Epileptiform spikes in specific left temporal and mesial temporal structures disrupt verbal episodic memory encoding

TL;DR

This study shows that epileptiform spikes in specific temporal brain regions during memory encoding significantly impair verbal recall in epilepsy patients, highlighting a neural basis for cognitive deficits.

Contribution

It identifies precise neuroanatomical regions where epileptiform spikes disrupt verbal memory encoding, using machine learning analysis in a large patient cohort.

Findings

Spikes in left BA21 reduce recall by 11.9%

Spikes in left BA38 reduce recall by 49.7%

Spikes in right BA38 reduce recall by 32.2%

Abstract

Patients diagnosed with epilepsy experience cognitive dysfunction that may be due to a transient cognitive/memory impairment (TCI/TMI) caused by spontaneous epileptiform spikes. We asked in a cohort of 166 adult patients with medically refractory focal epilepsy if spikes in specific neuroanatomical regions during verbal episodic memory encoding would significantly decrease the probability of recall. We found using a na\"ive Bayesian machine learning model that the probability of correct word recall decreased significantly by 11.9% when spikes occurred in left Brodmann area 21 (BA)21, (p<0.001), 49.7% in left BA38 (p=0.01), and 32.2% in right BA38 (p<0.001), and 21.4% in left BA36 (p<0.01). We also examined the influence of the seizure-onset zone and the language dominant hemisphere on this effect. Our results demonstrate that spontaneous epileptiform spikes produce a large effect TCI/TMI in brain regions known to be important in semantic processing and episodic memory. Thus memory impairment in patients with epilepsy may be attributable to cellular events associated with abnormal inter-ictal electrical events.