Hi,

I am using 3dNLfim to do non-linear fitting to the impulse response function (IRF) data calculated using 3dDeconvolve. The IRF looks as one would expect in the areas of activation, such as early visual cortex.

The command is

3dNLfim -input input_AA1+orig -ignore 0 -noise Constant -signal GammaVar -nconstr 0 -1000.0 1000.0 -sconstr 0 0 2 -sconstr 1 -1000.0 1000.0 -sconstr 2 8 9 -sconstr 3 0.15 0.45 -nrand 500 -nbest 10 -fdisp 10 -rmsmin 1.0 -bucket 0 NLfit_out

I also tried it with (removing constraints on parameters)

3dNLfim -input input_AA1+orig -ignore 0 -noise Constant -signal GammaVar -nrand 500 -nbest 10 -fdisp 10 -rmsmin 1.0 -bucket 0 NLfit_out

The first parameters (out of the 5) is a small negative value between 0 and -1.
The other parameters of theGamma fit is that it is ZERO for all the voxels in the entire brain except for various areas (perhaps at most 50 voxels) where vascular effects would dominate the BOLD signal.

Any ideas as to what may be the problem? I checked the input in to the 3dNLfim command and the data looks like a typical IRF (used a TENT function in the 3dDeconvolve command).

Cheers,
Arun