Dear SPM experts,
I hope this email finds you well. I am currently working on a research project involving the use of the SPM software. I have a question regarding the Hemodynamic Response Function (HRF) function in the spm_hrf.m file.
I have gone through the code and I understand that there are seven parameters (p(1) to p(7)) involved in modeling the HRF. However, I would appreciate some clarification on the specific meanings of each parameter.
% Haemodynamic response function
% FORMAT [hrf,p] = spm_hrf(RT,p,T)
% RT - scan repeat time
% p - parameters of the response function (two Gamma functions)
%
% defaults
% {seconds}
% p(1) - delay of response (relative to onset) 6
% p(2) - delay of undershoot (relative to onset) 16
% p(3) - dispersion of response 1
% p(4) - dispersion of undershoot 1
% p(5) - ratio of response to undershoot 6
% p(6) - onset {seconds} 0
% p(7) - length of kernel {seconds} 32
%
% T - microtime resolution [Default: 16]
%
% hrf - haemodynamic response function
% p - parameters of the response function
I am particularly interested in understanding the mathematical or physiological significance of each parameter and how they interact to define the HRF.
Best regards,
Xiangnan Tian
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