Hello all,
We are trying to simulate a DCM data using the same connectivity model presented in DCM paper [1]. We use the spm_dcm_create.m function (SPM5), considering a SNR of 7 and the following parameters:
Load factors.mat (it is a file containing the vectors phot, mot and att, which presents information about the onsets of the three applied conditions; it can be obtained in the SPM web page http://www.fil.ion.ucl.ac.uk/spm/data/attention/)
Enter number of regions [4]
Name for Region 1 [V1]
Name for Region 2 [V5]
Name for Region 3 [PPC]
Name for Region 4 [PFC]
Spm_dcm_create: Basic parameters…
Interscan interval {secs} [3.22]
scans per session e.g. 256 [ 360]
Specify design in [scans]
Number of conditions/trials [3]
Name for condition/trial 1? [Photic]
vector of onsets - Photic [phot]
duration[s] (events=0) [10]
Parametric modulation [None]
Name for condition/trial 2? [Motion]
vector of onsets - Motion [mot]
duration[s] (events=0) [10]
Parametric modulation [None]
Name for condition/trial 3? [Attention]
vector of onsets - Attention [att]
duration[s] (events=0) [10]
Parametric modulation [None]
Specify intrinsic connections
-1 1 0 0
1 -1 1 0
0 1 -1 1
0 0 1 -1
Effects of Photic on regions…and connections
V1 1 0 0 0 0
V5 0 0 0 0 0
PPC 0 0 0 0 0
PFC 0 0 0 0 0
Effects of Motion on regions…and connections
V1 0 0 0 0 0
V5 0 1 0 0 0
PPC 0 0 0 0 0
PFC 0 0 0 0 0
Effects of Attention on regions…and connections
V1 0 0 0 0 0
V5 0 0 0 1 0
PPC 0 0 0 0 1
PFC 0 0 0 0 0
Then we obtained the following error:
“Modelled system is potentially unstable: Lyapunov exponent of combined connectivity matrix is 0.61803”
Check the output to ensure that values are in a normal range.”
We´ll appreciate any help about this.
Best regards,
1- Friston, K.J., Harrison , L. and Penny W. Dynamic causal modeling. NeuroImage 19 (2003) 1273-1302.(please, see figure 24 for more details)