The distribution of BOLD susceptibility effects in the brain is non-Gaussian.

A key assumption underlying fMRI analysis in the general linear model is that the underlying distribution of BOLD Susceptibility is gaussian. Analysis of several common data sets and experimental paradigms shows that the underlying distribution for the BOLD signal is non-Gaussian. Further identification shows that the distribution is probably Gamma and implications for hemodynamic modeling are discussed as well as recommendations concerning inferential testing in heavy-tailed environments.