A thought-provoking paper has just been published in one of my favourite journals, the Proceedings of the National Academy of Sciences USA. I probably shouldn't spend so much time reading PNAS, but there's almost always something of interest, as well as the satisfying feeling of skipping past all the pieces I don't have to read. This particular paper is by Robert Shulman and colleagues, and it tackles the spiky problem of consciousness, bottom-up. 
You can find the abstract here, at least for the moment. The title is: Baseline brain energy supports the state of consciousness. The claim is that high levels of brain energy are necessary (not sufficient) for people (not brains) to be conscious. That is, consciousness is a property of persons: not brains, but the whole wet, squamous, physiological mess.
When I say thought-provoking, I mean it; this is no casual repetition of what I call the Heinz doctrine of neuroscience: the uninterrogated claim that brainz meanz mindz. These people have encountered Bennett and Hacker's critique of cognitive neuroscience, and have made use of it. They see cognitive neuroscience as beset by problems of interpretation, researchers smuggling in subjective terms and thereby polluting what should be objective measurements.
To avoid this problem, Shulman et al. define consciousness operationally, as ‘the behavioral ability to respond meaningfully to stimuli'. They review research suggesting that the conscious state is associated with widespread fMRI activity and with high frequency neuronal firing - both of which need plenty of fuel. As an anaesthetic induces unconsciousness cerebral metabolism almost halves, high frequency (e.g. gamma-band) electrical activity reduces, and changes in cerebral oxygen consumption occur which appear proportional to changes in neuronal firing rates. Hence the idea that high global brain energy supports and is necessary for the state of consciousness.
Why this approach? Here's what the authors say:
"Our experimental protocols are describing brain properties of the person in the state of consciousness. This approach does not promise descriptions of the contents of consciousness, which would be defining subjective mental processes in objective terms. However, it has identified brain properties for the human in a conscious state that change with loss of consciousness; properties, at the neuronal level which in their interconnections display the characteristics of consciousness.
"Why do we identify the conscious state in so limited a behavioral way, by the human's response to stimuli, which is simplistic compared with psychological efforts to formulate its meaning? Certainly, the property of responding to a stimulus does not do justice to the richness of mental processes usually intended for the word. However, the very jarring nature of this limited test for the existence of consciousness illustrates an important point that we have made above and elsewhere. Namely, to study mental processes, we do not assume them to be already described by cognitive psychology. Generalizations of psychological concepts like fear, memory, attention, or cognition are of great utility in everyday life, but assuming them introduces subjectivity into brain research. In gaining scientific objectivity by avoiding the study of subjective concepts, we have confined our studies to bottom-up neuronal properties that are sketching a neuronal basis for a behaviorally defined state of consciousness."
A pity, therefore, that the authors define consciousness as ‘the behavioral ability to respond meaningfully to stimuli'. Isn't that a hint of subjectivity creeping back in?
There's an intriguing implication of Shulman et al.'s research which especially interests me, not least because it supports an argument I've been making for years! (Published speculations can be found on my website (search for consciousness), or in my book Brainwashing, pp. 182-185.) If consciousness requires high brain energy, then the ‘automatization' which takes place as we learn reflects a transition to less energetic states. If the brain, like the rest of the body, is geared towards efficient energy usage by the demands of survival in our evolutionary past, then consciousness may be a marker of inefficiency. Which makes the prime function of brains not ‘thinking' after all, but rather ‘thinking avoidance' wherever possible.
Think about that, and human behaviour starts to make much more sense.
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