Seizures accelerate forgetting in patients with left-sided temporal lobe epilepsy

The effects of slow wave sleep characteristics on semantic, episodic, and procedural memory in people with epilepsy

Slow wave sleep (SWS) is highly relevant for verbal and non-verbal/spatial memory in healthy individuals, but also in people with epilepsy. However, contradictory findings exist regarding the effect of seizures on overnight memory retention, particularly relating to procedural and non-verbal memory, and thorough examination of episodic memory retention with ecologically valid tests is missing. This research explores the interaction of SWS duration with epilepsy-relevant factors, as well as the relation of spectral characteristics of SWS on overnight retention of procedural, verbal, and episodic memory. In an epilepsy monitoring unit, epilepsy patients (N = 40) underwent learning, immediate and 12 h delayed testing of memory retention for a fingertapping task (procedural memory), a word-pair task (verbal memory), and an innovative virtual reality task (episodic memory). We used multiple linear regression to examine the impact of SWS duration, spectral characteristics of SWS, seizure occurrence, medication, depression, seizure type, gender, and epilepsy duration on overnight memory retention. Results indicated that none of the candidate variables significantly predicted overnight changes for procedural memory performance. For verbal memory, the occurrence of tonic-clonic seizures negatively impacted memory retention and higher psychoactive medication load showed a tendency for lower verbal memory retention. Episodic memory was significantly impacted by epilepsy duration, displaying a potential nonlinear impact with a longer duration than 10 years negatively affecting memory performance. Higher drug load of anti-seizure medication was by tendency related to better overnight retention of episodic memory. Contrary to expectations longer SWS duration showed a trend towards decreased episodic memory performance. Analyses on associations between memory types and EEG band power during SWS revealed lower alpha-band power in the frontal right region as significant predictor for better episodic memory retention. In conclusion, this research reveals that memory modalities are not equally affected by important epilepsy factors such as duration of epilepsy and medication, as well as SWS spectral characteristics.

Atrophy of the hippocampal CA1 subfield relates to long-term forgetting in focal epilepsy

OBJECTIVE

The mechanisms underlying accelerated long-term forgetting (ALF) in patients with epilepsy are still under investigation. We examined the contribution of hippocampal subfields and their morphology to long-term memory performance in patients with focal epilepsy.

METHODS

We prospectively assessed long-term memory and performed magnetic resonance imaging in 80 patients with focal epilepsy (61 with temporal lobe epilepsy and 19 with extratemporal lobe epilepsy) and 30 healthy controls. The patients also underwent electroencephalography recording. Verbal and visuospatial memory was tested 30 seconds, 10 minutes, and 1 week after learning. We assessed the volumes of the whole hippocampus and seven subfields and deformation of the hippocampal shape. The contributions of the hippocampal volumes and shape deformation to long-term forgetting, controlling for confounding factors, including the presence of interictal epileptiform discharges, were assessed by multiple regression analyses.

RESULTS

Patients with focal epilepsy had lower intelligence quotients and route recall scores at 10 minutes than controls. The focal epilepsy group had smaller volumes of both the right and left hippocampal tails than the control group, but there were no significant group differences for the volumes of the whole hippocampus or other hippocampal subfields. Multiple regression analyses showed a significant association between the left CA1 volume and the 1-week story retention (β = 7.76; Bonferroni-corrected P = 0.044), but this was not found for the whole hippocampus or other subfield volumes. Hippocampal shape analyses revealed that atrophy of the superior-lateral, superior-central, and inferior-medial regions of the left hippocampus, corresponding to CA1 and CA2/3, was associated with the verbal retention rate.

SIGNIFICANCE

Our results suggest that atrophy of the hippocampal CA1 region and its associated structures disrupts long-term memory consolidation in focal epilepsy. Neuronal cell loss in specific hippocampal subfields could be a key underlying cause of ALF in patients with epilepsy.

Accelerated long-term forgetting in children with temporal lobe epilepsy: A timescale investigation of material specificity and executive skills

Recently, children with temporal lobe epilepsy (TLE) were found to be at risk of accelerated long-term forgetting (ALF). In this study, we examined the temporal trajectory of ALF, while exploring the relationship between ALF, executive skills, and epilepsy variables. Fifty-one children, (23 with TLE and 28 typically developing) completed a battery of neuropsychological tests of verbal and visual memory, executive skills, and two experimental memory tasks (verbal and visual) involving recall after short (30-min) and extended (1-day and 2-week) delays. Side of seizure focus and hippocampal integrity were considered. On the visual task (Scene Memory), children with TLE performed comparably to typically developing children following a 30-min and 1-day delay, although worse than typically developing children at 2 weeks: ALF was observed in children with right TLE focus. The two groups did not differ on the experimental verbal memory task. Children with TLE also had worse performance than typically developing children on standardized verbal memory test and on tests of executive skills (i.e., verbal generativity, inhibition, working memory, complex attention). Only complex attention was associated with visual ALF. ALF was present for visuo-spatial materials in children with TLE at two weeks, and children with right TLE were most susceptible. A relationship was identified between complex attention and long-term forgetting. The findings extend our understanding of difficulties in long-term memory formation experienced by children with TLE.

Accelerated long-term forgetting in adult patients with genetic generalized epilepsy

OBJECTIVE

Accelerated long-term forgetting (ALF) has been demonstrated among children but not adults with genetic generalized epilepsy (GGE). We investigated (1) how forgetting patterns of verbal and visuospatial material differ between patients with GGE and healthy controls (HCs) and (2) whether ALF is associated with ictal or interictal epileptic activity.

METHODS

Forty-two patients with GGE (39, 92.9% experiencing seizures) were compared to 57 HCs in word, logical story, and Rey-Osterrieth complex figure recall tasks by testing after intervals of 30 min and 4 weeks. Ambulatory electroencephalography (EEG) was performed before testing to detect generalized epileptic activity, and patients were asked to document the number of seizures during the 4-week interval.

RESULTS

A two-way repeated measures ANOVA indicated that individuals with GGE have different forgetting patterns in comparison to HCs in tasks of word (delay by group interaction F_{1.5, 142.5}  = 4.5, p = .02, η p 2  = .04) and figure (F_{2, 194}  = 15.9, p < .001, η p 2  = .14) but not story (F_{1.6 151.1}  = .5, p = .58, η p 2  = .005) recall. Last learning trial-adjusted scores of word recall were comparable between HCs and patients with epilepsy (PWEs) at 30 min (p = .21) but not at 4 weeks (p = .006). Individuals with GGE performed worse than HCs in figure recall at 30 min and 4 weeks (p < .001), with lower performance after the 4-week interval present only among seizure-positive and EEG-positive individuals (p < .001) during subgroup analysis. Performance on memory tests was unrelated to overall seizure frequency, the number of antiseizure drugs used, and epilepsy duration.

SIGNIFICANCE

Our study supports the presence of ALF in a task of word recall among adult patients with GGE. The pattern of forgetting visuospatial information suggests greater forgetting of material before the first delay and ongoing deficits among PWEs with epileptic activity. Future studies should confirm our findings and investigate the functional or pathological mechanisms of memory dysfunction in GGE.

The syndrome of transient epileptic amnesia: a combined series of 115 cases and literature review

The term transient epileptic amnesia was coined in 1990 to describe a form of epilepsy causing predominantly amnestic seizures which could be confused with episodes of Transient Global Amnesia. Subsequent descriptions have highlighted its association with ‘atypical’ forms of memory disturbance including accelerated long-term forgetting, disproportionate autobiographical amnesia and topographical amnesia. However, this highly treatment-responsive condition remains under-recognized and undertreated. We describe the clinical and neuropsychological features in 65 consecutive cases of transient epileptic amnesia referred to our study, comparing these to our previous cohort of 50 patients and to those reported in 102 literature cases described since our 2008 review. Findings in our two cohorts are substantially consistent: The onset of transient epileptic amnesia occurs at an average age of 62 years, giving rise to amnestic episodes at a frequency of around 1/month, typically lasting 15–30 min and often occurring on waking. Amnesia is the only manifestation of epilepsy in 24% of patients; olfactory hallucinations occur in 43%, motor automatisms in 41%, brief unresponsiveness in 39%. The majority of patients describe at least one of the atypical forms of memory disturbance mentioned above; easily provoked tearfulness is a common accompanying feature. There is a male predominance (85:30). Epileptiform changes were present in 35% of cases, while suspected causative magnetic resonance imaging abnormalities were detected in only 5%. Seizures ceased with anticonvulsant treatment in 93% of cases. Some clinical features were detected more commonly in the second series than the first, probably as a result of heightened awareness. Neuropsychological testing and comparison to two age and IQ-matched control groups (n = 24 and 22) revealed consistent findings across the two cohorts, namely elevated mean IQ, preserved executive function, mild impairment at the group level on standard measures of memory, with additional evidence for accelerated long-term forgetting and autobiographical amnesia, particularly affecting episodic recollection. Review of the literature cases revealed broadly consistent features except that topographical amnesia, olfactory hallucinations and emotionality have been reported rarely to date by other researchers. We conclude that transient epileptic amnesia is a distinctive syndrome of late-onset limbic epilepsy of unknown cause, typically occurring in late middle age. It is an important, treatable cause of memory loss in older people, often mistaken for dementia, cerebrovascular disease and functional amnesia. Its aetiology, the monthly occurrence of seizures in some patients and the mechanisms and interrelationships of the interictal features—amnestic and affective—all warrant further study.

Investigating the Effects of Seizures on Procedural Memory Performance in Patients with Epilepsy

Memory complaints are frequently reported by patients with epilepsy and are associated with seizure occurrence. Yet, the direct effects of seizures on memory retention are difficult to assess given their unpredictability. Furthermore, previous investigations have predominantly assessed declarative memory. This study evaluated within-subject effects of seizure occurrence on retention and consolidation of a procedural motor sequence learning task in patients with epilepsy undergoing continuous monitoring for five consecutive days. Of the total sample of patients considered for analyses (N = 53, M_age = 32.92 ± 13.80 y, range = 18–66 y; 43% male), 15 patients experienced seizures and were used for within-patient analyses. Within-patient contrasts showed general improvements over seizure-free (day + night) and seizure-affected retention periods. Yet, exploratory within-subject contrasts for patients diagnosed with temporal lobe epilepsy (n = 10) showed that only seizure-free retention periods resulted in significant improvements, as no performance changes were observed following seizure-affected retention. These results indicate general performance improvements and offline consolidation of procedural memory during the day and night. Furthermore, these results suggest the relevance of healthy temporal lobe functioning for successful consolidation of procedural information, as well as the importance of seizure control for effective retention and consolidation of procedural memory.

Accelerated long-term forgetting in focal epilepsy: Do interictal spikes during sleep matter?

Accelerated long-term forgetting (ALF) is a particular form of amnesia mostly encountered in focal epilepsy, particularly in temporal lobe epilepsy. This type of memory loss is characterized by an impairment of long-term consolidation of declarative memory, and its mechanisms remain poorly understood. In particular, the respective contribution of lesion, seizures, interictal epileptic discharges, and sleep is still debated. Here, we provide an overview of the relationships intertwining epilepsy, sleep, and memory consolidation and, based on recent findings from intracranial electroencephalographic recordings, we propose a model of ALF pathophysiology that integrates the differential role of interictal spikes during wakefulness and sleep. This model provides a framework to account for the different timescales at which ALF may occur.

Hippocampal Interictal Spikes during Sleep Impact Long-Term Memory Consolidation

OBJECTIVE

Non-rapid eye movement (NREM) sleep is supposed to play a key role in long-term memory consolidation transferring information from hippocampus to neocortex. However, sleep also activates epileptic activities in medial temporal regions. This study investigated whether interictal hippocampal spikes during sleep would impair long-term memory consolidation.

METHOD

We prospectively measured visual and verbal memory performance in 20 patients with epilepsy investigated with stereoelectroencephalography (SEEG) at immediate, 30-minute, and 1-week delays, and studied the correlations between interictal hippocampal spike frequency during waking and the first cycle of NREM sleep and memory performance, taking into account the number of seizures occurring during the consolidation period and other possible confounding factors, such as age and epilepsy duration.

RESULTS

Retention of verbal memory over 1 week was negatively correlated with hippocampal spike frequency during sleep, whereas no significant correlation was found with hippocampal interictal spikes during waking. No significant result was found for visual memory. Regression tree analysis showed that the number of seizures was the first factor that impaired the verbal memory retention between 30 minutes and 1 week. When the number of seizures was below 5, spike frequency during sleep higher than 13 minutes was associated with impaired memory retention over 1 week.

INTERPRETATION

Our results show that activation of interictal spikes in the hippocampus during sleep and seizures specifically impair long-term memory consolidation. We hypothesize that hippocampal interictal spikes during sleep interrupt hippocampal-neocortical transfer of information. ANN NEUROL 2020;87:976-987.

Cortisol and trait anxiety as relevant factors involved in memory performance in people with drug-resistant epilepsy

People with drug-resistant epilepsy are exposed to unpredictable and uncontrollable seizures, which can be considered as a chronic stress condition. Additionally, these patients present memory deficits and a high prevalence of depression and anxiety. Cortisol, the main stress hormone, has a modulatory role on memory in healthy individuals and patients with emotional disorders, but its role in memory and emotional processes remains unclear in people with epilepsy. This study analyzes the differences in cortisol levels in people with epilepsy with high and low memory performance, and the relationships among cortisol levels, epilepsy-related factors, memory, anxiety, and depression. Fifty-two adults with drug-resistant epilepsy underwent a neuropsychological evaluation, in which nine saliva samples were collected to analyze the ability of the hypothalamic-pituitary-adrenal axis to descend in accordance with the circadian rhythm. Cortisol area under the curve (AUC) was computed to study the global cortisol changes. Patients with low immediate and delayed memory performance and left-hemisphere focus showed higher cortisol levels. Additionally, patients with low memory scores had higher cortisol AUC, and therefore slower declining levels in the afternoon. Memory performance was negatively related to the cortisol AUC and trait anxiety, being both reliable predictors of memory performance, especially in patients with left-hemisphere focus. These results suggest that memory deficits in people with drug-resistant epilepsy may be influenced by exposure to cortisol derived from chronic stress. Additionally, trait anxiety could contribute to increasing the vulnerability to stress.

Quality of life in drug-resistant epilepsy: relationships with negative affectivity, memory, somatic symptoms and social support

OBJECTIVE

To investigate the relative contribution of factors non-directly related to seizures such as negative affectivity, social support, somatic symptoms and memory performance on quality of life (QOL) in patients with drug-resistant epilepsy.

METHODS

This is a cross-sectional study. Seventy patients with drug-resistant epilepsy were consecutively recruited from the inpatient Epilepsy Unit, Hospital Universitario y Politécnico La Fe, between April 2015 and October 2017. Medical history provided demographic characteristics of the patients (sex, age, and educational level), and clinical data (age at epilepsy onset, duration of epilepsy in years, frequency of seizures per month, type of seizures and number of AEDs). Pre-surgical assessment included diagnosis of the type of epilepsy and the lateralization of the epileptogenic area. All the patients underwent a neuropsychological assessment in which QOL (QOLIE-31), negative affectivity, social support, somatic symptoms, and memory were evaluated.

RESULTS

Negative affectivity (including anxiety-trait and depression), social support, neurosensory symptoms, and long-term verbal memory were significantly related to QOL composite score (for all, p < .009), subscales of QOL showing different sensitivities to them. Even after controlling for negative affectivity, neurosensory symptoms and long-term verbal memory significantly contribute to QOL composite score (p = .0001).

CONCLUSION

Results suggest that clinical management of patients with drug-resistant epilepsy should consider the treatment of verbal memory impairments at an early stage. Recognition of negative affectivity, poor social support and high somatic symptoms would also lead health professionals to develop different strategies to improve the QOL of patients with drug-resistant epilepsy.

Slow wave sleep and accelerated forgetting

We investigated whether the benefit of slow wave sleep (SWS) for memory consolidation typically observed in healthy individuals is disrupted in people with accelerated long-term forgetting (ALF) due to epilepsy. SWS is thought to play an active role in declarative memory in healthy individuals and, furthermore, electrographic epileptiform activity is often more prevalent during SWS than during wakefulness or other sleep stages. We studied the relationship between SWS and the benefit of sleep for memory retention using a word-pair associates task. In both the ALF and the healthy control groups, sleep conferred a memory benefit. However, the relationship between the amount of SWS and sleep-related memory benefits differed significantly between the groups. In healthy participants, the amount of SWS correlated positively with sleep-related memory benefits. In stark contrast, the more SWS, the smaller the sleep-related memory benefit in the ALF group. Therefore, contrary to its role in healthy people, SWS-associated brain activity appears to be deleterious for memory in patients with ALF.

REM Sleep Is Causal to Successful Consolidation of Dangerous and Safety Stimuli and Reduces Return of Fear after Extinction

Sleep has a profound impact on memory consolidation. In this study, human participants underwent Pavlovian conditioning and extinction before we manipulated nocturnal memory consolidation by a split-night protocol with 80 healthy male participants in four groups. Recall after a second (recovery) night of sleep revealed that sleeping the first half of the night, which is dominated by slow-wave sleep, did not improve recall. Conversely, sleeping the second half of the night, which is dominated by rapid eye movement (REM) sleep, led to better discrimination between fear-relevant and neutral stimuli in behavioral and autonomic measures. Meanwhile, staying awake in the second half of the night led to an increase of discrimination between extinguished and neutral stimuli, which was paralleled by an activation of the ventromedial prefrontal cortex and amygdala. We conclude that sleep, especially REM sleep, is causal to successful consolidation of dangerous and safety stimuli and reduces return of fear after extinction.

SIGNIFICANCE STATEMENT

We use a split-night protocol to investigate the influence of different sleep phases on successful consolidation of conditioned fear and extinction. Such a protocol uses the fact that in humans the first half of the night is dominated by slow-wave sleep, whereas during the second half, rapid eye movement (REM) sleep is more predominant. Our data show that only REM-rich sleep during the second half of the night promoted good discrimination between fear-relevant and neutral stimuli during recall, while staying awake led to a recovery of discrimination between extinguished and neutral stimuli. This suggests that sleep following extinction contributes independently to successful extinction memory consolidation.

Is There a Relation between EEG-Slow Waves and Memory Dysfunction in Epilepsy? A Critical Appraisal

Is there a relationship between peri-ictal slow waves, loss of consciousness, memory, and slow-wave sleep, in patients with different forms of epilepsy? We hypothesize that mechanisms, which result in peri-ictal slow-wave activity as detected by the electroencephalogram, could negatively affect memory processes. Slow waves (≤4 Hz) can be found in seizures with impairment of consciousness and also occur in focal seizures without impairment of consciousness but with inhibited access to memory functions. Peri-ictal slow waves are regarded as dysfunctional and are probably caused by mechanisms, which are essential to disturb the consolidation of memory entries in these patients. This is in strong contrast to physiological slow-wave activity during deep sleep, which is thought to group memory-consolidating fast oscillatory activity. In patients with epilepsy, slow waves may not only correlate with the peri-ictal clouding of consciousness, but could be the epiphenomenon of mechanisms, which interfere with normal brain function in a wider range. These mechanisms may have transient impacts on memory, such as temporary inhibition of memory systems, altered patterns of hippocampal-neocortical interactions during slow-wave sleep, or disturbed cross-frequency coupling of slow and fast oscillations. In addition, repeated tonic-clonic seizures over the years in uncontrolled chronic epilepsy may cause a progressive cognitive decline. This hypothesis can only be assessed in long-term prospective studies. These studies could disentangle the reversible short-term impacts of seizures, and the impacts of chronic uncontrolled seizures. Chronic uncontrolled seizures lead to irreversible memory impairment. By contrast, short-term impacts do not necessarily lead to a progressive cognitive decline but result in significantly impaired peri-ictal memory performance.

Accelerated long-term forgetting in temporal lobe epilepsy: verbal, nonverbal and autobiographical memory

Patients with temporal lobe epilepsy (TLE) often present with memory complaints despite performing within normal limits on standard memory tests. One possible explanation for this phenomenon is accelerated long-term forgetting (ALF). The present study investigated material-specific ALF in patients with unilateral TLE and also examined whether ALF could be demonstrated on a novel, standardized anterograde autobiographical memory (ABM) task. Fourteen patients with TLE and 17 controls were administered verbal, nonverbal and ABM event memory tasks. The participants were tested for immediate recall, recall and recognition at 30-minute delay, and recall and recognition after four weeks. The extent of ALF was calculated based on the percentage decay of memory from the 30-minute delay trial to the four-week delay trial. Patients with left TLE showed significantly greater ALF for verbal material and a trend towards greater forgetting of ABM. Patients with right TLE showed a non-significant trend towards greater ALF for nonverbal material. Patients with unilateral hippocampal abnormalities showed greater ALF compared to patients without hippocampal abnormalities. Patients with seizures that generalize had more global memory deficits and greater ALF. We conclude that patients with unilateral TLE show material-specific ALF, which appears to be more pronounced with an abnormal hippocampus or seizures that secondarily generalize.

Effective group-based memory training for patients with epilepsy

Patients with epilepsy experience memory problems, but there have been few attempts to provide and evaluate the effectiveness of memory training. We designed a 6-week, group-based, psychoeducation and strategy course that was evaluated using a waitlist crossover design, with three assessments conducted 12 weeks apart. Thirty-one patients with a history of seizures participated. Significant gains were found on tests of anterograde (Rey Auditory Verbal Learning Test) and appointment memory. In addition, patients reported using more strategies and experiencing fewer prospective memory difficulties in daily life. Memory was more likely to improve in participants who were younger, less educated, and less depressed. Moreover, lower baseline memory, but better attention corresponded to better outcome. Of the clinical variables related to epilepsy, only number of anticonvulsant medications was found to be associated with outcome. Our study provides evidence that a relatively short intervention can improve memory functioning in patients with epilepsy.

Clinical features of the postictal state: correlation with seizure variables

The postictal period is defined by changes in behavior, motor function, and neuropsychological performance that last until the return to a presumed baseline. The postictal period has not received as much attention as the time of seizure onset or the seizure itself. It may offer information that could be helpful in the definition of the epileptogenic zone and its lateralization. Here we review different behavioral, neuropsychological, and EEG phenomena of the postictal state and discuss several semiological features of the postictal period with respect to patient characteristics, seizure duration, influences of drug treatment, and secondary generalization. Further evaluation may reveal information that could be helpful particularly with respect to resective epilepsy surgery, possibly allowing better localization and lateralization.

Recurrent seizures induce a reversible impairment in a spatial hidden goal task

A major question concerning the learning and memory deficits characteristic of epilepsy is the relative importance of the initial insult that leads to recurrent, unprovoked seizures versus the seizures themselves. A related issue is whether seizure-induced cognitive decline is permanent or reversible when convulsions cease. To address these problems, adult rats were extensively trained in the "spatial accuracy task," a dry-land analog of the Morris water maze. This task allows the rat's estimate of the location of a hidden goal zone to be repeatedly measured within each behavioral session. One aim was to measure, in well-trained animals, the time course of any cognitive impairment caused by a daily flurothyl-induced generalized seizure over 11 days. A second aim was to look for possible recovery during 9 subsequent days with no seizures. We saw a cumulative degradation in spatial performance during the seizure days and reversal of the deficit after seizures were stopped such that performance returned to baseline. Interestingly, the rate of learning to an asymptote, the rate of performance decline during one-per-day seizures and the rate of relearning during the recovery period were all similar. Given that the hippocampus plays an important role in spatial memory and that it is the brain structure most vulnerable to abnormal excitation the implication is that the hippocampus remains essential for precise spatial navigation even after prolonged training in locating a fixed goal zone. Clinically, this finding questions the assumption that patients who experience seizures should return to a baseline cognitive level within hours.

Changes in retrograde memory following temporal lobectomy

Extensive retrograde memory deficits have been detected in patients with temporal lobe epilepsy (TLE) and in patients who have undergone temporal lobectomy (TL). To date, no group study has used a prospective longitudinal design. We assessed memory for public and autobiographical facts and events in patients (n=15) with focal left- or right-sided TLE before and after TL using a battery of tests that covered the life span. Patients who underwent TL demonstrated material-specific memory decline in retrograde memory. Left TL was associated with a significant drop in recall of famous people's names. Patients who underwent right TL exhibited a significant decline in the recall of autobiographical events from across the life span. Our study indicates for the first time that TL is associated with a risk of mild, material-specific retrograde memory decline. Verifications with a larger sample size and other measures of remote memory are needed.

Memory consolidation and accelerated forgetting in children with idiopathic generalized epilepsy

Whether children with idiopathic generalized epilepsy exhibit accelerated forgetting of verbal and nonverbal information in comparison to healthy controls matched for age and IQ was explored. Twenty-one children with IGE were compared with 21 healthy controls on measures of verbal and visuospatial memory at delays of 30 minutes and 1 week by use of a minimum-learning criterion controlled for initial learning. For the auditory-verbal memory test, group performance was comparable at 30 minutes, but children with IGE recalled significantly less than controls at 1 week. When the number of learning trials to criterion was controlled, the main effects of group and delay became nonsignificant. No group differences were found with respect to recognition performance. Comparisons for the visuospatial task were nonsignificant. Overall, poor initial learning efficiency led to retrieval difficulties, specifically at the longer delay, and was more common in the IGE group. These results, although preliminary, have implications for education planning in childhood IGE.

Impaired single cell firing and long-term potentiation parallels memory impairment following recurrent seizures

Patients with epilepsy are at substantial risk for memory impairment. Animal studies have paralleled these clinical observations, demonstrating impaired hippocampal function as measured by spatial memory in rodents subjected to seizures. However, the mechanism of seizure-induced hippocampal impairment is unclear. Here we investigated the effects of recurrent seizures on water-maze performance, a behavioural measure of learning and memory, long-term potentiation (LTP; considered a test of synaptic plasticity and memory) and place-cell firing patterns, a single-cell indicator of spatial memory. LTP and CA1 place-cell activity were examined in separate groups of freely moving rats, before and after 10 flurothyl-induced seizures. Water maze performance was examined in a third group of rats, five with previously induced seizures and five controls. Recurrent flurothyl seizures were associated with marked impairment in LTP and a reduction in the frequency of the peak theta power. Compared to baseline recordings, place-cell firing patterns following recurrent seizures were significantly less precise, had lower firing rates and were less stable. Impaired place-cell firing was seen as early as after two seizures and persisted at least 72 h after the last seizure. Water-maze performance was also significantly impaired in animals that underwent recurrent seizures. No cell loss or synaptic reorganization was observed in the hippocampus or in several other cortical areas that are vulnerable to seizures. These results demonstrate that relatively brief excitatory events, not producing visible cell damage, can nevertheless cause long-lasting changes in hippocampal physiology, observable as impairments in place-cell function, LTP and spatial memory.

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.

Effects of Temporal Lobe Epilepsy on Retrograde Memory

PURPOSE

In a previous investigation (Lah et al., 2004), we found deficits in retrograde memory in patients who had undergone temporal lobectomy (TL). In this study, we set out to determine whether such deficits are present before surgery in patients with temporal lobe epilepsy (TLE).

METHODS

Memory for public and autobiographic facts and events was assessed in patients with focal left-sided (n=15) or right-sided (n=14) TLE and healthy control subjects (n=15). The impact of epilepsy and underlying cognitive deficits on retrograde memory also was examined.

RESULTS

Patients with left TLE demonstrated retrograde memory deficits across domains. Patients with right TLE showed defective recall only in the autobiographic domain. Young age at onset (younger than 14 years) was associated with greater difficulties in recall of famous events, and patients receiving polytherapy had significantly reduced recall of autobiographic events compared with those receiving monotherapy. In most cases, deficient memory for the past was associated with impairments in other cognitive skills, especially language abilities.

CONCLUSIONS

In unoperated-on patients with TLE, we found deficits in retrograde memory that were similar to those seen after TL, with the pattern of deficits being influenced by side of lesion, anticonvulsant medication, and word-finding deficits. Unlike patients tested after right TL, patients with right TLE did not have difficulty recalling details of famous events, which raises the possibility that right TL results in a decline in this aspect of retrograde memory.

Lateralizing signs during seizures in focal epilepsy

This article reviews lateralizing semiological signs during epileptic seizures with respect to prediction of the side of the epileptogenic zone and, therefore, presurgical diagnostic value. The lateralizing significance of semiological signs and symptoms can frequently be concluded from knowledge of the cortical representation. Visual, auditory, painful, and autonomic auras, as well as ictal motor manifestations, e.g., version, clonic and tonic activity, unilateral epileptic spasms, dystonic posturing and unilateral automatisms, automatisms with preserved responsiveness, ictal spitting and vomiting, emotional facial asymmetry, unilateral eye blinking, ictal nystagmus, and akinesia, have been shown to have lateralizing value. Furthermore, ictal language manifestations and postictal features, such as Todd's palsy, postictal aphasia, postictal nosewiping, postictal memory dysfunction, as well as peri-ictal water drinking, peri-ictal headache, and ipsilateral tongue biting, are reviewed. Knowledge and recognition of semiological lateralizing signs during seizures is an important component of the presurgical evaluation of epilepsy surgery candidates and adds further information to video/EEG monitoring, neuroimaging, functional mapping, and neuropsychological evaluation.

Temporal lobe epilepsy and the selective reminding test: the conventional 30-minute delay suffices

Conventional memory assessment may fail to identify memory dysfunction characterized by intact recall for a relatively brief period but rapid forgetting thereafter. This study assessed learning and retention after 30-min and 24-hr delays on auditory and visual selective reminding tests (SRTs) in right (n=20) and left (n=22) temporal lobe epilepsy (TLE) patients and controls (n=49). The left TLE group performed significantly worse than controls on all 3 trials of both tests. The right TLE group differed from the controls on all 3 visual SRT trials and on learning for the auditory SRT. There were no between-groups differences in rate of information lost at the 30-min versus the 24-hr delay. At the individual level, there was no difference in the percentage of patients versus controls who demonstrated isolated memory impairment at the 24-hr delay. Accelerated forgetting over 24 hr is uncommon in TLE patients.

Determining the effects of antiepileptic drugs on cognitive function in pediatric patients with epilepsy

The majority of children with epilepsy are of normal intelligence; however, a significant subset suffers from temporary or permanent cognitive impairment. Factors that affect cognitive function are myriad and include the neuropathology underlying the epilepsy, seizures, epileptiform activity, psychosocial problems, and antiepileptic drug side effects. Although cognitive impairment is often wrongly attributed to the effects of antiepileptic drugs, antiepileptic drugs do impair cognition in some children. Clinicians should be aware of the differential cognitive effects of antiepileptic drugs and should monitor cognitive function closely when adding or changing therapy. Based on published data from prospective, chronic dosing studies, phenobarbital and topiramate have the highest potential for causing cognitive dysfunction.

Epilepsy and cognition

Patients with epilepsy are more prone to cognitive and behavioral deficits. Epilepsy per se may induce or exacerbate an underlying cognitive impairment, a variety of factors contribute to such deficits, i.e., underlying neuropathology, seizure type, age of onset, psychosocial problems, and treatment side effects. Epilepsy treatment may offset the cognitive and behavioral impairments by stopping or decreasing the seizures, but it may also induce untoward effects on cognition and behavior. The neurocognitive burden of epilepsy may even start through in utero exposure to medications. Epilepsy surgery can also induce certain cognitive deficits, although in most cases this can be minimized. Clinicians should consider cognitive side effect profiles of antiepileptic medications, particularly in extreme age groups. While no effective treatments are available for cognitive and behavioral impairments in epilepsy, comprehensive pretreatment evaluation and meticulous selection of antiepileptic drugs or surgical approach may minimize such untoward effects.

Ictal urinary urge: further evidence for lateralization to the nondominant hemisphere

PURPOSE

To determine the lateralizing value of ictal urinary urgency.

METHODS

A retrospective database search was performed for patients with ictal urinary urgency admitted to the Epilepsy Monitoring Unit at the Cleveland Clinic between 1994 and 2001.

RESULTS

Six patients were identified; intracarotid amytal test demonstrated left hemispheric speech dominance in five cases. The sixth patient continued to speak during right temporal seizures. EEG and imaging data supported right temporal or frontotemporal epilepsy in all six cases. Two patients were seizure free after focal right hemispheric resection.

CONCLUSIONS

Ictal urinary urge appears to be a lateralizing sign for nondominant temporal lobe epilepsy.

Differential cognitive effects of antiepileptic drugs

As a group, children and adolescents with epilepsy have a higher prevalence of cognitive and behavioral disorders, although many fall within the normal distribution. For those affected, several causes have been identified, some of which may be interrelated. It has proven to be methodologically sound to isolate the role of specific antiepileptic drugs as a cause of cognitive impairment. The large body of literature that has accumulated on this topic is characterized by a relatively high proportion of inconclusive or contradictory observations. This may be due in part to the many methodological pitfalls in this area of research. The emerging picture is that cognitive effects caused by antiepileptic drugs are neither the rule nor the exception. Although certain drugs appear more likely to be involved, no single drug causes problems in every patient, and no drug can be assumed never to cause any cognitive impairment. The subgroup of patients that are at higher risk cannot be easily defined. Early detection of cognitive effects is based on actively eliciting reports of symptoms. This can be complemented by a screening battery in case of suspicion.