Assessing robustness against potential publication bias in Activation Likelihood Estimation (ALE) meta-analyses for fMRI
Fig 2
Step-by-step overview of the ALE algorithm.
From an entire Statistical Parametric Map (SPM) usually only peak coordinates (foci) are reported. These are entered in an empty brain for every study individually. Spatial uncertainty is accounted for by constructing Gaussian kernels around the foci of which the size depends on the sample size of that study (smaller studies have more spatial uncertainty and larger kernels). The result of this process is a set of MA-maps. An ALE-map is constructed by calculating the union of the MA-maps. Eventually the ALE-map is thresholded to determine at which locations the convergence of foci is larger than can be expected by chance.