When "long-term memory" no longer means "forever": analysis of accelerated long-term forgetting in a patient with temporal lobe epilepsy

Repeat testing enhances long-term verbal memory in children with epilepsy

To (i) determine whether accelerated long-term forgetting (ALF) can be found using standardized verbal memory test materials in children with genetic generalized epilepsy (GGE) and temporal lobe epilepsy (TLE), and (ii) to establish whether ALF is impacted by executive skills and repeat testing over long delays. One hundred and twenty-three children aged 8 to 16, (28 with GGE, 23 with TLE, and 72 typically developing; TD) completed a battery of standardized tests assessing executive functioning and memory for two stories. Stories were recalled immediately and after a 30-min delay. To examine whether repeat testing impacts long-term forgetting, one story was tested via free recall at 1-day and 2-weeks, and the other at 2-weeks only. Recognition was then tested for both stories at 2-weeks. Children with epilepsy recalled fewer story details, both immediately and after 30-min relative to TD children. Compared to TD children, the GGE group, but not the TLE group, showed ALF, having significantly poorer recall of the story tested only at the longest delay. Poor executive skills were significantly correlated with ALF for children with epilepsy. Standard story memory materials can detect ALF in children with epilepsy when administered over long delays. Our findings suggest that (i) ALF is related to poor executive skills in children with epilepsy, and (ii) repeated testing may ameliorate ALF in some children.

Cognitive dysfunction in drug-naïve late-onset temporal lobe epilepsy

OBJECTIVES

To evaluate cognitive functions including memory in middle-aged and elderly patients with antiseizure drug-naïve late-onset temporal lobe epilepsy (TLE).

METHODS

We performed assessments with the Wechsler Adult Intelligence Scale-III (WAIS-III) and Wechsler Memory Scale-Revised (WMS-R) in 26 antiseizure drug-naïve patients with late-onset TLE, in comparison to 30 healthy subjects. We investigated the relationships between these cognitive function scores and clinical characteristics, seizure frequency, and frequency of interictal epileptic discharges (IEDs).

RESULTS

Patients with epilepsy had a significantly lower score than healthy controls in the verbal intelligence quotient (IQ), the performance IQ, and full-scale IQ in intelligence testing. Patients showed significantly decrease in the verbal memory scores, visual memory scores, general memory scores, and delayed recall scores compared with those in the control subjects. Delayed recall scores were significantly negatively correlated with recent seizure frequency and the total IEDs count per minute, but not with age of onset or duration of illness.

SIGNIFICANCE

Patients with antiseizure drug-naïve late-onset TLE displayed cognitive deficits including the domains of memory by using standard clinical neuropsychological test. Patients with late-onset epilepsy need to be considered for cognitive dysfunction at the time of diagnosis of TLE because they may have their daily life and work affected not only by epileptic seizures but also by cognitive deficits. Appearance of seizures and EEG abnormalities may affect the memory function in patients with late-onset TLE.

Forgetting rates of gist and peripheral episodic details in prose recall

In a seminal study, Slamecka and McElree showed that the degree of initial learning of verbal material affected the intercepts but not the slopes of forgetting curves. However, more recent work has reported that memories for central events (gist) and memory for secondary details (peripheral) were forgotten at different rates over periods of days, with gist memory retained more consistently over time than details. The present experiments aimed to investigate whether qualitatively different types of memory scoring (gist vs. peripheral) are forgotten at different rates in prose recall. In three experiments, 232 participants listened to two prose narratives and were subsequently asked to freely recall the stories. In the first two experiments participants were tested repeatedly after days and a month, while in the third experiment they were tested only after a month to control for repeated retrieval. Memory for gist was higher than for peripheral details, which were forgotten at a faster rate over a month, with or without the presence of intermediate recall. Moreover, repeated retrieval had a significant benefit on both memory for gist and peripheral details. We conclude that the different nature of gist and peripheral details leads to a differential forgetting in prose free recall, while repeated retrieval does not have a differential effect on the retention of these different episodic details.

Improving Amnesia Diagnostic Accuracy with RAVLT Single Scores and Composite Indices: Italian Normative Data

Objective

The Rey Auditory Verbal Learning Test (RAVLT) is a widely used verbal memory measure that provides scores for different aspects of memory. It involves repeated auditory presentation and recall of a 15-item word list (List A) followed by presentation and recall of a distractor list (List B) and then un-cued immediate and delayed recalls (at 15 min and 1 week) of List A as well as recognition testing. Aims of this study are to provide Italian normative data for certain RAVLT Scores and Composite Indices to improve the diagnostic accuracy of the test in clinical settings and to provide further evidence on how RAVLT can differentiate different amnesia profiles due to focal lesions.

Methods

We enrolled 440 healthy participants and RAVLT Single Scores and Composite Indices have been analyzed by means of multiple regression to verify the influence of age, education, and gender.

Results

We computed the best linear models with RAVLT Single Scores and Composite Indices, as dependent variables, and the most suitable transformation of independent variables. By reversing the signs of the regression coefficients, the adjustment factors for each level of age and, if needed, education and gender have been computed and the adjusted scores have been standardized into Equivalent Scores.

Conclusion

Using these standardized measures, we differentiate three profiles of amnesia due to selective hippocampal sclerosis with severe encoding deficit, fornix lesions with source memory problems, and temporal lobe epilepsy with consolidation failure.

Case Report: Cognitive Assessment Before an Amnesic Seizure in Transient Epileptic Amnesia Syndrome

A patient with transient epileptic amnesia syndrome presented a clinically observable amnesic seizure immediately after a neuropsychological assessment. An hour and a half before the onset of the seizure, the patient progressively developed an isolated alteration of episodic memory. These data question the ictal/interictal distinction in this syndrome as well as the speed of propagation of an epileptic activity.

EXPRESS: Accelerated forgetting in healthy older samples: implications for methodology, future ageing studies and early identification of risk of dementia

Accelerated long-term forgetting (ALF) has been reported in healthy older individuals, and is a possible early marker for risk of developing Alzheimer's disease (AD). The Verbal Associative Learning & Memory Test (VALMT; McGibbon & Jansari, 2013) addresses methodological weaknesses in existing clinical tests and has detected ALF in epilepsy within an hour. We used VALMT to investigate learning and forgetting in healthy older participants. Older (60-69yrs) and Younger (19-31yrs) participants were compared. Using VALMT, unrelated word-pairs were learnt to criterion, then cued-recall tested at delays of 5, 30 and 55 minutes. Unique pairs were tested at each delay. Subjective memory complaints data was gathered, and the Wechsler Memory Scale Logical Memory test (WMS-LM; a standard clinical measure) was administered. VALMT identified a significant difference in delayed recall between Younger and Older groups by 55 minutes (d = 1.32). While 'fast-learning' Older participants scored similarly to Younger participants, 'slow-learning' Older participants were impaired at all delays. Forgetting rates suggested degradation of memory starts during early synaptic consolidation rather than later system-level consolidation. Increased subjective memory complaints were associated with reduced VALMT scores. By contrast, WMS-LM failed to identify significant differences between any groups, and did not correlate with memory complaints. We conclude VALMT may be better able than WMS-LM to identify subtle impairments in healthy older adults within a single clinical visit, and VALMT results better reflect subjective experience. Older slow-learners forget faster and report more subjective memory complaints, which may indicate a group at risk of developing AD.

Detecting accelerated long-term forgetting: A problem and some solutions

While many memory disorders occur with normal rates of forgetting, an accelerated rate of long-term forgetting (ALF) may occur, sometimes in the absence of a learning deficit. Detecting ALF presents a problem as it is desirable that the learned material is re-tested after each of several delays. This may result in earlier retrievals confounding later tests, with evidence suggesting that both positive and negative interaction can occur between successive tests. An earlier study (Baddeley et al., 2019) tested cued recall of a series of four crimes or four visual scenes by probing a different sample of features from all four crimes/scenes at each delay. Even though no question was asked twice, the interpolated tests markedly reduced the rate of forgetting. We suggest that this decelerated forgetting effect may result from the retrieval of probed features activating other associated features within that episode, hence facilitating their recall on subsequent tests. If so, the effect should be removed when only single and separate episodes, or individual items, are tested at each delay. We test this by probing a separate episode at each delay (Experiment 1), or by replacing integrated episodes with recognition memory for isolated words (Experiments 2 and 3) or visual scenes (Experiments 4 and 5). As predicted, we find no reduction in the rate of forgetting, in contrast to our earlier studies. The theoretical and clinical implications of our results are discussed. We conclude that the previously developed Crimes and Four Doors Tests (Baddeley et al., 2019) and the present single item recognition tests are complementary and are both likely to be necessary to ensure the reliable detection of ALF.

Accelerated forgetting in temporal lobe epilepsy: When does it occur?

OBJECTIVE

The main goal of the study was to analyse differences in the forgetting rates of Temporal Lobe Epilepsy (TLE) patients at different intervals (30 sec, 10 min, 1 day and 1 week) compared with those of healthy controls. A secondary aim of this research was to provide an assessment of the relationship between clinical epilepsy-related variables and forgetting rates in TLE patients.

METHOD

The sample was composed of 14 TLE patients and 14 healthy matched controls. All participants underwent a full standardised neuropsychological assessment including general intelligence, executive functioning, memory, language and other variables, such as depression, anxiety or everyday memory failures. Two specific memory tasks, consisting of cued recall of 4 short stories and 4 routes, were carried out at four different intervals.

RESULTS

There was a significant difference between groups at 10-min interval on the stories task, with the TLE group displaying greater forgetting than healthy controls. None of the other intervals on either task showed significant group differences. No differences were found when controlling for clinical epilepsy-related variables.

CONCLUSION

Forgetting of verbal information at 10 min was greater in patients with TLE compared with controls, but accelerated longer term forgetting was not found. This study suggests that a late consolidation process is not necessarily impaired in TLE patients.

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.

Electroconvulsive therapy related autobiographical amnesia: a review and case report

Introduction: While short-term cognitive impairment following electroconvulsive therapy (ECT) is well described and acknowledged, the relationship between ECT and persistent memory impairment, particularly of autobiographical memory, has been controversial. Methods: We describe the case of a 70-year-old consultant neurophysiologist, AW, who developed prominent, selective autobiographical memory loss following two courses of ECT for treatment-resistant depression. Results: His performance on standard measures of IQ, semantic and episodic memory, executive function and mood was normal, while he performed significantly below controls on measures of episodic autobiographical memory. Conclusions: Explanations in terms of mood-related memory loss and somatoform disorder appear unlikely. We relate AW's autobiographical memory impairment, following his ECT, to reports of similar autobiographical memory impairment occurring in the context of epilepsy, and emphasise the importance of using sensitive approaches to AbM assessment.

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.

Accelerated long-term forgetting in children with genetic generalized epilepsy: The temporal trajectory and contribution of executive skills

PURPOSE

Long-term memory, which is critical for social and vocational functioning, is impaired in children with genetic generalized epilepsy (GGE). In this study, we examined the relationship between the temporal pattern of long-term forgetting for visual and verbal materials and executive skills in children with GGE.

METHOD

Thirty-two children, 17 with GGE and 25 typically developing age-matched controls completed standardized tests of short-term memory (recall after a 30-minute delay), executive skills, and experimental long-term memory tasks (one verbal and one visual) involving recall after one short (30-minute), and two long (1-day, 2-week) delays.

RESULTS

On the long-term visual memory task, children with GGE performed comparably with typically developing children at a 30-minute delay (p = .298), although obtained lower object placement accuracy score, at 1 day (p = .039) and at 2 weeks (p = .022) relative to typically developing children. On the verbal task, the between-group difference was not significant at any delay. In children with GGE, poorer object placement accuracy at two weeks correlated with lower visuospatial short-term memory (r = -0.624, p = .005) and verbal working memory (r = -0.448, p = .041).

CONCLUSIONS

This study provided several novel findings. For the first time, accelerated long-term forgetting (ALF) was found in long-term visual memory in children with GGE, despite comparable learning and recall at 30 min. Study results indicated that deficits in long-term visual memory are present after one day, increase over time, and may relate to reduced executive skills. Our findings can be used to inform our understanding of the temporal trajectory of ALF and contribution of executive skills.

Actigraphy-recorded sleep efficiency and hippocampal volume are related to visual and verbal rate of forgetting in older adults

This study aimed to determine if older adults "at-risk" for dementia (those with MCI or SMC) exhibit accelerated long-term forgetting (ALF) and whether rate of forgetting (RoF) is associated with sleep efficiency, hippocampal volume and demographic/clinical features. Forty-nine "at-risk" participants and eighteen controls underwent examination. Memory was assessed using the Scene Memory Task (SMT) and WMS-III Logical Memory (LM) subtest. Tests were administered at baseline, 24 hours and 2 weeks. While our study did not find ALF in those "at-risk" for dementia, on the SMT, RoF over 24 hours and 2 weeks was negatively correlated with sleep efficiency. For LM, RoF at 2 weeks was moderately associated with left hippocampal volume. Neither visual or verbal RoF was correlated with demographic or clinical variables (age, MMSE, IQ, GDS-15). While ALF was not observed in this sample, our results suggest that visual and verbal forgetting have differential predictors.

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.

Forgetting in Alzheimer's disease: Is it fast? Is it affected by repeated retrieval?

OBJECTIVES

Whether people with Alzheimer's Disease present with accelerated long term forgetting compared to healthy controls is still debated. Typically, accelerated long term forgetting implies testing the same participants repeatedly over several delays. This testing method raises the issue of confounding repetition effects with forgetting rates. We used a novel procedure to disentangle the two effects.

METHODS

Four short stories were presented during an initial in-person assessment of 40 patients with Alzheimer's Disease and 42 age-matched healthy controls. Our aim was for participants to reach a score of 70% correct (9 out of 13 questions) at encoding. If this criterion was not achieved after the first trial, the four stories were presented again (in a different order); participants took the 1 min filler task again and were then retested. We repeated this process until participants reached the 70% criterion or to a maximum of four trials. Cued recall memory tests were completed during follow-up telephone call(s) at different delay intervals. Study material was presented only at encoding, then probed with different question sets on all other delays. Each question set tested different sub-parts of the material. The experiment employed a mixed design. Participants were randomly allocated to either a condition without retrieval practice or a condition with retrieval practice. Participants in the condition without retrieval practice were only tested at two delays: post encoding filled delay and at one month. Participants in the condition with retrieval practice were tested at four delays: post encoding filled delay, one day, one week and one month. Our methodological design allowed us to separate the effects of retesting from the effects of delay.

RESULTS

Alzheimer's Disease patients showed a significant encoding deficit reflected in the higher number of trials required to reach criterion. Using Linear Mixed Models, we found no group by delay interactions between the post encoding filled delay retrieval and one month delays, with Alzheimer's Disease groups having a similar decline in performance to healthy controls, irrespective of testing condition. Significant condition by delay interactions were found for both groups (Alzheimer's Disease and healthy controls), with better performance at one month in the condition with retrieval practice.

CONCLUSIONS

Our data showed that Alzheimer's Disease is not characterised by accelerated long term forgetting, patients in our sample forgot at the same rate as healthy controls. Given the additional trials required by Alzheimer's patients to reach the 70% correct criterion, their memory impairment appears to be one of encoding. Moreover, Alzheimer's Disease patients benefited from repeated testing to the same extent as healthy controls. Due to our methodological design, we were also able to show that performance improved under repeated testing conditions, even with partial testing (sampling different features from each narrative on every test session/delay) in both healthy controls and Alzheimer's Disease.

Memory Rehabilitation in Patients with Epilepsy: a Systematic Review

Memory failure is a common clinical concern of patients with epilepsy and is associated with significant functional impairments. Thus, memory rehabilitation is of critical clinical importance. In this article, we aimed to systematically evaluate the efficacy of memory rehabilitation in patients with epilepsy. The Preferred Items for Systematic Reviews and Meta-Analyses (PRISMA) was used to guide searches, extraction and reporting of data in this review. PsycINFO, Medline and PsychBITE searches yielded 95 studies. Twelve papers met inclusion criteria, reporting outcomes of cognitive or behavioural interventions that specifically targeted the rehabilitation of memory in patients with epilepsy. Methodological rigour was rated using the Single-Case Experimental Design (SCED) scale for single-case studies and a modified version of the Downs and Black checklist for group studies. Twelve prospective studies, nine group (six pre-post design, one waitlist crossover, two randomised controlled trials) and three single-case studies were identified. Eleven of the studies included adults, eight of which involved adults with temporal lobe epilepsy (TLE). One paediatric study was identified. The quality of group studies ranged from 36% (poor) to 72% (good), using the modified Downs and Black checklist. Single-case studies were assessed using the SCED scale and assessed to range in quality from four to seven out to 11. Overall, memory rehabilitation was associated with improved memory function in all studies. Verbal memory outcomes were most commonly examined and associated with improvements. This review found that the level of evidence available to support rehabilitation of memory in patients with epilepsy was generally weak and inconsistent. Nevertheless, studies conducted to date, albeit of limited methodological quality, offer preliminary evidence that memory rehabilitation is associated with improvements in verbal memory in patients with temporal lobe epilepsy. Little is known about the efficacy of memory rehabilitation in patients with non-TLE, children, and other aspects of memory difficulties. Guidelines for future research are proposed.

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.

Profound anterograde amnesia following routine anesthetic and dental procedure: a new classification of amnesia characterized by intermediate-to-late-stage consolidation failure?

Anterograde amnesia caused by bilateral hippocampal or diencephalon damage manifests in characteristic symptoms of preserved intellect and implicit learning, and short span of awareness with complete and rapid forgetting of episodic material. A new case, WO, 38-year-old male with anterograde amnesia, in the absence of structural brain changes or psychological explanation is presented, along with four comparison cases from the extant literature that share commonalities between them including preserved intellect, span of awareness greater than working memory, and complete forgetting within hours or days following successful learning, including notably for both explicit and implicit material. WO's amnesia onset coincided with anesthetic injection and root canal procedure, with extended vasovagal-like incident. The commonalities between the five cases presented may suggest a shared biological mechanism involving the breakdown of intermediate-to-late-stage consolidation that does not depend on the structural integrity of the hippocampi. Speculation on the mechanism of consolidation breakdown and diagnostic implications are discussed.

Disruption of learning and long-term retention of prose passages in patients with focal epilepsy

Recent investigations of accelerated long-term forgetting, a condition in which newly acquired memory is normal initially but decays rapidly over days or weeks, indicate that multiple factors might influence whether this phenomenon is seen in patients with epilepsy. Test-based differences such as learning condition or type of memory measure (e.g., recall vs recognition) as well as epilepsy variables (e.g., side, site, or frequency of epileptiform activity) may be important. The present study sought to characterize factors affecting learning and memory for prose passages in patients with focal epilepsy. We enrolled 21 patients with temporal lobe epilepsy, with and without hippocampal lesions, 11 patients with extratemporal epilepsy (ETE), and 29 healthy controls. Two matched passages were used to compare effects of initial learning condition (one exposure versus learning-to-criterion) on subsequent patterns of retention. Recall and recognition were tested at different delays (i.e., immediately, 30min, 24h, and 4days). Regression analyses and one-way ANOVAs indicated that having a left-hemisphere epileptic focus had a negative impact on learning, whilst presence of a hippocampal lesion (irrespective of side) was associated with deterioration in recall for intervals up to 24h postencoding. Learning condition affected patterns of memory decay in that the ETE group showed significant decline in recall between 24h and 4days only when stories were learned to criterion. In contrast with recall, no changes over time were evident in recognition memory, as patients with hippocampal lesions were impaired from 30min onward. Epilepsy variables other than side and site of epilepsy/lesion did not influence performance. In conclusion, the left hemisphere is involved in learning of prose material, and the hippocampus is involved in the consolidation of this material mainly for the first 24h. After this, cortical regions outside the hippocampus become important for recall.

Third International Congress on Epilepsy, Brain and Mind: Part 1

Epilepsy is both a disease of the brain and the mind. Here, we present the first of two papers with extended summaries of selected presentations of the Third International Congress on Epilepsy, Brain and Mind (April 3-5, 2014; Brno, Czech Republic). Epilepsy in history and the arts and its relationships with religion were discussed, as were overviews of epilepsy and relevant aspects of social cognition, handedness, accelerated forgetting and autobiographical amnesia, and large-scale brain networks.

Old dogs with new tricks: Detecting accelerated long-term forgetting by extending traditional measures

Accelerated long-term forgetting (ALF) is a condition in which normal memory performance is displayed after short delays, but significant memory loss is detected when memory is tested after several days or weeks. This condition has been reported in patients with epilepsy, but there are few normative scores available for its detection in clinical practice. In the present study, we assessed 60 healthy control subjects 18-60years of age on three memory measures [Rey Auditory Verbal Learning (RAVLT), Logical Memory (LM), and Aggie Figures] at delays of 30min and 7days. With these normative values, we determined cutoff scores to look for ALF and then categorized the performance of 15 patients with focal epilepsy on the same tasks. Seven of the patients showed ALF, and, in four of these, no other memory deficits (i.e., deficits at 30min on at least one task) were detected. Of the several demographic and epilepsy factors examined, only higher estimated IQ and older age predicted ALF (and only on one task: RAVLT). The findings provide a useful set of data to be applied in the clinic and some insight into the factors that influence retention within the first week.

Accelerated long-term forgetting can become apparent within 3-8 hours of wakefulness in patients with transient epileptic amnesia

Objective: Accelerated long-term forgetting (ALF) is typically defined as a memory disorder in which information that is learned and retained normally over standard intervals (∼30 min) is forgotten at an abnormally rapid rate thereafter. ALF has been reported, in particular, among patients with transient epileptic amnesia (TEA). Previous work in TEA has revealed ALF 24 hr - 1 week after initial memory acquisition. It is unclear, however, if ALF observed 24 hr after acquisition reflects (a) an impairment of sleep consolidation processes taking place during the first night’s sleep, or (b) an impairment of daytime consolidation processes taking place during the day of acquisition. Here we focus on the daytime-forgetting hypothesis of ALF in TEA by tracking in detail the time course of ALF over the day of acquisition, as well as over 24 hr and 1 week. Method: Eleven TEA patients who showed ALF at 1 week and 16 matched controls learned 4 categorical word lists on the morning of the day of acquisition. We subsequently probed word-list retention 30 min, 3 hr, and 8 hr postacquisition (i.e., over the day of acquisition), as well as 24-hr and 1-week post acquisition. Results: ALF became apparent in the TEA group over the course of the day of acquisition 3–8 hr after learning. No further forgetting was observed over the first night in either group. Conclusions: The results of this study show that ALF in TEA can result from a deficit in memory consolidation occurring within hours of learning without a requirement for intervening sleep.

Sleep-dependent memory consolidation and accelerated forgetting

Accelerated long-term forgetting (ALF) is a form of memory impairment in which learning and initial retention of information appear normal but subsequent forgetting is excessively rapid. ALF is most commonly associated with epilepsy and, in particular, a form of late-onset epilepsy called transient epileptic amnesia (TEA). ALF provides a novel opportunity to investigate post-encoding memory processes, such as consolidation. Sleep is implicated in the consolidation of memory in healthy people and a deficit in sleep-dependent memory consolidation has been proposed as an explanation for ALF. If this proposal were correct, then sleep would not benefit memory retention in people with ALF as much as in healthy people, and ALF might only be apparent when the retention interval contains sleep. To test this theory, we compared performance on a sleep-sensitive memory task over a night of sleep and a day of wakefulness. We found, contrary to the hypothesis, that sleep benefits memory retention in TEA patients with ALF and that this benefit is no smaller in magnitude than that seen in healthy controls. Indeed, the patients performed significantly more poorly than the controls only in the wake condition and not the sleep condition. Patients were matched to controls on learning rate, initial retention, and the effect of time of day on cognitive performance. These results indicate that ALF is not caused by a disruption of sleep-dependent memory consolidation. Instead, ALF may be due to an encoding abnormality that goes undetected on behavioural assessments of learning, or by a deficit in memory consolidation processes that are not sleep-dependent.

Measuring forgetting: a critical review of accelerated long-term forgetting studies

Accelerated long-term forgetting (ALF) refers to abnormal forgetting over hours to weeks despite normal acquisition or initial consolidation. Since standardised assessments of memory typically only test at delays of up to 40-minutes, ALF may go undetected in clinical practice. The memory difficulties associated with ALF can however cause considerable distress to patients. It is important therefore that clinicians are aware that ALF may represent a distinct phenomenon that will require additional and careful assessment to aid patients' understanding of the condition and assist in developing strategies to address its effects. At the same time, ALF may also provide insight into long-term memory processes. Studies of ALF in patients with epilepsy have so far demonstrated mixed results, which may reflect differences in methodology. This review explores the methodological issues that can affect forgetting, such as the effects of age, general cognitive function, test sensitivity and initial learning. It then evaluates the extent to which existing studies have considered these key issues. We outline the points to consider when designing ALF studies that can be used to help improve their validity. These issues can also help to explain some of the mixed findings in studies of ALF and inform the design of standardised tests for assessing ALF in clinical practice.

Real-life memory and spatial navigation in patients with focal epilepsy: ecological validity of a virtual reality supermarket task

Ecological assessment and training of real-life cognitive functions such as visual-spatial abilities in patients with epilepsy remain challenging. Some studies have applied virtual reality (VR) paradigms, but external validity of VR programs has not sufficiently been proven. Patients with focal epilepsy (EG, n=14) accomplished an 8-day program in a VR supermarket, which consisted of learning and buying items on a shopping list. Performance of the EG was compared with that of healthy controls (HCG, n=19). A comprehensive neuropsychological examination was administered. Real-life performance was investigated in a real supermarket. Learning in the VR supermarket was significantly impaired in the EG on different VR measures. Delayed free recall of products did not differ between the EG and the HCG. Virtual reality scores were correlated with neuropsychological measures of visual-spatial cognition, subjective estimates of memory, and performance in the real supermarket. The data indicate that our VR approach allows for the assessment of real-life visual-spatial memory and cognition in patients with focal epilepsy. The multimodal, active, and complex VR paradigm may particularly enhance visual-spatial cognitive resources.

Accelerated long-term forgetting in temporal lobe epilepsy: evidence of improvement after left temporal pole lobectomy

Accelerated long term forgetting (ALF) is a characteristic cognitive aspect in patients affected by temporal lobe epilepsy that is probably due to an impairment of memory consolidation and retrieval caused by epileptic activity in hippocampal and parahippocampal regions. We describe a case of a patient with TLE who showed improvement in ALF and in remote memory impairment after an anterior left temporal pole lobectomy including the uncus and amygdala. Our findings confirm that impairment of hippocampal functioning leads to pathological ALF, whereas restoration of hippocampal functioning brings ALF to a level comparable to that of controls.