Dendritic bias of neurons in rat somatosensory cortex associated with a functional boundary

Sensory information is encoded throughout the central nervous system by act ivation of specific groups of neurons. Neurons encoding information from a particular modality are grouped together and constitute an ordered neural r epresentation or "map" of the stimulus. The organization of these represent ations is not static, but is capable of significant alteration in response to changes in the patterns of inputs delivered to the cortex in the appropr iate behavioral context. Therefore, understanding the basic mechanisms that account for discontinuities in cortical representations are important for understanding both information processing in the cortex and plasticity of c ortical organization. It is clear that both anatomic and physiologic mechan isms underlie both the genesis and the plasticity of these representations; however, their exact contributions are not fully understood. To examine ne uronal anatomy around a representational border in rat primary somatosensor y cortex (S1), a novel in vivo/in vitro preparation was used in which the l ocation of the border between the forepaw and lower jaw representations in rat S1 was determined electrophysiologically and marked by dye iontophoresi s in vivo. By using in vitro slices from the region in which this border wa s marked, the morphologies of single cortical layer 2/3 neurons close to an d far from the border were determined by intracellular injection of biocyti n. Neurons close to the border had dendritic arbors that were significantly biased away from the border; neurons far from the border did not. This bia s was due to a decrease in the number of neurites that specifically crossed the border with a concomitant increase in other near-border parts of the n euron, consistent with the ideas that patterns of activity are important fo r neurite outgrowth and that neurons maintain a relatively constant total n eurite extent. These findings confirm the close association of cortical ana tomy and physiology and illustrate their relationships with cortical repres entational discontinuities. (C) 1999 Wiley-Liss, Inc.