Interictal epileptiform discharges impair word recall in multiple brain areas

Abstract

Summary Objectives Interictal epileptiform discharges (IEDs) have been linked to memory impairment, but the spatial and temporal dynamics of this relationship remain elusive. In the present study, we aim to systematically characterize the brain areas and times at which IEDs affect memory. Methods Eighty epilepsy patients participated in a delayed free recall task while undergoing intracranial EEG monitoring. We analyzed the locations and timing of IEDs relative to the behavioral data in order to measure their effects on memory. Results Overall IED rates did not correlate with task performance across subjects (r = 0.03, p = 0.8). However, at a finer temporal scale, within-subject memory was negatively affected by IEDs during the encoding and recall periods of the task but not during the rest and distractor periods (p < 0.01, p < 0.001, p = 0.3, and p = 0.8 respectively). The effects of IEDs during encoding and recall were stronger in the left hemisphere than in the right (p < 0.05). Out of six brain areas analyzed, IEDs in the inferior temporal, medial temporal, and parietal areas significantly affected memory (false discovery rate < 0.05). Significance These findings reveal a network of brain areas sensitive to IEDs with key nodes in temporal as well as parietal lobes. They also demonstrate the time-dependent effects of IEDs in this network on memory.

Spatial and episodic memory tasks promote temporal lobe interictal spikes

“…Although IISs have been proposed to negatively correlate with performance in visual recognition and word recall tasks, task‐related increases in spike activity have not previously been reported. This underlines the importance of removing IIS before analyzing task‐related changes in oscillatory power, as they could make a strong and task‐dependent contribution.…”

A method for the topographical identification and quantification of high frequency oscillations in intracranial electroencephalography recordings

“…Utilization of this method will assist in the determination of whether true HFO events are generated by distinct mechanisms as compared with false HFO events. Further, it will aid in the investigation of true and false RonS with respect to understanding and differentiating their mechanisms of generation (Schevon et al, 2009; Keller et al, 2010), utility for identifying epileptogenic regions (Burnos et al, 2016), role during seizures (Eissa et al, 2016), and also their ability to disrupt normal cognition (Horak et al, 2017). The topographical method we describe is one of many “computer vision” based approaches to identifying multiple distinct brief oscillatory events that overlap in time, but are unique in spectral content (Burnos et al, 2014; Kucewicz et al, 2017).…”

Contextually Mediated Spontaneous Retrieval Is Specific to the Hippocampus

“…Given that our data are from neurological patients, epileptic activity may potentially contaminate the effects of interest. Indeed, epileptiform activity during retrieval can negatively impact memory performance [42], and thus, further research may help to clarify the degree to which electrophysiological differences between successful and unsuccessful retrieval periods reflect pathological neural activity.…”