Motor assessment of developing common marmosets.

Motor development has been extensively studied in human infants and children, with several established scales for the evaluation of motor functions. However, the study of the neuronal mechanisms underlying human motor development is hampered by the lack of good animal models. The common marmoset (Callithrix jacchus), a small New World monkey, has recently attracted much attention as a potential nonhuman primate model for understanding human physiology and diseases. However, little is known about its gross motor development. In the present study, we found that marmosets have a critical period for motor development in postnatal weeks 2 to 5, and acquire most of their motor skills by 8 weeks of age. We also developed methods to assess their motor functions, which will be useful for the evaluation of motor performance in marmoset models of human diseases. In addition, we found that marmosets exhibit a "head-to-tail" sequence of motor development similar to that found in humans, further supporting the notion that they provide a good animal model for studying the neuronal mechanisms underlying human motor development.