Dear Felix,
My apologies for the delay in replying. You asked about functions containing the DCM neuronal model for fMRI (fx) and the haemodynamic model (gx). I have confirmed the following with Karl:
spm_*_fmri.m - Functions for DCM (fMRI)
spm_gx_state_fmri.m - Function used by spm_dcm_generate for simulating data
spm_*_hdm.m - Functions for the Neural demo toolbox
spm_*_dcm.m - Redundant and will be removed in a future released.
Regarding the relationship between the priors in spm_dcm_fmri_priors and spm_fx_fmri... The former are log scale parameters on the values hard coded in spm_fx_fmri.
I hope that helps.
Best,
Peter.
Peter Zeidman, PhD
Methods Group
Wellcome Trust Centre for Neuroimaging
12 Queen Square
London WC1N 3BG
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-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On Behalf Of Felix Schlegel
Sent: 23 October 2014 11:39
To: [log in to unmask]
Subject: [SPM] Confusion about DCM functions, names & changes in SPM12
Hello,
I would like to play around with DCM parameters to create some artificial BOLD responses.
Is there a simple way to use SPM for this didactic purpose (no real input data, only considering a single brain region)?
I think the demo script "spm_neil.m" (in SPM12) seems to be closest to what I want (it calls spm_hdm_priors.m, which I can manipulate manually, but which does not seem to be used by the other dcm routines anymore), although the neuronal response is not modeled in that demo, but fixed.
In general, I am very confused about the files containing the state equations: In older SPM versions (which most tutorials refer to), "spm_fx_dcm" and "spm_gx_dcm" seem to be used quite consistently.
In SPM12, however, when I want to create some artificial data using "spm_dcm_generate", it specifies the model by referring to "spm_fx_fmri" and "spm_gx_state_fmri".
Could someone help me to solve my confusion? The files "spm_gx_dcm", "spm_gx_fmri", "spm_gx_hdm" all have more or less the same header and I wonder when which of those is used. (The same goes for the spm_fx_* files). Or are some of those files just relics of older SPM versions?
Also, the file spm_fx_fmri.m, which seems to be used in SPM12, contains a hard coded version of the hemodynamic parameters (line 175), which differ in their values from spm_hdm_priors.m.
Thank you for any answer or if you could refer me to a more detailed manual/description of the spm functions.
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