Localization and duration dependent effects of pediatric refractory epilepsy on language function

We studied effects of duration of epilepsy and location of epileptogenic zone (EZ) on visual naming (VN) and auditory naming (AN) response latencies in pediatric focal drug-resistant epilepsy. We also analyzed temporal profiles of high-gamma modulations (HGMs) during VN and AN in peri-sylvian language areas, with respect to AN and VN response latencies.

Kernel density distributions of AN and VN response latencies were k-means clustered, and the resulting groups were compared for relevant outcomes. Response latencies and kernel densities were analyzed as functions of age, age of seizure onset, and duration of epilepsy using linear mixed-effects models.

Shorter response latencies and higher peak densities (more consistent response times) were associated with shorter duration of epilepsy, older age at seizure onset, localized EZ, and higher proportion of seizure-freedom (80 % vs 41 %). Response latencies shortened with age and age of seizure onset and lengthened with increasing duration of epilepsy. Peak kernel densities, indicating consistency of responses, increased with age and age of seizure onset, and decreased with duration of epilepsy. Epilepsy duration over 5.9 years for AN and over 5.3 years for VN were associated with a higher likelihood of prolonged response latencies. Temporal envelopes for HGM during AN were different in the Broca's area for patients with short and long response latencies. Also, HGM envelopes during VN were different in the visual cortex for these 2 groups.

The duration-dependent network dysfunction in refractory epilepsy, interfering with naming, supports early surgical intervention before language function is irreversibly compromised.