Dear Klaas/Karl
When looking through the code of spm_hdm_ui, I was confused by the following commentary:
% P(1) - signal decay - d(ds/dt)/ds) half-life = log(2)/P(2) ~ 1sec
% P(2) - autoregulation - d(ds/dt)/df) 2*pi*sqrt(1/P(3)) ~ 10 sec
% P(3) - transit time (t0) ~ 1 sec
% P(4) - exponent for Fout(v) (alpha) c.f. Grubb's exponent (~ 0.38)
% P(5) - resting oxygen extraction (E0) ~ range 20 - 50%
% P(5 + 1:m) - input efficacies - d(ds/dt)/du) ~0.3 per event
Why is the half life computed by half-life = log(2)/P(2) and not half-life = log(2)/P(1 <- here's the difference)
Same for the autoregulation: Why 2*pi*sqrt(1/P(3)) and not 2*pi*sqrt(1/P(2))
Could it be, that the numbers have been mistaken here?
If you plug in empirical values,
[half-life = log(2)/P(1) and autoregulation = 2*pi*sqrt(1/P(2)) ] fit the approximations quite well,
[half-life = log(2)/P(2) and autoregulation = 2*pi*sqrt(1/P(3)) ] don't.
Any help would be greatly apprechiated
Cheers
Simon
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Simon Eickhoff
Institut for Medicine (IME); Research Center Jülich
Leo-Brandt-Str. 5; 52425 Juelich, Germany
Phone + 49 2461-61-5219 / Fax + 49 2461-61-2820
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