„ Linear models arenÕt everything
H e.g., could try to fit HRF of the
form
H Unknowns b and c appear nonlinearly in this formula
„ Program 3dNLfim
can do nonlinear regression (including nonlinear
deconvolution)
H User must provide a C function that
computes the model time series, given a set
of parameters (e.g., a, b, c)
H Program then drives this C function
repeatedly, searching for the set of parameters
that best fit each voxel
H Has been used to fit pharmacological
wash-in/wash-out models (difference of two
exponentials) to FMRI data acquired during
pharmacological challenges
o e.g.,
injection of nicotine, cocaine, etc.
o these are
tricky experiments, at best