A new group analysis method to summarize the task-related BOLD responses based on independent
component analysis (ICA) was presented. As opposite to the previously proposed group ICA (gICA)
method, which first combined multi-subject fMRI data in either temporal or spatial domain and applied
ICA decomposition only once to the combined fMRI data to extract the task-related BOLD effects, the
method presented here applied ICA decomposition to the individual subjects' fMRI data to first find the
independent BOLD effects specifically for each individual subject. Then, the task-related independent
BOLD component was selected among the resulting independent components from the single-subject ICA
decomposition and hence grouped across subjects to derive the group inference. In this new ICA group
analysis (ICAga) method, one does not need to assume that the task-related BOLD time courses are
identical across brain areas and subjects as used in the grand ICA decomposition on the spatially
concatenated fMRI data. Neither does one need to assume that after spatial normalization, the voxels at
the same coordinates represent exactly the same functional or structural brain anatomies across different
subjects. These two assumptions have been problematic given the recent BOLD activation evidences.
Further, since the independent BOLD effects were obtained from each individual subject, the ICAga method can better account for the individual differences in the task-related BOLD effects. Unlike the gICA approach whereby the task-related BOLD effects could only be accounted for by a single unified BOLD model across multiple subjects. As a result, the newly proposed method, ICAga, was able to better fit the task-related BOLD effects at individual level and thus allow grouping more appropriate multisubject
BOLD effects in the group analysis.