Network alterations in temporal lobe epilepsy during non-rapid eye movement sleep and wakefulness

Abstract

ObjectiveInvestigate sleep and temporal lobe epilepsy (TLE) effects on EEG-derived brain networks.MethodsHigh-density EEG was recorded during non-REM sleep (N2) and wakefulness in 23 patients and healthy controls (HC). Epochs without epileptic discharges were source-reconstructed in 72 brain regions and connectivity was estimated. Network integration (Efficiency, E) and segregation (Clustering Coefficient, CC) at global and hemispheric level (GE, avgCC, HE, HCC) were calculated. These were compared between groups across frequency bands and correlated with the individual proportion of wakefulness-or sleep-related seizures.ResultsPatients had higher delta GE, delta avgCC and theta avgCC than controls, irrespective of the vigilance state (TLE > HC, p<.01). During wakefulness, theta GE of patients was higher than controls (p<.001) and, for patients, theta GE during wakefulness was higher than during N2 (p<.05). Wake-to-sleep differences in TLE were notable only in the ipsilateral hemisphere (HE and HCC, p<.05). Only measures from wakefulness recordings correlated with the proportion of wakefulness-or sleep-related seizures.ConclusionsTLE network alterations are more prominent during wakefulness and at lower frequencies. Increased integrationandsegregation suggest a pathological ‘small world’ configuration with a possible inhibitory role.SignificanceNetwork alterations in TLE occur and are easier to detect during wakefulness.