Seizure Lateralization Research Articles

Differential neuropsychological test sensitivity to left temporal lobe epilepsy

We examined the sensitivity of the Rey Auditory Verbal Learning Test (AVLT), California Verbal Learning Test (CVLT), Boston Naming Test (BNT), and Multilingual Aphasia Examination Visual Naming subtest (MAE VN) to lateralized temporal lobe epilepsy (TLE) in patients who subsequently underwent anterior temporal lobectomy. For the AVLT (n = 189), left TLE patients performed more poorly than their right TLE counterparts [left TLE = 42.9 (10.6), right TLE = 47.7 (9.9); p < .002 (Cohen's d = .47)]. Although statistically significant, the CVLT group difference (n = 212) was of a smaller magnitude [left LTE = 40.7 (11.1), right TLE = 43.8 (9.9); (p < .03, Cohen's d = .29)] than the AVLT. Group differences were also present for both measures of confrontation naming ability [BNT: left LTE = 43.1 (8.9), right TLE = 48.1 (8.9); p < .001 (Cohen's d = .56); MAE VN: left TLE = 42.2, right TLE = 45.6, p = .02 (Cohen's d = .36)]. When these data were modeled in independent logistic regression analyses, the AVLT and BNT both significantly predicted side of seizure focus, although the positive likelihood ratios were modest. In the subset of 108 patients receiving both BNT and AVLT, the AVLT was the only significant predictor of seizure laterality, suggesting individual patient variability regarding whether naming or memory testing may be more sensitive to lateralized TLE.

The diagnostic value of oral lacerations and incontinence during convulsive “seizures”

Oral lacerations and urinary incontinence have long been considered useful clinical features for the diagnosis of epileptic seizures; however, both are also reported in patients with psychogenic nonepileptic seizures (PNES). The aims of the study were (1) to investigate whether the presence and nature of oral lacerations or incontinence during convulsive seizures of patients with epilepsy differed from those with PNES, and (2) whether the side of the oral laceration has any correlation with the epilepsy syndrome or lateralization. Eighty-four consecutive patients who experienced at least one convulsive event during video-EEG monitoring (VEM) were questioned and examined for oral lacerations and incontinence. Seizure classification was determined by a team of epileptologists based on the VEM findings and other clinical and investigational data, blinded to the oral laceration and incontinence information. The presence of oral lacerations among patients with epileptic seizures was 26% (17/66), in contrast it was 0% (0/18) with PNES (p = 0.01). Of the oral lacerations sustained by patients during an epileptic seizure, 14 were to the side of the tongue, one to the tip of the tongue, two to the cheek, and three to the lip. No significant relationships were observed between seizure lateralization and oral lacerations. Incontinence occurred in 23% (15/66) of epilepsy patients and 6% (1/18) of PNES patients (p = 0.09). There was no relationship between epilepsy type or lateralization and the prevalence of incontinence. Despite frequent reports of oral lacerations and incontinence by patients with PNES, objective evidence for this is highly specific to convulsive epileptic seizures.

The appropriacy of fluency tests in assessing epileptic seizure lateralization in children with partial epilepsy

Fluency tests are frequently used in clinical practice to asses executive functions. The literature data are not unequivocal although in a great number of papers is pointed out the importance of the left hemisphere, specially of the left frontal lobes in the mediation of phonological fluency and the right hemisphere in the mediation of nonverbal fluency. This paper considers the suitability of fluency tests for the detection of left versus right seizure laterality. The sample consisted of thirty-two epilepsy patients divided into two groups: LHF-participants with the seizure focus in the left hemisphere (n=16), and DHF-participants with the seizure focus in the right hemisphere (n=16), and K-the control group of t age-matched healthy children (n=50) aged 7-11 years. The qualitative and quantitative comparison of the phonological and nonverbal fluency performance was carried out in consideration of the seizure laterality as well as compared to the healthy controls. The results of phonological fluency performance revealed that the performance of the LHF group was significantly reduced as compared to both DHF and K group. The analysis of nonverbal fluency performance revealed that the performance of the DHF group was significantly reduced as compared to both LHF and K group The qualitative analysis obtained valuable data, which could additionally contribute to the neuropsychological evaluation of the left versus right seizure laterality.

Ictal scalp EEG recording during sleep and wakefulness: Diagnostic implications for seizure localization and lateralization

To determine the localizing value of electroencephalography (EEG) for seizures during sleep versus seizures during wakefulness, we compared scalp EEG for 58 seizures that occurred during sleep with 76 seizures during wake in 28 consecutive patients with temporal lobe epilepsy. Regression analysis showed that seizures during sleep are 2.5 times more likely to have focal EEG onset (p = 0.01) and 4 times more likely to correctly localize seizure onset (p = 0.04) than seizures during wake. EEG seizure onset preceded clinical onset by a longer duration in sleep seizures (mean, 4.69 s) than in wake seizures (mean, 1.23 s; p < 0.01). Sleep seizures showed fewer artifacts, but the difference was not significant (p = 0.07). For temporal lobectomy candidates undergoing video-EEG monitoring, the recording of seizures during sleep may be favored.

Autonomic consequences: Why the most severe seizures are not always the most disturbing

In the literature, tachycardia and hypertension are impressively common in all types of seizures. With implanted depth electrode recording, a predominant laterality of seizures causing tachycardia has not been consistently found. Rather, spread of seizures seems to be necessary to produce tachycardia, and changes in heart rate are likely correlated with the extent of cortex involved. Studies of ictal bradycardia in the setting of focal seizures indicate a modest but clear left-sided predominance for the epileptogenic site, particularly for seizures originating in medial temporal or frontal areas.

Multivariate Neuropsychological Prediction of Seizure Lateralization in Temporal Epilepsy Surgical Cases

Neuropsychological assessment can be of assistance in determining seizure lateralization in cases where EEG and MRI findings do not provide clear lateralizing data. While several studies have examined the lateralizing value of individual neuropsychological measures, clinicians are still in need of a statistically sound method that permits the incorporation of multiple neuropsychological variables to predict seizure lateralization in the individual patient. The present study investigated the lateralizing value of several commonly used neuropsychological measures in a large sample of patients (n = 217) who eventually underwent surgical resection to treat their epilepsy. Side of surgery was used to operationally define seizure lateralization. A comparison of the relative utility of a multivariate versus univariate approach to predict seizure lateralization was conducted in temporal epilepsy cases. The results provide evidence for the incremental validity of neuropsychological measures, other than memory and IQ tests, in the prediction of seizure lateralization in patients with medically intractable epilepsy. These data indicate that a multivariate approach increases the accuracy of prediction of seizure lateralization for temporal lobe epilepsy cases. This study supports the use of a multivariate approach using neuropsychological measures to predict seizure lateralization in temporal epilepsy surgical candidates. Regression formulas are provided to enhance the clinical utility of these findings.

Clinical Seizure Lateralization in Frontal Lobe Epilepsy

We systematically analyzed the lateralizing value of clinical seizure semiology in patients with frontal lobe epilepsy (FLE). We studied the incidence, positive predictive value (PPV), and the lateralizing significance of various clinical symptoms in 228 seizures (s) of 31 patients (p) with medically refractory FLE (17 with left-sided and 14 with right-sided seizure onset). Seizures recorded during prolonged video-EEG monitoring were assessed by two independent reviewers blinded for the patient's clinical data. Analysis was performed both for patients and seizures. Version [16 p (52%); PPV, 94%; p=0.001; 47 s (21%); PPV, 75%; p=0.001], unilateral clonic movements [16 p (52%); PPV, 81%; p=0.021; 32 s (14%); PPV, 81%; p=0.001], unilateral dystonic posturing [eight p (26%); PPV, 75%; p=0.289; 46 s (20%); PPV, 80%; p=0.001], unilateral tonic posturing [10 p (32%); PPV, 80%; p=0.109; 19 s (7.4%); PPV, 79%; p=0.019], and unilateral grimacing [10 p (32%); PPV, 100%; p=0.002; 19 s (8%); PPV, 100%; p=0.001] were of lateralizing significance, indicating a contralateral seizure onset. Asymmetric ending [five p (16%); PPV, 80%; p=0.375; nine s (4%); PPV, 89%; p=0.039] after secondarily generalized tonic-clonic seizures was significantly associated with an ipsilateral seizure onset. Pure ictal vocalizations occurred significantly more frequently in seizures of right hemispheric onset [13 p (42%); PPV, 62%; p=0.581; 63 s (28%); PPV, 73%; p=0. 001], whereas in individual patients, this symptom showed no lateralizing significance. The remaining clinical symptoms (figure 4 sign, unilateral hand automatisms, early head turning, postictal nose wiping, and unilateral eye blinking) were not of lateralizing significance in our patients. The results of clinical seizure lateralization corresponded with the final lateralization of the seizure-onset zone in 81% of our patients. Clinical seizure semiology can provide correct information on the lateralization of the seizure-onset zone in >80% of patients with medically refractory frontal lobe epilepsy.

Ictal localization by source analysis of infraslow activity in DC-coupled scalp EEG recordings

New bedside long-term DC-coupled EEG techniques have demonstrated that infraslow (<0.5 Hz) activity lateralizes temporal lobe seizures (Vanhatalo, S., Holmes, M.D., Tallgren, P., Voipio, J., Kaila, K., Miller, J.W., 2003a. Very slow EEG responses indicate the laterality of temporal lobe seizures: a DC-EEG study. Neurology 60, 1098–1104). However, even high amplitude infraslow activity is difficult to localize by simple visual inspection if there is overlying faster EEG activity or slow artifact. In this study, we address this with improved DC-coupled EEG recording and analysis techniques and also extend observation to both temporal and extratemporal seizures. Recordings were performed during presurgical evaluation of medically intractable epilepsy, with 20 seizures in 11 patients analyzed. A commercial DC-coupled recording device was used, with sintered Ag/AgCl electrodes in a standard 10-10 system array, with additional anterior temporal and subtemporal electrodes. Seizures were localized with a software package by means of source montage analysis. Infraslow signals occurred with all seizures, often with amplitude orders of magnitude higher than conventional frequencies (0.5 to 70 Hz). The most reliable method to localize these signals and distinguish them from artifacts used a source montage after low-pass filtering below 0.5 Hz. Five of the eight patients who received epilepsy surgery had follow-up documenting significant seizure reduction, and infraslow signal analysis correctly localized the region of seizure onset in all five, while conventional noninvasive EEG recording and analysis localized only three of the five. Several seizures were also analyzed using principle component analysis source localization methods, with the results less consistently localizing than source montage analysis. DC-coupled EEG recordings give clinically useful information to noninvasively localize the seizure focus. The value of this method is increased by source analysis tools that reveal localized changes more clearly than direct visual inspection.

Complete change of seizure and spike lateralization in temporal lobe epilepsy at two separate monitorings

ObjectiveTo report complete change of seizure and spike lateralization over time in bilateral temporal lobe epilepsies (TLE). MethodsRepetition of video-EEG monitorings in 115 patients; 2 cases are reported in detail; 113 other severe partial epilepsies were included to estimate retrospectively the frequency of the reported phenomenon. ResultsIn 2 cases, two video-EEG monitorings, separated by several months, revealed the first time one unilateral TL (temporal lobe) seizure and spike focus and the second time a distinct seizure and spike focus located in the opposite TL. The second monitoring was planned for these two patients because of the presence of a discordant lesion or, in the absence of a lesion, of some bilateral or discordant functional (EEG, SPECT and PET) abnormalities. No patient among the other 113 cases had this video-EEG pattern. ConclusionsIn TLE, two video-EEG sessions may be necessary to disclose two opposite TL epileptogenic foci. SignificanceIn rare bilateral TLE cases, the expression of seizure and spike foci can alternate between hemispheres.

Effect of interseizure interval on seizure lateralization in patients with bilateral seizure foci

We investigated whether there is a cluster effect depending on localization of seizure foci in patients with bilateral seizure foci. We evaluated 171 seizure pairs from 193 seizures recorded in 28 patients. Seizure lateralization was determined by the lateralization of ictal discharges; if the ictal EEG pattern was not lateralized, lateralization was determined by clinical seizure semiology. The logarithm of the interseizure interval (ISI) was significantly related to seizure concordance only in patients with extratemporal seizure foci, but not in those with bitemporal foci. In the former group, the mean ISI for concordant seizure pairs was significantly shorter than that for discordant seizures pairs (292 min versus 631 min, p=0.023). Seizure types composing seizure pairs had a significant influence on ISI regardless of the localization of seizure foci. ISIs were shortest in seizure pairs with only partial seizures. However, types of seizure pairs were significantly related to concordance rates of seizure lateralization only in patients with extratemporal foci (p=0.005). In conclusion, our results suggest that the cluster effect on seizure localization exists in patients with extratemporal seizure foci, but not in those with bitemporal foci.

Value and Limitations of Seizure Semiology in Localizing Seizure Onset

Seizure semiology has been the foundation of clinical diagnosis of seizure disorders. This article discusses the value and the limitations of behavioral features of seizure episodes in localizing seizure onset. Studies have shown that some semiologic features of seizures are highly accurate in the hemispheric lateralization and lobar localization of seizures. There is good agreement between blinded reviewers in lateralizing video-recorded seizures in temporal lobe and extratemporal lobe epilepsies. However, seizure semiology alone should not be used to determine the site of seizure onset. Each semiologic feature may falsely localize seizure onset. Seizure semiology in some patients may signify the site of seizure propagation rather than origination. Moreover, seizure semiology may not be as reliable in multifocal epilepsies as it is in unifocal epilepsies. Many semiologic features of seizures of adults are often missing in seizures of children. Seizure semiology should be analyzed and integrated with EEG and neuroimaging data to localize the seizure focus. A sample of the recorded seizures should be shown to the patient's relatives or friends to verify that it is representative of habitual seizures.

Foramen Ovale Electrodes Can Identify a Focal Seizure Onset When Surface EEG Fails in Mesial Temporal Lobe Epilepsy

We analyze a series of patients with mesial temporal lobe epilepsy (MTLE) associated with hippocampal sclerosis (HS) submitted to presurgical investigation with scalp sphenoidal, followed by foramen ovale electrodes (FO), and, when necessary, with depth temporal electrodes. We sought to evaluate the clinical utility of FO in patients with MTLE-HS. We included patients who had phase I investigation with bitemporal independent seizures, nonlateralized ictal onsets, or ictal onset initiating in the side contralateral to the side of hippocampal sclerosis. Patients whose implanted FO failed to demonstrate an unambiguous unilateral ictal onset were later evaluated with depth hippocampal electrodes. Between May 1994 and December 2004, 64 patients met our inclusion criteria: 33 female (51.5%) and 31 male subjects (48.5%). The mean age at enrollment was 37.66+/-10.6 years (range, 12-56 years). The groups with nonlateralized surface ictal EEG onsets and contralateral EEG onsets had a greater chance of lateralization with FO when compared with the group with bilateral independent seizures on surface EEG (p<0.01). Foramen ovale electrodes lateralized the seizures in 60% of patients. Seventy percent of patients became seizure free after temporal lobectomy. Five patients were implanted with depth temporal electrodes after FO video-EEG monitoring. The depth-electrode EEG onsets confirmed the results of FO video-EEG monitoring in all patients, and the surgery was refused. In MTLE-HS, FO is a reliable method for lateralization of seizures that are not clearly recorded by surface EEGs.

The Ictal Bradycardia Syndrome: Localization and Lateralization

Previous studies have established the importance of the insular cortex and temporal lobe in cardiovascular autonomic modulation. Some investigators, based on the results of cortical stimulation response, functional imaging, EEG recordings of seizures, and lesional studies, have suggested that cardiac sympathetic and parasympathetic function may be lateralized, with sympathetic representation lateralized to the right insula, and parasympathetic, to the left. These studies have suggested that ictal bradycardia is most commonly a manifestation of activation of the left temporal and insular cortex. However, the evidence for this is inconsistent. We sought to assess critically the predictable value of ictal bradycardia for seizure localization and lateralization. In this study, we reviewed the localization of seizure activity in 13 consecutive patients with ictal bradycardia diagnosed during prolonged video-EEG monitoring at Mayo Clinic Rochester. The localization of electrographic seizure activity at seizure onset and bradycardia onset was identified in all patients. In addition, we performed a comprehensive review of the ictal bradycardia literature focusing on localization of seizure activity in ictal bradycardia cases. All occurrences of ictal bradycardia in the 13 identified patients were associated with temporal lobe-onset seizures. However, no consistent lateralization of seizure activity was found at onset of seizure activity or at onset of bradycardia in this population. Seizure activity was bilateral at bradycardia onset in nine of 13 patients. The results from the literature review also showed that a predominance of patients had bilateral activity at bradycardia onset; however, more of the ictal bradycardia cases from the literature had left hemispheric localization of seizure onset. Ictal bradycardia most often occurs in association with bilateral hemispheric seizure activity and is not a consistent lateralizing sign in localizing seizure onset. Our data do not support the existence of a strictly unilateral parasympathetic cardiomotor representation in the left hemisphere, as has been suggested.

Factors Contributing to Clinical Seizure Lateralization in Patients with Mesial Temporal Lobe Epilepsy

Clinical seizure semiology can provide important information on the lateralization of the epileptogenic zone. We investigated factors associated with clinical seizure lateralization in patients with pathologically proven mesial temporal sclerosis. We reviewed 243 seizures of 58 patients. Clinical lateralization was possible in 155 (63.8%) of 243 seizures. Lateralization was correct in 144 (92.9%) of 155 lateralized seizures. Logistic regression analysis showed that age at onset (p = 0.001; odds ra tio = 1.089, 95% confidence interval = 1.035–1.145) and the contralateral propagation pattern of ictal discharges (p = 0.001; odds ratio = 3.544, 95% confidence interval = 1.723–7.289) correlated with clinical seizure lateralization. The patient group with clinically lateralized seizures had a younger age at onset of habitual seizures compared to the clinically nonlateralized group (11.1 ± 6.3 vs. 15.6 ± 8.4 years; p < 0.001). Of seizures without bitemporal asynchrony or switch of lateralization, 70.7% were clinically lateralized compared with only 46.4% of seizures with asynchrony or lateralization switch. The present results suggest that the age of epilepsy onset and the ictal scalp EEG propagation pattern affect clinical seizure lateralization in patients with mesial temporal sclerosis.

Clinical Neurophysiology: EEG–Video Monitoring

Clinical Neurophysiology: EEG–Video Monitoring

A tale of two promises

Depression episodes in epilepsy is the most common commorbidity, affecting between 11% and 62% of patients with epilepsy. Although researchers have documented a strong association between epilepsy and psychiatric comorbidities, the nature of this relationship is poorly understood.The manifestation of depression in epilepsy is a complex issue having many interacting neurobiological and psychosocial determinants, including clinical features of epilepsy (seizure frequency, type, foci, or lateralization of foci) and neurochemical or iatrogenic mechanisms. Other risk factors are a family history of psychiatric illness, particularly depression, a lack of control over the seizures and iatrogenic causes (pharmacologic and surgical). In addition, treatment with antiepileptic drugs (AEDs) as well as social coping and adaptation skills have also been recognised as risk factors of depression associated with epilepsy.Epilepsy may foster the development of depression through being exposed to chronic stress. The uncertainty and unpredictability of seizures may instigate sadness, loneliness, despair, low self-esteem, and self-reproach in patients with epilepsy and lead to social isolation, stigmatization, or disability. Often, depression is viewed as a reaction to epilepsy’s stigma and the associated poor quality of life. Moreover, patients with epilepsy display a 4–5 higher rate of depression and suicide compared with healthy population.

Self-report of cognitive abilities in temporal lobe epilepsy: cognitive, psychosocial, and emotional factors

Self-report of cognitive functioning using the Multiple Abilities Self-Report Questionnaire (MASQ) was examined in 57 left (LTLE) and 36 right (RTLE) temporal lobe epilepsy patients. The MASQ is a 38-item self-report measure assessing five domains of self-perceived cognitive functioning: Language, Visual–Perceptual Abilities, Verbal Memory, Visual–Spatial Memory, and Attention/Concentration. Overall, LTLE patients self-reported more cognitive difficulties across all domains. Language was the only domain to emerge as a robust indicator of seizure lateralization (LTLE patients reporting more problems). Neuropsychological test performance did not emerge as a significant predictor for any domain, whereas measures of psychosocial and emotional functioning accounted for a significant but modest amount of variance in all of them. The results suggest caution in using such self-report measures as an ecological extension of objective testing, but suggest a role in assessing self-appraisal of deficits.

Surdités, acouphènes : les thérapies pharmacologiques de demain

The objectives of this study were to determine how hemispheric laterality of seizure activity influences periictal heart rate variability (HRV) and investigate the ability of HRV parameters to discriminate right- and left-sided seizures.Long-term video electroencephalogram-electrocardiogram recordings of 54 focal seizures in 25 patients with focal epilepsy were reviewed. Using linear mixed models, we examined the effect of seizure laterality on linear (standard deviation of R-R intervals [SDNN], root mean square of successive differences [RMSSD], low frequency [LF] and high frequency [HF] power of HRV, and LF/HF) and nonlinear (standard deviation [SD]1, SD2, and SD2/SD1 derived from Poincaré plots) periictal HRV parameters, the magnitude of heart rate (HR) changes, and the onset time of increased HR. Receiver operating characteristics (ROC) were used to determine the ability of these parameters to discriminate between right- and left-sided seizures.Postictal SDNN, RMSSD, LF, HF, SD1, and SD2 were higher in right- than left-sided seizures. Root mean square of successive difference and HF were decreased after left- but not right-sided seizures. Standard deviation of R-R intervals, LF, and SD1 were increased after right- but not left-sided seizures. Increased ictal HR was earlier and larger in right- than left-sided seizures. Postictal HF showed the greatest area under the ROC curve (AUC) (0.87) for discriminating right- and left-sided seizures.Our data suggest that postictal parasympathetic activity is higher, whereas ictal HR increase is greater, in right- than left-sided seizures. Involvement of the right hemisphere may be associated with postictal autonomic instability. Postictal HRV parameters may provide useful information on hemispheric laterality of seizure activity.

Verbal Memory Loss after ATL based on Degree of Hippocampal Sclerosis.

Risk to Verbal Memory After Anterior Temporal Lobectomy in Patients with Severe Left-Sided Hippocampal Sclerosis Martin RC, Kretzmer T, Palmer C, Sawrie S, Knowlton R, Faught E, Morawetz R, Kuzniecky R Arch Neurol 2002;59:1895–1901 Background Previous investigations indicate low risk for memory loss after anterior temporal lobectomy (ATL) in patients with severe hippocampal sclerosis (HS) compared with patients with mild HS. However, these conclusions have been established primarily with group-level analyses. Purpose To investigate individual base rate risk for verbal memory loss after ATL in patients who have pathologically verified mild, moderate, or severe HS. Methods One hundred fifteen patients with unilateral temporal lobe epilepsy (68 with left-sided and 47 with right-sided epilepsy) were included. Acquisition, retrieval, and recognition components of verbal memory, as measured by the California Verbal Learning Test, were assessed before and after ATL. Postoperatively, the degree of neuronal loss and reactive gliosis of the hippocampus was assessed with a three-tiered rating system establishing mild, moderate, and severe pathologic features. Patients with preoperative magnetic resonance imaging-based evidence of lesions outside the mesial temporal area (side of surgical resection) were excluded. Results Neither seizure laterality nor severity of HS was associated with preoperative verbal memory performance. Postoperatively, the left-sided ATL group demonstrated significant decline across the acquisition ( P &lt; 0.01), retrieval ( P &lt; 0.001), and recognition ( P &lt; 0.001) verbal memory components compared with the right-sided ATL group. Patients who underwent left-sided ATL and had mild HS displayed the largest magnitude and percentage proportion of postoperative decline across all verbal memory components. However, 28 (48%) of the 58 patients who underwent left-sided ATL and who had moderate and severe HS displayed statistically reliable declines on retrieval aspects of verbal memory. Most patients undergoing right-sided ATL, regardless of the extent of hippocampal pathologic features, displayed no postoperative memory change. Conclusions Substantial individual heterogeneity of memory outcome exists across groups of patients undergoing ATL, with various degrees of pathologically verified HS. Patients undergoing left-sided ATL who have mild HS seem at greatest risk for broad-spectrum verbal memory decline. However, in examining outcome on a patient-by-patient basis, many patients undergoing left-sided ATL who have moderate to severe HS were also vulnerable to verbal memory loss. This risk seems selective to a retrieval-based aspect of verbal memory.

Material-specific memory in temporal lobe epilepsy: Effects of seizure laterality and language dominance.

This study investigated the effects of seizure laterality and language dominance on material-specific memory in temporal lobe epilepsy (TLE). Left TLE (LTLE) patients with left-hemisphere language dominance (LHLD) showed significantly higher nonverbal than verbal memory capacity, whereas right TLE patients with LHLD showed significantly better verbal than nonverbal memory capacity. LTLE patients with non-left-hemisphere language dominance (NLHLD) showed significantly better verbal memory capacity compared with LTLE patients with LHLD. Thus, selective verbal or nonverbal memory deficits that are dependent on side of seizure onset were apparent in patients with LHLD but not in patients with NLHLD. Relative sparing of verbal memory capacity in LTLE patients with NLHLD may reflect interhemispheric reorganization of verbal memory function.