Sex differences in anterior commissure size in the rat

Earlier studies have shown that the corpus callosum of rats tends to be larger in males than in females. We report here that the anterior commissure of rats is also larger in males than in females. The sizes of the two commissures were positively correlated in both sexes, but significantly more so in females than in males. The anterior commissure size difference in rats reported here is opposite in direction from that reported elsewhere for humans, and we speculate that this may derive from differences in the relative proportions of the constituent fibers that make up the anterior commissure in the two species.