P05-F Sleep stage dependent functional connectivity in SEEG

Abstract

Objective To determine changes in cortical functional connectivity in relation to sleep stage. Method We analyzed intracranial EEG (iEEG) data recorded from 5 patients with intractable focal epilepsy undergoing presurgical work-up with depth electrodes. Additionally, patients underwent parallel scalp-EEG recording, giving the opportunity for sleep staging. In each patient we analyzed 30 s long segments of iEEG recordings from NREM N2 and REM sleep using a non-linear correlation method, H2 (Wendling, 2001). We compared the mean strength of overall correlation for each corresponding contiguous pair of cortical contacts in REM versus NREM sleep-stage. Functional connectivity was evaluated for the whole spectrum of frequencies and supplementary in an extended gamma-range (30–120 Hz). Results We consistently observed a significant reduction of the mean strength of whole-spectrum correlation in REM versus NREM N2 sleep in contact pairs positioned in the frontal cortex. Additionally we observed a drop in connectivity of the insular cortex, albeit with a larger inter-individual variability. Conversely there was a consistent increase in connectivity in REM versus NREM N2 sleep of the lateral temporal structures (mainly the middle temporal gyrus). The extended gamma-spectrum changes did not always mirror the whole-spectrum changes in connectivity, either by not obtaining significance or by having contradictory values. Conclusions cortical connectivity changes with sleep stage; frontal and insular cortices have a lower overall connectivity during REM sleep as compared to NREM N2 sleep, while lateral temporal structures demonstrate an increase in connectivity. These changes are at most minimally accounted for by changes in gamma-spectrum connectivity.