Dear SPM experts,
I have two questions about DCM. Can anyone help me?
The first question: How to speicify the contextual input(adaptation) of
DCM in SPM2.
An contextual input, adaptation, is mentioned in the paper "Dynamic
Causal Modelling" (K.J. Fristion et al., NeuroImage 19, 2003). This input
is modelled as an exponential function of the time elapsed. It is very
different from the conventional input(eg. stimulus vector) because it is a
function decayed with time. How should I specify this sort of contextual
input in SPM2?
The second question: What do the negative coupling parameters mean?
Sometimes the estimates of the coupling parameters is negative and I
was confused by them. the paper "Dynamic Causal Modelling" says that: the
strength of the coupling parameters correspond to rates and a strong
connection means an influence that is expressed quickly or with a small
time constant. What do the negative coupling parameters mean on earth?
Bestregards,
Meng Liang
