Comparison of the patterns of callosal connections in lateral parietal cortex of the rat, mouse and hamster.

In a recent study of the second somatosensory area (SmII) in the rat it was reported that the somatotopic map in the cortex lateral to the primary somatosensory area (SmI) is closely related to local features of the callosal pattern. The existence of this relationship suggests that knowledge of the overall pattern of callosal connections in the cortex lateral to SmI may facilitate the description of the somatotopic organization of lateral parietal cortex in other rodents. We tested this suggestion by comparing the callosal patterns in lateral parietal cortex in the rat, mouse and hamster. Our finding that the callosal pattern in the mouse closely resembles that in the rat supports the idea that the callosal pattern reflects the underlying somatotopy because the maps of SmII described previously in the mouse and rat are very similar to each other. In addition, on the basis of our observation that the callosal pattern in the hamster is very similar to that in the rat and mouse, we predict that these three rodent species share a common somatotopic plan in lateral parietal cortex.