Hej, Hej,
I am working on a simple motor task and am trying to model connectivity patterns in core motor regions.
Concerning DCM for induced responses, I have two basic questions and am happy for any consideration.
.
First, you have the option for several inputs when you define your model. I am considering a time window of 1000ms and
the induced activity linked to movement starts around 150-250 ms (with trial-to-trial variability). I am thinking now if I may use
several inputs, e.g. 100 200 300 400 500ms because 1. of the variability of the onset 2. the induced components are not nearly as sharp
as an averaged ERP and 3. the movement needs to bei maintained steadily consciously which I interpret as ongoing input which I want to put into the model;
I donĀ“t have any results with just one input, which might be due to the prior for the A-Matrix (see DCM.M.pE.A), so that the modell reaches very early convergence?? The other thing that prevented too fast convergence was changing the scaling factor in the spm_cond_units.m script (e.g. to fixed number of 1000) though I am not completely aware of the effect of this.
.
My second question: When I am only analyzing one condition, the values for the A- and B-Matrix are the same. Is it therefore advisable in general to use a second, contrasting condition (e.g. rest). I think that I should not use a similiar condition (e.g. fast and slow finger movement). In general, when I am sure about the sources I am using in the modell and that these are engaged in the task, is it even better to use only one condition without the contrast to a control condition.
.
Dear all, thank you very much for reply. All considerations are welcome.
Carlo
(Carlo Huber, University Hospital Cologne, Neurology, Germany)
|