Chemotopic Arrangement for Taste Quality Discrimination in the Cortical Taste Area

Abstract

Signals from various sensory organs are delivered to the brain where sensory information is generated from the signals. The information is represented on the brain in the form of temporal and spatial codes, which enable us to create inner an representation of the outer world (Florey, 1990). In the neocortex, the information consisting of the spatial codes is principally arranged in the primary sensory area as a receptive field, by way of anatomical column formation. The information consisting of temporal codes, such as frequency and phase dynamics, also plays an important role for synchronization of neural activities or strengthening signal amplitudes. Interaction or integration of the information by way of intra-cortical or cortico-cortical connections enables the temporal and spatial codes to link (Singer and Gray, 1995; Gilbert et al., 1996; Salinas and Sejnowski, 2001). As for taste information processing, controversy still exists as to whether cortical taste neurons use temporal codes or spatial codes for discriminating taste information in the cortical taste area. However, it may be presumed that cortical taste neurons use spatial codes as well as frequency codes in order to discriminate taste information efficiently. Previous electrophysiological studies predict that there is a chemotopic arrangement for taste quality discrimination in the cortical taste area, but this hypothesis has not been confirmed because of lacking for the evidence with high resolution of spatial dimension. Optical imaging based on intrinsic signals has a high spatial resolution (Frostig et al., 1990) and is useful for studying the functional organization of the brain (Bonhoeffer and Grinvald, 1996). Here, we investigated the spatial aspects of optical intrinsic signal (OIS) responses in the gustatory insular cortex that were elicited by delivering a solution of tastants on the tongue.