Host: The Physiological Society of Japan
A behavior consists of elementary actions, which must be assembled in a proper sequence in order to successfully achieve the intended behavior. The present study examined how monkeys learn to take and use forceps to pick food. They had already learned to use 'hand-held forceps' to pick up food. We investigated the step of reach-grasp movement toward forceps by comparing responses in tasks of different contexts. (1) When the forceps was placed on a plate with food stuck at its tip, monkeys reached for and grasped the forceps while opening the finger (pre-shaping) and then grasped it as though automatically, and brought the attached food to the mouth, indicating that they had a capability to perform the sensorimotor transformation necessary for grasping forceps. However, (2) when the forceps and food were placed apart each other on a plate to be picked up, they did not execute actions on the forceps; instead, they brought their hand toward the food and mimed to use the forceps for taking food. After the practice under the experimenter's guide, monkeys began to reach out the clenched-hand for the forceps and hooked, rather than grasped, the forceps with the fingers. With further practice, they began to open/close the fingers aiming at the forceps, but this was only after their hand contacted the forceps. Finally they became to reach for the forceps while opening the fingers, that was pre-shaping. The results suggest that the control of grasping involved in tool-use actions is dissociated from that for the inherent behavior. [J Physiol Sci. 2008;58 Suppl:S193]
