Evolution

[vulcanlogician]

Here ya go, Rik:

An individual, human or animal, is defined to be in a conscious state empirically by the behavioral ability to respond meaningfully to stimuli, whereas the loss of consciousness is defined by unresponsiveness... Because baseline brain energy consumption has been shown by 13C magnetic resonance spectroscopy to be almost exclusively dedicated to neuronal signaling, we propose that the high level of brain energy is a necessary property of the conscious state.
...
[This study] 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.

http://www.pnas.org/content/106/27/11096

I just read the abstract and the conclusion, but this study shows a direct correlation between consciousness and brain states. I had a bit of trouble following all the details, but I'm pretty sure this experiment links conscious states with high level brain energy.