ABSTRACT
The capacity of the human brain to sustain complex dynamics consistently drops when consciousness fades. Several recent studies in humans found a remarkable reduction of the complexity of cortical responses to local stimulation during dreamless sleep, general anaesthesia, and coma. So far, this perturbational complexity has never been estimated in non-human animals in vivo. Here, we quantify the complexity of electroencephalographic responses to intracranial electrical stimulation in rats, comparing wakefulness to propofol, sevoflurane, and ketamine anaesthesia. We confirm the changes previously observed in humans: from highly complex evoked activity during wakefulness, to simpler responses, suppression of high frequencies, and reduced phase-locking with propofol and sevoflurane. We then deepen our mechanistic understanding by analyzing functional connectivity, and by showing how these parameters dissociate with ketamine, and depend on intensity and site of stimulation. This approach opens the way for further direct investigations of the mechanisms underlying brain complexity and consciousness.
