prepulses did not alter currents evoked by exogenous applications of glutamate and GABA. These findings suggest that hyperpolarizing prepulses preferentially enhance eacs over iacs, and that they do so, in part, by overcoming conduction block or by activating silent synapses.