Neurophysiological assessment of consciousness: methods and mechanisms

rom experiments, but both methods and theories need further testing. In this project, we will test, compare, and seek to improve different theoretically based methods for objective assessment of consciousness in humans. In particular: In the last year we have: (1) Tested a method using magnetic brain stimulation (TMS) and measures the resulting electrical brain waves (by electroencephalography, EEG) in new ways. (2) Tested another EEG-based method that we recently developed (DTFI) using data from other laboratories. (3) Tested the P3b method, which records the brain waves (EEG) evoked by stimuli. Thereby, we also test. We have also started test analying EEG-data (from other laboratories) recorded during transient anesthesia of one hemisphere for testing theoretical predictions.

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.