Brief communication: Proportions of the ventral half of the cerebellar dentate nucleus in humans and great apes.

In a previous study about volume comparisons of the cerebellar complex in some hominoid species (1997), progressive development of only the lateral zone group of nuclei was found in the human cerebellar complex. This development was considered to be related not to bipedalism, but to versatile and coordinated finger movement, evolving after bipedalism was established. It was also considered a prerequisite for the evolution of human language. The lateral zone groups of nuclei are represented by the dentate nucleus. Therefore, the present study reports the development of the dentate nucleus in humans in comparison with that in some great apes. One finding is that the average value of ratios for nucleus size of the ventral half (v) to the dorsal half (d) (v/d) was found to be 2.11 in humans, while it was 1.64 in great apes. This finding shows that the greater part of progressive development of the dentate nucleus in humans is due to the development of its ventral half. Therefore, the fiber connection to the frontal association area from the cerebellar cortex, which is involved in the performance of higher cerebellar functions such as cognitive and language functions, would be mediated by the ventral half of the dentate nucleus. Copyright 2001 Wiley-Liss, Inc.