Interictal Epileptiform Discharges are Task Dependent and are Associated with Lasting Electrocorticographic Changes

Abstract

The factors that control the occurrence of interictal epileptiform discharges (IEDs) are not well understood. We suspected that this phenomenon reflects an attention-dependent suppression of interictal epileptiform activity. We hypothesized that IEDs would occur less frequently when a subject viewed a task-relevant stimulus compared to viewing a blank screen. Furthermore, IEDs have been shown to impair memory when they occur in certain regions during the encoding or recall phases of a memory task. Although these discharges have a short duration, their impact on memory suggests that they have longer lasting electrophysiological effects. We found that IEDs were associated with an increase in low frequency power and a change in the balance between low and high frequency oscillations for several seconds. We found that the occurrence of IEDs is modified by whether a subject is attending to a word displayed on screen or is observing a blank screen. Additionally, we found that discharges in brain regions in every lobe impair memory. These findings elucidate the relationship between IEDs and memory impairment and reveal the task dependence of the occurrence of IEDs.

Single‐neuron correlate of epilepsy‐related cognitive deficits in visual recognition memory in right mesial temporal lobe

“…Second, what is the relationship between our findings and interictal discharges (IEDs)? Although IEDs are generally rare, their occurrence is correlated with impaired memory 42 , 43 , 44 and they transiently entrain neurons within the MTL. 45 It remains an open question whether the selective impairment of MS but not VS cells can be explained by selective entrainment of these neurons by IEDs.…”

Functional Reorganization of the Mesial Frontal Premotor Cortex in Patients With Supplementary Motor Area Seizures

“…We coregistered postimplant head computed tomographies with preoperative brain MRIs to obtain accurate 3D location data for each electrode 11 (Figure 1), using a rigid-body registration method from Statistical Parametric Mapping 12 toolbox (SPM12, https://www.fil.ion.ucl.ac.uk/spm/). 12-16 After manual segmentation, electrodes were projected to the nearest cortical surface using the iterative closest point algorithm to account for brain shift 17 and translated into Montreal Neurologic Institute (MNI) brain space on a normalized brain model 18 to facilitate comparison of mapping across subjects.…”

“…ucl.ac.uk/spm/). [12][13][14][15][16] After manual segmentation, electrodes were projected to the nearest cortical surface using the iterative closest point algorithm to account for brain shift 17 and translated into Montreal Neurologic Institute (MNI) brain space on a normalized brain model 18 to facilitate comparison of mapping across subjects.…”

Features of intracranial interictal epileptiform discharges associated with memory encoding

“…The final spectrum was then utilized to calculate the average spectral power within the following frequency bands: delta (2–4 Hz), theta (4–7 Hz), alpha (8–12 Hz), beta (12–30 Hz), gamma (25–40 Hz), and high‐frequency activity (40–100 Hz) 19 . We used a 1‐s gap to measure relevant power changes surrounding an IED, while minimizing IED perturbations from post‐IED slow waves; this was motivated by our previous work, which revealed that the optimal powerband change was in the +1‐ to +2‐s post‐IED window 20 …”

“…This method convolved orthogonal Slepian sequences with the preprocessed iEEG, providing periodograms that were used to compute a final spectrum. The final spectrum was then utilized to calculate the average spectral power within the following frequency bands: delta (2-4 Hz), theta (4-7 Hz), alpha (8-12 Hz), beta (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), gamma (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40), and high-frequency activity (40-100 Hz). 19 We used a 1-s gap to measure relevant power changes surrounding an IED, while minimizing IED perturbations from post-IED slow waves; this was F I G U R E 1 Task design and analysis methods.…”