PCI-like measure in rodents

The aim of this task is to record evoked related potentials (ERPs) following a cortical perturbation, from a large number of cortical areas of rats exposed to general anaesthesia and during wakefulness. The recorded evoked cortical activity is used to quantify cortical complexity and to study its relation to (un)consciousness (Massimini et al. Science, 2005) in rodents. According to the Integrated Information Theory (IIT), any physical system generates consciousness as it is able to integrate information (Tononi BMC Neurosci , 2004; Tononi et al. Nat Rev Neurosci, 2016). In terms of brain functioning, this is reflected in the ability to support complex activity patterns that are widely distributed among interacting neuronal ensembles (integration) and differentiated in both time and space (information content). This ability of the brain can be quantified by the Perturbational Complexity Index (PCI; Casali et al. Sci. Transl. Med., 2013; Comolatti et al. Brain Stimul., 2019) and, in agreement with IIT, this index has proved able to reliably discriminate between conscious and unconscious brain states in humans (Casali et al. Sci. Transl. Med., 2013; Sarasso et al. Curr. Biol. 2015; Casarotto et al. Ann. Neurol., 2016). Since PCI quantifies the complexity of EEG activity following a cortical perturbation, it is objective and does not require any verbal interaction, allowing it to be applied also to non-human animal models. Multi-channel EEG activity is recorded by means of 16 epidural stainless-steel electrodes chronically implanted across the scalp of head-restrained rats, covering most of cortical areas. Cortical perturbation is given by brief current pulses through a bipolar tungsten electrode placed in the right secondary motor cortex. The resulting evoked potentials are recorded from each rat in 3 different days during wakefulness and during general anaesthesia induced by 3 different anaesthetics (propofol, sevoflurane, ketamine). Then, a new version of PCI (PCIST, Comolatti et al. Brain Stimul., 2019) is applied during the analysis, in order to quantify variations of cortical complexity in rodents across conditions (wakefulness and general anaesthesia).