Neurophysiological assessment of consciousness: methods and mechanisms

What is consciousness? How can physical brain processes give rise to experiences? These are profound, unresolved biological problems with broad theoretical, clinical, and ethical implications. Particularly for patients with disorders of consciousness following brain injury, and during anesthesia (general anesthesia), reliable methods are needed to assess the state of consciousness. Recent research has led to theoretical advances and new, promising measurement methods. The Global Neuronal Workspace (GNW) model suggests that consciousness depends on an ignition of activity in a network of neurons in the brain that broadcasts information to more specialized brain areas. The Integrated Information Theory (IIT) posits that consciousness relies on a strongly unified (integrated) and information-rich system within the cerebral cortex. Both theories have recently received experimental support, but both the theories and the methods require further testing. In this project, we have tested, compared, and attempted to improve on various theory-based methods for the objective assessment of consciousness in humans. We have, i.a.: Tested a method using magnetic brain stimulation (TMS) combined with measurement of electrical brain waves (electroencephalography, EEG) in novel ways. Tested another EEG-based method that we developed earlier (DTFI). Analyzed brain wave data (EEG) from other laboratories during transient anesthesia of only one brain hemisphere (Wada test) and discovered evidence of new mechanisms (CSUR) that are relevant for consciousness.

The results of this project provide new insights into methods for assessing consciousness under altered brain states (anesthesia, psychedelic, sleep and dreaming), emphasizing complementary roles of perturbational(PCI)- and spontaneous EEG-based measures. The project provides improved foundation for more refined methods, and a new, clinically relevant NRC project on assessing covert consciousness in non-communicating patients. The results also suggest a novel principle for regulation of consciousness across and within hemispheres (CSUR: “cross-state unreceptiveness”).

The nature of consciousness is one of the deepest unsolved problems in biology, with wide-ranging theoretical, clinical and ethical implications. In particular, for patients with disorders of consciousness (DOC), and in anesthesia, reliable methods for assessing consciousness are urgently needed. Recent progress has yielded promising new methods and theoretical advances. The Global Neuronal Workspace (GNW) model states that consciousness depends on ignition of a fronto-parietal workspace that broadcasts information. The integrated information theory (IIT) claims that consciousness depends on a highly integrated and differentiated cortical system. Both theories have recently received remarkable experimental support, but data are still limited, and both methods and theories need further testing. In this project, we will test, compare, and seek to improve different, theoretically based, non-invasive electrophysiological methods for objective assessment of consciousness in humans, in particular: (1) Perturbational Complexity Index (PCI), which is based on IIT, and measured by electroencephalography (EEG) combined with transcranial magnetic stimulation (TMS); (2) A novel, connectivity-based EEG method that we recently developed (DTFI); and (3) the so-called global P3b response, which is based on the GNW model, and is recorded as event-related potentials (ERPs) evoked by series of auditory stimuli. Thereby, we also test the validity of the underlying theories, GNW and IIT. We will test and develop variants of these promising, EEG-based methods for assessing consciousness and connectivity under different conditions, such as sleep, rest (default mode, DM) vs. activity (external mode, EM), anesthesia, and in DOC patients. In particular, we will for the first time test the theories during transient anesthesia of one hemisphere (Wada test), which offers a unique opportunity for testing theoretical predictions, thus, contributing to the understanding of consciousness.