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Published online 21 January 2009 | Nature | doi:10.1038/news.2009.48
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Brain imaging measures more than we think
Anticipatory brain mechanism may be complicating MRI studies.
Popular brain-imaging techniques may be painting a misleading picture of brain activity, according to a new study.
Scientists using techniques such as functional magnetic resonance imaging (fMRI) make the assumption that blood flow into a particular brain region is directly linked to the amount of activity in the cells of that region.
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Hello, If something causes an anticipation of a "stimulius" after previous experiences, the anticipation itself becomes the stimulus. It could be like Pavlov's dog, where the bell caused salivation, or trigged anticipation for the previously experienced Gestalts. Simple, yes? What then goes on in the ?anticipation? process? RMT
RE: "Intentionality" vs. "Attentionality" -- [my interpretations in parenthesis] -- I think Das and Sirotin might have had stumbled upon the neuronal activity of "intentionality" that they had not expected; as they described: "The electrode and blood measurements coincided when the monkeys were looking at a dot, as expected." -- [they were clearly looking at the neuronal activity of "attentionality" detected in the visual cortices.] Whereas: "But when they were expecting to see something, and nothing actually appeared, there was an increase in the flow of oxygen-rich blood to the visual cortex without a corresponding electrode signal." -- [they clearly had observed a new phenomenon of the monkeys' "intentionality" at work, while without sending any electrical impulses as yet; however, if the monkeys did send out any corresponding electrode signals, these signals would have had been detected in their premotor cortices, and not in their visual cortices!?] Best wishes, Mong 1/21/9usct4:39p; author "Decoding Scientism" and "Consciousness & the Subconscious" (works in progress since July 2007), "Gods, Genes, Conscience" (2006: http://www.iuniverse.com/bookstore/book_detail.asp?isbn=0595379907 ) and "Gods, Genes, Conscience: Global Dialogues Now" (blogging avidly since 2006: http://www2.blogger.com/profile/18303146609950569778 ).
This should not come as a surprise to scientists. There are well documented studies which support these results. Most research into neural activity actually supports the half second delay between neural response and stimuli. Humans actually respond to stimuli .5s before any stimuli is even observed.
Kerri Smith wrote: "Popular brain-imaging techniques may be painting a misleading picture of brain activity, according to a new study." It might be the other way around: popular 'neuronal recording' techniques may be underestimating an important signal of brain activity. Neuronal recording techniques (spikes, MUA, and LFP) do miss aspects of sub-threshold synaptical activity (Brecht et al 2004, Nature). Apparently, some important neuronal activity that is involved in encoding predictions is missed in these recording techniques. The sub-threshold activity in V1 might be initiated by feedback of spiking activity in higher cortical areas and might trigger precise predictions. In V1 this activation could lead to sub-threshold synaptical processing that leads eventually to haemodynamic response ? but no LFP activity ? as shown in the article of Sirotin and Das. It remains to be shown how complex these predictions are. They could either just be simple rhythms as shown by Sirotin and Das or more complex predictions as suggested by various theories (i.e. Mumford 1992; Hawkins 2004). Previously, we have reported fMRI signal response from non-stimulated areas in V1 that is specific to the subjective perception of a visual illusion (Muckli et al. 2005, PLoS-Biol). The signal reflected the subjective interpretation of an ambiguous visual illusion. This might be an indication that there is rich predictive computation at the synaptic level detected by BOLD-fMRI but missed by extracellular recording techniques.
The findings of this study affirm one more time that neurofunctional brain imaging methods measuring changes in local blood flow do not necessarily permit us to identify the neural mechanisms underlying the detected changes. Rather, they suggest that blood-flow based imaging data must be considered with great prudence, when complex behaviors are examined that involve the subjects' active participation and anticipation. The findings should caution those who strife to correlate patterns of cerebral blood flow with human social behaviors in the hope of developing novel predictors for these behaviors.