Spectral analysis of sphenoidal evoked potentials predicts epileptic focus

Scalp-recorded auditory P300 event-related potentials in new-onset untreated temporal lobe epilepsy

We studied scalp-recorded auditory event-related potentials (ERPs) of 30 untreated patients with new-onset temporal lobe epilepsy and 30 age- and sex-matched normal controls. This study was designed to eliminate the effects of intractability of seizures and chronic use of antiepileptic drugs on P300 auditory ERPs. There were no statistically significant differences in both latency and amplitude of P300 between the two groups. Similar methods were also used to analyze component latencies and amplitudes of ERPs of 9 patients who had hippocampal sclerosis with comparison to control subjects. There were no statistically significant differences between these two groups as well. Our study evidently does not support temporal lobe sources of P300 scalp-recorded auditory ERPs. We also conclude that the scalp-recorded auditory ERPs procedure is not a useful tool to evaluate temporal lobe epilepsy.

The localizing value of auditory event-related potentials (P300) in patients with medically intractable temporal lobe epilepsy

The localizing value of postictal versus interictal event-related potentials (ERPs) was studied in patients with medically intractable TLE admitted for long-term video EEG monitoring. Ten patients with partial seizures and secondary generalization underwent preictal (upon hospital admission), postictal (</=6h after seizure), and interictal (7-48h after seizure) ERP recordings of an auditory oddball paradigm. Preictal ERPs were compared to postictal and interictal recordings. Intraclass correlations, transformed into z scores, were utilized to analyze amplitude differences between electrodes placed on the hemisphere ipsilateral versus contralateral to the epileptogenic focus. The results showed that in 9 out of 10 patients the ERP amplitude was reduced in postictal compared to preictal recordings for electrodes placed ipsilateral to the epileptogenic focus (P<0.0001). However, there was no difference in amplitude between ipsilateral and contralateral electrodes in preictal and interictal recordings. These findings suggest that postictal ERPs are of localizing value in patients with TLE while interictal ERPs are not.

Visual and auditory event related potentials in epileptic children: a comparison with normal and abnormal MRI findings

Visual and auditory event related potentials (VERPs and AERPs) in 32 epileptic children with magnetic resonance imaging (MRI) abnormalities and 18 with normal MRI were recorded and compared to the data of 21 healthy children. Of all 50 epileptic children (34 male, 16 female) aged 14.42+/-4.27 (7-20) years, 21 were medically intractable and receiving polytherapy. The mean latencies of N2 and P3 components of VERPs and AERPs in all epileptic children were significantly higher than those of the controls (P<0.05). Epileptic children with structural abnormalities had more prolonged latencies of N2 and P3 components of AERPs and VERPs than those of the healthy children (P<0.05). The epileptic children with normal MRI had significantly more prolonged latency of N2 and P3 of VERPs and P3 of AERPs than those of the controls (P<0.05). The difference of the mean latency of N2 and P3 components or the mean amplitude of P3 components of ERPs between the two epileptic groups was insignificant. The type of medication (mono- versus polytherapy) did not affect the wave components of ERPs. We suggest that epileptic activity, itself, leads to prolonged N2 and P3 components of AERPs and VERPs. The presence of structural abnormality indicated by imaging is not a predictor of ERPs abnormalities.

Lateralization of event-related potentials during discontinuation of antiepileptic medication

The effect of short-term withdrawal of antiepileptic drugs (AEDs) on auditory event-related potentials (ERPs) was studied in 16 patients undergoing preoperative evaluation for epilepsy surgery. ERPs were performed for all patients during treatment with full medication and after a 1-week period during ongoing tapering of AEDs. To clarify whether AED discontinuation would provide evidence of lateralizing for ERPs, we also studied the subgroup of 9 patients who had already undergone temporal lobectomies (TLE group). In the TLE group, if habitual seizures occurred < 30 h before the ERP recording session, auditory N1 and P3 amplitudes across sphenoidal electrodes were markedly decreased on the side ipsilateral to the epileptic focus. If seizures did not occur, asymmetries in amplitudes were equivocal and not of lateralizing value. In the whole group, midline N1 latencies for standard responses decreased significantly during AED discontinuation. At baseline, long-term habituation of the N1 component for standard responses was attenuated as compared with that of controls. During AED discontinuation, however, enhanced habituation of N1 was observed in TLE patients who did not exhibit seizures before ERP recording.

P3 latency jitter assessed using 2 techniques. II. Surface and sphenoidal recordings in subjects with focal epilepsy

We compared the latency variability in auditory P3s of 13 subjects with unilateral temporal lobe epilepsy (TLE) to that of normal controls. We predicted that increased latency jitter would occur in TLE subjects, particularly on the epileptic side. ERPs were recorded from scalp and sphenoidal sites relative to a balanced non-cephalic reference. Signal-to-noise ratios (SNRs) were calculated for each subject. Data were excluded if SNRs fell below 0.4. P3 latency jitter was estimated using 2 methods: Woody's algorithm and the maximum likelihood technique (MLT), a novel method of jitter assessment. SNRs were significantly higher in controls and were maximal posteriorly for both groups. P3 peak amplitude was significantly smaller in TLE subjects at temporal sites. Latency jitter (MLT method) was greatest in posterior sites and mirrored the jitter profiles of controls. Latency jitter was significantly higher in TLE subjects in bilateral frontal and temporal sites, but was not higher on the side of the focus and could not be attributed to lower SNRs. The increased bilateral latency jitter in these patients may be related to effects of anticonvulsants or the more extensive nature of the underlying epileptic disorder.

Status of quantitative EEG (QEEG) in clinical practice, 1994

Clinical quantitative EEG (qEEG) is a complex specialty that may include not only standard EEG but also digital ("paperless") EEG, topographic mapping, spectral analysis, spectral coherence, long latency and event related potentials (EP), significance probability mapping (SPM), dipole source localization methodology (DLM), and discriminant function analysis. There are three basic clinical uses: non-specific detection of organicity/encephalopathy, specific categorization of disease or clinical condition, and epileptic source localization. Extreme variations exist in the competency of laboratories practicing clinical qEEG; universally agreed upon standards of practice have not been established but there are a number of efforts to do so. As expected, the clinical value of qEEG to patients varies similarly. Criticisms of qEEG have now been answered: Color displays need not be deceptive. Statistical "capitalization upon chance" can be easily avoided. By training and with newer analytic procedures, artifacts can be recognized and often removed. Data based upon spectral analysis and EP can reliably classify clinical conditions thereby demonstrating a greater sensitivity to EEG/EP data than possible by conventional visual inspection. QEEG is clearly of clinical value when performed in concert with standard EEG and analyzed by clinicians with demonstrated competency in standard EEG followed by specialized training and demonstrated competency in qEEG. QEEG is not a simple substitute for conventional EEG and cannot be seen as a substitute for clinical competence. Although continuing to develop, qEEG technology has matured sufficiently and is now well established. Concerns regarding its clinical use have primarily resulted from its misapplication and misinterpretation stemming, largely, from inadequate personnel training and expertise.

Pre- and postoperative auditory event-related potentials in temporal lobe epilepsy

We studied auditory event-related potentials (ERPs) in 11 surgically treated patients with intractable temporal lobe epilepsy (TLE) pre- and postoperatively. ERPs through sphenoidal electrodes (Sp1-T3, Sp2-T4) provided clinically relevant and correctly lateralizing electrophysiologic evidence of temporal lobe dysfunction in 9 of 11 patients, confirmed by EEGs, electrocorticograms, neuroradiologic, and neuropsychological results, and clinical follow-up. Lateralizing asymmetries were noted in P300 amplitude, but latencies were prolonged bilaterally. Sphenoidal ERPs might serve as a new functional indicator of temporal lobe dysfunction in patients evaluated for epilepsy surgery.

Scalp and limbic P3 event-related potentials in the assessment of patients with temporal lobe epilepsy

Auditory oddball scalp and limbic P3s were recorded from 18 patients with unilateral temporal lobe epilepsy (TLE) prior to seizure surgery. Limbic P3s were unilaterally absent ipsilateral to the seizure focus and were present in the nonepileptogenic temporal lobe in all 18 cases studied. Scalp P3s, recorded from C3 and C4, on the other hand, were elicited bilaterally and there was no significant difference in amplitude or latency between the epileptogenic and nonepileptogenic sides. These data concur with studies of scalp P3 performed following surgery and suggest that the assessment of the contribution of limbic P3 to scalp P3 may be masked by volume conduction effects and other generators of P3. We conclude that the P3 recorded from central scalp sites, unlike its limbic counterpart, offers little clinical information in the presurgical assessment of patients with TLE.

Long-latency evoked potentials during aura of temporal lobe origin

Long-latency evoked potentials recorded from scalp or scalp/sphenoidal electrodes have been shown to have diminished amplitude and power during interictal recordings on the side ipsilateral to an unilateral mesial temporal lobe (MTL) focus. We now report recordings of long-latency evoked potentials both during a prolonged aura and also on two seizure-free days. P3 amplitude and sphenoidal evoked potential (SpEP) spectral power in the scalp/sphenoidal channels were less, ipsilateral to the MTL focus. During the aura, the SpEPs had reduced power and reduced amplitude. However, the amplitude of the N2 component for the target averages in the CZ-A1A2 channel was markedly enhanced during the aura.