A New Approach to the Study of Consciousness from the Theory of Integrated Information Point of View (Review)

The continuously increasing number of patients with chronic disorders of consciousness results in a growing need for an objective method of evaluating the level of consciousness in this category of patients in the clinical practice of neurologists and critical care physicians. One of the up-to-date approaches is based on the integrated information theory (IITC; Tononi, 2004, 2012, 2014). According to this theory the mechanisms determining the state of consciousness are integrally connected with certain conceptually coordinated structures that are closely interrelated with each other, and exist independently of external influences. On the basis of this theory Casali et al. (2013) developed approaches to the quantitative evaluation of integrated information in the neuronal system that depend on cause-and-effect relationships between its different elements. As a result, the term ‘perturbational complexity index’ has been introduced in respect of consciousness. It allows measurement of the integrity and spatio-temporal structure of the pattern of cortical excitation caused by non-invasive stimulation of the brain cortex, and, therefore, a description of the degree of complexity of the electrical signals in the brain. The values of this index differ in various states of consciousness (e.g., wakefulness, deep sleep, anesthesia, vegetative state etc.) that supports its use in patients with chronic disorders of consciousness as a new diagnostic tool.

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