Diversity of grip in Macaca mulatta.

Much of the research on the neuronal basis of prehension focuses on macaque monkeys. Yet most of the behavioral description of grip types pertains to humans and apes. The purpose of the present study was to provide a catalogue and description of basic grip behavior in macaque monkeys. The observational study explored the diversity of grasping behavior in 157 semi-free ranging rhesus macaques. Video footage of monkeys grasping objects ad libitum was analyzed frame-by-frame, and grips were classified based on the skin surface areas that contacted the object. When monkeys held objects for manipulation, 15 distinct grip categories were observed. When monkeys held support points during climbing, two grip categories were observed. Not all grips were performed with the hand. Some involved the mouth, the foot, or an opposition between the forearm and chest. Grip in macaque monkeys is more diverse than the narrow range of grip that is typically studied.