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Topological Analysis of Differential Effects of Ketamine and Propofol Anesthesia on Brain Dynamics

Research into the neural correlates of consciousness has found that the vividness and complexity of conscious experience is related to the structure of brain dynamics, and that alterations to consciousness track changes in temporal evolution of brain states. Despite inducing externally similar states, propofol and ketamine produce different subjective states of consciousness: here we explore the different effects of these two anaesthetics on the structure of dynamical attractors reconstructed from electrophysiological activity recorded from cerebral cortex of two non-human primates. We used two different methods of attractor reconstruction: the first embeds the recordings in a continuous high-dimensional manifold on which we use topological data analysis to infer the presence (or absence) of higher-order dynamics. The second reconstruction, an ordinal partition network embedding, allows us to create a discrete state-transition network approximation of a continuous attractor, which is amenable to information-theoretic analysis and contains rich information about state-transition dynamics. We find that the awake condition generally had the “richest” structure, with the widest repertoire of available states, the presence of pronounced higher-order structures, and the least deterministic dynamics. In contrast, the propofol condition had the most dissimilar dynamics to normal consciousness, transitioning to a more impoverished, constrained, low-structure regime. The ketamine condition, interestingly, seemed to combine aspects of both: while it was generally less complex than the awake condition, it remained well above propofol in almost all measures. These results may provides insights into how consciousness can persist under the influence of ketamine and the battery of measures used provides deeper and more comprehensive insights than what is typically gained by using point-measures of complexity.