Brain Physiology, Cognition and Consciousness group: topic
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Energy for Conscious Processing
Alfredo Pereira Jr
Tuesday, 22 April 2008 14:04 UTC
[Forwarded Message from Bernard Baars]
The article by Marieke L. Schölvinck, Clare Howarth, and
David Attwell in NeuroImage (just published) might be of interest to
everyone. It suggests that “conscious perception reflects
surprisingly small local alterations in mean cortical neuronal firing rate
and energy consumption: perceiving visual stimulus movement, altered
tactile vibration frequency, or tone stream separation, changes local
cortical energy use by less than 6%. energy use is the basis of functional
imaging techniques such as positron emission tomography (PET) and blood
oxygen level dependent functional magnetic resonance imaging (BOLD fMRI).”
I’ve been surprised that the conscious component doesn’t simply leap out of
the evoked potential trace in studies like Stan Dehaene’s lab does so
beautifully. Del Cul, Baillet & Dehaene recently showed that the difference
starts off quite small, and then becomes noticeably larger. Antti Revonsuo
and his students show similar results. I don’t know what the energetics of
that might be.
Notice, by the way, that Schölvinck et al are NOT doing conscious-
unconscious comparisons, but perceptual discriminations. From our point of
view, of course, that suggests they are not looking at “conscious perception
AS SUCH,” but rather “differences between conscious percepts.” They are not
doing contrastive analysis, to use the best term I’ve been able to think of.
I’d love to know what you think of this interesting finding.
With warm wishes,
Bernard Baars
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Dear Hans:
I agree with you that there is still a missing link. If we knew that consciousness depends on “activity X” in the brain we could detect changes in this activity and possible related (small) changes in energy consumption. The problem is that we do not have agreement about “activity X”. The paper authors assume it is firing rates. Peter Cariani thinks it is the temporal pattern of firing and in this case there is no reason to expect changes in energy consumption between different conscious episodes. I think it is the pattern of post-synaptic potentials in large populations, and in this case a small variation of energy consumption is expected to occur between e.g. a highly emotional episode and a boring one (just like energy consumption in muscles when a person is walking compared to standing still – otherwise one would not need physical activity to fight obesity…).
Finally, please do not forget that in more sophisticated studies (including fMRI) the researchers find a way to subtract non-conscious activity from the total (conscious + non-conscious) recorded brain activity, finding a difference that is attributed to conscious activity.Best Regards,
Alfredo
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Alfredo – you wrote:
“If we knew that consciousness depends on “activity X” in the brain we could detect changes in this activity and possible related (small) changes in energy consumption. The problem is that we do not have agreement about “activity X”. "Libet’s work does. In learning new skills, the delay present when awareness is present brings out the mediating aspect of consciousness where such can elicit a response time delay of 0.5 seconds or more. Once a task is learnt this delay goes away and we are left with the usual stimulus-response dynamic – IOW with awareness there is a stimulus-considered_response at work.
Review Libet’s work to come up with experimental design covering the point of engagment of the delay and the point of departure of such – and so the changes involved that indicate the presence of consciousness followed by its withdrawal.
(summary of his work is in his book “Mind Time”)
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Hans Ricke states an objection to my previous post.
“There I see a general difficulty in the neurobiological approach that I have mentioned before. Conscious perception as such, is happening almost all day long. It apparently happens even while dreaming. These studies are all looking into the brain physiology.”
This is a super-tricky metaphysical topic, namely the mind-body issue, which was raised roughly 6th century BCE and is still hotly debated in philosophy. In my view, scientists have to define a position that does not require a consensus on the M/B problem, because you’ll never see it. For that reason, in all of my work I’ve emphasized either (1) contrastive experimental cases, i.e. matched conscious and unconscious brain events; or (2) experimental comparisons between conscious stimuli (or other conscious contents), which comes down to standard perception and psychophysics, and its brain basis. Both of them presuppose some sort of mind-body monism, so that mind-body arguments can be avoided. I sometimes think of it as “dual-source inductivism,” meaning that it’s inductive, not a metaphysical position but one sensitive to evidence, and dual-source meaning that obviously we have two sources of relevant scientific evidence, namely that which is filtered through human heads, and that which is based on physical measures not primarily dependent on human heads. Again, I would insist that an empirical approach to consciousness must find a stable position that scientists can agree upon, including mind-body agnosticism, and which does not require prior consent from philosophers, because nobody has obtained that in two-and-a-half millenia. The reason why scientists have made a great deal of progress in the last two or three decades is because they have side-stepped mind-body debates.
Best to all,
Bernard
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Dear Bernard,
I did not mean to go into any metaphysical topic and I am all for bypassing these issues and the agnostic position seems a perfect starting point. I am for a down to earth approach.
I was trying to get back to your initial wondering why consciousness does not seem to use as much energy in the Schölvinck study, whereas it does in Stan Dehaene’s. It would require a deeper diving into both studies than I can do at the moment, but the difference may be due to the two things you brought up.
One being consciousness ‘as such’, which may not require energy at all, or in another sense just require a kind of sustaining energy after someone got up and is in his/her normal state of being awake and alert, which happen during most of the daytime. ( The content of consciousness just changes without much energy needed – everyday, much known percepts )
The other would be different kinds of processes that take place when ‘certain’ percepts are happening. The possible processes while these percepts happen are probably ranging over the directly involved sensory processes, over mental associations to the percept, to emotional responses, to thought processes that will be triggered and of course that one of these processes or more of them become conscious.Which of these aspects is ‘caught’ by the research is simply due to the research design. That is why I hesitate to make a more precise statement: I do not know the different research designs well enough.
I am in general very reluctant to accept any research as referring to NCCs. If the research design is improper the correlate may just refer to some emotional or mental response to the percept and NOT to the consciousness of the percept.
Yours friendly
Hans
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