Optimizing parameters for terminating cortical afterdischarges with pulse stimulation

PURPOSE: We previously reported that brief pulses of electrical stimulation (BPSs) can terminate afterdischarges (ADs) during cortical stimulation. We investigated conditions under which BPS is more likely to suppress ADs. METHODS: We analyzed parameters altering BPS effectiveness on 200 ADs in seven patients with implanted subdural electrodes. RESULTS: The odds of BPSs stopping ADs was 8.6 times greater at primary sites (directly stimulated electrodes) than at secondary sites (adjacent electrodes) (p = 0.016). BPS applied within 4.5 s after onset of AD had 2 times greater odds of stopping ADs (p = 0.014). BPS applied when AD voltage was negative was 1.9 times more likely to stop ADs (p = 0.012). ADs with rhythmic pattern responded best (p < 0.0001). BPS stopped 100% of ADs not starting immediately after localization stimulus (LS) versus 29% of those starting immediately (p < 0.0001). CONCLUSIONS: BPS is more likely to terminate ADs at primary electrodes, if given early, if applied to the negative peak of the AD waveform, if AD has a rhythmic pattern, and if AD did not start immediately after LS.     

Afterdischarges during cortical stimulation at different frequencies and intensities

PURPOSE: The occurrence of unwanted afterdischarges (ADs) impedes cortical stimulation for mapping purposes. We investigated the safety of several stimulation paradigms. METHODS: We compared the incidence of ADs and behavioral responses of two stimulation frequencies (50 and 100 Hz), at two intensities (1 and 0.2 ms pulse widths). RESULTS: Stimulation with 100 Hz was more likely to cause ADs than 50 Hz, and stimulation using 1 ms pulse width was more likely to cause ADs than 0.2 ms. CONCLUSIONS: Stimulation using 50 Hz frequency with a pulse width of 0.2 ms might be safer during cortical mapping.     

An early sodium and a late calcium phase in the afterdischarge of peptide-secreting neurons ofAplysia

Following brief electrical stimulation of a pleuroabdominal connective nerve, the clusters of peptidergic bag cell neurons of Aplysia generate a long-lasting (or approximately 30 min) synchronous afterdischarge. In a normal seawater medium, the afterdischarge comprises an early phase of rapid firing (2-6 Hz) lasting for less than one minute, followed by a second, prolonged phase of lowering firing rate (less than 0.5 Hz). We have found that the transition from the first, rapid-firing phase to the prolonged second phase of afterdischarge is associated with an increase both in the width and height of intracellularly recorded action potentials. In addition, we find that in the presence of the potassium channel-blocker, TEA, such biphasic afterdischarges may be triggered by depolarizing current that evokes action potentials in a single bag cell neuron in a cluster. Afterdischarges resembling either the first or the second phase of a normal afterdischarge may be produced by using media deficient in calcium or sodium, respectively, in combination with potassium channel-blockers. Brief stimulation in media deficient in calcium give rise to afterdischarges of high firing frequency (2-6 Hz) lasting for less than one minute (mean duration = 41 s) while, in a sodium-free medium, longer afterdischarges (mean duration = 18 min) of lower firing rate (less than 0.3 Hz) were generated. At the end of afterdischarge in a normal seawater medium, containing both sodium and calcium ions, the bag cell neurons become refractory to stimulation. Thus, further stimulation either fails to induce afterdischarge or results in afterdischarges that are attenuated both in frequency of firing and in duration compared with the first afterdischarge. In these experiments we found that the brief afterdischarges, observed in low-calcium media, which resemble the first phase of a normal afterdischarge, did not induce subsequent refractoriness while afterdischarges evoked in the normal calcium, sodium-free medium did result in refractoriness to further afterdischarge. Our data indicate that both phases of a bag cell afterdischarge are due to intrinsic bag cell mechanisms and suggest that the firing pattern in the first phase is largely sodium dependent and that of the second, slow phase is calcium dependent. Moreover, our data indicate that it is the second, calcium-dependent phase that induces the refractoriness that follows bag cell afterdischarge.     

Frequency-related, bidirectional limbic responses to cocaine: Comparisons with amphetamine and lidocaine

Dual effects of cocaine on the electrical excitability of limbic structures were investigated by determining current thresholds for afterdischarges (AD) evoked by low and high frequency electrical stimulation. Cocaine, lidocaine and D-amphetamine treatments were compared in order to assess the extent to which cocaine's local anesthetic and monoaminergic actions contribute to its effects on limbic afterdischarges. Afterdischarge threshold, duration and propagation for both 3 and 50 Hz stimulation of the amygdala, hippocampus and septal area were tested following saline, cocaine (5 mg/kg), lidocaine (5 mg/kg) and D-amphetamine (2.5-5 mg/kg). Results provide clear evidence that cocaine has a bidirectional effect on hippocampal and amygdalar AD thresholds--significantly increasing sensitivity to low frequency stimulation while significantly decreasing sensitivity to high frequency stimulation at identical brain sites. A frequency-dependent threshold effect also occurred at the septal area. In addition, cocaine reduced limbic AD duration and propagation; these effects proved unrelated to the direction of AD threshold changes. Cocaine effects on afterdischarges differed significantly from those of amphetamine and lidocaine. Comparisons with amphetamine and lidocaine suggest that cocaine's local anesthetic action, but not its monoaminergic properties, may contribute to reductions in limbic afterdischarge duration and propagation. However, it is unlikely that either monoaminergic or local anesthetic actions are responsible for cocaine's pronounced dual effect on the electrical excitability of major limbic structures. This bidirectional drug effect has interesting neurobiological implications and, in addition, offers a potentially valuable tool for new research on frequency-related functions of the limbic system.     

脑皮质电刺激对癫痫大鼠脑皮质兴奋性的影响

目的 观察重复脑皮质电刺激对氯化铁诱发慢性癫痫大鼠模型脑皮质兴奋性的影响.方法 通过在运动感觉区脑皮质注射氯化铁建立慢性癫痫大鼠模型,给予脑皮质低频(1 Hz)低强度(0.1 mA)和低频(1 Hz)高强度(1.0 mA)、高频(100 Hz)低强度(0.1 mA)和高频(100 Hz)高强度(1.0 mA)不同的重复电刺激,检测电刺激前后脑皮质后放电阈值、后放电时程和行为学评分.假刺激慢性癫痫大鼠作为对照组.结果 后放电阈值低频低强度组(2.10±0.38)mA与对照组(1.50±0.33)mA相比差异有统计学意义(P＜0.05).行为学评分和后放电时程各组与对照组相比差异无统计学意义.行为学评分与后放电阈值的比值低频低强度组(1.88±0.60)和低频高强度组(2.18±0.38)与对照组(3.22±0.67)相比差异有统计学意义(P＜0.01和P＜0.05).结论 重复低频低强度脑皮质电刺激可以升高氯化铁诱发慢性癫痫大鼠模型的脑皮质后放电阈值,降低脑皮质兴奋性,提示合适参数的脑皮质电刺激对氯化铁诱发大鼠癜痫具有抑制作用.     

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.     

Neurostimulators in epilepsy

A review of electrical stimulation in patients with refractory epilepsy, including animal and human data, shows that there is anatomic and physiologic evidence supporting the role of the thalamus in epilepsy. The most recent reports in patients with refractory epilepsy suggest that deep brain stimulation and cortical electrical stimulation of the anterior thalamic nucleus and hippocampus may reduce seizure frequency in patients with refractory partial and secondarily generalized seizures. This has led to a multicenter, prospective randomized trial called the Stimulation of the Anterior Nucleus of the Thalamus for Epilepsy (SANTE trial) that is currently being conducted at several centers in the United States. There is also a multicenter clinical trial for patients with refractory partial epilepsy treated with a cranially implanted responsive neurostimulator (RNS) system. Preliminary reports from the RNS system feasibility trial (the NeuroPace trial) suggest that electrographic seizures can be detected before they evolve into clinical seizures, and that electrical stimulation of the epileptogenic zone can then terminate the electrographic seizures. The preliminary data in patients using deep brain stimulation of the anterior thalamic nucleus and hippocampus, and cortical stimulation studies of the epileptogenic zone are promising and suggest a reduction in seizure frequency in some patients with refractory partial and secondarily generalized seizures. The exact mechanism of action and the best parameters used during electrical stimulation remain unknown and are the subject of ongoing research.     

Oral automatisms induced by stimulation of the mesial frontal cortex

Extraoperative electrical stimulation is frequently used to identify eloquent areas in patients with pharmacoresistant epilepsy who undergo subdural grid evaluation for epilepsy surgery. Oral automatisms elicited by cortical stimulation have been described in the mesial temporal lobe, but also in the mesial frontal lobe, particularly the cingulate gyrus. However oral automatisms attributed to stimulation in the superior frontal gyrus without afterdischarges have never been reported. Herein we present two patients with right frontal lobe epilepsy with oral automatisms induced by electrical stimulation of the right mesial superior frontal gyrus.     

Peptidergic neurons of Aplysia lose their response to cyclic adenosine 3':5'-monophosphate during a prolonged refractory period

Although the peptidergic bag cell neurons of Aplysia are ordinarily silent, they respond to brief electrical stimulation by producing an afterdischarge of about 30 min duration. This afterdischarge is followed by a refractory period lasting many hours during which electrical stimulation either fails to initiate afterdischarges or produces discharges of much shorter duration. Previous work has demonstrated that cyclic AMP plays a role in the genesis of afterdischarge, both in intact bag cell clusters and in isolated cultured bag cells. We have now examined the hypothesis that in the refractory period either the synthesis of cyclic AMP or the response to cyclic AMP is attenuated. Direct measurements of cyclic AMP showed that cyclic AMP levels in the bag cell neurons are elevated to a similar extent after stimulation in refractory and nonrefractory clusters of neurons. We have found, however, that the response to cyclic AMP is altered during the refractory period. The electrophysiological responses of bag cell neurons were first examined in intact clusters of cells within the abdominal ganglion. Cyclic AMP levels were elevated using the adenylate cyclase activator, forskolin, in the presence of theophylline (FT). The duration of a first bag cell afterdischarge could be greatly increased if FT was added before stimulation. The duration of a stimulated second bag cell afterdischarge could also be significantly increased if FT was added within a brief period following the end of the first afterdischarge. Furthermore, at these times the addition of FT often resulted in the onset of spontaneous afterdischarges.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effectiveness of low-frequency stimulation for mapping cortical function

OBJECTIVE: To establish the efficacy and safety of low-frequency electrical stimulation for cortical brain mapping. METHODS: Cortical function was mapped using electrical stimulation in epilepsy patients with chronically implanted intracranial subdural electrodes. Contacts overlying motor, sensory, visual, and language cortex were stimulated at frequencies of 5, 10, and 50 Hz, using current levels ranging from 1 to 17.5 mA for 3-5 s. The current intensity and incidence at which functional alterations and afterdischarges (ADs) occurred were recorded. The modified McNemar test for nonindependent measures was used to analyze the data. RESULTS: 122 electrode contact pairs were electrically stimulated at least two different frequencies in 14 patients. Functional alterations were obtained at all stimulation frequencies (5, 10, and 50 Hz) at generally similar rates. The likelihood of producing an AD correlated with stimulation frequency, and lower-frequency stimulation was less likely to provoke an AD. Higher current intensity was required to induce both functional responses and ADs at low-frequency stimulation than high-frequency stimulation. While overall rates of producing functional changes were similar, differences in functional response with regard to frequency were noted at individual cortical sites. CONCLUSION: 5- and 10-Hz stimulation are as effective for mapping cortical function as 50-Hz stimulation and produce fewer ADs. We recommend that mapping of cortical function be started with 5-Hz-frequency stimulation. Higher frequencies should be used in suspect cortex if no symptoms or signs are produced with 5-Hz stimulation.     

皮质电刺激在难治性癫病人语言区定位的应用

目的探讨皮质电刺激在难治性癫病人语言区定位的作用。方法 10例癫病人经颅内电极行脑皮质电刺激,记录其语言行为学表现及相应电流强度,个体化定位语言区以指导剪裁式致灶切除术。术后评估病人语言功能。结果 5例病人应用皮质电刺激测得语言区,其分布变异大,但4例病人干扰语言功能的电流强度阈值之间无明显差异(P>0.05)。所有病人术后均未出现语言功能障碍。结论应用特定参数的脑皮质电刺激行个体化语言区定位,有利于降低难治性癫病人致灶切除术后发生语言障碍的风险。     

Dynamic mechanisms underlying afterdischarge: A human subdural recording study

ObjectiveNo synoptic understanding exists of how and why afterdischarges (ADs) occur following electrical stimulation of the cerebral cortex. Based on human observations, we formulated a general mechanism for the emergence of ADs.MethodsWe retrospectively analysed spectra of AD time-series and control segments of the resting electrocorticogram (ECoG) in 15 epilepsy patients who underwent cortical stimulation mapping. The observations led to the development of phenomenological models for AD emergence and morphology.ResultsAn analytical relationship exists between the spectrum of the baseline ECoG and the ensuing AD, characterised by ‘condensation’ of the main baseline spectral cluster, with variable inclusion of higher harmonics of the condensate.ConclusionsADs arise by synchronisation of pre-existing local field potentials, likely through temporary inactivation of inhibitory interneurons from repetitive stimulation-induced depolarization. The appearance of higher harmonics indicates that ADs are further modulated by recurrent feedback, likely from the entrained activity of single units.SignificanceFor the first time, a putative mechanism is suggested for AD emergence following electrical stimulation of the cerebral cortex. Insight is also offered into several empirical observations regarding ADs, detailed in the main text. More generally, a novel conceptual synthesis emerges between the behaviour of electrically-excited cortex and the physics of nonlinearly coupled multi-oscillator systems.     

Anticonvulsant action of three neurosteroids against cortical epileptic afterdischarges in immature rats

Neurosteroids exhibit anticonvulsant action probably by positive modulatory influence on GABA-A receptors. The action of three neurosteroids was tested against cortical epileptic afterdischarges in immature rats with implanted electrodes. Afterdischarges (ADs) were elicited by rhythmic electrical stimulation (biphasic pulses at 8 Hz frequency for 15s) of sensorimotor cortical region with a slightly suprathreshold current intensity. Drugs were administered intraperitoneally after the first afterdischarge and stimulation was repeated five more times with the same intensity. Allopregnanolone in doses of 20 and 30 mg/kg i.p. was found to be active in 12-day-old rats; there was no effect in 18-day-old rats and only a tendency in 25-day-old ones. Therefore, the effects of pregnanolone and a new derivative THDOC-conjugate (20 and 40 mg/kg) were compared with those of allopregnanolone (40 mg/kg) only in 12- and 25-day-old rats in the second part of study. All three neurosteroids blocked progressive prolongation of repeated ADs seen in control 12-day-old rats. In addition, pregnanolone was able to shorten the ADs. In contrast, duration of ADs in 25-day-old animals was significantly shorter than the duration of the first, predrug AD only after administration of the 40 mg/kg dose of pregnanolone; if corresponding ADs in the control and drug groups were compared, pregnanolone and THDOC-conjugate led to significantly shorter ADs, changes after allopregnanolone administration were statistically significant only in the fourth AD. None of the studied neurosteroids was able to suppress movements directly bound to stimulation as well as clonic seizures accompanying afterdischarges. Among the three drugs studied, pregnanolone was found to be the most potent one. As developmental changes are concerned, the youngest animals exhibited the highest sensitivity to anticonvulsant action of neurosteroids.     

Characteristics of prolonged afterdischarges in children with malformations of cortical development

We investigated aberrant cortical excitability in malformations of cortical development From subdural electrodes, we recorded afterdischarges lasting > or = 6 seconds in 12 of 13 patients with malformations of cortical development and 6 of 10 pediatric patients with nonmalformations of cortical development and reviewed amperage thresholds, distribution of afterdischarges, and motor responses. In patients with malformation of cortical development, motor response thresholds were high; afterdischarge and motor response thresholds, which essentially overlapped, inversely correlated with age (P < .01); afterdischarge thresholds declined with age; and 8 patients showed afterdischarges in remote sites. In nonmalformation of cortical development, afterdischarge thresholds did not significantly correlate with age; motor response thresholds tended to decline with age; and 2 patients had remote afterdischarges. Adolescent patients with malformations of cortical development had lower afterdischarge thresholds than adolescents with nonmalformation of cortical development (P < .05). From their high afterdischarge (and motor response) thresholds, we concluded that preadolescent patients with malformation of cortical development have less excitable, immature cortices, whereas adolescent patients with malformation of cortical development with low afterdischarge thresholds have hyperexcitable cortices. Remote afterdischarges over focal dysplastic cortex suggest aberrant cortical excitability and neural circuits.     

Electrophysiological effects and clinical results of direct brain stimulation for intractable epilepsy

Objective: Epilepsy can be considered as a result of the imbalance of the excitatory and inhibitory processes. Therefore, the artificial enhancement of the activity of brain inhibitory mechanisms might lead to a beneficial therapeutic effect for intractable epilepsy patients. Material and methods: Studies of the inhibitory effects of electrical stimulation of the head of the caudate nucleus (HCN), cerebellar dentate nucleus (CDN), thalamic centromedian nucleus (CM), and neocortical and temporal lobe mesiobasal epileptic foci were performed on 150 patients with implanted intracerebral electrodes. Chronic brain stimulation with implanted neurostimulators was performed on 54 patients. Sixteen were followed up to 1.5 years (mean 1.2 years). Results: The study demonstrated that 4–8 Hz HCN and 50–100 Hz CDN stimulation suppressed the subclinical epileptic discharges and reduced the frequency of generalized, complex partial, and secondary generalized seizures. CM stimulation (20–130 Hz) desynchronized the EEG and suppressed partial motor seizures. Direct subthreshold 1–3 Hz stimulation of the epileptic focus may suppress rhythmic afterdischarges (ADs). Seizures were eliminated for 26 of 54 patients (48%), worthwhile improvement was achieved for 23 of 54 patients (43%), and no improvement was observed in 5 of 54 patients (9%). Conclusion: The artificial increase of the activity of brain inhibitory system may suppress the activity of epileptic foci, and, in long run, stabilize this epileptic foci activity at a lower, perhaps normal, level. Therapeutic direct brain stimulation, therefore, might serve as a useful tool in the treatment of intractable and multifocal epilepsy, and might be combined with ablative surgical methods.     

Cognitive effort decreases beta,alpha, and theta coherence and ends afterdischarges in human brain

ObjectiveMental activation has been reported to modify the occurrence of epileptiform activity. We studied its effect on afterdischarges.MethodIn 15 patients with implanted electrodes we presented cognitive tasks when afterdischarges occurred. We developed a wavelet cross-coherence function to analyze the electrocorticography before and after the tasks and compared findings when cognitive tasks did or did not result in afterdischarge termination. Six patients returned for functional MRI (fMRI) testing, using similar tasks.ResultsCognitive tasks often could terminate afterdischarges when direct abortive stimulation could not. Wavelet cross-coherence analysis showed that, when afterdischarges stopped, there was decreased coherence throughout the brain in the 7.13–22.53 Hz frequency ranges (p values 0.008–0.034). This occurred a) regardless of whether an area activated on fMRI and b) regardless of whether there were afterdischarges in the area.ConclusionsIt is known that cognitive tasks can alter localized or network synchronization. Our results show that they can change activity throughout the brain. These changes in turn can terminate localized epileptiform activity.SignificanceCognitive tasks result in diffuse brain changes that can modify focal brain activity. Combined with a seizure detection device, cognitive activation might provide a non-invasive method of terminating or modifying seizures.     

Comparison of bipolar versus monopolar extraoperative electrical cortical stimulation mapping in patients with focal epilepsy

ObjectiveExtraoperative cortical stimulation (CS) for mapping of eloquent cortex in patients prior to epilepsy surgery is not standardized across centres. Two different techniques are in use, referred to as bipolar and monopolar CS. We compared the ability of bipolar versus monopolar CS to identify eloquent cortex and their safety profile in patients undergoing subdural EEG recordings.MethodsFive patients undergoing intracranial EEG recordings and extraoperative CS. Systematic comparison of stimulus parameters, clinical signs and afterdischarges of bipolar versus monopolar CS.ResultsBipolar CS requires less stimulation current but is more time consuming and more likely to produce afterdischarges when compared to monopolar CS. None of the stimulations elicited seizures. The area defined as eloquent by either bipolar or monopolar CS reveals only minor discordances, involving mainly the outer row and edge of the electrode array producing clinical signs with monopolar CS only. Qualitatively, bi- and monopolar CS reproduced similar movements and types of muscle contractions.ConclusionsBipolar and monopolar CS are safe procedures identifying similar cortical areas as eloquent, although monopolar cortical stimulation is less time consuming.SignificanceFindings advocate the use of monopolar CS in a clinical setting.     

Unequal development of thresholds for various phenomena induced by cortical stimulation in rats

Electrical stimulation of sensorimotor cortical area was performed in 9-, 12-, 18-, 25-, 35- and 90-day-old rats with implanted electrodes to establish threshold intensities of currents necessary to elicit four different motor or EEG phenomena. Two different stimulation frequencies (8 and 50 Hz) were used. Development of thresholds for stimulation-bound movements, spike-and-wave afterdischarges and clonic seizures accompanying these afterdischarges was similar: the lowest threshold was found in 18-, respectively, in 18- and 25-day-old rats with the 8 and 50 Hz frequencies. Younger as well as older animals exhibited higher threshold intensities. The fourth phenomenon, transition into another, 'limbic' type of afterdischarges appeared only exceptionally in the youngest rats and its incidence increased whereas the threshold decreased with age. Higher frequency was more efficient in elicitation of limbic afterdischarges than the 8 Hz stimulation in rats aged 18 and more days. Our data represent a background for pharmacological studies and indicate the development of cortical excitability and of connections between the thalamocortical system and limbic structures.     

神经导航经颅磁刺激在癫痫术前语言区评估中的应用

目的探讨神经导航经颅磁刺激(n TMS)在术前皮质语言区评估中的临床应用价值。方法选取14例接受颅内硬膜下电极埋置术的癫痫患者,在神经导航引导下,采用4~10Hz重复经颅磁刺激(r TMS),对患者语言区进行定侧、定位分析。通过与颅内电极皮质电刺激(ECS)语言功能定位结果进行比较,评估nT MS在术前语言区定位中的临床应用价值。结果在14例患者中,nT MS诱发出明确语言停顿或明显语言干扰的患者12例,2例未出现明显语言干扰现象。术前nT MS诱发出语言障碍的12例患者,在ECS过程中均出现明确语言功能障碍。提高刺激强度可以提高诱发语言干扰的几率,频率4~6Hz刺激在语言区定位中,可以较好地兼顾患者的耐受性和刺激效果。结论对于不适合接受ECS等有创性评估的患者,术前nT MS可以提供有价值的语言功能定位信息。     

Electric stimulation on human cortex suppresses fast cortical activity and epileptic spikes

Summary:  Purpose: To investigate underlying mechanisms and adequate parameters for electric cortical stimulation to inhibit epileptic focus in humans.
Methods: A patient with intractable partial epilepsy had subdural electrodes implanted for preoperative evaluation. Cortical functional mapping was performed by using 50-Hz alternating square pulse of 0.3-ms duration, 1 to 7 mA, within 5 s. Spike frequency and electrocorticogram (ECoG) power spectra were compared before and after the stimulation when epileptic focus and distant area were stimulated. A similar comparison also was performed in low-frequency stimulation of 0.9 Hz applied for 15 min.
Results: Interictal spikes were reduced after electric cortical stimulation of the epileptic area at a frequency of 50 Hz as well as 0.9 Hz, with concomitant decrease in the electrographic fast activities at 50-Hz stimulation.
Conclusions: These data suggest that electric cortical stimulation at both high and low frequency has a suppressive effect on epileptic activities in human cortex, possibly through distinct mechanisms.