Anterior neurons projecting back to the hindbrain. (a) Transverse section revealing the overall pattern at the level of the postotic commissure. A large amount of DiI was injected, resulting in the back-labeling of ALL neurons on the ipsilateral side as well as of central neurons at the midbrain-forebrain boundary. (b) Higher magnification revealing fibers that follow the post-optic commissure. Since such fibers are only observed when back-projecting neurons are labeled, we believe that they belong to the latter. (c) Detail of the same preparation cleaned with the 'Rapid Deconvolution' program of IPLab (see Materials and methods) to enhance the cell bodies of the back-projecting neurons. Also present on the contralateral side of this section is a fiber of ALc extending dorsally, possibly into the pretectum, as well as the anteriormost branchlet of a LT fiber that extends into the optic tectum.