Notes from a consciousness conference – Part 2: The neural symphony of consciousness fading

This is the second part of my report on the recent consciousness science conference (ASSC) in Brighton, UK.  After the first day, where I attended workshops on the science of hypnosis and magic, the four day conference began in earnest.

Fascinating piecemeal new details about consciousness were revealed at regular intervals throughout the conference.  For instance, have a look at this image below:

Believe it or not, the inner circles on the left and right are the same size (this is known as the Ebbinghaus illusion). Intriguingly, some people are more susceptible to this illusion than others (young children are hardly susceptible to it at all).  Geraint Rees’s lab has been looking into why this might be, and has found that those with a larger primary visual cortex have a less intense illusion.  Exactly why this is remains unclear, though Rees speculates that it’s as if there is a greater resolving power of more neurons in a larger visual cortex, so less opportunity to get confused in such ways.

Another exciting new feature of consciousness revealed at the conference relates to the question of whether consciousness is an all or nothing affair, or a continuum. Say there is a faint object in front of you – are there only two options: Fully consciously perceiving it, or being completely unconscious of the object? Or, instead, are there many different levels, where you can at times be partially aware of the object? The answer, as Bert Windey and colleagues showed, is that it actually depends on what you are trying to perceive.  If it’s a simple feature, such as a colour, then our consciousness works in a more graded fashion, where we can catch weak glimpses of the object at times. But if the feature is something more conceptual and high level, like a number, then the situation is much more as if we are either are conscious of it or we aren’t – there is no in between.

But the highlight of the early part of the conference for me was a fascinating symposium by Gernot Supp, Melanie Boly and Emery Brown, on what happens in the brain when consciousness fades. A common way of studying this is to examine what happens when a general anesthetic drug is administered.  The current answer is that the prefrontal cortex at the front of the brain and the thalamus (a central hub in the brain’s network, situated in the middle of the brain) start to sing the same tune: Their rhythms become tightly harmonized in the alpha band (about 10 Hz). Given that alpha waves are linked with relaxation, this is all unsurprising so far.  What is more surprising, though, is the mechanism by which this shuts down consciousness. The prefrontal cortex and thalamus are closely linked with consciousness, probably by acting as a general purpose staging area for any specific conscious contents arriving from elsewhere in the brain.  In anesthesia, these two key brain areas for consciousness are generating such an intense, harmonious (alpha wave) duet that the rest of the brain is barred from the song, and other cortical areas become isolated. And so those other parts of cortex that give detail to consciousness – managing our senses or memories, for instance – can’t access this consciousness network, and without any specific content to consciousness, there is no consciousness. This cutting edge research highlights the emerging picture of the neuroscience consciousness, where local islands of activity are simply not good enough. Instead, much of the cortex has to collaborate in a global wave of activity for consciousness to occur.  If you are interested in learning more about how the brain generates consciousness, you might like to take a look at my upcoming book, The Ravenous Brain.

In the next and final part of my report on the recent ASSC conference, I’ll be discussing the main theoretical debate of the conference: Whether our awareness is far broader than the limited part of our world we can consciously describe.