The purpose of the present study was to investigate the organization of choline acetyltransferase (ChAT)-immunoreactive (IR) fibers in the visual cortex of the microbat, using standard immunocytochemistry and confocal microscopy. ChAT-IR fibers were distributed throughout all layers of the visual cortex, with the highest density in layer III and the lowest density in layer I. However, no ChAT-IR cells were found in the microbat visual cortex. ChAT-IR fibers were classified into two types: small and large varicose fibers. Previously identified sources of cholinergic fibers in the mammalian visual cortex, the nucleus of the diagonal band, the substantia innominata, and the nucleus basalis magnocellularis, all contained strongly labeled ChAT-IR cells in the microbat. The average diameter of ChAT-IR cells in the nucleus of the diagonal band, the substantia innominata, and the nucleus basalis magnocellularis was 16.12 μm, 13.37 μm, and 13.90 μm, respectively. Our double-labeling study with ChAT and gamma-aminobutyric acid (GABA), and triple labeling with ChAT, GABA, and post synaptic density 95 (PSD-95), suggest that some ChAT-IR fibers make contact with GABAergic cells in the microbat visual cortex. Our results should provide a better understanding of the nocturnal bat visual system.
Color is one of the fundamental information in human vision. However, cortical representation of color information is not well understood. It is known that differences of cone responses represent color information at the lower levels of visual system and the higher order visual tasks, e.g., color memory, use categorical representation. We investigated the color representation in human visual cortex by measuring brain activities in adults and in infants. The fMRI study using differential phase encoding technique and adaptation experiments revealed that neural systems that selectively respond to intermediate colors are present at the level of primary visual cortex. The NIRS study in prelingual infants was conducted by investigating cortical response changes while presenting color pairs that span across a border of color category or that stays within a category. The result revealed that the categorical color representation is already. Implications from these studies will be discussed in the talk.