Representation of the stomatopod's retinal midband in the optic lobes: Putative neural substrates for integrating chromatic, achromatic and polarization information.

Stomatopods have an elaborate visual system served by a retina that is unique to this class of pancrustaceans. Its upper and lower eye hemispheres encode luminance and linear polarization while an equatorial band of photoreceptors termed the midband detects color, circularly polarized light and linear polarization in the ultraviolet. In common with many malacostracan crustaceans, stomatopods have stalked eyes, but they can move these independently within three degrees of rotational freedom. Both eyes separately use saccadic and scanning movements but they can also move in a coordinated fashion to track selected targets or maintain a forward eyestalk posture during swimming. Visual information is initially processed in the first two optic neuropils, the lamina and the medulla, where the eye's midband is represented by enlarged regions within each neuropil that contain populations of neurons, the axons of which are segregated from the neuropil regions subtending the hemispheres. Neuronal channels representing the midband extend from the medulla to the lobula where populations of putative inhibitory glutamic acid decarboxylase-positive neurons and tyrosine hydroxylase-positive neurons intrinsic to the lobula have specific associations with the midband. Here we investigate the organization of the midband representation in the medulla and the lobula in the context of their overall architecture. We discuss the implications of observed arrangements, in which midband inputs to the lobula send out collaterals that extend across the retinotopic mosaic pertaining to the hemispheres. This organization suggests an integrative design that diverges from the eumalacostracan ground pattern and, for the stomatopod, enables color and polarization information to be integrated with luminance information that presumably encodes shape and motion.