Event-related potentials in epileptic children treated with monotherapy

The P3 event-related potential is a biomarker for the efficacy of vagus nerve stimulation in patients with epilepsy

Currently, the mechanism of action of vagus nerve stimulation (VNS) is not fully understood, and it is unclear which factors determine a patient's response to treatment. Recent preclinical experiments indicate that activation of the locus coeruleus noradrenergic system is critical for the antiepileptic effect of VNS. This study aims to evaluate the effect of VNS on noradrenergic signaling in the human brain through a noninvasive marker of locus coeruleus noradrenergic activity: the P3 component of the event-related potential. We investigated whether VNS differentially modulates the P3 component in VNS responders versus VNS nonresponders. For this purpose, we recruited 20 patients with refractory epilepsy who had been treated with VNS for at least 18 months. Patients were divided into 2 groups with regard to their reduction in mean monthly seizure frequency: 10 responders (>50 %) and 10 nonresponders (≤50 %). Two stimulation conditions were compared: VNS OFF and VNS ON. In each condition, the P3 component was measured during an auditory oddball paradigm. VNS induced a significant increase of the P3 amplitude at the parietal midline electrode, in VNS responders only. In addition, logistic regression analysis showed that the increase of P3 amplitude can be used as a noninvasive indicator for VNS responders. These results support the hypothesis that activation of the locus coeruleus noradrenergic system is associated with the antiepileptic effect of VNS. Modulation of the P3 amplitude should be further investigated as a noninvasive biomarker for the therapeutic efficacy of VNS in patients with refractory epilepsy.

Impaired spatial working memory in children with well-controlled epilepsy: an event-related potentials study

PURPOSE

To find out whether children with epilepsy did show different event-related potentials (ERP) compared to healthy children during performance in a visuo-spatial working memory (WM) task.

METHODS

Multichannel ERPs were measured during a visuo-spatial backmatching task. A quantitative analysis technique, based on Statistical Parametric Mapping, was used to analyze the ERP data. 62 children were tested (6-16 years old): 31 children with well-controlled epilepsy and 31 age- and intelligence-matched healthy children. One-backmatching (BM1) and two-backmatching (BM2) tasks were performed. Behavioral performance and target and nontarget ERPs were compared across groups in both tasks.

RESULTS

No behavioral differences were found between groups in the easy BM1 task. In the difficult BM2 task, children with epilepsy made significantly more omission errors. ERP analysis showed significantly higher amplitudes over frontal and central regions between 300 and 500 ms poststimulus in the epilepsy group compared to the control group. This effect was most pronounced in BM2.

DISCUSSION

This study shows that children with well-controlled epilepsy and normal intelligence demonstrate compensatory recruitment of their WM network during a visuo-spatial working memory task. Increasing the difficulty of the task (BM2) enhances this general neurophysiological finding and parallels the behavioral performance.

SIGNIFICANCE

Our results illustrate that epilepsy induces different cortical activity during working memory tasks, even when behavioral performance is normal.

Seizure frequency affects event-related potentials (P300) in epilepsy

To analyse the effect of epilepsy an P300 event-related potentials we studied 27 patients with idiopathic generalized epilepsy (IGE), 13 patients with temporal lobe epilepsy (TLE) and 60 normal controls. The prolongation of P300 latencies was highly cor related with increasing age in controls but not epileptic patients. The age-corrected P300 latency used in this study was actual P300 latency-predicted P300 latency (predicted P300 (msec)=306.20+0.79 age, P=0.001, R2=0.32). By using ANOVA analysis, the age-corrected latencies of P300 were significantly longer in TLE patients (19.72+/-47.82 msec, mean+/-SD) than in IGE patients (10.97+/-36.97 msec) and controls (0.23+/-20.28 msec). Likewise, significantly prolonged P300 latencies were seen in the epileptic patients with a seizure frequency more than 400 times (37.21+/-47.50 msec). The multivariate-adjusted odds ratio for those who had TLE was 10.97 (95% CI=3.99 - 30.14 ) in the prolonged latencies of P300 compared with that of IGE patients. The odds ratio of longer latencies of P300 was 7.43 (95% CI=2.75 - 20.08) among those who had a high seizure frequency (> or =400 times) compared with those who had a low seizure frequency. No interaction between TLE and high frequency of attacks was found. The age at onset of seizure and duration of illness was not associated with P300 latency prolongation. From the above results, we might infer that the seizure type of TLE and a high frequency of seizure are two major independent precipitate factors for abnormal latencies of P300 in the epileptic patients.

Comparison the cognitive effect of anti-epileptic drugs in seizure-free children with epilepsy before and after drug withdrawal

We studied the cognitive effects of antiepileptic drugs (AED), by investigating epileptic children who were seizure-free for at least 2 years and who had undergone fixed monotherapy. Seventy consecutive epileptic children (25 with carbamazepine (CBZ), 22 with phenobarbital (PB), and 23 with valproate (VPA)) were examined by Wechsler Intelligence Scale for Children-Revised (WISC-R) and auditory event-related potentials (P(300)) at three sessions: before AED reduction, then 1 and 7 months after complete withdrawal of treatment. There were no significant differences in IQ and subtests scores of WISC-R in any group at any of the three sessions. P(300) latencies were significantly increased in the children receiving PB but not in children receiving CBZ or VPA. P(300) amplitudes were increased but not significantly different among the three groups. These findings suggest that PB may affect cognitive function on children, but the changes of P(300) latencies may improve after discontinuation.

The effects of carbamazepine on an appetitive-to-aversive transfer task: comparison to untreated and phenytoin

1. Concerns over negative consequences resulting from chronic maintenance with antiepileptic medications have led to increased research regarding such impairments, often with disparate results. The authors have previously reported that phenytoin profoundly impairs the ability of adult rats, in comparison to controls. To learn a tone-signaled active avoidance response after learning a tone-signaled appetitive response (Banks et al., 1995; Banks et al., 1999). Such results lend further support to the suggestion that pharmacological treatment itself can produce cognitive difficulties that are comparable to those experienced by epileptic patients (Meador, 1994; Smith et al., 1987). 2. In the present experiments, the authors have continued their investigation of antiepileptic compounds by treating rats with carbamazepine, another commonly prescribed "first-line defense" antiepileptic medication. In comparison to intact animals, carbamazepine-treated rats demonstrate variable deficiencies in the acquisition of the secondarily acquired avoidance response. 3. This result is in agreement with the finding for phenytoin-treated animals, albeit to a lesser degree. Continuing experiments are needed to investigate the relative nature of the deficits produced by such antiepileptic medications, as well as the underlying neurobiological mechanism(s).

Effects of high-dose antiepileptic drugs on event-related potentials in epileptic children

N200 and P300 of event-related potentials (ERPs) were recorded from 22 epileptic children receiving high-dose antiepileptic drugs. The patients were undergoing monotherapy with supratherapeutic serum level and were not mentally retarded. P300 latency was prolonged in 5 of 8 patients (62.5%) of the carbamazepine (CBZ) group and in 4 of 7 patients (57.1%) of the phenytoin (PHT) group. Only one child of the PHT group showed abnormality in brain-stem auditory evoked potentials (BAEPs). Abnormality of P300 was more frequent than that of BAEP. In patients of the PHT group who underwent examinations consecutively before and after changing the dose, P300 latency was prolonged rapidly when the PHT level exceeded 30 micrograms/ml. This suggested that the prolongation was dose dependent. In all patients of the valproic acid (VPA) group, P300 latency was normal. Only 2 patients of the PHT group had P300 prolongation simultaneously with clinical signs of intoxication. Others demonstrated changes in P300 without symptoms of side effects.