¥ FMRI only measures changes due to neural ÒactivityÓ
H Baseline level of signal in a voxel
means little or nothing about neural
activity
H Also, baseline level tends to drift
around slowly (100 s time scale or
so)
¥ Therefore, an FMRI experiment must have at least 2 different neural
conditions (ÒtasksÓ and/or ÒstimuliÓ)
H Then statistically test for differences
in the MRI signal level between
conditions
H Many experiments: one condition is
ÒrestÓ
¥ Baseline is modeled separately from
activation signals, and baseline model includes ÒrestÓ periods