Transient epileptic amnesia: regional brain atrophy and its relationship to memory deficits

Integrating a multi-omics strategy framework to screen potential targets in cognitive impairment-related epilepsy

Epilepsy is a prevalent neurological disorder that affects over 70 million individuals worldwide and is often associated with cognitive impairments. Despite the widespread impact of epilepsy and cognitive impairments, the genetic basis and causal relationships underlying these conditions remain uncertain, prompting us to conduct a comprehensive investigation into the molecular mechanisms involved. In this study, we utilized statistical data from the third National Health and Nutrition Examination Survey (NHANES III) to evaluate correlation and large-scale pan-phenotype genome-wide association study (GWAS) data to establish genetic correlation and causality. Leveraging multi-omics datasets, we performed a comprehensive post-analysis that included variant prioritization, gene analysis, tissue and cell type enrichment, and pathway annotation. An integrated strategy-multi-trait analysis of GWAS (MTAG), transcriptome-wide association study (TWAS), summary-data-based Mendelian Randomization (SMR), and protein quantitative trait locus (pQTL)-MR-was performed to investigate the shared genetic architecture. Based on multiple orthogonal lines of evidence, we thereby identified 40 single nucleotide polymorphisms (SNPs) and 85 genes common to both conditions. Additionally, we optimized candidate genes such as GNAQ, FADS1, and PTK2 by single-cell expression analysis and molecular pathway mechanisms, thereby highlighting potential shared genetic pathways. These findings elucidate the genetic interplay and co-occurring mechanisms between epilepsy and cognitive impairments, providing crucial insights for future research and therapeutic strategies.

Associations between accelerated forgetting, amyloid deposition and brain atrophy in older adults

Accelerated long-term forgetting (ALF) is the phenomenon whereby material is retained normally over short intervals (e.g. minutes) but forgotten abnormally rapidly over longer periods (days or weeks). ALF might be an early marker of cognitive decline, but little is known about its relationships with preclinical Alzheimer's disease pathology and how memory selectivity might influence which material is forgotten. We assessed ALF in 'Insight 46', a sub-study of the MRC National Survey of Health and Development (a population-based cohort born during the same week in 1946) (n = 429; 47% female; assessed at age ∼73 years). ALF assessment comprised visual and verbal memory tests: complex figure drawing and the face-name associative memory exam (FNAME). ALF scores were calculated as the percentage of material retained after 7 days, relative to 30 min. In 306 cognitively normal participants, we investigated effects on ALF of β-amyloid pathology (quantified using 18F-Florbetapir-PET, classified as positive/negative) and whole-brain and hippocampal atrophy rate (quantified from serial T1-MRI over ∼2.4 years preceding the ALF assessment), in addition to interactions between these pathologies. We categorized complex figure drawing items as 'outline' or 'detail', to test our hypothesis that forgetting the outline of the structure would be more sensitive to the effect of brain pathologies. We also investigated associations between ALF and subjective cognitive decline, measured with the MyCog questionnaire. Complex figure 'outline' items were better retained than 'detail' items (mean retention over 7 days = 94% versus 72%). Amyloid-positive participants showed greater forgetting of the complex figure outline compared with amyloid-negative participants (90% versus 95%; P < 0.01). There were interactions between amyloid pathology and cerebral atrophy, such that whole-brain and hippocampal atrophy predicted greater ALF on complex figure drawing among amyloid-positive participants only [e.g. 1.9 percentage-points lower retention per ml/year of whole-brain atrophy (95% confidence intervals 0.5, 3.7); P < 0.05]. Greater ALF on FNAME was associated with increased rate of hippocampal atrophy. ALF on complex figure drawing was also correlated with subjective cognitive decline [-0.45 percentage-points per MyCog point (-0.85, -0.05); P < 0.05]. These results provide evidence of associations between some measures of ALF and biomarkers of brain pathologies and subjective cognitive decline in cognitively normal older adults. On complex figure drawing, 'outline' items were better remembered than 'detail' items, illustrating the strategic role of memory selectivity, but 'outline' items were also relatively more vulnerable to ALF in individuals with amyloid pathology. Overall, our findings suggest that ALF might be a sensitive marker of cognitive changes in preclinical Alzheimer's disease.

Using remote, digital, multi-day testing to characterize long-term forgetting in cognitively unimpaired older adults

INTRODUCTION

Accelerated long-term forgetting (LTF) might be an early marker of subtle memory changes in older adults at risk for Alzheimer's disease (AD). We leveraged remote, multi-day digital testing to characterize LTF in older adults and investigated its association with initial learning and AD imaging biomarkers.

METHODS

One hundred four cognitively unimpaired older adults completed a face-name memory task for seven consecutive days and were asked to recognize face-name pairs 1 week later. LTF was computed as the number of correctly identified stimuli divided by a participant's maximum performance during learning.

RESULTS

Better learning was associated with less LTF (β = 0.52, 95% confidence interval [CI]:0.34-0.71, p < 0.001). Accelerated LTF was associated with cortical thinning in AD-signature regions (β = 0.33, 95% CI: 0.13-0.52, p = 0.001), but associations with regional tau were more subtle.

DISCUSSION

Remote, multi-day testing may facilitate the assessment of LTF as an early cognitive marker of preclinical AD, but further replication is needed.

HIGHLIGHTS

Using digital, remote assessments, we evaluated long-term forgetting in cognitively unimpaired older adults. We found a potential association between long-term forgetting and tau in Alzheimer's disease (AD)-related regions. Assessing long-term forgetting may facilitate early detection of AD-related cognitive decline.

Engrams across diseases: Different pathologies - unifying mechanisms?

Memories are our reservoir of knowledge and thus, are crucial for guiding decisions and defining our self. The physical correlate of a memory in the brain is termed an engram and since decades helps researchers to elucidate the intricate nature of our imprinted experiences and knowledge. Given the importance that memories have for our lives, their impairment can present a tremendous burden. In this review we aim to discuss engram malfunctioning across diseases, covering dementia-associated pathologies, epilepsy, chronic pain and psychiatric disorders. Current neuroscientific tools allow to witness the emergence and fate of engram cells and enable their manipulation. We further suggest that specific mechanisms of mnemonic malfunction can be derived from engram cell readouts. While depicting the way diseases act on the mnemonic component - specifically, on the cellular engram - we emphasize a differentiation between forms of amnesia and hypermnesia. Finally, we highlight commonalities and distinctions of engram impairments on the cellular level across diseases independent of their pathogenic origins and discuss prospective therapeutic measures.

Memory compromise at extended delays in people with new-onset epilepsy

OBJECTIVE

Memory is one of the most sensitive markers of cognitive compromise in people with new-onset epilepsy. Nonetheless, around half of these cases score within the normal range on standard memory testing. Here we explore whether memory retention at a 1-week delay reveals otherwise undetected memory compromise in such individuals, and how it relates to subjective memory complaints and mood.

METHODS

Using a prospective design, 38 adults with new-onset epilepsy underwent baseline memory screening via telephone using an abbreviated Rey Auditory Verbal Learning Test (RAVLT). Psychological screening occurred via online questionnaires. One week later, without forewarning, participants completed three follow-up memory tasks. Of particular focus, we explored longer-term memory performances and forgetting trajectories in those individuals (n = 23) who demonstrated normal memory performances (scores >10th percentile) at baseline (30-min delay). Outcomes were compared to 32 healthy controls, matched for age, sex, and education.

RESULTS

As a group, people with epilepsy performed worse than controls on all memory measures, with 44 percent impaired at baseline testing. Of those unimpaired at baseline, the rate and volume of information loss over 1 week was significantly greater than for controls. Contextual memory performance at 1 week was also significantly poorer for people with epilepsy. At the individual level, the prevalence of impaired forgetting was not significantly different between patients and controls. Subjective memory complaints were not related to any objective tests but were strongly related to self-reported mood and anxiety symptoms.

SIGNIFICANCE

People with new-onset epilepsy show reduced memory at short and extended intervals. For those showing normal memory at baseline, information does appear to be forgotten more quickly than in healthy controls, though the effect is not large. The findings indicate that while extended delay memory testing is not essential in all new epilepsy cases, it could provide useful information for particular individuals.

PLAIN LANGUAGE STATEMENT

Memory problems are common in people with epilepsy shortly after seizure onset, however, many individuals still show normal memory performances on standard neuropsychological testing. Through testing memory at an extended timepoint (1 week), our study found that on average, these individuals showed a slightly quicker rate of forgetting over a 1-week period than people without a brain condition. Self-reported memory complaints in people with new epilepsy were unrelated to their actual memory skills on testing at short and long timepoints but were rather linked to lower mood and quality of life.

Clinical differences between transient epileptic amnesia (TEA) and recurrent transient global amnesia (r-TGA)

Both transient epileptic amnesia (TEA) and transient global amnesia (TGA) are clinically characterized by temporary amnesic symptoms. TEA involves recurring amnesic episodes, while TGA typically manifests as a singular occurrence. TGA rarely occurs repeatedly, known as recurrent TGA (r-TGA), which complicates differentiation, and raises the possibility of overlap between two disorders. Given the effectiveness of suitable antiseizure medications (ASMs) in treating TEA, accurate diagnosis of the initial event is crucial. In this study, We retrospectively analyzed cases of sudden-onset amnesia at Juntendo University Hospital over the past 14 years. Our investigation identified a total of 17 patients with TEA who met the criteria established by Zeman, along with a total of 9 patients with r-TGA meeting Hodges' criteria. Compared to r-TGA, TEA exhibited a higher recurrent rate, shorter symptoms, more additional symptoms, and increased structural abnormalities on head magnetic resonance imaging (MRI), and more abnormalities electroencephalography (EEG). Moreover, individual amnestic episode duration varied in both TEA and r-TGA. Our study reveals that TGA retains key features in recurrent cases and demonstrates distinctions from TEA. Nevertheless, distinguishing between the two conditions based solely on initial episodes remains challenging.

Accelerated long-term forgetting in patients with acquired brain injury

OBJECTIVE

Recent research suggests that patients with neurological disorders without overt seizures may also experience accelerated long-term forgetting (ALF). This term describes unimpaired learning and memory performance after standard retention intervals, but an excessive rate of forgetting over delays of days or weeks. The objective of this retrospective study was to investigate ALF in patients with an acquired brain injury (ABI) and to associate memory performance with executive functions.

METHODS

Verbal memory performance (short-term recall, 30-min recall, 1-week recall) was assessed in 34 adult patients with ABI and compared to a healthy control group (n = 54) using an auditory word learning and memory test.

RESULTS

Repeated measure analysis showed significant effects of time and group as well as interaction effects between time and group regarding recall and recognition performance. Patients with ABI had a significantly impaired 1-week recall and recognition performance compared to the healthy control group. Correlations between recall performance and executive functions were nonsignificant.

DISCUSSION

Our results demonstrate that non-epileptic patients with ABI, especially patients with frontal and fronto-temporal lesions, are prone to ALF. Additionally, our data support the assumption that ALF results from a consolidation impairment since verbal recall and recognition were impaired in patients with ABI.

Could Accelerated Long-Term Forgetting Be a Feature of the Higher Rate of Memory Complaints Associated with Subjective Cognitive Decline? An Exploratory Study

Background

Recently, subjective cognitive decline (SCD) was proposed as an early risk factor for future Alzheimer's disease (AD).

Objective

In this study, we investigated whether accelerated long-term forgetting (ALF), assessed with extended testing intervals than those adopted in clinical practice, might be a cognitive feature of SCD. Using an explorative MRI analysis of the SCD sample, we attempted to investigate the areas most likely involved in the ALF pattern.

Methods

We recruited 31 individuals with SCD from our memory clinic and subdivided them based on their rate of memory complaints into mild SCDs (n = 18) and severe SCDs (n = 13). A long-term forgetting procedure, involving the recall of verbal and visuo-spatial material at four testing delays (i.e., immediate, 30 min, 24 h, and 7 days post-encoding) was used to compare the two sub-groups of SCDs with a healthy control group (HC; n = 16).

Results

No significant between-group difference was found on the standard neuropsychological tests, nor in the immediate and 30 min recall of the experimental procedure. By contrast, on the verbal test severe SCDs forgot significantly more than HCs in the prolonged intervals (i.e., 24 h and 7 days), with the greatest decline between 30 min and 24 h. Finally, in the whole SCD sample, we found significant associations between functional connectivity values within some cortical networks involved in memory (default mode network, salience network, and fronto-parietal network) and verbal long-term measures.

Conclusions

Our preliminary findings suggest that long-term forgetting procedures could be a sensitive neuropsychological tool for detecting memory concerns in SCDs, contributing to early AD detection.

Delayed episodic memory recall after one week is associated with executive functions and divided attention in pediatric epilepsy patients

AIM

Recent studies suggest that although children with epilepsy may show normal learning and memory performance, accelerated long-term forgetting (ALF) may become evident over time. Our study examined associations between delayed episodic memory performance (recall 1-week after learning) and executive functions.

METHOD

A consecutive sample of children with a diagnosis of idiopathic epilepsy with focal or generalized seizures, without morphologic or metabolic abnormalities (n = 20, mean age: 11.70 years) was compared to an IQ-matched healthy control group (n = 20, mean age: 11.55 years). We also assessed parents' and children's rating of forgetting in everyday life and explored its association with delayed episodic memory recall.

RESULTS

Similar to results from recent studies of pediatric patients with temporal lobe epilepsy or genetic generalized epilepsy, our pediatric epilepsy patients showed a significantly elevated recall loss over time, although verbal learning, immediate and 30-minute recall was comparable to the matched control group. Additionally, delayed memory recall in patients was moderately associated with their subjective rating of forgetting, as well as with executive functions (verbal fluency and switching) and divided attention.

INTERPRETATION

We assume that executive functions play a crucial role in deep memory encoding, facilitating stronger and more enduring memory traces. Given that approximately 20% of epilepsy patients - compared to a healthy reference sample - had a significantly reduced delayed recall and due to the clinical relevance of long-term memory, age-appropriate standard norms for free memory recall after 1-week are desirable.

Transient epileptic amnesia: a retrospective cohort study of 127 cases, including CSF amyloid and tau features

BACKGROUND

Transient epileptic amnesia (TEA) is a late-onset epilepsy syndrome encompassing transient iterative amnesias and interictal cognitive impairment, two features that overlap with incipient neurodegenerative dementias. We, therefore, examined the yield of CSF amyloid and tau biomarkers in TEA.

METHODS

In this retrospective study, 127 TEA patients with unremarkable imaging findings were divided into 2 groups, namely, CSF (n = 71) and no-CSF (n = 56). Both were compared for demographics; medical history; baseline neurological, cognitive, and behavioral features; baseline mesial temporal lobe atrophy; and cognitive follow-up at a median of 13 months. CSF samples were examined for amyloid β-42 peptide as well as phospho-tau and total-tau levels.

RESULTS

At baseline, the CSF-TEA group had significantly (p < 0.01) more frequent mild parkinsonism (42.9% vs. 20%) and cognitive concerns (31% vs. 10.7%), a more blunted sense of smell (34.3% vs. 9.4%), a lower baseline MMSE score (27 vs. 28.9), a more frequent amnestic mild cognitive impairment profile (69% vs. 42.6%), and more atrophic hippocampal changes. At follow-up, the CSF-TEA group had significantly (p < 0.01) lower MMSE scores (27.8 vs. 28.9). CSF analyses revealed amyloid and/or tau changes in 27 patients (38%), including an Alzheimer's disease (AD) profile in 17 (24%).

CONCLUSIONS

This study shows a good diagnostic value of CSF sampling in a specific population of TEA with characteristics suggestive of incipient degenerative diseases (i.e., red flags). It argues for TEA being the inaugurating feature in some cases of AD. More broadly, our results suggest an etiological heterogeneity in TEA.

Accelerated long-term forgetting of recall and recognition memory in people with epilepsy

PURPOSE

Persons with epilepsy (PWE) report memory deficits as one of the most distressing aspects of their disorder. Recently, a long-term memory deficit known as Accelerated Long-Term Forgetting (ALF) has been described in PWE. ALF is characterized by the initial retention of learned information, followed by an accelerated rate of memory decay. However, the rate of ALF varies widely across literature and it is unclear how it impacts different memory retrieval types. The current study aimed to capture the time course of ALF on both free recall and recognition memory using a movie-based task in PWE.

METHODS

A sample of 30 PWE and 30 healthy comparison (HC) subjects watched a nature documentary and were tested on their recall and recognition of the film's content immediately after viewing and at delays of 24 hours, 48 hours, and 72 hours. Participants also rated the confidence they had in their recognition memory trial responses.

RESULTS

For recall, PWE exhibit ALF at 72 hours (β = -19.840, SE = 3.743, z(226) = -5.301, p < 0.001). For recognition, PWE had decreased performance compared to controls at the 24-hour (β = -10.165, SE = 4.174, z(224) = -3.166, p = 0.004), 48-hour (β = -8.113, SE = 3.701, z(224) = -2.195, p = 0.044), and 72-hour (β = -10.794, SE = 3.017, z(224) = -3.295, p = 0.003) delays. The PWE group showed positive correlations (tau = 0.165, p < 0.001) between confidence ratings and accuracy, with higher confidence reflecting successful recognition. PWE were 49% less likely to answer either retrieval type correctly at 72 hours (OR 0.51, 95% CI [0.35, 0.74], p < 0.001). Left hemispheric seizure onset decreased the odds of successful retrieval by 88% (OR 0.12, 95% CI [0.01, 0.42], p = 0.019).

CONCLUSIONS

These findings provide evidence of ALF in PWE, with a differential impact on recall and recognition memory. This further supports the call to include ALF assessments in standard memory evaluations in PWE. Additionally, identifying the neural correlates of ALF in the future will be important in developing targeted therapies to alleviate the burden of memory impairment for PWE.

How May a Brief Seizure Lead to Prolonged Epileptic Amnesia?

Pure amnestic seizures are defined as self-limited episodes with isolated, anterograde memory loss and have been attributed to bilateral dysfunction of mesial temporal structures. This type of seizure can occur in patients with different forms of temporal lobe epilepsy and has been more recently associated with a late-onset epileptic syndrome, called transient epileptic amnesia (TEA). The mechanisms of such prolonged manifestations are not well known and notably its ictal or post-ictal origin remains poorly understood. We report a case of prolonged anterograde amnesia (lasting several hours) following a brief seizure induced by stimulation of the left entorhinal cortex, recorded during stereo-EEG (SEEG). This episode was associated with prolonged changes in the intracerebral EEG signal complexity (entropy) within bilateral mesial temporal structures, particularly the entorhinal cortices, with a progressive normalization paralleling the clinical recovery. Our case shows that long-lasting (hours) memory impairment may follow brief seizure that led to prolonged electrophysiological signals alterations in bilateral mesial temporal structures.

Chemo-kindling in adult zebrafish alters spatial cognition but not social novelty recognition

In the past decades, zebrafish have gathered immense attention and importance in the field of neurological sciences. In the case of epilepsy, zebrafish have appeared as a promising acute animal model for the screening and identification of potential antiepileptic molecules. However, the necessity for establishing competent chronic models of epilepsy in zebrafish is apparent. In this regard, recently we developed a chemo-kindling zebrafish model with a better clinical resemblance. In the present study, an attempt to examine the effect of pentylenetetrazole (PTZ)-induced kindling on the cognitive functions of zebrafish was made. In brief, adult zebrafish were repetitively given a sub-effective concentration of PTZ, till the onset of clonic-tonic seizures, entitled as kindled. Thereafter, T-maze test and social recognition memory test were conducted to evaluate spatial memory and social novelty recognition memory of the fish. At the end, both the groups were sacrificed and the brains were isolated to estimate neurotransmitter and gene expression levels. It was observed that PTZ kindling induced spatial cognition deficits and lower social exploration in zebrafish. However, it didn't change the novelty recognition memory of kindled zebrafish. The results of genes and neurotransmitters estimations in the brain also supported the behavioural findings. The results concluded that PTZ kindling alters spatial cognitive functions in adult zebrafish without affecting the social novelty recognition memory.

The Role of Aberrant Neural Oscillations in the Hippocampal-Medial Prefrontal Cortex Circuit in Neurodevelopmental and Neurological Disorders

The hippocampus (HPC) and medial prefrontal cortex (mPFC) have well-established roles in cognition, emotion, and sensory processing. In recent years, interests have shifted towards developing a deeper understanding of the mechanisms underlying interactions between the HPC and mPFC in achieving these functions. Considerable research supports the idea that synchronized activity between the HPC and the mPFC is a general mechanism by which brain functions are regulated. In this review, we summarize current knowledge on the hippocampal-medial prefrontal cortex (HPC-mPFC) circuit in normal brain function with a focus on oscillations and highlight several neurodevelopmental and neurological disorders associated with aberrant HPC-mPFC circuitry. We further discuss oscillatory dynamics across the HPC-mPFC circuit as potentially useful biomarkers to assess interventions for neurodevelopmental and neurological disorders. Finally, advancements in brain stimulation, gene therapy and pharmacotherapy are explored as promising therapies for disorders with aberrant HPC-mPFC circuit dynamics.

Accelerated long-term forgetting in neurodegenerative disorders: A systematic review of the literature

Accelerated Long-term Forgetting (ALF) is a memory deficit characterised by normal retention up to relatively short intervals (e.g., minutes, hours) with increased forgetting over longer periods (e.g., days, weeks). ALF is often underestimated due to a lack of common memory assessments beyond 30-60 min. The purpose of this review was to provide an overview of ALF occurrence in neurodegenerative disorders, evaluating whether it can be considered a cognitive deficit useful for diagnosing and monitoring patients. We included 19 experimental studies that investigated ALF in neurodegenerative disorders. Most papers were focused on Alzheimer's disease (AD) dementia and related forms of cognitive decline (Mild Cognitive Impairment, Subjective Cognitive decline, Pre-symptomatic subjects at risk of AD dementia). The major finding of the present work concerns the presence of ALF in very early forms of cognitive decline related to AD. These findings, supporting the hypothesis that ALF is a subtle and undetected hallmark of pre-clinical AD, highlights the importance of investigating forgetting over a longer period and devising standardised measures to be included in clinical practice.

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.

Forgetting the Unforgettable: Transient Global Amnesia Part II: A Clinical Road Map

Transient global amnesia (TGA) is a clinical syndrome characterized by the sudden onset of a temporary memory disorder with profound anterograde amnesia and a variable impairment of the past memory. Usually, the attacks are preceded by a precipitating event, last up to 24 h and are not associated with other neurological deficits. Diagnosis can be challenging because the identification of TGA requires the exclusion of some acute amnestic syndromes that occur in emergency situations and share structural or functional alterations of memory circuits. Magnetic Resonance Imaging (MRI) studies performed 24–96 h after symptom onset can help to confirm the diagnosis by identifying lesions in the CA1 field of the hippocampal cornu ammonis, but their practical utility in changing the management of patients is a matter of discussion. In this review, we aim to provide a practical approach to early recognition of this condition in daily practice, highlighting both the lights and the shadows of the diagnostic criteria. For this purpose, we summarize current knowledge about the clinical presentation, diagnostic pathways, differential diagnosis, and the expected long-term outcome of TGA.

Accelerated Long-Term Forgetting: Prolonged Delayed Recognition as Sensitive Measurement for Different Profiles of Long-Term Memory and Metacognitive Confidence in Stroke Patients

OBJECTIVE

Deficits in episodic memory are frequently reported after ischemic stroke. In standard clinical care, episodic memory is assessed after a 20-30 min delay, with abnormal memory decay over this period being characterized as rapid forgetting (RF). Previous studies have shown abnormal forgetting over a prolonged interval (days to weeks) despite normal acquisition, referred to as accelerated long-term forgetting (ALF).

METHOD

We examined whether ALF is present in stroke patients (N = 91) using immediate testing (T1), testing after a short delay (20-30 min, T2), and testing after a prolonged delay (one week, T3). Based on performance compared to matched controls (N = 85), patients were divided into (1) patients without forgetting, (2) patients with RF between T1 and T2, and (3) patients with ALF at T3. Furthermore, confidence ratings were assessed.

RESULTS

ALF was present in a moderate amount of stroke patients (17%), but ALF was even more prevalent in our stroke sample than RF after a 20-30 min delay (which was found in only 13% of our patients). Patients reported a lower confidence for their responses, independent of their actual performance.

CONCLUSIONS

Adding a one-week delayed measurement may potentially assist in identifying patients with memory decrements that may otherwise go undetected.

Transient epileptic amnesia is significantly associated with discrete CA1-located hippocampal calcifications but not with atrophic changes on brain imaging

BACKGROUND

The exact etiology of transient epileptic amnesia (TEA) is currently unknown. In older individuals, common neurodegenerative dementias and small-vessel diseases (SVDs) could be major contributors. We examined these hypotheses on the basis of imaging analysis.

METHODS

In total, 36 TEA patients were compared with 25 healthy controls for (1) cortical atrophic changes (in the mesial temporal, frontal, anterior temporal, and parietal regions) using four established MRI-based visual rating scales, and for (2) SVD evidence using two MRI-based visual rating scales (Fazekas and MARS scores). In 24 TEAs cases, there were also brain CT scans available that were compared with 57 controls for the presence of hippocampal calcifications (HCs).

RESULTS

We did not find significant differences in cortical atrophy between TEAs and controls, nor did we observe a different SVD brain load on MRI. However, TEAs were significantly associated (p < 0.01) with uni- or bilateral CA1-located HCs in half of the patients compared with the controls (less than 20 %).

CONCLUSIONS

This study argues in favor of a hippocampal-restricted SVD (as indicated by HCs) as one of the major etiologies of TEA, while neurodegenerative dementias are probably minor causes. It furthermore highlights the pivotal role of the CA1 hippocampal subfield in the pathophysiology of this syndrome.

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.

A reappraisal of acute doses of benzodiazepines as a model of anterograde amnesia

OBJECTIVE

Acute administration of benzodiazepines is considered a pharmacological model of general organic anterograde amnesias (OAA). We sought to determine which type of amnesia these drugs best model by comparing the effects of diazepam with those reported in amnesiacs regarding working memory capacity (WMC), susceptibility to retroactive interference (RI), and accelerated forgetting.

METHODS

In this double-blind, parallel-group design study, 30 undergraduates were randomly allocated to acute oral treatments with 15 mg diazepam or placebo. WMC and story recall were assessed pre- and post-treatment. Story presentation was succeeded by 10 min of RI (spotting differences in pictures) or minimal RI (doing nothing in a darkened room). Delayed story recall was assessed under diazepam and 7 days later in a drug-free session to assess accelerated forgetting.

RESULTS

Recall of stories encoded under diazepam, whether reactivated or not, was severely impaired (anterograde amnesia). However, diazepam did not impair WMC, increase susceptibility to RI, or accelerate forgetting.

CONCLUSIONS

Diazepam's amnestic effects mirror those in patients with probable severe medial temporal damage, mostly restricted to initial consolidation and differ from other OAA (Korsakoff syndrome, frontal, transient epileptic, posttraumatic amnesia, and most progressive amnesias) in terms of WMC, susceptibility to RI and accelerated forgetting.

Worth the Wait: Delayed Recall after 1 Week Predicts Cognitive and Medial Temporal Lobe Trajectories in Older Adults

METHOD

Clinically normal older adults (52-92 years old) were followed longitudinally for up to 8 years after completing a memory paradigm at baseline [Story Recall Test (SRT)] that assessed delayed recall at 30 min and 1 week. Subsets of the cohort underwent neuroimaging (N = 134, mean age = 75) and neuropsychological testing (N = 178-207, mean ages = 74-76) at annual study visits occurring approximately 15-18 months apart. Mixed-effects regression models evaluated if baseline SRT performance predicted longitudinal changes in gray matter volumes and cognitive composite scores, controlling for demographics.

RESULTS

Worse SRT 1-week recall was associated with more precipitous rates of longitudinal decline in medial temporal lobe volumes (p = .037), episodic memory (p = .003), and executive functioning (p = .011), but not occipital lobe or total gray matter volumes (demonstrating neuroanatomical specificity; p > .58). By contrast, SRT 30-min recall was only associated with longitudinal decline in executive functioning (p = .044).

CONCLUSIONS

Memory paradigms that capture longer-term recall may be particularly sensitive to age-related medial temporal lobe changes and neurodegenerative disease trajectories. (JINS, 2020, xx, xx-xx).

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.

Fatigue and cognitive functions in epilepsy: A review of the literature

Epilepsy is a common neurological disorder affecting people of all ages and inducing cognitive impairments. While research has advanced in terms of neuropsychological enquiries of the various epileptic syndromes, the understanding of more complex and ill-defined phenomena such as fatigue is still unclear for epilepsy. It is suggested that fatigue is not just physical, but there can also be a cognitive element to it. Although studies in other conditions have been able to identify a relationship between fatigue and particular cognitive components, similar evidence is sparse in patients with epilepsy. This review is an attempt to gather, analyze, integrate, and critically discuss available information on fatigue and its rapport with various aspects of epilepsy, particularly focusing on cognition. Future directions are discussed urging researchers to target cognitive components of fatigue.

A Review of Accelerated Long-Term Forgetting in Epilepsy

Accelerated long-term forgetting (ALF) is a memory disorder that manifests by a distinct pattern of normal memory for up to an hour after learning, but an increased rate of forgetting during the subsequent hours and days. The topic of ALF has gained much attention in group studies with epilepsy patients and the phenomenon has been shown to have contradictory associations with seizures, epileptiform activity, imaging data, sleep, and antiepileptic medication. The aim of this review was to explore how clinical and imaging data could help determine the topographic and physiological substrate of ALF, and what is the possible use of this information in the clinical setting. We have reviewed 51 group studies in English to provide a synthesis of the existing findings concerning ALF in epilepsy. Analysis of recently reported data among patients with temporal lobe epilepsy, transient epileptic amnesia, and generalized and extratemporal epilepsies provided further indication that ALF is likely a disorder of late memory consolidation. The spatial substrate of ALF might be located along the parts of the hippocampal-neocortical network and novel studies reveal the increasingly possible importance of damage in extrahippocampal sites. Further research is needed to explore the mechanisms of cellular impairment in ALF and to develop effective methods of care for patients with the disorder.

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.

Acute amnestic syndromes

Acute amnestic syndromes are usually rare clinical events occurring in emergency situations. Etiological diagnosis can be challenging and underlying causes diverse. They can be transient and totally reversible, or accompanied by other neurological symptoms resulting in serious and irreversible brain damage. Pathophysiology of these syndromes mainly corresponds to structural or functional alteration of memory circuits, including those in the hippocampus. One of the most frequent forms is transient global amnesia (TGA), characterized by sudden onset of anterograde amnesia lasting less than 24  hours, in the absence of other neurological signs or symptoms. Another acute and transient memory disorder is transient epileptic amnesia (TEA), due to focal crisis activity. Stroke injuries occurring at strategic memory-related sites can also present as sudden episodes of amnesia. In addition to neurological etiologies, amnesia may be a symptom of a psychiatric disorder (dissociative amnesia). Traumatic brain injuries, autoimmune encephalitis and acute toxic metabolic disorders can also cause amnesia and should be included among the differential diagnoses. In this review, we summarize the most relevant clinical findings in acute amnestic syndromes, and discuss the different ancillary tests needed to establish a correct diagnosis and management as well the best treatment options. Relevant anatomical and pathophysiological aspects underlying these conditions will be also be presented.

Accelerated long-term forgetting is not evident in adults with genetic generalized epilepsy irrespective of the paradigm used

Accelerated long-term forgetting (ALF) is a recently discovered memory disorder characterized by intact acquisition and retention over short delays, followed by abnormally fast rates of forgetting. Accelerated long-term forgetting has been repeatedly found in children, but not in adults, with genetic generalized epilepsy (GGE). It is possible that this discrepancy is due to a difference in paradigms used in these studies. The current study aimed to determine whether adults with GGE displayed ALF using two paradigms, one that required complete learning and another one that did not. In addition, we explored the relationships with everyday memory difficulties, working memory, mood, and epilepsy variables. Fourteen adults with GGE were compared with 16 healthy controls on two verbal memory tests: a modified version of the California Verbal Learning Test learned to a criterion of 100% (complete learning) and Logical Memory from the Wechsler Memory Scale (Fourth Edition) presented only once (incomplete learning). Recall was tested at 2 min, 30 min, and 1 week, and recognition at 1 week only. Working memory, everyday memory, and mood were also assessed. We found no evidence of ALF on either of the two verbal memory paradigms on recall or recognition tests although patients displayed significantly poorer working memory. Moreover, patients with GGE reported significantly more memory difficulties in everyday life, and these were associated with greater mood disturbances but not with memory tests scores. Greater number of antiepileptic drugs and epilepsy severity also related to memory scores on some tests. Our study suggests that a difference in paradigms used to investigate ALF in children and adults with GGE is unlikely to explain the differences in findings. The study tentatively raises a hypothesis that developmental factors may play a role in ALF in patients with GGE; children with GGE may grow out of ALF. Nevertheless, this hypothesis would need to be tested in a longitudinal study that would follow patients from childhood to early adulthood.

Contribution of autobiographic memory impairment to subjective memory complaints in focal epilepsy

"My memory is terrible!" is a common refrain among people with epilepsy, but such complaints are not reliably linked to poor performances on standard tests of memory. Negative affect like depression and anxiety are the most robust predictor of these complaints; however, neither do they entirely account for the phenomenon. The contribution of autobiographic memory impairment to subjective memory complaints in focal epilepsy has not been well-explored despite autobiographic memory impairments being common in patients with epilepsy, and the face validity of relating day-to-day memory failings to such a personally relevant form of memory. The current study sought to clarify whether autobiographic memory dysfunction contributes to subjective complaints in epilepsy, above and beyond negative affect, objective memory impairment, and epileptological factors in a large sample of patients with drug-resistant focal epilepsy relative to healthy controls (N = 135). Patients were stratified into groups with mesial temporal (MT; n = 40) versus nonmesial temporal (NMT; n = 46) foci. Compared to controls (n = 46), both patient groups reported more bitter subjective memory complaints (p < 0.001, large effect size), demonstrated poorer episodic (p = 0.001, large effect size) and semantic autobiographical recall (p = 0.004, medium effect size), and had higher levels of depressive symptomatology (p = 0.011, medium effect size), and trait neuroticism (p = 0.015, medium effect size). Contrary to expectations, multiple regression analyses revealed that autobiographic memory function was not an independent predictor of subjective memory complaints in either group with epilepsy. In people with epilepsy with MT foci, objective verbal memory dysfunction, neuroticism, and female gender predicted memory complaints (R² = 0.70, p = 0.015), whereas only neuroticism predicted memory complaints in people with epilepsy with NMT foci (R² = 0.21, p = 0.001). Although patients' poor recall of their autobiographical memories did not contribute to their concerns about their day-to-day memory function, the findings indicate that the location of the epileptogenic focus can provide clues as to the underlying contributors to subjective memory complaints in focal epilepsy. Important clinical implications to stem from these findings include the need for clinicians to adopt a patient-tailored, multifactorial lens when managing memory complaints in people with epilepsy, taking into account both psychological and cognitive factors.

Transient Epileptic Amnesia: A Treatable Cause of Spells Associated With Persistent Cognitive Symptoms

Objective: To characterize the clinical, EEG, and neuroimaging profiles of transient epileptic amnesia (TEA).

Methods: We performed a retrospective analysis of patients diagnosed with TEA at the Mayo Clinic Minnesota from January 1, 1998 to September 21, 2017. Diagnostic criteria included the presence of recurrent episodes of transient amnesia with preservation of other cognitive functions and evidence for epilepsy [epileptiform abnormalities on EEG, clinical features of seizures, or symptomatic response to anti-seizure medications (ASMs)].

Results: Nineteen patients were identified (14 men, 5 women) with median onset age 66 years and median time to diagnosis 2 years. Thirteen patients (68%) reported persistent cognitive/behavioral symptoms, including 4 (21%) for whom these were the chief presenting complaints. EEG revealed epileptiform abnormalities involving the frontal and/or temporal regions in 12/19 individuals (63%), including activation during sleep in all of these cases. In numerous cases, sleep and prolonged EEG evaluations identified abnormalities not previously seen on shorter or awake-state studies. Brain MRI revealed focal abnormalities in only 4/19 cases (21%). FDG-PET identified focal hypometabolism in 2/8 cases where it was performed, both involving the frontal and/or temporal regions. Anti-seizure therapy, most often with a single agent, resulted in improvement (reduction in spell frequency and/or subjective improvement in interictal cognitive/behavioral complaints) in all 17 cases with available follow-up.

Conclusions: TEA is a treatable cause of amnestic spells in older adults. This syndrome is frequently associated with persistent interictal cognitive/behavioral symptoms and thus can be mistaken for common mimics. In the appropriate clinical context, our findings support the use of early prolonged EEG with emphasis on sleep monitoring as a key diagnostic tool. FDG-PET may also complement MRI in distinguishing TEA from neurodegenerative disease when suspected.

Accelerated long-term forgetting in presymptomatic autosomal dominant Alzheimer's disease: a cross-sectional study

Background

Tests sensitive to presymptomatic changes in Alzheimer's disease could be valuable for clinical trials. Accelerated long-term forgetting—during which memory impairment becomes apparent over longer periods than usually assessed, despite normal performance on standard cognitive testing—has been identified in other temporal lobe disorders. We assessed whether accelerated long-term forgetting is a feature of presymptomatic autosomal dominant (familial) Alzheimer's disease, and whether there is an association between accelerated long-term forgetting and early subjective memory changes.

Methods

This was a cross-sectional study at the Dementia Research Centre, University College London (London, UK). Participants were recruited from a cohort of autosomal dominant Alzheimer's disease families already involved in research at University College London, and had to have a parent known to be affected by an autosomal dominant Alzheimer's disease mutation, and not report any current symptoms of cognitive decline. Accelerated long-term forgetting of three tasks (list, story, and figure recall) was assessed by comparing 7-day recall with initial learning and 30-min recall. 7-day recognition was also assessed. Subjective memory was assessed using the Everyday Memory Questionnaire. The primary outcome measure for each task was the proportion of material retained at 30 min that was recalled 7 days later (ie, 7-day recall divided by 30-min recall). We used linear regression to compare accelerated long-term forgetting scores between mutation carriers and non-carriers (adjusting for age, IQ, and test set) and, for mutation carriers, to assess whether there was an association between accelerated long-term forgetting and estimated years to symptom onset (EYO). Spearman's correlation was used to examine the association between accelerated long-term forgetting and subjective memory scores.

Findings

Between Feb 17, 2015 and March 30, 2016, we recruited 35 people. 21 participants were mutation carriers (mean EYO 7·2 years, SD 4·5). Across the three tasks, we detected no differences between carriers and non-carriers for initial learning or 30-min recall. The proportion of material recalled at 7 days was lower in carriers than non-carriers for list (estimated difference in mean for list recall −30·94 percentage points, 95% CI −45·16 to −16·73; p=0·0002), story (–20·10, −33·28 to −6·91; p=0·0048), and figure (–15·41, −26·88 to −3·93; p=0·012) recall. Accelerated long-term forgetting was greater in carriers nearer to their estimated age at onset (p≤0·01 for all three tests). Mutation carriers' 7-day recognition memory was also lower across all tasks (list [mean difference −5·80, 95% CI −9·96 to −2·47; p<0·01], story [–6·84, −10·94 to −3·37; p<0·01], and figure [–17·61, −27·68 to −7·72; p<0·01] recognition). Subjective memory scores were poorer in asymptomatic carriers compared with non-carriers (adjusted difference in means 7·88, 95% CI 1·36 to 14·41; p=0·016), and we found a correlation between accelerated long-term forgetting and subjective memory in mutation carriers.

Interpretation

Accelerated long-term forgetting is an early presymptomatic feature of autosomal dominant Alzheimer's disease, which appears to pre-date other amnestic deficits and might underpin subjective memory complaints in Alzheimer's disease. Accelerated long-term forgetting testing might be useful in presymptomatic Alzheimer's disease trials.

Funding

MRC, NIHR, Alzheimer's Research UK, Dementias Platform UK, Dunhill Medical Trust, ERUK, Great Western Research, Health Foundation, Patrick Berthoud Trust.

Longitudinal study of accelerated long-term forgetting in children with genetic generalized epilepsy: Evidence of ongoing deficits

Accelerated long-term forgetting (ALF) is a recently described memory disorder characterised by adequate recall after short, but not long delays. Currently, the prevailing conceptualisation of ALF is of a seizure related phenomenon. The main aim of this study was to assess whether ALF subsides as epilepsy severity and seizures abate in children with genetic generalized epilepsy (GGE). Eighteen children with GGE were compared over time to 29 healthy controls on a range of cognitive measures. The primary outcome was a modified version of the California Verbal Learning Test for Children with a long delay (seven day) recall component. At approximately two years follow up, ALF was apparent, although epilepsy severity subsided and seizures resolved in many children. This result contrasts with the dominant conceptualisation of ALF being a seizure related phenomenon. Moreover, at follow-up, worse recall at the long delay was related to greater epilepsy severity at baseline and earlier age of seizure onset, but not to being seizure free at follow-up. While at follow-up worse recall at the long delay related to the worse baseline recall at the long delay, this recall did not relate to scores obtained on standardised memory tests at baseline. Our study suggests that ALF may not be seizure related and identifies factors associated with risk of ALF in children with GGE.

A single seizure selectively impairs hippocampal-dependent memory and is associated with alterations in PI3K/Akt/mTOR and FMRP signaling

Objective

A single brief seizure before learning leads to spatial and contextual memory impairment in rodents without chronic epilepsy. These results suggest that memory can be impacted by seizure activity in the absence of epilepsy pathology. In this study, we investigated the types of memory affected by a seizure and the time course of impairment. We also examined alterations to mammalian target of rapamycin (mTOR) and fragile X mental retardation protein (FMRP) signaling, which modulate elements of the synapse and may underlie impairment.

Methods

We induced a single seizure and investigated hippocampal and nonhippocampal memory using trace fear conditioning, novel object recognition (NOR), and accelerating rotarod to determine the specificity of impairment in mice. We used western blot analysis to examine for changes to cellular signaling and synaptic proteins 1 h, 24 h, and 1 week after a seizure. We also included a histologic examination to determine if cell loss or gross lesions might alternatively explain memory deficits.

Results

Behavioral results indicated that a seizure before learning leads to impairment of trace fear memory that worsens over time. In contrast, nonhippocampal memory was unaffected by a seizure in the NOR and rotarod tasks. Western analysis indicated increased hippocampal phospho‐S6 and total FMRP 1 h following a seizure. Tissue taken 24 h after a seizure indicated increased hippocampal GluA1, suggesting increased α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptor expression. Histologic analysis indicated that neither cell loss nor lesions are present after a single seizure.

Significance

The presence of memory impairment in the absence of damage suggests that memory impairment caused by seizure activity differs from general memory impairment in epilepsy. Instead, memory impairment after a single seizure is associated with alterations to mTOR and FMRP signaling, which leads to a disruption of synaptic proteins involved in consolidation of long‐term memory. These results have implications for understanding memory impairment in epilepsy.

Encoding-related brain activity and accelerated forgetting in transient epileptic amnesia

The accelerated forgetting of newly learned information is common amongst patients with epilepsy and, in particular, in the syndrome of transient epileptic amnesia (TEA). However, the neural mechanisms underlying accelerated forgetting are poorly understood. It has been hypothesised that interictal epileptiform activity during longer retention intervals disrupts normally established memory traces. Here, we tested a distinct hypothesis-that accelerated forgetting relates to the abnormal encoding of memories. We studied a group of 15 patients with TEA together with matched, healthy control subjects. Despite normal performance on standard anterograde memory tasks, patients showed accelerated forgetting of a word list over one week. We used a subsequent memory paradigm to compare encoding-related brain activity in patients and controls. Participants studied a series of visually presented scenes whilst undergoing functional MRI scanning. Recognition memory for these scenes was then probed outside the scanner after delays of 45 min and of 4 days. Patients showed poorer memory for the scenes compared with controls. In the patients but not the controls, subsequently forgotten stimuli were associated with reduced hippocampal activation at encoding. Furthermore, patients demonstrated reduced deactivation of posteromedial cortex regions upon viewing subsequently remembered stimuli as compared to subsequently forgotten ones. These data suggest that abnormal encoding-related activity in key memory areas of the brain contributes to accelerated forgetting in TEA. We propose that abnormally encoded memory traces may be particularly vulnerable to interference from subsequently encountered material and hence be forgotten more rapidly. Our results shed light on the mechanisms underlying memory impairment in epilepsy, and offer support to the proposal that accelerated forgetting may be a useful marker of subtle dysfunction in memory-related brain systems.

Neurocognitive problems in epilepsy

Cognitive dysfunction is one of the major contributors to the burden of epilepsy. It can significantly disrupt intellectual development in children and functional status and quality of life in adults. Epilepsy affects cognition through a number of mechanisms in complex interrelationship. Cognitive deficits in epilepsy may be treated indirectly through aggressive seizure control using anti-epileptic drugs or surgery, and by treating comorbid conditions such as depression. The beneficial effects of reducing seizures may offset the adverse cognitive side-effects of these therapies. Direct treatment of cognitive impairment in epilepsy mainly involves memory rehabilitation. Other direct treatments are mostly experimental and their evidence base is currently poor.

The evolution of accelerated long-term forgetting: Evidence from the TIME study

OBJECTIVE

Accelerated long-term forgetting (ALF) occurs when newly learned information decays faster than normal over extended delays. It has been recognised most frequently in temporal lobe epilepsy, including Transient Epileptic Amnesia (TEA), but can also be drug-induced. Little is known about the evolution of ALF over time and its impacts upon other memory functions, such as autobiographical memory (ABM). Here we investigate the long-term outcome of ALF and ABM in a group of patients with TEA and a single case of baclofen-induced ALF.

METHODS

Study 1 involved a longitudinal follow-up of 14 patients with TEA over a 10-year period. Patients repeated a neuropsychological battery, three ALF measures (with free recall probed at 30-min and 1-week), and a modified Autobiographical Memory Interview (MAMI). Performance was compared with a group of healthy age-matched controls. In Study 2, patient CS, who previously experienced baclofen-induced ALF, was followed over 4 years, and re-tested now, 18 months after ceasing baclofen. CS repeated a neuropsychological battery, three ALF experimental tasks (each probed after 30 min and 1 week), and a modified autobiographical interview (AI). Her performance was compared with healthy age-matched controls.

RESULTS

On ALF measures, the TEA group performed significantly below controls, but when analysed individually, 4 of the 7 patients who originally showed ALF no longer did so. In two, this was accompanied by improvements in ABM for recent but not remote memory. Patient CS no longer demonstrated ALF on standard lab-based tests and now appeared to retain new episodic autobiographical events with a similar degree of episodic richness as controls.

CONCLUSION

Long-term follow up suggests that ALF can resolve, with improvements translating to recent ABM in some cases.

Performance on a 1-week delayed recall task is associated with medial temporal lobe structures in neurologically normal older adults

OBJECTIVE

Traditional episodic memory tests employ a delayed recall length ranging from 10 to 30 min. The neurobiological process of memory consolidation extends well beyond these time intervals, however, raising the possibility that these tests might not be fully sensitive to the subtle neurocognitive changes found in early disease or age-related decline. We aimed to determine the sensitivity of a 1-week delayed recall paradigm to medial temporal lobe (MTL) structure among neurologically normal older adults.

METHODS

One hundred and forty functionally intact, older adults (mean age = 75.8) completed a story recall test in which participants learned to 90% criterion. Recall was tested after 30-min and 1-week. Participants also completed a standardized list learning task with a 20-min delay (n = 129) and a structural brain MRI. The MTL, including the parahippocampal gyrus, hippocampus, and entorhinal, was our primary region of interest.

RESULTS

Controlling for age, education, gender and total intracranial volume, the standard 20- and 30-min recalls showed no significant relationship with MTL. In contrast, 1-week recall was uniquely associated with MTL structure (partial r = .24, p = .006), specifically entorhinal (partial r = .27; p = .001) and hippocampal (partial r = .21, p = .02) volumes.

CONCLUSION

Memory paradigms that utilize 1-week delays are more sensitive than standard paradigms to MTL volumes in neurologically normal older adults. Longer delay periods may improve detection of memory consolidation abilities associated with age-related, and potentially pathological, neurobehavioral change.

Accelerated long-term forgetting and autobiographical memory disorders in temporal lobe epilepsy: One entity or two?

Temporal lobe epilepsy (TLE) is a type of epilepsy that often has a negative impact on patients' memory. Despite the importance of patients' complaints in this regard, the difficulties described by these patients are often not easy to demonstrate through a standard neuropsychological assessment. Accelerated long-term forgetting and autobiographical memory disorders are the two main memory impairments reported in the literature in patients with TLE. However, the methods used by different authors to evaluate long-term memory and autobiographical memory are heterogeneous. This heterogeneity can lead to differences in the observed results as well as how they are interpreted. Yet, despite the methodological differences, objectification of such memory deficits appears to be both specific and robust within this patient population. Analysis of the literature shows that accelerated long-term forgetting and autobiographical memory disorders share the same clinical characteristics. This leads to the assumption that they are, in fact, only one entity and that their evaluation may be done through a single procedure. Our proposal is to place this evaluation within the context of memory consolidation disorders. With such a perspective, evaluation of accelerated forgetting in autobiographical memory should consist of identifying a disorder in the formation and/or recovery of new memory traces.

Accelerated Long Term Forgetting in patients with focal seizures: Incidence rate and contributing factors

BACKGROUND

Accelerated Long Term Forgetting (ALF) is usually defined as a memory impairment that is seen only at long delays (e.g., after days or weeks) and not at shorter delays (e.g., 30min) typically used in clinical settings. Research indicates that ALF occurs in some patients with epilepsy, but the incidence rates and underlying causes have not been established. In this study, we considered these issues.

METHODS

Forty-four patients with a history of focal seizures were tested at 30min and 7day delays for material from the Rey Auditory Verbal Learning Test (RAVLT) and Aggie Figures Test. Recently published norms from a matched group of 60 control subjects (Miller et al., 2015 ) were used to determine whether patients demonstrated ALF, impairment at 30min or intact memory performance.

RESULTS

The incidence of ALF in the epilepsy patients (18%) was >3 times higher than normal on the RAVLT, but no different (7%) from the incidence in normal subjects on the Aggie Figures. A different, but again significantly high, proportion of patients (36%) showed shorter-term memory deficits on at least one task. ALF was found mainly in patients with temporal-lobe epilepsy, but also occurred in one patient with an extratemporal seizure focus. Presence of a hippocampal lesion was the main predicting factor of ALF.

CONCLUSIONS

Many patients with a focal seizure disorder show memory deficits after longer delays that are not evident on standard assessment. The present study explored the factors associated with this ALF memory profile. These new findings will enhance clinical practice, particularly the management of patients with memory complaints.

On the nose: Olfactory disturbances in patients with transient epileptic amnesia

OBJECTIVE

While olfactory hallucinations are relatively rare in epilepsy, a high prevalence (up to 42%) has been reported in one form - Transient Epileptic Amnesia (TEA). TEA is characterized by recurring amnestic seizures and is commonly associated with persistent interictal memory deficits. Despite reports of changes in smell, olfactory ability has not been objectively assessed in this group. The aim of this study was to measure olfactory ability in patients with TEA and explore whether olfactory symptoms relate to other clinical variables.

METHODS

Fifty-five participants with TEA were recruited from The Impairment of Memory in Epilepsy project database. The presence of olfactory symptoms was obtained via case notes and clinical interview. Participants completed questionnaires to evaluate their olfaction and memory function subjectively. Olfactory ability was measured using the University of Pennsylvania Smell Identification Test (UPSIT). TEA participants' performance was compared to 50 matched healthy control participants. A subset of TEA participants (n=26) also completed a battery of memory tests including standard neuropsychological measures, and assessment of accelerated long-term forgetting and autobiographical memory.

RESULTS

Olfactory hallucinations were reported in 55% of patients with TEA. A significant reduction in smell identification (UPSIT) was found between patients with TEA and healthy controls (p<0.001). Epilepsy variables, including history of olfactory hallucinations, were not predictive of olfactory ability. Patients reported ongoing memory difficulties and performed below normative values on objective tests. While no correlation was found between objective measures of memory and olfactory performance, subjective complaints of route finding difficulty was associated with UPSIT score.

CONCLUSIONS

Impairments in odor identification are common in patients with TEA and exceed changes that occur in normal aging. Olfactory hallucinations occurs in approximately half of patients with TEA, but do not always coincide with reduced sense of smell. Olfactory impairment and interictal memory problems both occur frequently in TEA but are not closely associated.

[Transient epileptic amnesia]

Transient epileptic amnesia (TEA) is a sub-type of mesial temporal lobe epilepsy, with amnesic seizures. TEA is characterized by recurrent episodes of amnesia. Diagnostic criteria are available for TEA, and these memory disturbances should not be misdiagnosed with transient global amnesia. The neuropsychological evaluation is normal, however, autobiographical memory impairment is present in 70% of the cases and accelerated long term forgetting in 44%. When a patient complains of memory disturbances, especially autobiographical memory, TEA must be considered especially if there was an amnesic episode and symptoms that suggest temporal epilepsia. Video electroencephalography monitoring of sleep is a precious diagnostic tool, as epileptiform activities are found during sleep in 83% cases. TEA is pharmaco-sensitive, with full treatment response in 73 to 96% of the cases.

Transient Epileptic Amnesia over twenty years: Long-term follow-up of a case series with three detailed reports

Purpose

Transient Epileptic Amnesia (TEA) is a form of adult onset temporal lobe epilepsy characterised by ictal amnesia. The amnesic seizures are often accompanied by interical memory disturbance, involving autobiographical amnesia and accelerated long-term forgetting. Short-term follow-up studies suggest a relatively stable cognitive profile once treated, but recent case reports raise concerns regarding the risk of developing Alzheimer’s Disease (AD). The current study reports clinical and cognitive outcome in TEA patients over a 20-year period.

Methods

A cohort of ten TEA patients first reported in 1998 were followed up at two time intervals, each 10 years apart. Information regarding clinical outcomes and subjective reports of memory functioning was gained via GP records and clinical interview. Objective memory function was determined at each time point via a comprehensive neuropsychological assessment, where possible.

Results

Information was obtained for nine of the original 10 participants. Over the 20-year period, 4 participants died, with no indication of dementia prior to death. One participant was diagnosed with Vascular Dementia. Seizures were generally well controlled. Subjective reports of memory varied, including no concerns, stable memory difficulties, and worsening memory. Neuropsychological assessment at 10 years showed stable performances across most measures. At the 20-year follow up, there was no evidence of a general cognitive decline. Participants showed stability on some measures, with reductions on others. Performance was not consistent with AD.

Conclusions

No elevated risk of dementia was evident from this TEA series. Although memory difficulties persist over time, the prognosis of TEA appears generally benign.

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.

Four-hour delayed memory recall for stories: Theoretical and clinical implications of measuring accelerated long-term forgetting

It has been noted that clinical neuropsychological assessment is "blind" to certain abnormalities of consolidation that occur beyond standard 30-min delay intervals. For example, normal forgetting at 30-min delays has been followed by enhanced forgetting at longer delays in temporal-lobe epilepsy, termed accelerated long-term forgetting (ALF). To evaluate whether ALF could be identified in the neuropsychological assessment of a small sample of examinees with head injuries or other neurological diagnoses (n = 42), a 4-hr delayed recall condition was added to the Logical Memory subtest of the Wechsler Memory Scale-Third Edition. A small percentage of examinees (5/42 or 11%), despite exhibiting unimpaired story recall immediately and after 30-min delays, showed increased forgetting when compared with the average retention of stories (M = 0.83, SD = 0.17) after a 4-hr delay. Three of these 5 examinees also had impaired scores on 20-min delayed recall of the California Verbal Learning Test-Second Edition (CVLT-II) and would have been identified as having memory impairment without an extended, 4-hr delayed recall. In fact, the highest correlation among memory indexes was between 4-hr delayed recall of stories and delayed recall of the CVLT-II word list (r = .59, p < .0001), suggesting different consolidation rates for relational and nonrelational material.