ABC Radio’s The Philospher’s Zone has just had a two-part special on the problem of consciousness – with particular reference to sleep.
The first and second parts are both from a talk by Professor Giulio Tononi, a neuroscientist from the University of Wisconsin Madison.
Tononi discusses particular difficulties in looking for the ‘neural correlates of consciousness’ and particularly addresses what sleep tells us about conscious states.
In fact, Tononi heads up the Centre for Sleep and Consciousness that aims to understand “the mechanisms and functions of sleep and the neural substrates of consciousness” and gives a fascinating run-through of some of his most recent thinking on the area.
UPDATE: The first part seems to have disappeared off the website. The second part works just as well on its own, however.
Link to Part 1: ‘Higher levels of consciousness’.
Link to Part 2: ‘How Not To Be Unconscious’.
Mind Hacks 
The link to Part 1: ‘Higher levels of consciousness’ seems to be down. I tried posting a URL to a cached copy in this comment, but it doesn’t want to accept html code.