Brain reboot: Anaesthetic awakening

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  • Published: May 1, 2012
  • Author: David Bradley
  • Channels: MRI Spectroscopy
thumbnail image: Brain reboot: Anaesthetic awakening

Bootstrapping

Returning from oblivion - Imaging the neural core of consciousness. Positron emission tomography (PET) findings showing 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 showing 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 showing no evident activations. (Credit: Turku PET Center) 
Returning from oblivion
(Credit: Turku PET Center)

A new imaging study has demonstrated how the lower, more primitive part of the brain seem to pull consciousness up by its bootstraps, almost as a computer "boots" before the graphical user interface that is full self-awareness produced by the higher parts of the brain are initiated.

For many people coming round from an anaesthetic, as opposed to simply waking from a slumber, gives them an initial feeling of struggling to grasp at self-awareness before they become fully orientated and conscious. Personal perception of being put under anaesthetic seems not to be the reverse as one might imagine, rather than a clinging on to fading consciousness, full, general anaesthesia seems to cause a sudden "drop" into unconsciousness almost pulling the plug rather than putting the computer in standby, as it were.

The work on awakening from anaesthesia, however, suggests new clues for investigating the origins and reality of consciousness. It also hints at how animals that lack those parts of the brain that we consider the "higher", human regions, might perceive their surroundings and point to a better understanding of animal perception and awareness.

Harry Scheinin of the University of Turku in Finland, has collaborated with colleagues at the University of California, Irvine, in the USA, to take a close look at how the brain reboots after anaesthesia. They have found important differences in the timing of the activation of the primitive brain and the evolutionarily younger neocortex. The study is a component of a wider Research Programme on Neuroscience managed by the Academy of Finland.

Voluntary scanning

The team recruited twenty healthy, young volunteers and put them in a brain scanner while inducing anaesthesia in the volunteers using dexmedetomidine or propofol anaesthetic drugs. The subjects were woken up and their brain activity recorded as they emerged from the unconscious state. Dexmedetomidine is a commonly used sedative in hospital intensive care units while propofol is more commonly used to induce and maintain general anaesthesia during surgery, for instance.

The researchers explain that the anaesthesia triggered by dexmedetomidine is more akin to normal sleep as it can be reversed by mild physical stimulation or loud noise. This difference from general anaesthesia meant that the team could distinguish between changes in brain activity associated with a changing level of consciousness rather than the changes due to the direct pharmacological effects of the drug on the brain.

The team assessed the emergence of consciousness and full awareness in the volunteers between the unconscious state and their motor response to a spoken command. This was correlated with the activation of a core network involving sub-cortical and limbic regions. These apparently become functional and are coupled with parts of the frontal and inferior parietal cortices upon waking from the anaesthesia induced by dexmedetomidine. This reactivation of this network thus gives us subjective awareness of the external world and allows us to respond consciously through voluntary responses. The team found that the same deep-brain structures, i.e. the brain stem, thalamus, hypothalamus and the anterior cingulate cortex, are also activated first as the volunteers emerged from propofol anaesthesia. This suggests that there is a common mechanism of arousal that is independent of the mode of action of the drugs themselves in inducing anaesthesia. For either drug, activations when consciousness returns is largely localized in deep, evolutionarily older parts of the brain rather than in the neocortex.

"We expected to see the outer bits of brain, the cerebral cortex (often thought to be the seat of higher human consciousness), would turn back on when consciousness was restored following anaesthesia," says Scheinin. "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 conscious state must be restored before higher order conscious activity can occur," he adds.

Conscious separation

It would be interesting if we could investigate and separate responsiveness vs. consciousness from each other, and the state of consciousness from higher order ("contents") of consciousness," Scheinin told SpectroscopyNOW, "This might be difficult but we have some ideas. The ultimate goal should be to solve the unsolvable 'hard problem' of consciousness."

Related Links

Returning from Oblivion: Imaging the Neural Core of Consciousness, J Neurosci, 2012, 32, 4935-4943

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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