Scientists from the University of Turku and from the University of California have now imaged the process of returning consciousness after general anesthesia. Results help to understand the human consciousness and they reveal, that primitive consciousness emerges first as you awaken from anesthesia. Using brain imaging techniques in healthy volunteers, a team of scientists led by Adjunct Professor Harry Scheinin, M.D. from the University of Turku, Turku, Finland in collaboration with investigators from the University of California, Irvine, USA, have imaged the process of returning consciousness after general anesthesia. This study was designed to give the clearest picture so far of the internal brain processes involved in this phenomenon. The emergence of consciousness was found to be associated with activations of deep, primitive brain structures rather than the evolutionary younger
neocortex. The study is published in the 4th of April 2012 issue of The Journal of Neuroscience.Primitive consciousness emerges. Awakening from anesthesia is often associated with an initial phase of delirious struggle before the full restoration of awareness and orientation to one’s surroundings. “We expected to see the outer bits of brain, the cerebral cortex, which is often thought to be the seat of higher human consciousness, to turn back on when consciousness was restored following anesthesia. Surprisingly, that is not what the images showed us” Scheinin tells. “In fact, the central core structures of the more primitive brain structures including the thalamus and parts of the limbic system appeared to become functional first, suggesting that a foundational primitive conscious state must be restored before higher order conscious activity can occur” Scheinin says. In the study twenty volunteers were put under anesthesia in a brain scanner and they were then woken up while brain activity pictures were being taken. The state-related changes in brain activity were imaged with positron emission tomography (PET).The subjects were put under anesthesia using either dexmedetomidine or propofol anesthetic drugs. Dexmedetomidine is used as a sedative in the intensive care unit setting and propofol is widely used for induction and maintenance of general anesthesia. Dexmedetomidine-induced unconsciousness has a close resemblance to normal physiological sleep, as it can be reversed with mild physical stimulation or loud voices without requiring any change in the dosing of the drug. This unique property was critical to the study design, as it enabled the investigators to
separate the brain activity changes associated with the changing level of consciousness from the drug-related effects on the brain. The emergence of consciousness, as assessed with a motor response to a spoken command, was associated with the activation of a core network involving subcortical and limbic regions that became functionally coupled with parts of frontal and inferior parietal cortices upon awakening from dexmedetomidine-induced unconsciousness. This network thus enabled the subjective awareness of the external world and the capacity to behaviorally express the contents of consciousness through voluntary responses. Interestingly, the same deep brain structures, i.e. the brain stem, thalamus, hypothalamus and the anterior cingulate cortex, were activated also upon emergence from propofol anesthesia, suggesting a common, drug-independent mechanism of arousal. For both drugs, activations seen upon regaining consciousness were thus mostly localized in deep, phylogenetically old brain structures rather than in the neocortex. A need for better depth-of-anesthesia technology. The researchers speculate that because current depth-of-anesthesia monitoring technology is based on cortical electroencephalography (EEG) measurement (i.e., measuring electrical signals on the surface of the scalp that arise from the brain’s cortical surface), their results help to explain why
these devices fail in differentiating the conscious and unconscious states and why patient awareness during general anesthesia may not always be detected. The results presented here also add to the current understanding of anesthesia mechanisms and form the foundation for developing more reliable depth-of-anesthesia technology. The unique awareness of self. The demonstration of which brain mechanisms are involved in the emergence of the conscious state is an important step forward in the scientific explanation of consciousness. Anesthesia offers a unique window for imaging internal brain activity when the subjective phenomenon of consciousness first vanishes and then re-emerges. Yet, the ultimate nature of consciousness still remains a mystery. How and why do these neural mechanisms create the subjective feeling of being, the awareness of self and environment – the state of being conscious? That´s the next big challenge to resolve.News from: The University of Turku is an internationally acknowledged, multidisciplinary scientific university located on the Southwest coast of Finland, in the vivid student city of Turku. It is one of the major universities in Finland.
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