Large scale multi-channel EEG in rats

The aim of this task is to develop a protocol and a set-up for recording EEG signal from a large number of cortical areas in head-restrained rats exposed to anesthesia and during wakefulness. In order to quantify cortical complexity and its relation to (un)consciousness, a large scale EEG that samples activity from most of cortical areas is needed (Massimini et al. Science, 2005; Casali et al. Sci Transl Med, 2013). Unfortunately, only few existing probes allow this large scale recording in rodents (Megévand et al. Neuroimage, 2008; Choi et al. J Neurophysiol, 2010). Besides, since those probes are designed to be laid down on the skull surface, the obtained scalp EEG is subjected to the filtering action of the skull tissue, which separates the brain surface from the electrode. This would reduce the amplitude and the high frequency resolution of the cortical signal (Buzsáki et al. Nat Rev Neuroscience, 2012). Alternatively, epidural screw electrodes, by directly contacting the outer surface of the dura mater, showed a high signal amplitude and resolution, even for high frequencies (Arena et al. J Physiol, 2016). Therefore, we expanded the spatial density of epidural electrodes and optimized a protocol for the surgical implantation of a chronic array of 17 stainless steel electrodes by covering most of the cortical areas of a rat brain. Then, in combination with protocol for head restraining (Moore et al. Nat Protocols, 2014), we obtained multi-channel spontaneous EEG recordings from rats during wakefulness and during the exposure to low and high doses of 3 different anesthetics (propofol, sevoflurane and ketamine).