Primitive consciousness emerges first as you awaken from anesthesia

April 4, 2012
This image shows one returning from oblivion -- imaging the neural core of consciousness. Positron emission tomography (PET) findings show that the emergence of consciousness after anesthesia is associated with activation of deep, phylogenetically old brain structures rather than the neocortex. Left: Sagittal (top) and axial (bottom) sections show activation in the anterior cingulate cortex (i), thalamus (ii) and the brainstem (iii) locus coeruleus/parabrachial area overlaid on magnetic resonance image (MRI) slices. Right: Cortical renderings show no evident activations. Credit: Turku PET Center

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. Scientists now know why this may occur: primitive consciousness emerges first. Using brain imaging techniques in healthy volunteers, a team of scientists led by Adjunct Professor Harry Scheinin, M.D. from the University of Turku, Finland in collaboration with investigators from the University of California, Irvine, have now imaged the process of returning consciousness after general anesthesia. The emergence of consciousness was found to be associated with activations of deep, primitive brain structures rather than the evolutionary younger neocortex.

These results may represent an important step forward in the scientific explanation of human consciousness.

"We expected to see the outer bits of , the (often thought to be the seat of higher human consciousness), would turn back on when consciousness was restored following anesthesia. Surprisingly, that is not what the images showed us. 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 must be restored before higher order can occur" Scheinin said.

Twenty young healthy volunteers were put under anesthesia in a brain scanner using either dexme-detomidine or propofol . The subjects were then woken up while brain activity pictures were being taken. is used as a sedative in the setting and propofol is widely used for induction and maintenance of general anesthesia. Dexmedetomidineinduced 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 drugrelated effects on the brain. The staterelated changes in brain activity were imaged with positron emission tomography (PET).

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 dexme-detomidine-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, drugindependent 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.

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 sur-face 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 anesthetized brain provides new views into the emergence of consciousness. Anesthetic agents are clinically useful for their remarkable property of being able to manipulate the state of consciousness. When given a sufficient dose of an anesthetic, a person will lose the precious but mysterious capacity of being aware of one's own self and the surrounding world, and will sink into a state of oblivion. Conversely, when the dose is lightened or wears off, the brain almost magically recreates a subjective sense of being as experience and awareness returns. The ultimate nature of consciousness remains a mystery, but anesthesia offers a unique window for imaging internal when the subjective phenomenon of consciousness first vanishes and then re-emerges. This study was designed to give the clearest picture so far of the internal brain processes involved in this phenomenon.

The results may also have broader implications. 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 . Yet, much harder questions remain. How and why do these neural mechanisms create the subjective feeling of being, the awareness of self and environment the state of being conscious?

Explore further: A combined method for detecting consciousness

More information: Jaakko W. Långsjö, Michael T. Alkire, Kimmo Kaskinoro, Hiroki Hayama, Anu Maksimow, Kaike K. Kaisti, Sargo Aalto, Riku Aantaa, Satu K. Jääskeläinen, Antti Revonsuo and Harry Scheinin. Re-turning from Oblivion: Imaging the Neural Core of Consciousness. The Journal of Neuroscience 2012;32(14):4935-4943.

Related Stories

A combined method for detecting consciousness

January 9, 2012
The combination of transcranial magnetic stimulation and electroencephalography constitutes a new method allowing the traces of conscious activity to be revealed in brain injured patients.

Patients in a minimally conscious state remain capable of dreaming during their sleep

August 16, 2011
The question of sleep in patients with seriously altered states of consciousness has rarely been studied. Do ‘vegetative' patients (now also called patients in a state of unresponsive wakefulness) or minimally conscious ...

Recommended for you

Memory for details matures gradually

September 26, 2017
In contrast to previous assumptions, the hippocampus, a brain structure that is central to learning and memory, does not complete its maturation until adolescence. Scientists of the Max Planck Institute for Human Development, ...

No evidence of hidden hearing loss from common recreational noise: study

September 26, 2017
Exposure to loud noises during common recreational activities is widely cited as a cause of "hidden hearing loss." A new study of young adults, however, finds that while hearing is temporarily affected after attending a loud ...

Premature birth linked to older 'brain age' in adult life

September 26, 2017
New King's College London research suggests that babies born very prematurely show accelerated brain development in adult life, as their brains look 'older' compared to non-premature babies.

Overturning widely held ideas: Visual attention drawn to meaning, not what stands out

September 25, 2017
Our visual attention is drawn to parts of a scene that have meaning, rather than to those that are salient or "stick out," according to new research from the Center for Mind and Brain at the University of California, Davis. ...

Study reveals breakthrough in decoding brain function

September 25, 2017
If there's a final frontier in understanding the human body, it's definitely not the pinky. It's the brain.

Brain guides body much sooner than previously believed

September 25, 2017
The brain plays an active and essential role much earlier than previously thought, according to new research from Tufts University scientists which shows that long before movement or other behaviors occur, the brain of an ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.