Consciousness & Brain Functional Complexity in Propofol Anaesthesia

Measures of algorithmic and process complexity, applied to functional MRI BOLD signals from individuals under propofol sedation, vary in their ability to distinguish sedation levels. Temporal complexity measures are more sensitive than topological ones. All measures strongly relate to a single underlying construct—termed 'overall complexity'—which explains most variance in the data, as assessed by principal component analysis. This overall complexity discriminates between sedation levels and propofol serum concentrations, supporting the idea that consciousness is linked to complexity, regardless of how complexity is measured.

Study at a glance

Abstract

The brain is possibly the most complex system known to mankind, and its complexity has been called upon to explain the emergence of consciousness. However, complexity has been defined in many ways by multiple different fields: here, we investigate measures of algorithmic and process complexity in both the temporal and topological domains, testing them on functional MRI BOLD signal data obtained from individuals undergoing various levels of sedation with the anaesthetic agent propofol, replicating our results in two separate datasets. We demonstrate that the various measures are differently able to discriminate between levels of sedation, with temporal measures showing higher sensitivity. Further, we show that all measures are strongly related to a single underlying construct explaining most of the variance, as assessed by Principal Component Analysis, which we interpret as a measure of "overall complexity" of our data. This overall complexity was also able to discriminate between levels of sedation and serum concentrations of propofol, supporting the hypothesis that consciousness is related to complexity - independent of how the latter is measured.