Amir Shmuel Neurophysiological and hemodynamic measurements of spontaneous activity and functional connectivity
Abstract: Recent functional MRI (fMRI) studies in humans have demonstrated large amplitude slow (< 0.1 Hz) fluctuations in the resting state. Importantly, these spontaneous fluctuations in the Blood-Oxygenation-Level-Dependent (BOLD) signal are often synchronized over distant parts of the brain, a phenomenon termed resting-state functional connectivity. Functional connectivity analysis identifies resting-state networks of areas that also coactivate in response to stimuli or tasks. In my talk, I'll first explore whether fMRI-measured spontaneous fluctuations reflect those seen in neurophysiological activity. I will then demonstrate that resting-state functional connectivity exists in a hierarchical manner in space. In addition to the commonly reported networks on the spatial scale of cortical areas, smaller networks can be observed at the resolution scales of sub-areas and cortical columns. I will conclude with hypotheses on the mechanisms involved, the role of spontaneous activity, and implications for clinical neuroscience.
http://www.ncbi.nlm.nih.gov/pubmed/22444074
Shmuel A, Leopold DA (2008) Neuronal Correlates of Spontaneous Fluctuations in fMRI Signals in Monkey Visual Cortex: Implications for Functional Connectivity at Rest. Hum Brain Mapp. 2008 Jul;29(7):751-61 http://www.ncbi.nlm.nih.gov/pubmed/18465799
Smith et al., 2009 Correspondence of the brain's functional architecture during activation and rest http://www.pnas.org/content/106/31/13040.full
Comments invited
Yet again, this talk makes me think about how complex and somewhat incoherent the brain (and the underlying cognitive processes) are. When I see all the very detailed sub-analyses that A. Shmuel does in his participants, I'm really understanding how far away we are from having resolved the easy problem of consciousness. Even though we anticipate the easy problem to be solved at some point in time, it's indeed very audacious from us to dare trying to understand the feeling emerging from the doing.
ReplyDeleteWe might be "more or less enthusiatic" about discoveries on the neural bases of consciousness, thinking that it'll never explain anything about the feeling of our behaviours. However, we're maybe at the very early beginnings of our researches, just like were the theories prior to the discovery of Higgs' bosons. They just succeeded in linking something that was thought to be linked, without ever being sure it could actually be linked, maybe we're on the same path?
I agree with the general notion that I believe comes up from this comment, namely that finding the neuronal mechanisms underlying consciousness is probably one of the hardest questions to address at this point, and also probably a question which is not well defined compared to other existing questions.
DeleteAmir Shmuel.
I realize I asked a stupid-sounding question at the discussion (it may indeed BE a stupid question). But what I still don't get is, if Dr. Shmuel showed that the spontaneous fluctuations in the metabolic fMRI/PET signal are correlated with a neural signal such as the LFP (local field potential), and other studies have shown correlation between the metabolic signal and breathing, how much of the spontaneous fluctuations reflect breathing-induced artifact and how much is induced by neural activity? Also this may be naive of me to ask, but is the breathing correlation really an artifact, or are neural signals also affected by breathing (at least at the .01 - .1Hz range as discussed by Dr. Shmuel)? It would have been informative to see fourier analysis of the LFP signal in this low-frequency range.
ReplyDeleteThis is not a stupid question at all.
DeleteThe following is a reference that quantifies the amount of variance in human resting-state activity that can be explained by breathing artifacts, and the amount of variance that can be explained by neurophysiological activity:
Bianciardi M, Fukunaga M, van Gelderen PO, Horovitz SG, de
Zwart JA, Shmueli K, Duyn JH. 2009. Sources of functional
magnetic resonance imaging signal fluctuations in the
human brain at rest: a 7 T study. Magn Reson Imaging 27:
1019–1029.
Based on other studies of hypercapnia and neurophysiology, I expect that the variation in breathing rate are not large enough to change neurophysiological activity, so these are two (neurophysiological activity and breathing rate) independent variables that influence fMRI-based resting state activity.
(I know I already asked Amir this question druing the question session but I think this is worth being on the blog)
ReplyDeleteFirst, I was wondering wether studies on default mode network had been done so far? and secondly, I was wondering to which extent the presence of a decreasing activity of the default mode network was thougth to be related to consciousness? that being said, I was wondering, if some some species don't have this decreasing activity in the default mode network, whether the default mode mode network might be use as a citerion to distinguish the species having cnsciousness or not?
On: 'whether studies on default mode network had been done so far': just google it, you'll find plenty.
DeleteOn: 'to which extent the presence of a decreasing activity of the default mode network was thougt to be related to consciousness': the following paper is the one that gets closer than any other paper I know to relating activity in the default mode network to consciousness:
Decoupling of the brain's default mode network during deep sleep. Silvina G. Horovitz et al. PNAS (2009).
On: 'if some some species don't have this decreasing activity in the default mode network, whether the default mode mode network might be use as a citerion to distinguish the species having cnsciousness or not?': well, if we believe that the default mode network does underlie consciousness, than your suggestion makes sense.
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DeleteThank you for the reference Dr. Shmuel, I was also wondering about potential involvement of the default mode network (DMN) in modulation of conscious awareness. A few of the talks during the Institute, and most recently, Dr. Plourde's, hinted at a role for the thalamus in modulation of conscious awareness. The DMN is made up of only cortical brain structures, namely the Anterior cingulate, Posterior cingulate, Medial Prefrontal and Inferior parietal cortices. It would make a stronger case both for involvement of the DMN and of the thalamus in modulation of conscious awareness if one could show coordinated activity between the two. Clinical reports may provide key insights into the coupling of these different brain regions. Mild Traumatic Brain Injury has been shown to cause disruption of activity in the MPFC (a key DMN region), and I also came across an article that showed that resting state thalamic activity was reduced in mTBI patients. This I thought was interesting because selection criteria for study participants were posttraumatic amnesia and/OR loss of consciousness. http://radiology.rsna.org/content/260/3/831.long
DeleteThese kinds of associations/questions can help further our understanding of consciousness, both 'normal' and impaired.
Xavier Dery @XavierDery
ReplyDeleteStill waiting for today's iteration of W. James quoting! QT @syka_tts: #TuringC W. James, the Most Cited Author of the summer school?
10:43 AM - 9 Jul 12 via Twicca Twitter app
REPLYING TO:
Simon @syka_tts
#TuringC W. James, the Most Cited Author of the summer school?
10:31 AM - 9 Jul 12
I am happy to find your distinguished way of writing the post.WHAT IS CONSCIOUSNESS
ReplyDelete