Temporal lobe interictal spikes disrupt encoding and retrieval of verbal memory: A subregion analysis

Abstract

Objective: The medial temporal lobe (MTL) encodes and recalls memories and can be a predominant site for interictal spikes (IS) in patients with focal epilepsy. It is unclear whether memory deficits are due to IS in the MTL producing a transient decline. Here, we investigated whether IS in the MTL subregions and lateral temporal cortex impact episodic memory encoding and recall. Methods: Seventy-eight participants undergoing presurgical evaluation for medically refractory focal epilepsy with depth electrodes placed in the temporal lobe participated in a verbal free recall task. IS were manually annotated during the pre-encoding, encoding, and recall epochs. We examined the effect of IS on word recall using mixed-effects logistic regression. Results: IS in the left hippocampus (odds ratio [OR] =.73, 95% confidence interval [CI] =.63–.84, p .05). IS during retrieval in right hippocampal (OR =.22, 95% CI =.08–.63, p =.01) and parahippocampal regions (OR =.24, 95% CI =.07–.8, p