70. Rehabilitation of verbal and visuospatial memory by oscillatory tDCS and sleep consolidation

Abstract

Temporal lobe epilepsy (TLE) is often associated with memory deficits. Given the putative role for sleep spindles in learning and encoding, the distribution of spindle generators skewed toward the affected lobe in TLE subjects may be a neurophysiological marker of defective memory. Slow-oscillatory transcranial direct current stimulation (sotDCS) has been shown to improve memory possibly by increasing slow-wave sleep and modulating sleep spindles. To test if excitatory anodal sotDCS over the affected temporal lobe affects sleep spindles, thus improving memory performance. In this randomized controlled cross-over study 12 people with TLE underwent either sotDCS (0.75 Hz; 0–250 μV, 30 min) or a sham procedure before a daytime nap. Declarative verbal and visuospatial learning were tested. Fast and slow spindle signals were recorded by 256-channel EEG during sleep. In both study arms, we used electrical source imaging (ESI) to localize cortical generators. Neuropsychological data were analyzed with general linear model statistics or the Kruskal–Wallis test (p or Z < 0.05), and neurophysiological data were tested with the Mann–Whitney t test and a binomial distribution test (p or Z < 0.05). An improvement in declarative (p = 0.05) and visuospatial memory performance (p = 0.048) was noted after sotDCS. SotDCS increased the current density of slow spindle generators (Z = 0.001), with a shift to the anterior cortical areas. Anodal sotDCS delivered over the affected temporal lobe can improve declarative and, to a lesser extent, visuospatial memory performance by modulating cortical source generators of slow sleep spindles. SotDCS appears to be a promising tool for memory rehabilitation in people with TLE.