We are working on a model to look at functional interaction in top-down
attentional control. The driving input (cue effect) is entered into the
model from occipital area. This occipital area only has bidirentional
intrinsic connection with parietal area, but does not has any connections
with other brain area. The problem we run into is that the value of
driving input is negative, both in session level and subject level ( each
subject has six sessions) and group level (19 subjects). When we looked at
the HRF of the extracted VOI from this occipital area, the deflection of
the HRF is positive.
My question is if the driving input could be negative in DCM?
specifically, under the condition with positive observed HRF. what is the
reason for this? what can we do further to clarify this issue?
Also, the modulation effect between these two areas (occipital and
parietal areas) is also negative, it is hard to interpret in this
Any suggestion would be appreciated!