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

Inhibition of the Integrated Stress Response Prevents Natural Forgetting and Corrects Accelerated Forgetting Associated with Epilepsy

The neural mechanisms underlying the natural and maladaptive forgetting of established memory remain largely unknown. Brain disease states might hijack the physiological forgetting mechanisms, resulting in maladaptive forgetting such as accelerated forgetting that contributes to cognitive decline in various neurologic conditions including epilepsy. Based on the key role of the integrated stress response (ISR) in memory storage and maintenance, we determined whether the ISR underpins natural and accelerated forgetting. Here, based on the object location recognition (OLR) and novel object recognition (NOR) paradigms in mice, we found that the ISR was activated while an established memory was naturally forgotten, which was denoted by increased levels of phosphorylated eukaryotic translation initiation factor 2α (eIF2α) and activating transcription factor 4 (ATF4), and reduced general protein synthesis. Multiple administrations of ISRIB, a small molecule ISR inhibitor, during the memory retention interval attenuated the ISR activation, and prevented the natural forgetting of established OLR and NOR memories. At the same time, a single injection of ISRIB has no effect on natural forgetting and memory retrieval. Moreover, administration of pentylenetetrazole (PTZ), an inducer of epileptic seizures, during the memory retention interval provoked the ISR activation and accelerated forgetting, which was corrected by ISRIB treatment. Together, our findings suggest that the ISR is critically involved in natural forgetting and accelerated forgetting associated with epilepsy, and pharmacological inhibition of the ISR may emerge as a novel intervention strategy for accelerated forgetting in patients with epilepsy.

Working memory deficit in patients with focal epilepsy is associated with higher interictal theta connectivity

OBJECTIVE

Interictal cognitive disturbances are frequent in patients with focal epilepsies and the links with alteration of resting state brain oscillations are not well known. Changes in theta oscillations, may contribute to cognitive impairment. This study aimed to investigate whether changes in theta activity are related to cognitive disturbances.

METHODS

Retrospective data of 23 patients with temporal/frontal lobe epilepsy were included. Theta connectivity, power and interictal spikes rate from five-minute interictal resting state stereoelectroencephalography datasets were computed. Cognitive performances were assessed by Wechsler Intelligence Scale (WAIS-IV) and Weschler Memory Scale (WMS-III). Linear regression was performed to evaluate effect of interictal activity and seizure related parameters on cognitive scores.

RESULTS

WAIS-IV working memory score in patients with epilepsy showed negative correlation with frontotemporal theta connectivity (F(1,17) = 5,239, p = 0,036, R2 = 0,200, β = -0,497). Moreover, theta connectivity was correlated with mesial temporal spike rate and theta power (F(2,17) = 10,967, p = 0,001, adj.R2 = 0,540).

CONCLUSIONS

Patients with focal epilepsy often encounter compromised cognitive functions, particularly notable in the domain of working memory. This impairment might be attributed to physiological mechanisms involving increased theta connectivity within the frontotemporal regions and interictal spiking.

SIGNIFICANCE

Our study highlights the relation between theta connectivity and working memory impairments in patients with focal epilepsy.

Does epilepsy differentially affect different types of memory?

Despite the recognition that epilepsy can substantially disrupt memory, there are few published accounts of whether and how this disruption varies across different types of memory and/or different types of epilepsy. This review explores four main questions: (1) Are working, episodic and semantic memory differentially affected by epilepsy? (2) Do various types of epilepsy, and their treatment, have different, specifiable effects on memory? (3) Are the usual forms of neuropsychological assessments of memory - many or most designed for other conditions - appropriate for patients with epilepsy? (4) How can research on epilepsy contribute to our understanding of the neuroscience of memory? We conclude that widespread and multifactorial problems are seen in working memory in all patient groups, while patients with temporal lobe epilepsy seem particularly prone to episodic memory deficit, and those with frontal lobe epilepsy to executive function deficits that may in turn impair semantic control. Currently, it is difficult to make individual patient predictions about likely memory deficits based on seizure aetiology and type, but it is possible to guide and tailor neuropsychological assessments in an individualised way. We make recommendations for future directions in validating and optimising neuropsychological assessments, and consider how to approach effective shared decision making about the pros and cons of seizure treatment strategies, especially at crucial educational stages such as adolescence.

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.

A Strategy for Allowing Earlier Diagnosis and Rigorous Evaluation of BACE1 Inhibitors in Preclinical Alzheimer's Disease

Given continued failure of BACE1 inhibitor programs at symptomatic and prodromal stages of Alzheimer's disease (AD), clinical trials need to target the earlier preclinical stage. However, trial design is complex in this population with negative diagnosis of classical hippocampal amnesia on standard memory tests. Besides recent advances in brain imaging, electroencephalogram, and fluid-based biomarkers, new cognitive markers should be established for earlier diagnosis that can optimize recruitment to BACE1 inhibitor trials in presymptomatic AD. Notably, accelerated long-term forgetting (ALF) is emerging as a sensitive cognitive measure that can discriminate between asymptomatic individuals with high risks for developing AD and healthy controls. ALF is a form of declarative memory impairment characterized by increased forgetting rates over longer delays (days to months) despite normal storage within the standard delays of testing (20-60 min). Therefore, ALF may represent a harbinger of preclinical dementia and the impairment of systems memory consolidation, during which memory traces temporarily stored in the hippocampus become gradually integrated into cortical networks. This review provides an overview of the utility of ALF in a rational design of next-generation BACE1 inhibitor trials in preclinical AD. I explore potential mechanisms underlying ALF and relevant early-stage biomarkers useful for BACE1 inhibitor evaluation, including synaptic protein alterations, astrocytic dysregulation and neuron hyperactivity in the hippocampal-cortical network. Furthermore, given the physiological role of the isoform BACE2 as an AD-suppressor gene, I also discuss the possible association between the poor selectivity of BACE1 inhibitors and their side effects (e.g., cognitive worsening) in prior clinical trials.

Sleep and epilepsy: A clinical and pathophysiological overview

The interaction between sleep and epilepsy is complex. A better understanding of the mechanisms linking sleep and epilepsy appears increasingly important as it may improve diagnosis and therapeutic strategies in patients with epilepsy. In this narrative review, we aim to (i) provide an overview of the physiological and pathophysiological processes linking sleep and epilepsy; (ii) present common sleep disorders in patients with epilepsy; (iii) discuss how sleep and sleep disorders should be considered in new therapeutic approaches to epilepsy such as neurostimulation; and (iv) present the overall nocturnal manifestations and differential diagnosis between epileptic seizures and parasomnia.

Spontaneous fast-ultradian dynamics of polymorphic interictal events in drug-resistant focal epilepsy

OBJECTIVE

We studied the rate dynamics of interictal events occurring over fast-ultradian time scales, as commonly examined in clinics to guide surgical planning in epilepsy.

METHODS

Stereo-electroencephalography (SEEG) traces of 35 patients with good surgical outcome (Engel I) were analyzed. For this we developed a general data mining method aimed at clustering the plethora of transient waveform shapes including interictal epileptiform discharges (IEDs) and assessed the temporal fluctuations in the capability of mapping the epileptogenic zone (EZ) of each type of event.

RESULTS

We found that the fast-ultradian dynamics of the IED rate may effectively impair the precision of EZ identification, and appear to occur spontaneously, that is, not triggered by or exclusively associated with a particular cognitive task, wakefulness, sleep, seizure occurrence, post-ictal state, or antiepileptic drug withdrawal. Propagation of IEDs from the EZ to the propagation zone (PZ) could explain the observed fast-ultradian fluctuations in a reduced fraction of the analyzed patients, suggesting that other factors like the excitability of the epileptogenic tissue could play a more relevant role. A novel link was found between the fast-ultradian dynamics of the overall rate of polymorphic events and the rate of specific IEDs subtypes. We exploited this feature to estimate in each patient the 5 min interictal epoch for near-optimal EZ and resected-zone (RZ) localization. This approach produces at the population level a better EZ/RZ classification when compared to both (1) the whole time series available in each patient (p = .084 for EZ, p < .001 for RZ, Wilcoxon signed-rank test) and (2) 5 min epochs sampled randomly from the interictal recordings of each patient (p < .05 for EZ, p < .001 for RZ, 105 random samplings).

SIGNIFICANCE

Our results highlight the relevance of the fast-ultradian IED dynamics in mapping the EZ, and show how this dynamics can be estimated prospectively to inform surgical planning in epilepsy.

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.

EEG-Findings during long-term treatment with Everolimus in TSC-associated and therapy-resistant epilepsies in children

AIM

This prospective observational study evaluated the long-term EEG changes in children treated with everolimus (EVO) for refractory TSC-associated epilepsy. Changes in EEG-abnormalities were related to developmental outcomes.

METHODS

Thirteen children treated with EVO were examined for EEG-recorded seizures and interictal epileptic discharges (IED) during a 72-hour-video-EEG-monitoring, which was performed at baseline and repeated at follow-up intervals of at least 9 months. Antiseizure medication was left unchanged for at least 27 months. Changes in cognitive developmental parameters were related to reduction of seizures and IED at the last monitoring.

RESULTS

We found a significant reduction of recorded seizures and IED during sleep at the first as well as the last follow-up recording. The reduction of IED was especially prominent during sleep. For patients who continued for more than one monitoring under EVO (n = 8), number of seizures further decreased. In patients with developmental examination (n = 9), we observed that only (nearly) full cessation of IED was related to acquisition of new skills.

DISCUSSION

In children with TSC, EVO was effective in reducing recorded seizures and IED; long-term EVO treatment led to a more pronounced reduction and an improvement of nocturnal IED even when the patient was initially not seizure-free. Cessation of IED in children with developmental improvement may point to the importance of healthy sleep for cognition.

Memories in Persons with Epilepsy: They Are More Fragile Than You Think

“Hidden Objective Memory Deficits Behind Subjective Memory Complaints in Patients with Temporal Lobe Epilepsy”

Lemesle B, Barbeau EJ, Milongo Rigal E, Denuelle M, Valton L, Pariente J, Curot J. Neurology. 2022 Feb 22;98(8):e818-e828. doi: 10.1212/WNL.0000000000013212. Epub 2021 Dec 14. PMID: 34906979.

“Background and objectives:

The aim of this work was to test the hypothesis that patients with temporal lobe epilepsy (TLE) with subjective initial memory complaints (not confirmed by an objective standard assessment) and various phenotypes also show objective very long-term memory deficit with accelerated long-term forgetting. We tested patients with TLE with 2 surprise memory tests after 3 weeks: the standard Free and Cued Selective Reminding Test (FCSRT) and Epireal, a new test specifically designed to capture more ecologic aspects of autobiographical memory.

Methods:

Forty-seven patients with TLE (12 with hippocampal sclerosis, 12 with amygdala enlargement, 11 with extensive lesions, 12 with normal MRI) who complained about their memory, but for whom the standard neuropsychological assessment did not reveal any memory impairment after a standard delay of 20 minutes, underwent 2 surprise memory tests after 3 weeks. They were compared to 35 healthy controls.

Results:

After 3 weeks, FCSRT and Epireal recall scores were significantly lower in patients than in controls (P < .001). There was no significant correlation between FCSRT and Epireal scores (P = .99). Seventy-six percent of patients with TLE had objective impairment on at least 1 of these very long-term memory tests, regardless of the existence and type of lesion or response to antiseizure medication. Easily applicable, Epireal had a higher effect size, detected deficits in 28% more patients, and is a useful addition to the standard workup.

Discussion:

Assessing long-term memory should be broadened to a wide spectrum of patients with TLE with a memory complaint, regardless of the epileptic syndrome, regardless of whether it is associated with a lesion. This could lead to rethinking TLE nosology associated with memory.”

Sleep and epilepsy: A snapshot of knowledge and future research lines

Sleep and epilepsy have a reciprocal relationship, and have been recognized as bedfellows since antiquity. However, research on this topic has made a big step forward only in recent years. In this narrative review we summarize the most stimulating discoveries and insights reached by the "European school." In particular, different aspects concerning the sleep-epilepsy interactions are analysed: (a) the effects of sleep on epilepsy; (b) the effects of epilepsy on sleep structure; (c) the relationship between epilepsy, sleep and epileptogenesis; (d) the impact of epileptic activity during sleep on cognition; (e) the relationship between epilepsy and the circadian rhythm; (f) the history and features of sleep hypermotor epilepsy and its differential diagnosis; (g) the relationship between epilepsy and sleep disorders.

Barbeau E, Pariente J, Dahan L, Valton L. Sleep: The Tip of the Iceberg in the Bidirectional Link Between Alzheimer's Disease and Epilepsy

The observation that a pathophysiological link might exist between Alzheimer's disease (AD) and epilepsy dates back to the identification of the first cases of the pathology itself and is now strongly supported by an ever-increasing mountain of literature. An overwhelming majority of data suggests not only a higher prevalence of epilepsy in Alzheimer's disease compared to healthy aging, but also that AD patients with a comorbid epileptic syndrome, even subclinical, have a steeper cognitive decline. Moreover, clinical and preclinical investigations have revealed a marked sleep-related increase in the frequency of epileptic activities. This characteristic might provide clues to the pathophysiological pathways underlying this comorbidity. Furthermore, the preferential sleep-related occurrence of epileptic events opens up the possibility that they might hasten cognitive decline by interfering with the delicately orchestrated synchrony of oscillatory activities implicated in sleep-related memory consolidation. Therefore, we scrutinized the literature for mechanisms that might promote sleep-related epileptic activity in AD and, possibly dementia onset in epilepsy, and we also aimed to determine to what degree and through which processes such events might alter the progression of AD. Finally, we discuss the implications for patient care and try to identify a common basis for methodological considerations for future research and clinical practice.

Epileptic seizures and link to memory processes

Epileptogenesis is a complex and not well understood phenomenon. Here, we explore the hypothesis that epileptogenesis could be "hijacking" normal memory processes, and how this hypothesis may provide new directions for epilepsy treatment. First, we review similarities between the hypersynchronous circuits observed in epilepsy and memory consolidation processes involved in strengthening neuronal connections. Next, we describe the kindling model of seizures and its relation to long-term potentiation model of synaptic plasticity. We also examine how the strengthening of epileptic circuits is facilitated during the physiological slow wave sleep, similarly as episodic memories. Furthermore, we present studies showing that specific memories can directly trigger reflex seizures. The neuronal hypersynchrony in early stages of Alzheimer's disease, and the use of anti-epileptic drugs to improve the cognitive symptoms in this disease also suggests a connection between memory systems and epilepsy. Given the commonalities between memory processes and epilepsy, we propose that therapies for memory disorders might provide new avenues for treatment of epileptic patients.

Hidden Objective Memory Deficits Behind Subjective Memory Complaints in Patients With Temporal Lobe Epilepsy

OBJECTIVE

To test the hypothesis that temporal lobe epilepsy (TLE) patients with subjective initial memory complaints (not confirmed by an objective standard assessment) and various phenotypes also show objective very long-term memory deficit with accelerated long-term forgetting. We tested TLE patients with two surprise memory tests after three weeks: the standard Free and Cued Selective Reminding Test (FCSRT), and Epireal, a new test specifically designed to capture more ecological aspects of autobiographical memory.

METHODS

47 TLE patients (12 hippocampal sclerosis, 12 amygdala enlargement, 11 extensive lesions, 12 normal MRI) who complained about their memory, but for whom the standard neuropsychological assessment did not reveal any memory impairment after a standard delay of 20 minutes, underwent two surprise memory tests after three weeks. They were compared to 35 healthy control subjects.

RESULTS

After three weeks, FCSRT and Epireal recall scores were significantly lower in patients than in controls (p<0.001). There was no significant correlation between FCSRT and Epireal scores (p=0.99). Seventy-six percent of TLE patients had objective impairment on at least one of these very long-term memory tests, regardless of the existence and type of lesion or response to antiseizure medication. Easily applicable, Epireal had a higher effect size, detected deficits in 28% more patients, and is a useful addition to the standard workup.

CONCLUSION

Assessing long-term memory should be broadened to a wide spectrum of TLE patients with a memory complaint, regardless of the epileptic syndrome, whether or not associated with a lesion. This could lead to rethinking TLE nosology associated with memory.

Relationship Between Epilepsy and Dreaming: Current Knowledge, Hypotheses, and Perspectives

The interactions between epilepsy and sleep are numerous and the impact of epilepsy on cognition is well documented. Epilepsy is therefore likely to influence dreaming as one sleep-related cognitive activity. The frequency of dream recall is indeed decreased in patients with epilepsy, especially in those with primary generalized seizures. The content of dreams is also disturbed in epilepsy patients, being more negative and with more familiar settings. While several confounding factors (anti-seizure medications, depression and anxiety disorders, cognitive impairment) may partly account for these changes, some observations suggest an effect of seizures themselves on dreams. Indeed, the incorporation of seizure symptoms in dream content has been described, concomitant or not with a focal epileptic discharge during sleep, suggesting that epilepsy might directly or indirectly interfere with dreaming. These observations, together with current knowledge on dream neurophysiology and the links between epilepsy and sleep, suggest that epilepsy may impact not only wake- but also sleep-related cognition.

Effect of Cannabidiol on Interictal Epileptiform Activity and Sleep Architecture in Children with Intractable Epilepsy: A Prospective Open-Label Study

BACKGROUND

Cannabidiol has been shown to be effective in seizure reduction in patients with Dravet syndrome, Lennox-Gastaut syndrome, and tuberous sclerosis. However, very little is known about its potential to reduce interictal epileptiform activity and improve sleep architecture.

OBJECTIVE

The objective of this prospective study was to evaluate the influence of cannabidiol therapy on the frequency of interictal epileptiform discharges (IEDs) and sleep microstructure in a cohort of children with drug-resistant epilepsy.

METHODS

Children with drug-resistant epilepsy were prospectively followed from November 2019 to January 2021 during an open-label trial of cannabidiol at a dose of 20 mg/kg/day (to a maximum of 50 mg/kg/day) and stable concomitant medication. Electroencephalograms were recorded at baseline (T0) and after 3 months (T1). Two independent raters, blinded to clinical outcome, evaluated 5-min segments of sleep stage 2 or low-noise awake state. IEDs were visually identified and rates per minute calculated. Sleep microstructure was considered improved if sleep structures were seen at T1 that were not present at T0. IED rates at T0 and T1 were compared and correlated with seizure outcome, cannabidiol dose, initial IED rate, and disease duration.

RESULTS

In total, 35 children (mean ± standard deviation age 10.1 ± 0.86) were included. The IED rate at T1 was significantly lower than at T0 (19.6 ± 19.5 vs. 36.8 ± 27.2, respectively; p < 0.0001). We found a moderate correlation between IED reduction and percentage of seizure reduction compared with baseline (Pearson's r = 0.39; p = 0.02), a moderate negative correlation between IED reduction and IED rate at T0 (r = - 0.34; p = 0.04), and a trend towards a moderate negative correlation between IED reduction and disease duration (r = - 0.32; p = 0.06). Sleep was recorded in 23 patients. Sleep microstructure was initially abnormal in 56.5% of sleep recordings and improved in 84.6% of those cases.

CONCLUSION

Our results strongly suggest the utility of cannabidiol in reducing IEDs and improving sleep microstructure in children with drug-resistant epilepsy. Larger controlled studies are needed to evaluate the clinical relevance of this effect in different epilepsy types.

TRIAL REGISTRATION

DRKS00013177; 25 June 2019.