returns a hemodynamic response function
FORMAT [hrf,p] = pr_spm_hrf(RT,[p]);
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
hrf - hemodynamic response function
p - parameters of the response function
_______________________________________________________________________
Copyright (C) 2005 Wellcome Department of Imaging Neuroscience
0001 function [hrf,p] = pr_spm_hrf(RT,P); 0002 % returns a hemodynamic response function 0003 % FORMAT [hrf,p] = pr_spm_hrf(RT,[p]); 0004 % RT - scan repeat time 0005 % p - parameters of the response function (two gamma functions) 0006 % 0007 % defaults 0008 % (seconds) 0009 % p(1) - delay of response (relative to onset) 6 0010 % p(2) - delay of undershoot (relative to onset) 16 0011 % p(3) - dispersion of response 1 0012 % p(4) - dispersion of undershoot 1 0013 % p(5) - ratio of response to undershoot 6 0014 % p(6) - onset (seconds) 0 0015 % p(7) - length of kernel (seconds) 32 0016 % 0017 % hrf - hemodynamic response function 0018 % p - parameters of the response function 0019 %_______________________________________________________________________ 0020 % Copyright (C) 2005 Wellcome Department of Imaging Neuroscience 0021 0022 % Karl Friston 0023 % $Id: spm_hrf.m 387 2005-12-17 18:31:23Z klaas $ 0024 0025 0026 % global parameter 0027 %----------------------------------------------------------------------- 0028 global defaults 0029 try 0030 fMRI_T = defaults.stats.fmri.t; 0031 catch 0032 fMRI_T = 16; 0033 end; 0034 0035 % default parameters 0036 %----------------------------------------------------------------------- 0037 p = [6 16 1 1 6 0 32]; 0038 if nargin > 1 0039 p(1:length(P)) = P; 0040 end 0041 0042 % modelled hemodynamic response function - {mixture of Gammas} 0043 %----------------------------------------------------------------------- 0044 dt = RT/fMRI_T; 0045 u = [0:(p(7)/dt)] - p(6)/dt; 0046 hrf = pr_spm_gpdf(u,p(1)/p(3),dt/p(3)) - pr_spm_gpdf(u,p(2)/p(4),dt/p(4))/p(5); 0047 hrf = hrf([0:(p(7)/RT)]*fMRI_T + 1); 0048 hrf = hrf'/sum(hrf);