„ Linear models arenÕt everything
H For example, 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
² e.g., injection of nicotine, cocaine,
etc.