[The physiology of consciousness]

Since 1990, the number of papers on the biological basis of consciousness has increased sharply. Some aspects of consciousness, such as its localization in the brain structure, relation of conscious and unconscious processes, selective attention and the waking state may be analyzed by objective means. According to the model proposed by Dennett and Kinsbourne (1990) and called Multiple Drafts Model, there is no isolated module in the brain structure where consciousness is located. Conscious experience is a serial stream of activity integrating various sources of information. All conscious processes are generated in various parts of the central nervous system and the state of consciousness moves throughout the brain structure. Consciousness is therefore not identical with the global activity of the brain. Information may enter the consciousness or stay out of it in relation to the actual contents of the conscious process. Experimental data supporting this notion were obtained by electrophysiology, positron emission tomography, nuclear magnetic resonance, measuring of blood flow and other metabolic methods. These studies indicate that the state of consciousness is characterized by an increased neuronal activity and they may show which part of the brain is activated at any given moment. Of all brain areas involved in conscious processes, the role of the frontal lobe is widely documented in clinical and physiological papers. Entry of any information into consciousness requires about 350 to 500 ms of neuronal activity. Subjective timing of conscious recognition of events in the outside world is then retroactively returned to the moment when the information enters the neural processing. Recent research indicates that the gap between the humanistic and neurophysiological approach becomes gradually narrowed. Still, we have to keep in mind that the basic question about the ideal or materialistic character of consciousness remains open.