Probing the reactivity of anesthetic burst-suppression EEG by transcranial direct current stimulation

Stefan Mirica (1), Alexandru-Catalin Paslaru (1), Denise Zahiu (1), Pavel Bogdan (1), Alexandra Oana Constantinescu (2), Andrei Ilie (2), Alexandru Calin (2), Ana-Maria Zagrean (1), Leon Zagrean (1), Mihai Moldovan (1,3), 1) Division of Physiology and Fundamental Neuroscience, "Carol Davila" University of Medicine and Pharmacy, Bucharest, Romania; 2) Oxford University, Oxford, United Kingdom; 3) Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark

SNN 2014 Conference
October 23 - October 25, Bucharest

Abstract published in Fiziologia - Physiology, 2014, Supp 2


Discontinuous burst-suppression (BS) EEG patterns consisting of bursts of activity lasting up to a few seconds on a suppressed background are associated with deep comatose states. When BS can be modulated by external stimuli the BS is referred to as “reactive”. Reactivity can be assessed by using intermittent external stimuli, typically photic or mechanical stimuli. As such, BS reactivity prognostic measures depend on the integrity of the activated sensory pathways. The aim of this study was to explore a novel approach. Instead of modulating the level of thalamocortical input, we aimed to alter cortical excitability. Specifically, we tested the effect of transcranial direct current stimulation (tDCS) on “spontaneous” BS patterns during anesthetic coma induced in Adult male Wistar rats. Under cortical EEG monitoring 2mA tDCS was applied via 2 large non-polarizable Ag/AgCl electrodes placed rostrally on the scalp (active) and on the abdomen (reference). One-minute anodal (excitatory) tDCS sessions were repeated at 5 minute intervals and were intercalated by brief stimulations with reversed polarity to reduce any confounding cumulative effects. Changes in cortical excitability were induced by using different anesthetics at increasing concentrations and by using kainate injections. In all conditions, anodal tDCS caused a prompt increase in bursting. These effects were not observed in control experiments when the active electrode was placed at the base of the neck to avoid current passing through the brain. Our data suggest that tDCS is a viable alternative to intermittent stimulation for monitoring the state of cortical excitability during induced BS comatose states.