This project, from a team directed by Irene Rembado at the Allen Institute, investigates two unknown questions related to consciousness research.

The first relates to a measure of consciousness based on a leading theory in the field. The Perturbational Complexity Index (PCI) is a measurement that has been shown to be directly related to the conscious state of healthy volunteers and patients. Based on a theoretical concept called neuronal integration and differentiation, this empirical measure of consciousness was derived from Integrated Information Theory (IIT), one of the most prominent theories of consciousness. Despite its recognized success in distinguishing between conscious and unconscious states in humans, little is known about the underlying mechanisms. In particular, we don’t know what happens to brain cells during this process, or why they act together in a way that produces such immense complexity.

The second question relates to what happens when consciousness is reduced, increased or altered in other ways. Such experiments can rarely be done in humans, so animal models provide the best alternative. This project will seek to answer both questions by using PCI and a range of other ways to alter consciousness whilst measuring the activity of brain cells - both at a small scale and in large networks.

The project team will develop a mouse model of this paradigm that combines large-scale EEG signals with recordings from multiple Neuropixels probes, small electrodes that can be inserted into rodent brains without causing any significant damage. The electrodes will measure both cortical and subcortical areas to cover a large region of the brain. This is important because consciousness cannot be reduced to the activity of a small number of brain cells. Instead, it seems to involve a vast network of complex interactions between these cells. To alter states of consciousness, the team will administer substances such as anesthetics and the psychedelic psilocybin, which has been used safely in research projects.

The main hypothesis is that PCI will track the conscious state of an animal by decreasing from wakefulness to anesthesia and increasing from wakefulness to psychedelic state. That said, it remains unclear whether psychedelic drugs really do increase consciousness or whether they just alter the experience of the individual. Thanks to a new and unique setup, the project will be able to probe the activity and interactions within/between different brain regions across the different states at multiple scales: from large areas to small clusters of brain cells.

If successful, this study will provide new information on which specific brain regions are responsible for the large-scale brain dynamic captured by the PCI measurement. By extension, it will therefore also inform us on how these regions allow for consciousness. New information about this method may support or oppose IIT as a leading theory of consciousness.