Sensory systems create neural representations of sensory world, which can be reformatted from one brain region to another depending on the computational tasks such as classification, discrimination, and associative memory. Insect olfactory systems offer numerous advantages to study sensory information processing in a network of multiple layers, such as the relatively simple olfactory circuit with common design features across phyla (including mammals), the easily accessible brains to electrophysiology in intact animals, the variety of odor-induced behaviors, and the powerful genetic tools available. At the first stage of olfactory processing, each odor is represented by a unique combination of olfactory receptor neurons. This activated neural population remains relatively fixed during odor response. Although neurons in the antennal lobe receive static odor inputs from olfactory receptor neurons, lateral inhibitions in the antennal lobe produce dynamic spatio-temporal representations of odors that rapidly reduce the similarity of spatial patterns between odors over time. This decorrelation process may provide foundations for both odor classification and discrimination. Kenyon cells in the mushroom body, the important neural population for associative memory, receive odor inputs from the antennal lobe and use a sparse coding scheme to represent odors. Here, I summarize recent progresses in insects and other animals.

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  The eyes of vertebrates are invariant from cyclostome to human in many aspects, including the structure of the organ, morphology of the photoreceptors and the signal transduction in the photoreceptor cell. How vertebrate eyes have been established in the evolutional process is still enigma. Ascidians are the closest living relatives of the vertebrates. The tadpole larvae share a basic body plan with vertebrates, including notochord and dorsal tubular central nervous system. Therefore, this animal is expected to provide clue to evolution of vertebrate eyes. The authors have isolated the genes expressing in photoreceptor cells of ascidian larvae and prepared antibodies against these gene products. Using the antibodies, the authors have revealed the structure of the photoreceptors. In this review, the authors discuss the relationship between ascidian photoreceptors and vertebrate eyes on the basis of the photoresponse of the ascidian larva as well as the morphology.

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  Fish and primates are highly polymorphic in color vision among vertebrates, possibly reflecting their remarkably variable light environment. To study the evolution of color vision in fish and primates, we have focused on gene duplication and allelic differentiation of their opsin genes.
  By using zebrafish and medaka as model fish, we have shown that gene duplications of opsins have occurred repeatedly during fish evolution, often accompanied by differentiation of their spectral sensitivity and spatiotemporal expression patterns in the retina. We have also shown that a similar regulatory mechanism has evolved independently in fish and primates in which a single regulatory region controls the array of duplicated opsin genes.
  Our behavioral observation for wild populations of New World monkeys has shown that dichromatic monkeys are more excellent in catching camouflaged insects and can be as good as trichromats in foraging fruits, implying that niche divergence or mutual benefits among different vision types may be the nature of the natural selection supporting the vision variation.

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