The Oscillatory Basis of Working Memory Function and Dysfunction in Epilepsy

Abstract

Working memory (WM) deficits are pervasive co-morbidities of epilepsy. Although the pathophysiological mechanisms underpinning these impairments remain elusive, it is thought that WM depends on oscillatory interactions within and between nodes of large-scale functional networks. These include the hippocampus and default mode network as well as the prefrontal cortex and frontoparietal central executive network. Here, we review the functional roles of neural oscillations in subserving WM and the putative mechanisms by which epilepsy disrupts normative activity, leading to aberrant oscillatory signatures. We highlight the particular role of interictal epileptic activity, including interictal epileptiform discharges and high frequency oscillations (HFOs) in WM deficits. We also discuss the translational opportunities presented by greater understanding of the oscillatory basis of WM function and dysfunction in epilepsy, including potential targets for neuromodulation.

Connectomic Profiles and Cognitive Trajectories After Epilepsy Surgery in Children

“…48 In addition, ongoing maturation of the temporal lobes during the second decade of life, as indicated by EEG, MRI, and postmortem studies, could enable temporal lobe networks to further reorganize and recover after temporal lobe epilepsy surgery. 5 Thus, the functional implications of the findings from the PLS analyses probing working memory and verbal memory are particularly notable; given that both abilities underpin academic learning and are associated with health-related quality of life, 24,42 elucidating markers for favorable postoperative outcomes in working memory and verbal memory functions is critical.…”

“…Conversely, low-frequency synchronization is thought to underlie contextdriven, top-down processing. 24 Indeed, previous work in resting-state MEG demonstrates that enhanced connectivity in the theta band is related to better cognitive performance in working memory and attention in particular. 25 On the other hand, studies leveraging MEG with children who were born very preterm or children with autism show reduced theta connectivity in cortical areas involved in working memory and attention, respectively.…”

Epilepsy disrupts hippocampal phase precision and impairs working memory

“…Within the WM network, hippocampal oscillatory activity is thought to underpin WM processing (for review, see Arski et al 10 ). The hippocampi play an important role in novelty detection and associative binding and are recruited consistently during the encoding, maintenance, and retrieval of information in WM 11,12 .…”

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

“…Collecting dream narratives in such epilepsy patients, following provoked awakenings after seizures or outside seizures, would allow to assess the direct influence of focal epileptic discharges on dreaming. The occurrence of focal seizures during sleep provides a model of acute transient and spatially limited brain dysfunction that can disrupt or hijack oscillatory interactions within and between networks involved in cognition and notably memory formation ( Mendes et al, 2019 ; Arski et al, 2020 ). Investigating the effect on dream recall and dream content of epileptic discharges involving the MPFC and/or the TPOJ—but also of other networks engaged in working memory—would advance our understanding of the neurophysiology of dreaming.…”

“…It can be hypothesized that the increased epileptic activity during NREM sleep might alter working memory notably by diminishing its capacity or erasing its content, which could explain the particular decrease in DRF observed upon NREM sleep awakenings in epilepsy patient ( Cipolli et al, 2004 ). Impaired working memory during wakefulness, frequent in epilepsy patients, could also diminish or suppress dream recall at awakening ( Arski et al, 2020 ). REM sleep dreaming would be expected to be less impaired than NREM dreaming in epilepsy patients, given that ictal and inter-ictal epileptic activity is less frequent in REM than in NREM sleep.…”