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Neal Prakash nprakash at rigel.oac.uci.edu
Sat Dec 6 17:10:19 EST 1997

On 6 Dec 1997, Mike Worden wrote:
|ablab at usa.net wrote:
|: I've seen there are some physicists out there also. Can someone explain
|: how Functional Magnetic Resonance (hope it's correct) works? It should
|: be one of the methods used in the brain function scanning. 
|...and it is.
|In a nutshell:
|Local increases in neural activity lead to
|local increases in local blood flow (outpacing demand for O2), leads to
Mike, What do you mean by this? My understanding of the situation now
(Malonek & Grinvald, 1996; and several others I don't have in front of me
right now) is that there is an initial increase in O2 demand, as seen
clearly by imaging spectroscopy studies, and now also by fMRI (with higher
temporal resolution than most previous work). So the "classic" BOLD signal
does indeed reflect local decreases in deoxyHg, but there is an initial
dip in the signal (with the proper temporal resolution) that reflects the
initial increase in deoxyHg.

Why do I bring this up??? Because this O2-demand signal is probably a
better spatial indicator of neuronal activity (i.e. from the capillary 
beds) that is uncontaminated by blood vessel signals (i.e. arteries and

|local decreases in the concentration of deoxyHg, leads to
|more homogenous local magnetic field, leads to
|less T2* transverse spin dephasing, leads to
|increased MR signal return in T2*-weighted images
|    __Mike Worden mworden at neurocog.lrdc.pitt.edu
|  o/  630 LRDC  University of Pittsburgh 
| <\__,Pittsburgh, PA 15260  412 624-5279
|  ">  http://neurocog.lrdc.pitt.edu/~mworden
|   `  -climb

-Neal Prakash 
Department of Psychobiology, College of Medicine

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