Decline in Verbal Memory Associated with Duration of Epilepsy: An Intracarotid Amobarbital Study

Background. Many patients with mesial temporal sclerosis (MTS) observe that their memory has declined over time, but objective evidence for this is scant.Method. Verbal memory scores were obtained during amobarbital injection of the right carotid artery in 30 right-handed patients with right mesial temporal sclerosis and unilateral right temporal lobe seizures. These were compared with duration of epilepsy and seizure frequency. An estimate of the total number of lifetime seizures was formed by multiplying epilepsy duration by seizure frequency.Results. Verbal memory function in the left temporal lobe was negatively associated with longer duration of epilepsy (P < 0.05). There was a strong negative correlation between verbal memory and increased lifetime number of seizures (P < 0.01).Conclusion. This study provides evidence that seizures arising in the right temporal lobe lead to progressive dysfunction of memory functions in the contralateral side.     

Cognitive Consequences of Two-Thirds Anterior Temporal Lobectomy on Verbal Memory in 144 Patients: A Three-Month Follow-Up Study

Previous studies have shown that left temporal lobectomy for intractable epilepsy can lead to verbal memory deficits. However, patients with left temporal lobe epilepsy (LTLE) frequently have impaired verbal memory preoperativel. The present analysis of 144 patients who underwent temporal lobe resections for either left (n = 68) or right (n = 76) temporal lobe epilepsy (LTLE, RTLE) addressed the questions of (a) whether a left two-thirds anterior temporal lobectomy (ATL) increases deficits in these qualitative aspects of verbal memory already impaired preoperatively, and (b) whether other aspects of verbal memory are additionally affected. We also evaluated possible determinants of preoperative abilities and postoperative changes, using multiple regression analysis. Preoperatively, patients with LTLE differed from patients with RTLE only in poorer performance on measures of long-term consolidation/retrieval (delayed recall). This was related to hippocampal pathology and seizure severity. Only left temporal lobe resections resulted in significant deterioration in verbal learning and memory. Acquisition over learning trials and recognition deteriorated most markedly, whereas performance in long-term consolidation/retrieval showed only minor changes. Preoperative performance levels, chronological age, the extent of the en bloc resection, preoperative performance on figural memory, and preoperative seizure severity were valuable determinants of postoperative changes in acquisition and recognition. In contrast, changes in consolidation/retrieval related only to preoperative ability. Left two-thirds ATL leads to new impairment in addition to preexisting memory deficits. The finding that left temporal lobectomy affects verbal acquisition and recognition more than long-term consolidatiodretrieval, including the different determinants of these changes, most likely reflects the differential effects of surgery on mesial temporal and neocortical temporal functions.     

Effect of age of onset of temporal lobe epilepsy on the severity and the nature of preoperative memory deficits

The nature and severity of pre-operative memory deficits observed in unilateral temporal lobe epilepsy depend upon a number of variables. Among these variables, age of seizure onset seems to be important. The age at which the lesion is sustained could modify the normal functional organization of the brain. Many studies have examined the effect of age of onset on the severity of memory deficits but have seldom focused on the nature of such deficits (verbal/nonverbal) as a function of epileptic focus laterality. This study investigates the effect of age of onset on the nature and severity of memory impairments. Fifty-six epileptics with unilateral temporal lobe epilepsy and 20 normal subjects were administered a neuropsychological evaluation. Four groups of patients were constituted: left or right temporal lobe epilepsy with early (0-5 years) or late (10 years and over) age of seizure onset. The early group showed major verbal and nonverbal memory deficits. The late group presented minor specific deficits: essentially verbal deficits with left temporal lobe seizures and nonverbal deficits with right temporal lobe seizures. These results may be interpreted in the framework of ontogenesis theories of hemispheric specialization.     

Semantic memory impairment in temporal lobe epilepsy associated with hippocampal sclerosis

Episodic memory impairment is a well-recognized feature of mesial temporal lobe epilepsy. Semantic memory has received much less attention in this patient population. In this study, semantic memory aspects (word-picture matching, word definition, confrontation and responsive naming, and word list generation) in 19 patients with left and right temporal lobe epilepsy secondary to mesial temporal sclerosis (MTS) were compared with those of normal controls. Patients with LMTS showed impaired performance in word definition (compared to controls and RMTS) and in responsive naming (compared to controls). RMTS and LMTS patients performed worse than controls in word-picture matching. Both patients with left and right mesial temporal lobe epilepsy performed worse than controls in word list generation and in confrontation naming tests. Attentional-executive dysfunction may have contributed to these deficits. We conclude that patients with left and right MTS display impaired aspects of semantic knowledge. A better understanding of semantic processing difficulties in these patients will provide better insight into the difficulties with activities of daily living in this patient population.     

Specificity of memory deficits after right or left temporal lobectomy

An impairment of verbal memory has consistently been associated with resection of the left dominant temporal lobe, whereas non-verbal memory deficits have been less reliably observed following resection of the right temporal lobe. Such a dissociation may be due to material-specific differences of processing between verbal and non-verbal information. Alternatively, the influence of the left and right limbic structures may vary according to the stage of memory processing. The aim of the study was to test these hypotheses by comparing verbal and spatial learning in patients with left or right temporal lobe resection for intractable epilepsy, using verbal and visuospatial memory tasks with the same design: control of encoding, multiple trial learning, free and cued recall, short and long delays. The results showed: (1) a similar pattern of learning and recall in the two groups; (2) a higher performance in spatial learning for patients with left temporal lobe resection and in verbal learning for patients with right temporal lobe resection; (3) material-specific effects characterized by a higher sensitivity to cues in the verbal domain and a better retention of information during delays in the spatial domain. These results suggest parallel processing of the two temporal lobes at the various memory stages, rather than an interaction between memory stage and side of the lesion similar to that already proposed for the frontal lobes. They also confirm a double dissociation between verbal/spatial information processing and side of temporal lobe resection.     

Material-specific lateralization of working memory in the medial temporal lobe

Mnemonic deficits in patients with medial temporal lobe (MTL) damage arising from temporal lobe epilepsy (TLE) are traditionally constrained to long-term episodic memory, sparing short-term and working memory (WM). This view of WM as being independent of MTL structures has recently been challenged by a small number of patient and neuroimaging studies, which have focused primarily on visual and visuospatial WM. In the present study we investigated material-specific lateralization of WM in 96 patients with unilateral damage to MTL stemming from TLE (56 left) and 30 control subjects using a pair of matched verbal and visuospatial supraspan tasks. Patients with unilateral TLE were impaired on both verbal and visuospatial WM tasks irrespective of the affected hemisphere. Patients with unilateral right TLE showed an additional deficit for visuospatial WM capacity when contrasted with patients with left TLE, whereas patients with unilateral left TLE showed increased intrusion errors on the verbal task when compared to patients with right TLE. These findings suggest a material-specific lateralization of WM in the MTL.     

Verbal memory outcome in patients with normal preoperative verbal memory and left mesial temporal sclerosis

PURPOSE: Previous studies have shown that structural integrity (i.e., presence/absence of mesial temporal sclerosis (MTS)) of the left mesial temporal lobe is associated with verbal memory outcome following left anterior temporal lobectomy (ATL). However, the functional integrity of the left temporal lobe, as exemplified by preoperative verbal memory performance, has also been associated with verbal memory outcome following surgery. We investigated the risk of verbal memory loss in patients with known structural abnormality (i.e., left mesial temporal sclerosis by MRI) and normal preoperative verbal memory performance who undergo left ATL. METHODS: Seventeen patients with left temporal lobe epilepsy, MRI-based exclusive left MTS, and normal preoperative verbal memory were identified. Normal verbal memory was defined as performance on both Acquisition (learning across trials 1-5) and Retrieval (long delayed free recall) portions of the California Verbal Learning Test (CVLT) above a T score of 40 (>16%ile). Postoperative verbal memory outcome was established by incorporating standardized regression-based (SRB) change scores. RESULTS: Postoperative declines across both CVLT Retrieval T scores and Acquisition T scores (average 20% and average 15% declines from baseline scores, respectively) were measured for the group. The average CVLT Retrieval SRB change score was -2.5, and the average CVLT Acquisition SRB change score was -1.0. A larger proportion of patients demonstrated postoperative declines on Retrieval scores than Acquisition scores (64.7% vs 17.6%, respectively). CONCLUSIONS: Even in the presence of left MTS, patients exhibiting normal presurgical verbal memory are at risk for verbal memory declines following ATL. These results suggest that the functional integrity of the left mesial temporal lobe may play an important role in the verbal memory outcome in this patient group.     

Prospective memory and mesial temporal epilepsy associated with hippocampal sclerosis

Episodic memory impairment is commonly observed in patients with epilepsy associated with mesial temporal sclerosis (MTS). Prospective memory (PM) is a set cognitive abilities that allow future performance of a present intention, in response to time- or event-based evocation cues, that trigger the intended action at the appropriate time. PM has not been evaluated in mesial temporal sclerosis. We evaluated the role of right and left hippocampal lesions on performance in both the retrospective and prospective PM components in patients with epilepsy secondary to mesial temporal sclerosis and correlated with performance in traditional neuropsychological tests, as well as with self-perception of memory impairment. We tested the hypotheses that a hippocampal lesion impacts on the prospective components of PM, and that a left-sided lesion had a greater impact on performance in the prospective component of PM than a right-sided lesion. We evaluated PM in 26 patients with right MTS, 22 left MTS patients, and 26 age-gender and education matched controls. The prospective component of PM was impaired in both patient groups, with both a lesion (patients performed significantly worse in the PM battery) and laterality effect (left MTS patients performed significantly worse than right MTS patients in the PM battery). Performance in the prospective component of the PM battery correlated with long-term delay performance in episodic verbal memory and self-perception of memory impairment in the left MTS group. The retrospective component was impaired in left MTS patients. Impaired performance was not accounted for solely by depression, anxiety or an antiepileptic drug effect. We conclude that mesial temporal lobe structures, including the hippocampus, play an important role in both the prospective and retrospective components of PM processes in tasks involving long delay intervals.     

Outcome after cortico-amygdalo-hippocampectomy in patients with severe bilateral mesial temporal sclerosis submitted to invasive recording

IntroductionAlthough some degree of bilateral hippocampal involvement might be frequent in patients with temporal lobe epilepsy, severe bilateral mesial temporal sclerosis (MTS) is very rare. We present our experience while treating patients with severe bilateral MTS submitted to invasive recordings.MethodsNine adult patients were studied. All patients had simple and complex partial seizures. All patients had bilateral independent interictal temporal lobe spiking and non-lateralizing video-EEG findings. MRI showed severe bilateral MTS and no other brain lesion. All patients had severe verbal and non-verbal memory deficits. All patients were submitted to invasive recordings after bilateral subdural grids implantation. Cortico-amygdalo-hippocampectomy (CAH) was performed in all patients on the side suggested by invasive recording. Follow-up time ranged from 5 to 10 years.ResultsInvasive video-EEG showed exclusively unilateral seizure onset in seven patients; in two patients, seizures originating from both temporal lobes were found (80% of them originated from one side). Five patients were submitted to left and four to right CAH. Seven patients were rendered seizure-free after surgery (Engel I); the other two were rated as Engel II. There was no additional memory decline. There was no surgical morbidity or mortality. Pathological examination showed MTS in all patients.DiscussionGood surgical outcome (77% seizure-free patients) could be obtained even in this apparently unsuitable group of patients. All patients benefit from the procedure. We did not see any cognitive decline in our patients with severe bilateral MTS. Patients with severe bilateral MTS would need invasive recordings despite any findings during surface video-EEG.     

A critical evaluation of the lateralizing significance of material-specific memory deficits in patients with mesial temporal lobe epilepsy with hippocampal sclerosis

To critically assess the value of material-specific memory deficits in lateralizing temporal lobe dysfunction preoperatively, we compared the neuropsychological data of 50 consecutive patients with unilateral mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS; right: 31, left: 19) with those of 50 age- and education-matched healthy control subjects. On case-control comparison, both the subcohorts with left and right MTLE-HS performed poorly on intelligence tests, in addition to individual memory tests. However, comparison of the verbal and visual memory functions between subcohorts with right and left MTLE-HS revealed that learning trials and delayed word list recall were the only tests that hypothesized left temporal lobe dysfunction. We conclude that material-specific memory deficits are largely test driven, but there is a lateralizing role for task-specific deficits in left MTLE-HS. Although neuropsychological data help to define baseline neuropsychological impairment, caution should be exercised in interpreting the lateralizing value of material-specific memory deficits prior to surgery.     

Cognitive consequences of coexisting temporal lobe developmental malformations and hippocampal sclerosis.

OBJECTIVE: To characterize patterns of cognitive functioning in a well-defined group of patients with MRI-identified coexisting left temporal lobe developmental malformations (TLDM) and mesial temporal sclerosis (MTS), and to examine neuropsychological outcome in this dual-pathology group following epilepsy surgery. METHODS: Cognitive functioning in patients with left TLDM and MTS (n = 15) was compared with patients with isolated left MTS (n = 40). TLDM and MTS were identified by high-quality MRI protocol. Patients were administered a battery of neuropsychology tests as part of their presurgical workup for possible epilepsy surgery. Unilateral temporal lobe resection was performed on 10 of the dual-pathology patients and 34 of the isolated MTS patients. Postoperative cognitive performance was also assessed. RESULTS: Both groups displayed impairments in verbal and visual memory, language, and academic achievement. Performance on measures of psychometric intelligence, executive function, and attention were not impaired and were similar between groups. Presence of dual pathology was associated with a significantly less efficient verbal encoding strategy on the word list learning task. Postoperatively, declines were noted for both groups across tasks of verbal memory and language. Groups were not different significantly in terms of neuropsychological outcome after surgery. CONCLUSION: Patients with coexisting TLDM and MTS have impaired cognitive functioning similar to MTS patients-in particular, with regard to episodic memory and language deficits. Temporal lobe resection produces similar cognitive changes in both groups.     

Cognitive correlates of 1H MRSI-detected hippocampal abnormalities in temporal lobe epilepsy

OBJECTIVES: To examine associations between 1H magnetic resonance spectroscopic imaging (1H MRSI)-detected hippocampal creatine to N-acetylaspartate (Cr/NAA) ratios and neuropsychological measures sensitive to mesial temporal lobe function. BACKGROUND: The measurement of 1H MRSI-detected hippocampal metabolites has proved effective in determining extent and lateralization of neuronal damage. However, relationships between 1H MRSI-detected hippocampal metabolic abnormalities and specific areas of cognitive functioning have received limited attention compared to other studies using MRI volumetry or cerebral blood flow techniques. METHODS: We analyzed right and left hippocampal Cr/NAA ratios in 46 adult mesial temporal lobe epilepsy patients (32 left, 14 right) by 1H MRSI at high magnetic field (4.1 T). We examined the relationship between the right and left Cr/NAA hippocampal ratios to measures of verbal and visual memory, intelligence, attention, visuoperception, and confrontation naming. RESULTS: Measures of episodic verbal memory (n = 33) and visual confrontation naming (n = 46) were selectively associated with left hippocampal metabolic function (p<0.004), whereas neuronal function of the right hippocampal region was strongly associated with performance on a measure of facial recognition (n = 46; p<0.02). CONCLUSIONS: This study shows that specific areas of cognitive function are related to hippocampal neuronal metabolic abnormalities as detected by spectroscopic imaging. The current study indicates that 1H MRSI offers a complimentary technique to structural imaging studies in the study of mesial temporal lobe epilepsy and may enhance understanding of the role of hippocampal function in complex cognitive systems.     

Semantic memory in partial epilepsy: verbal and non-verbal deficits and neuroanatomical relationships

Semantic memory was evaluated in 124 epilepsy patients, including 84 with left (n=44) or right temporal lobe epilepsy (TLE) (n=40) and 40 with left (n=25) or right frontal lobe epilepsy (FLE) (n=15), in order to determine their verbal and visual deficits, and the neuroanatomical relationships between them. The controls were 35 healthy subjects. Semantic memory was assessed by means of Picture Naming, Picture Pointing, the verbal Pyramid and Palm Trees Test (PPTT), the visual PPTT, Object Decision Hard, and Drawing From Memory. Episodic memory was assessed by means of the Short Story, Rey's Complex Figure, the Verbal and Visual Selective Reminding Procedure and Brown-Peterson Procedure. Factor analysis of the epilepsy patients distinguished their semantic memory scores from other neuropsychological domains. The semantic memory factor was significantly related to the side of the epileptic region, with lower scores in the left hemisphere and left TLE patients. In comparison with the controls, the left TLE patients were significantly impaired on Picture Naming, Picture Pointing, and Object Decision Hard. Subsequent analyses showed that, in comparison with the controls and the right TLE patients, the left TLE patients with lateral temporal lobe lesions were impaired in Picture Naming whereas, in comparison with the controls, the left TLE patients with mesial temporal lobe lesions were impaired in Object Decision Hard. On the contrary, the episodic memory factor was not related to the side of the epileptic region, and a few material-specific tests revealed opposite impairments in the left and right hemisphere patients. These results show that left TLE may cause semantic memory deficits involving verbal and visual information. Unlike the material-specific pattern of episodic memory, this pattern of impairment is in line with the view of an amodal semantic store in which all of the information about a thing overlaps. The semantic memory impairment may reflect damage in the lateral and mesial temporal lobe regions that impair neocortical functions in storing and retrieving information or hippocampal functions in processing meaningful stimuli.     

Impaired fear processing in right mesial temporal sclerosis: a fMRI study

Lesion and neuroimaging studies have demonstrated that the mesial temporal lobe is crucial for recognizing emotions from facial expressions. In humans, bilateral amygdala damage is followed by impaired recognition of facial expressions of fear. To evaluate the influence of unilateral mesial temporal lobe damage we examined recognition of facial expressions and functional magnetic resonance (fMRI) brain activation associated with incidental processing of fearful faces in thirteen mesial temporal lobe epilepsy (MTLE) patients (eight with right MTLE, five with left MTLE). We also examined the effect of early versus later damage, comparing subjects with hippocampal-amygdalar sclerosis (MTS) and seizures occurring before five years of age to epilepsy patients with late onset seizures. Fourteen healthy volunteers participated as controls. Neuropsychological testing demonstrated that the ability of right MTLE patients to recognize fearful facial expressions is impaired. Patients with early onset of seizures were the most severely impaired. This deficit was associated with defective activation of a neural network involved in the processing of fearful expressions, which in controls and left MTLE included the left inferior frontal cortex and several occipito-temporal structures of both hemispheres.     

Differences in memory performance and other clinical characteristics in patients with mesial temporal lobe epilepsy with and without hippocampal atrophy

Mesial temporal lobe epilepsy (MTLE) is usually accompanied by memory deficits due to damage to the hippocampal system. In most studies, however, the influence of hippocampal atrophy (HA) is confounded with other variables, such as: type of initial precipitating injury and pathological substrate, effect of lesion (HA) lateralization, history of febrile seizures, status epilepticus, age of seizure onset, duration of epilepsy, seizure frequency, and antiepileptic drugs (AEDs). To investigate the relationship between memory deficits and these variables, we studied 20 patients with MTLE and signs of HA on MRI and 15 MTLE patients with normal high-resolution MRI. The findings indicated that (1) HA, earlier onset of seizures, longer duration of epilepsy, higher seizure frequency, and AEDs (polytherapy) are associated with memory deficits; and (2) there is a close relationship between deficits of verbal memory and left HA, but not between visual memory and right HA.     

Neuropsychological functioning in children with temporal lobe epilepsy and hippocampal atrophy without mesial temporal sclerosis: A distinct clinical entity?

Unilateral hippocampal atrophy (HA) is considered as a precursor of mesial temporal sclerosis (MTS) in some patients with temporal lobe epilepsy. However, in other cases, it has been suggested that HA without MTS may constitute a distinct epileptic entity. Hippocampal atrophy without MTS was defined as HA without T2-weighted hyperintensity, loss of internal architecture, or associated lesion seen on the MRI data. To date, no study has focused on the cognitive pattern of children with epilepsy with HA without MTS. The objectives of the present study were to characterize the cognitive profile of these children and to investigate the presence (or the absence) of material-specific memory deficits in these young patients, as found in patients with MTS. Toward this end, 16 young patients with epilepsy with either left or right HA without MTS completed a set of neuropsychological tests, assessing overall intelligence, verbal memory and nonverbal memory, and some aspects of attention and executive functions. Results showed normal intellectual functioning without specific memory deficits in these patients. Furthermore, comparison between patients with left HA and patients with right HA failed to reveal a material-specific lateralized memory pattern. Instead, attention and executive functions were found to be impaired in most patients. These results suggest that HA may constitute a distinct epileptic entity, and this information may help health-care providers initiate appropriate and timely interventions.     

Postictal Courses of Cognitive Deficits in Focal Epilepsies

Summary: Patients with epileptic seizures frequently complain of long-lasting cognitive impairment after a seizure. We evaluated this issue in 31 patients with epileptic seizures of a frontal (n = 8) or temporal lobe origin [right temporal lobe (RTL) n = 8/left temporal lobe (LTL) n = 151. Seizures were secondarily generalized in 18 patients. Computerized testing of verbal and nonverbal recognition memory was performed before the seizure, directly after postictal reorientation, and 30 min and 1 h later. Repeated testing of 14 healthy persons served as control. The following results were obtained: Depending on seizure generalization, postictal reorientation times were 1–45 min. Frontal lobe seizures showed no effect on postictal memory performances, but verbal and visual recognition memory was significantly decreased after temporal lobe seizures. Decrease in either verbal or visual memory and time of recovery were related to lateralization of seizure onset. Functional recovery after reorientation lasted 30 min to 1 h. The decrease in performance was more severe after generalized seizures. Decision times during memory performance were not significantly affected by the seizures. Temporal lobe seizures lead to circumscribed and long-lasting memory deficits, which can be assumed to affect patients'capabilities seriously. Preand postictal testing is a useful tool for determining postictal cognitive impairment and in determining the site of seizure onset.     

Preserved memory in temporal lobe epilepsy patients after surgery for low-grade tumour. A pilot study

The objective was to carry out a pilot study exploring memory outcome in patients with temporal lobe epilepsy (TLE) and low-grade tumour. A prospective study using a competence-related memory assessment was carried out in the Laboratory of Neuropsychology, Epilepsy Center and Neurosurgical Department of the “C. Besta” National Neurological Institute in 24 TLE patients undergoing surgical resection for left (n=12) or right (n=12) low-grade tumours and 36 healthy subjects. Patients underwent mesial or lateral temporal lobe lesionectomy. Neuropsychological tests exploring verbal and visual short-term memory, learning, delayed recall and ability to control interference in memory were applied. Before and after surgery, significant verbal impairment was present in left TLE patients compared to controls and right TLE patients, and visual deficits were present in both groups compared to controls. After surgery, there was no significant decrease in mean verbal or visual memory scores related to the operated side. Some memory abilities subserved by the contralateral temporal lobe improved. Postoperative memory scores were related to preoperative scores, side of operation, age and education. In patients with TLE and low-grade tumour, temporal lobe surgery does not necessarily induce memory deficits. Improvement of memory abilities subserved by the unoperated temporal lobe may be expected.     

Memory performance following unilateral electrical stimulation of the hippocampus in a child with right temporal lobe epilepsy

Verbal and visual memory performance was evaluated during unilateral stimulation of the hippocampus in an 11-year-old child with complex partial epilepsy associated with a right mesial temporal lobe focus. Memory was assessed during left and right hippocampal stimulation as well as preoperatively and 6-months postoperatively following anterior temporal lobe resection including removal of the anterior portion of the hippocampus. Stimulation of the left hippocampus resulted in a mild to moderate decrement in both verbal and visual memory performance as compared with a right hippocampal stimulation. In addition, stable or improved performance on memory assessment as well as general neuropsychological evaluation was noted 6 months postoperatively. Taken together, these data suggest that, in this child with early seizure onset (8 months of age), visual learning/memory functions shifted to the contralateral hippocampus and associated structures following damage to the right mesial temporal lobe structures. In addition, verbal learning/memory continues to be mediated by the left hippocampus, as expected. Thus, it appears that, as in the case of language lateralization, there may be a distinct subset of temporal lobe seizure patients (i.e., early seizure onset, high seizure frequency, chronic duration) in whom the brain has the capacity to shift material-specific memory functions to the contralateral mesial temporal lobe structures.     

The effects of duration of intractable epilepsy on memory function

We assessed whether duration (time since diagnosis) of intractable epilepsy is associated with progressive memory loss in 250 individuals with left or right temporal lobe epilepsy and those diagnosed with psychogenic nonepileptic seizures. Verbal and nonverbal memory function was assessed using several memory assessment measures administered to all individuals as part of a larger neuropsychological assessment. Multivariate multiple regression analyses demonstrated that duration of temporal lobe epilepsy and age of seizure onset are significantly related to verbal memory deficits in patients with epilepsy. The interaction between duration of epilepsy and diagnostic group was nonsignificant, as was the interaction between age at spell onset and diagnostic group. As measured by several neuropsychological memory tests, duration of disease adversely affects verbal memory performance in patients diagnosed with temporal lobe epilepsy. Our study also supports the notion that age at seizure onset significantly affects verbal memory performance in this population. These results have implications for the strategy of treatment and counseling of patients with intractable temporal lobe epilepsy.