Sleep research and consciousness

The human brain… 100 billion neurons and an “infinite” amount of networks arising from communication between these neurons. To think there is something outside that, the mind as something separate from the brain (cfr. Descartes dualism) seems to me like an underestimation of this extraordinary organ. I feel like there’s always something going on in that brain of mine. I’m not saying these are always productive things, but it amazes me how the brain can jump from one thing to another with so much ease and on such a short time span, to a point I often not realise all these thoughts that are going on inside me. Or on the other hand sometimes to a point that these thoughts become compulsive, being amazed how much control thoughts can have and how they direct my behavior.

There aren’t many times I experience a “blankness”, a silence in my mind, but perhaps the most prominent one is when I’m asleep. Sleep, as well as clinical conditions of vegetative state, provide an opportunity to gain more insight into the abstract notion of consciousness…

The groups of Adrian OwenPierre MaquetGiulio Tononi (with Tononi publishing a book about his theory of consciousness next month, phi) have already contributed a lot to this field.

Below you can see a video of Adrian Owen explaining his work in vegetative patients and showing how functional MRI can be used to ascertain someone is conscious or not.


I think it’s an amazing use of fMRI and I think a lot of people feel the same way, since this work has gotten widespread attention in a lot of other blogs and news sites as well. But what does this tell us about “unconsciousness”? Well you can say on the one hand that when such brain activity or such “command following” (the issuing of a command and the following of an action, or more specifically in the case of the vegetative patient the following brain activity) is absent when one isn’t conscious. But if such command-following isn’t observed in a vegetative patient, what does it tell us about unconsciousness, because in this case we might be talking about someone who is never going to return to a conscious state again, an irreversible unconsciousness.

What about the unconsciousness during sleep, a state that is reversible? A lot of studies reveal there is still processing done during sleep and even learning might occur during slow wave sleep, as has been revealed in a recent paper by Antony Gobel on skill learning (procedural learning) during sleep that got wide attention as well [1]. Although nothing really new or revealing, since the earlier studies already showed this to be the case for different modalities as well, e.g. odor cues enhancing consolidation of declarative memory [2]. But we aren’t explicitly aware of this processing. I think the recent paper by Mélanie Boly and Vincent Perlbarg might shed light on this [3]. Boly et al. inferred that the activity of the brain during NREM sleep is more modular, i.e. brain regions operating more independent of one another and thus less likely to be able to integrate information, as opposed to what is the case for when we are awake when more information is exchanged within the main functional brain networks and between these networks.

The following figure (resource: http://www.pnas.org/content/109/15/5856/F1.large.jpg), reveals the six main functional brain networks (that are similar for wakefulness and NREM sleep (A)), the different levels by which one can study connectivity/activity (B), and the amount of between subsystem versus within subsystem integration (as expressed in the so-called Functional Connectivity Ratio-FCR) for wakefulness as opposed to NREM sleep (C). What you can derive from this last figure is that for all the main functional networks between-subsystem integration (Iws which is thus representing this increased modularity) is larger during NREM sleep than during wakefulness.
This also poses some future questions on how this method and these results might be integrated with the previously mentioned studies with regard to learning. E.g. would you expect during instances of memory replay during sleep that there is increased between system integration as opposed to within system integration?

Consciousness has long been related to more philosophical questions and issues, so it excites me that neuroscience has now taken a step towards understanding and elaborately studying this interesting concept as well.

[1] Antony, J. W., Gobel, E. W., O’Hare, J. K., Reber, P. J., & Paller, K. A. (2012). Cued memory reactivation during sleep influences skill learning. Nature neuroscience.
[2] Rasch, B., Büchel, C., Gais, S., & Born, J. (2007). Odor cues during slow-wave sleep prompt declarative memory consolidation. Science, 315(5817), 1426–1429.
[3] Boly, M., Perlbarg, V., Marrelec, G., Schabus, M., Laureys, S., Doyon, J., Pélégrini-Issac, M., et al. (2012). Hierarchical clustering of brain activity during human nonrapid eye movement sleep. PNAS, 109(15), 5856–5861.
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