9310945 Juraska Dramatic neuroanatomical differences have been found between the sexes in brain regions that are involved in reproductive function. More recently, sex differences in neuronal organization have been reported in parts of the brain that are associated with cognitive rather than reproduction function. Indeed, the hippocampus, and the cerebral cortex, including the corpus callosum, exhibit sexual dimorphisms at the cellular level. Much excitement has been generated about the possibility of sex differences in the size of the corpus callosum since this structure is the bundle of nerve fibers that connect the left and right hemispheres of the brain. While some laboratories report striking sex differences in its shape and size, others find that extensive individual variability hinders any meaningful interpretation. Dr. Juraska, during her previous NSF support, reported that the gross size of the corpus callosum in rats did not differ between the sexes, however, females have more axons in a specific region, the splenium, of the corpus callosum than males. These findings suggest that the cellular differences between the sexes are more complicated that the size difference indicates. Dr. Juraska also found that the number of neurons within the binocular region of the visual cortex is sexually dimorphic. She will now continue her work to understand sex differences in the neuronal organization and behavioral function of the largest area of the rat brain, the cerebral cortex and its major interconnecting pathway, the corpus callosum. Dr. Juraska will determine whether there is a hormonal basis for the observed sex differences and the role that cell death plays as a mechanism underlying the development of the observed dimorphism. Moreover, she will initiate a search for the functional significance of the morphological sex differences. This remains a controversial but important area. Her results will have broad implications for understanding the import ance of lateralization and its relationship to possible sex differences in verbal and spatial learning abilities in humans. ***
