The -tlrc_apar option requires the previous step of @auto_tlrc to be applied to an anatomical dataset. The align_epi_anat.py script extracts the affine transformation from that Talairached anatomical dataset and applies it in combination with the transformation computed for the alignment of the epi to the anat dataset (and also with an oblique transformation if one was used). The combined transformation matrix is applied to the original EPI datasets (base and child epi) to create Talairached and aligned EPI datasets.