PowerPoint Presentation - Time Series Analysis in AFNI

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Nonlinear Regression

• Linear models aren’t 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