My understanding supports your comments but in a backward direction.
Paradoxically the neurons use up energy and function anaerobically
while working. Then the increase in oxygen levels occur after a thought
to resupply the nerons. This results in a delayed picture
of neuro activity but a relatively accurate one for functional magnetic
resonnance.
Ron Blue
-----Original Message-----
From: Neal Prakash <nprakash at rigel.oac.uci.edu>
To: neur-sci at net.bio.net <neur-sci at net.bio.net>; Mike Worden
<mworden at neurocog.lrdc.pitt.edu>
Date: Saturday, December 06, 1997 5:25 PM
Subject: Re: FMR?
>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
>veins).
>>>|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
>|>|Voila!
>|>| __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
>http://meded.med.uci.edu/~nprakash>lab:714-824-5031
>fax:714-824-2447
>>>
