Dear Ingo,
A review of metabolic and neurophysiological
coupling which might be helpful is:
[1] Jueptner, M. and Weiller, C., Review: Does measurement of regional
cerebral blood flow reflect synaptic activity?-Implications for PET and
fMRI, Neuroimage, 2 (1995) 148-156.
The authors review results which (in accordance with Karl's
statements) support the idea that it is pre-synaptic activity
(both excitatory and inhibitory) which is directly related to
local metabolic responses.
Sincerely,
Eric
Eric Zarahn
University of Pennsylvania
>
> Dear Ingo,
>
> > my question concerns the use of the contrast 2 results of SPM
> > calculations fo fMRI data sets. Applying contrast 2 to PET data
> > indicated areas of deactivation or inhibition. Can this option
> > (negative contrast) also be applied to fMRI data in the same way. If
> > yes, how to explain a negative BOLD effect?
>
> This question will, I am sure, excite a lot of answers (in people's
> minds at least). In principle the situation is exactly the same for
> PET and fMRI. A deactivation in fMRI is simply an activation on
> comparing the baseline condition to the index condition. This reflects
> the relative nature of fMRI measures of neurophysiology. It becomes
> more interesting in event-related fMRI where one has to posit a
> reduction in BOLD signal that is presumably mediated by a local
> reduction in mean synaptic activity (below tonic resting or control
> levels). To do this one has to suppose that the synaptic
> activity-hemodynamic response coupling is monotonic over 'resting'
> levels (if not symmetric about them). I believe there are animal
> models of this effect using optical imaging but I cannot recall where I
> saw these data.
>
> With best wishes - Karl
>
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