Good post Neal. Excellent follow up. Sorry, I do not remember the
references.
But most likely it came from Science or Nature with in the last year.
Ron Blue
>>>>>>>>>>-----Original Message-----
From: Neal Prakash <nprakash at ea.oac.uci.edu>
To: Ron Blue <rcb5 at msn.com>
Cc: neur-sci at net.bio.net <neur-sci at net.bio.net>; Neal Prakash
<nprakash at ea.oac.uci.edu>; Mike Worden <mworden at neurocog.lrdc.pitt.edu>
Date: Sunday, December 07, 1997 2:12 AM
Subject: Re: FMR?
>Ron,
>>I think there is a mix up in the time scales we are talking about. First,
>on the millisecond range when neurons fire they probably act
>anaerobically (do you have a ref for this?), but as they recover their
>resting potential via the na/k atpase pump (tens to hundreds of
>millisecs), they work aerobically. this is when the oxygen
>use peaks and thus deoxyHg peaks (by 1 sec after activity). This peak has
>been documented for years spectroscopically (Frostig et al, 1990;
>revisted by Malonek and Grinvald, 1996) and only recently by fMRI (Li??et
>al, 1997). And if Magistretti (1996) is correct, then glial cells are the
>ones working anaerobically AND using up local glucose. Neurons rely on
>pyruvate shuttled over from the glial cells and predominantly oxygen from
>the capillaries for metabolism.
>>This increased O2 consumption is followed by increased blood flow, the
>positive BOLD signal. Unfortunately most fMRI and all PET studies lack the
>spatial resolution to distinguish brain from arteries and veins. That is
>why the spectroscopy data is more convincing as to what is happening.
>>>On Sat, 6 Dec 1997, Ron Blue wrote:
>>|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
>|>|>|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
>|>>|>>|>>>
