Tuesday, 10 July 2012

Comments Remain Open

EFC 2012
Dear All (including students enrolled for credit and other who are following the discussion online):

The comments remain open. If your comment is to a particular author, please post it as a comment on their paper. If it is for more several authors, it is best to post multiply, to each author, if you want a reply. If you just want to register the comment, you can do it on the discussion section for the day.

Sunday, 8 July 2012

X. Measuring Consciousness (Monday July 9)


Alain Ptito (McGill) Neural Mechanisms of Blindsight after Hemispherectomy: Tapping into the Unconscious
Amir Shmuel (McGill) Neurophysiological and hemodynamic measurements of spontaneous activity and functional connectivity
Gilles Plourde (McGill) General Anesthetics for the Study Consciousness
Amir Raz (McGill) Hypnosis as Experimental Tool to Study Metacognition, Causality and Volition
John Searle (Berkeley) Consciousness and Causalityabstract -- discussion thread (commentary invited) -- video (to come)

John Searle: Consciousness and Causality


            Abstract: How do neurobiological processes in the brain cause consciousness? I think this is the most important question in the biological sciences today. Two related questions: Where exactly is consciousness realized in the brain and how does it function causally in our behavior? We know consciousness happens and we know the brain does it. How does it work? How do we approach this problem scientifically? The standard way is to go through three steps. First, try to find the neurobiological correlate of consciousness. Second, try to test if the correlations are in fact causal. Do the neurobiological states cause consciousness? Third, try to formulate a theory. Why do these processes cause consciousness at all, and why do these specific processes cause these specific conscious states? One depressing feature of this entire research project is that it does not seem to be making much progress.

Mystery of consciousness  a book by me. NYRB book
The Problem of Consciousness:
How to study consciousness scientifically
Free Will as a Problem in Neurobiology

Comments invited

Amir Raz: Hypnosis as Experimental Tool to Study Metacognition, Causality and Volition


apologies: video not available
      Abstract: An early form of psychotherapy, hypnosis has been tarnished by a checkered history: stage shows, movies and cartoons that perpetuate specious myths; and individuals who unabashedly write 'hypnotist' on their business cards. Hypnosis is in the twilight zone alongside a few other mind–body exemplars. Although scientists are still unraveling how hypnosis works, little is mystical about this powerful top-down process, which is an important tool in the armamentarium of the cognitive scientist seeking to unlock topical conundrums.  Philosophical research has revealed a great deal about three categories of behavior: conscious decision-making, authorship, and sense of control. However, little conclusive evidence regarding their interdependent nature has been found, due to the difficulties in separating their influences on tasks such as decision-making.

      Demacheva, I, M Ladouceur, E Steinberg, G Pogossova, A Raz (2012) The Applied Cognitive Psychology of Attention: A Step Closer to Understanding Magic Tricks. Applied Cognitive Psychology http://www.jgh.ca/uploads/Psychiatry/Articles%20PDF/Magic1-Published.pdf
      Raz, A. (2011). Does Neuroimaging of Suggestion Elucidate Hypnotic Trance? International Journal of Clinical and Experimental Hypnosis, 59(3), 363-377.http://www.jgh.ca/uploads/Psychiatry/Articles%20PDF/IJCEH2011.pdf
      Raz, A (2011) Hypnosis: a twilight zone of the top-down variety. Trends in Cognitive Sciences, December 2011, Vol. 15, No. 12http://psycho.unibas.ch/fileadmin/psycho/redaktion/Abteilungen/Klinische_Psychologie_und_Psychotherapie/Raz_2011_TINS.pdf
      Raz, A., & Whatley, B. (2009) Consciousness reduced: Will neuroscience confine the mind to the brain? PsycCRITIQUES - Contemporary Psychology, 54(39).http://www.jgh.ca/uploads/Psychiatry/Articles%20PDF/PSYCCRITIQUES_consciousness_reduced.pdf
      Raz, A., & Zigman, P., (2009). Using Magic as a Vehicle to Elucidate Attention. In A. Finazzi AgrËœ et al. (Eds.), Encyclopedia of Life Sciences. London: John Wiley & Sons, Ltd.
      Raz, A. (2009) Varieties of Attention: A Research-Magician's Perspective. In G. Bernston and J. Cacioppo (Eds.), Handbook of Neuroscience for the Behavioural Sciences (pp. 361-369). Hoboken: John Wiley and Sons, Inc. http://bit.ly/RazHypno

Comments invited

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.
 
        Carbonell F, Bellec P, Shmuel A. (2011) Neuronal Correlates of Spontaneous Fluctuations in fMRI Signals in Monkey Visual Cortex: Implications for Functional Connectivity at Rest. Brain Connect. 2011;1(6):496-510
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

Gilles Plourde: General Anesthetics for the Study Consciousness


    Abstract: Although general anesthetics have been used for more than 150 years and suppress consciousness in a predictable manner, their mechanisms of action are not fully elucidated. Numerous studies have been devoted to understanding how general anesthetics impair consciousness in human subjects using either functional brain imaging or electrophysiology. These studies have obvious relevance for the study of consciousness, particularly for consciousness as a waking state and in regard to self-awareness. They have revealed the critical involvement of the thalamus and offered evidence supporting the hypothesis that the anesthetized state is associated with loss of connectivity and attenuation neuronal oscillations in the high-gamma range. In this lecture, I will first review the aspect of the pharmacology of general anesthetic that are essential to appreciate the possibilities that these drugs offer to study consciousness as well as their limitations. In the second part, I will summarize the main findings that emerge from the literature.

    Alkire MT, Hudetz AG, Tononi G. Consciousness and anesthesia. Science 2008; 322: 876-80 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2743249/
    Franks NP. General anaesthesia: from molecular targets to neuronal pathways of sleep and arousal. Nat Rev Neurosci 2008; 9: 370-86http://hopecenterdev.wustl.edu/training/bio5663/Documents/FRANKS_NATNEUROSCI_rev.pdf
    Critical involvement of the thalamus and precuneus during restoration of consciousness with physostigmine in humans during propofol anaesthesia: a positron emission tomography study http://bja.oxfordjournals.org/content/106/4/548.full

Comments invited

Alain Ptito Neural Mechanisms of Blindsight after Hemispherectomy: Tapping into the Unconscious


      Abstract: Hemispherectomy subjects (Hs) have offered a unique opportunity to study the role that subcortical structures play in blindsight because the hemisphere contralateral to the blind field is absent or non-functional. We first showed Hs could detect and localize simple targets and moving gratings, discriminate grating velocity and differentiate forms in their blind field. We suggested a role of subcortical pathways i.e. the superior colliculi (SC), with the participation of the remaining hemisphere. We reported the existence of residual vision with awareness in the blind field and showed that Hs were insensitive to motion-in-depth in their hemianopic field and that some possess blindsight as shown by a spatial summation effect i.e. subjects only react to the stimulus presented in their intact field, without being aware that the simultaneous presentation of another stimulus in their blind field lowers their reaction time. We hypothesized that this indirect method to evaluate blindsight could involve subcortical mechanisms without requiring cortical processing, and without the subject's awareness. We then reported that the cellular integrity and metabolism of the ipsilateral SC in the vervet monkey are much less affected than those of the dorsal lateral geniculate nucleus (dLGN) after neonatal hemispherectomy. We underlined the importance of controlling intraocular light scatter and published the first fMRI study on residual vision. We concluded that the SC are likely implicated in blindsight in Hs, and we recently utilized the color vision properties of collicular cells to demonstrate its involvement in the residual visual abilities of Hs. Since the primate SC does not receive retinal input from shortwave-sensitive (S-) cones involved in colour vision, consequently rendering them colour blind to blue yellow stimuli, we tested 3 Hs who had reliably shown blindsight. They demonstrated a spatial summation effect only to achromatic stimuli suggesting that their blindsight is colour-blind to blue/yellow stimuli and is not receiving input from retinal S-cones. We concluded that blindsight is likely mediated by the SC in Hs. We were the first to use Diffusion Tensor Imaging (DTI) Tractography to investigate pulvinar connectivity in humans and SC connectivity in Hs with and without blindsight. We demonstrated the presence of projections from the ipsi- and contralesional SC to primary visual areas, visual association areas, precentral areas/FEF and the internal capsule of the remaining hemisphere in Hs with 'Type I' or 'attention-blindsight' and an absence of these connections in Hs without it. In another study using fMRI, we demonstrated in Hs that achromatic stimuli but not S-cone-isolating stimuli in the blind field of a subject with blindsight activated visual areas FEF/ V5 and that the cortical activation pattern was enhanced by achromatic stimuli only. We concluded that the human SC is blind to S-cone-isolating stimuli, and that blindsight is mediated by an S-cone-independent collicular pathway, at least in Hs.
      The SC is the main recipient of retinal projections in lower mammals with a phylogenetically older and more primitive visual system than humans. Similar but weaker retinocollicular projections also exist in humans. Although existing SC connections to the remaining cortical areas seem to play a pivotal role in unconscious vision, blindsight subjects remain unaware of the information processed in their blind visual field. One possibility for the lack of awareness may lie in the lack of synchronicity in cerebral activation. The human visual pathways process information simultaneously and yet are able to work independently of each other (as is the case following a circumscribed lesion in a visual cortical area). For conscious perception, however, a specific synchronized activation pattern of different cortical areas involving ventral, parietal and frontal visual areas is believed to be crucial. Our results indicate that Hs with 'Type I' or'attention blindsight' are able to enhance visual performance in their blind field, but remain unaware of visual processing presumably because they are unable to access a more complex synchronous cortical activation pattern involving higher top-down mechanisms necessary for conscious vision.

      Neural substrates of blindsight after hemispherectomy http://unfweb.criugm.qc.ca/jdoyon/cours_6032/Neuroscientist%202007.pdf
      Unconscious vision: new insights into the neuronal correlate of blindsight using diffusion tractography http://brain.oxfordjournals.org/content/129/7/1822.full
      Neural Substrates of Blindsight in Hemispherectomized Subjects. http://www.bic.mni.mcgill.ca/~sandra/pdfs/Review_2007.pdf
      The nature of consciousness in the visually deprived brain http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3111253/

Comments invited