Variability of manual dexterity performance in non-human primates (Macaca fascicularis)

Abstract

The goal of this study was to quantify the inter-individual and intra-individual variability of manual (digits) skill in adult macaque monkeys, over a motor learning phase and, later on, when motor skills were consolidated. The hypothesis is that several attributes of the stable manual dexterity performance can be predicted from learning characteristics. The behavioral data were collected from 20 adult Macaca fascicularis, derived from their dominant hand, defined as the hand exhibiting a better performance than the other. Two manual dexterity tasks were tested:(i) the “modified Brinkman board” task, consisting in the retrieval of food pellets placed in 50 slots in a board, using the precision grip (opposition of the thumb and index finger); (ii) the “reach and grasp drawer” task, in which the grip force and the load force were continuously monitored while the monkey opened a drawer against a resistance, before grasping a pellet inside the drawer. The hypothesis was verified for the performance of manual dexterity after consolidation, correlated with the initial score before learning. Motor habit, reflected by the temporal order of sequential movements executed in the modified Brinkman board task, was established very early during the learning phase. As mostly expected, motor learning led to an optimization of manual dexterity parameters, such as score, contact time, as well as a decrease in intra-individual variability. Overall, the data demonstrate the substantial inter-individual variability of manual dexterity in non-human primates, to be considered for further pre-clinical applications based on this animal model.