Versatile grasping ability in power-grip actions by tufted capuchin monkeys (Sapajus spp.)

Moving

Examples of realized scientific careers can provide ideas and inspiration for others aiming to pursue such careers. Here I recount in brief the story of my long career in primatology (1973 to the present), focusing on one enduring theme in my research: the nature and genesis of goal-directed action (evident in movement). The story begins in graduate school, passes through developing my own laboratory, on to pursuing a spectrum of studies with mentees and collaborators, developing a theoretical explanatory framework for goal-directed action that I think holds promise for the field as a whole, and ends with an exciting field project that seems a suitable finale to my career. I mention the value to me, the field, and society of participation in scientific societies, including the American Society of Primatologists, throughout my career.

Compartmentalized dynamics within a common multi-area mesoscale manifold represent a repertoire of human hand movements

The human hand is unique in the animal kingdom for unparalleled dexterity, ranging from complex prehension to fine finger individuation. How does the brain represent such a diverse repertoire of movements? We evaluated mesoscale neural dynamics across the human "grasp network," using electrocorticography and dimensionality reduction methods, for a repertoire of hand movements. Strikingly, we found that the grasp network represented both finger and grasping movements alike. Specifically, the manifold characterizing the multi-areal neural covariance structure was preserved during all movements across this distributed network. In contrast, latent neural dynamics within this manifold were surprisingly specific to movement type. Aligning latent activity to kinematics further uncovered distinct submanifolds despite similarities in synergistic coupling of joints between movements. We thus find that despite preserved neural covariance at the distributed network level, mesoscale dynamics are compartmentalized into movement-specific submanifolds; this mesoscale organization may allow flexible switching between a repertoire of hand movements.

Planning actions with a magnetic tool: how initial tool orientation and number of functional ends influence motor planning abilities in capuchin monkeys (Sapajus spp.)

The way in which animals grasp objects to perform subsequent action execution allows studying their anticipatory abilities. We examined whether 11 capuchin monkeys (Sapajus spp.) were able to prospectively grasp a magnetic dowel to use it as a tool to retrieve a baited metallic container from a plexiglas box placed in front of them. We investigated whether and how initial dowel orientation (horizontal vs vertical) affected grasping and using the dowel to retrieve the container in two testing conditions: (1) 2-FE condition in which the dowel had two functional magnetic ends; (2) 1-FE condition in which the dowel had only one functional magnetic end. In the 2-FE condition, capuchins had to take into account the initial dowel orientation since both ends were functional, whereas in the 1-FE condition capuchins had also to take into account the initial functional end position when grasping the dowel. Capuchins were trained to grasp the dowel to put one functional end in contact with the metallic container. However, they did not learn to associate the functional end of the 1-FE dowel to successful retrieval. Capuchins showed better anticipatory planning (1) in 2-FE than in 1-FE condition and (2) when the dowel was initially positioned on the horizontal plane than on the vertical one. Moreover, hand preferences affected planning in the 1-FE condition. Results were discussed within the frameworks of primates' abilities to use abstract cues and on their abilities to process functional features and spatial cues and to perform mental rotations.

Anticipating future actions: Motor planning improves with age in wild bearded capuchin monkeys (Sapajus libidinosus)

Self-directed object manipulation tasks illuminate development of motor planning. Grasping strategies that lead to good object control to perform the following action(s) reveal second-order motor planning. Motor planning for efficient grips develops slowly in children. Age-related differences in other primates have been poorly investigated. Here, we investigated anticipatory motor planning of infant, juvenile and adult wild capuchin monkeys grasping a horizontally positioned stick baited to the left or right side (a version of the elevated spoon task). We recorded the grasps capuchins used to bring the baited end of the stick to the mouth. The percentage of efficient radial grips positively correlated with age and adults used efficient grips significantly more frequently than infants. Adult wild capuchins' use of radial grips was higher than that reported for adult captive capuchins in similar tasks, suggesting that experience throughout life may influence motor anticipation. Self-directed object manipulation tasks will be useful to compare this aspect of cognition across primates. A video abstract of this article can be viewed at https://youtu.be/a1Zbr_AQkb8.

Motor planning in different grasping tasks by capuchin monkeys (Sapajus spp.)

Studies on motor planning and action selection in object use reveal that what we choose to do in the present moment depends on our next planned action. In particular, many studies have shown that adult humans initially adopt uncomfortable hand postures to accommodate later task demands (i.e., the end-state comfort effect). Recent studies on action planning in different non-human primates species have provided contrasting results. Here, we tested whether capuchin monkeys (Sapajus spp.), natural tool users, would show planning abilities in two tasks with varying complexity: (i) an object-retrieval task involving self-directed actions (Experiment 1) and (ii) a tool-using task involving actions directed toward an external target (Experiment 2). In Experiment 1, six of 10 monkeys preferentially used a radial grip (i.e., with the thumb-side oriented towards the baited end) to grasp a horizontal dowel with either the left- or right-end baited and bring it to their mouth. In Experiment 2, all six tested capuchins preferentially used a radial grip (i.e., with the thumb-side oriented towards the center of the dowel) to grasp a dowel that was positioned horizontally at different orientations and to dislodge an out-of-reach food reward. Thus, we found that the capuchins showed second-order planning abilities in both tasks, but performance differences emerged in relation to hand preference and learning across sessions. Our findings support the idea that second-order motor planning occurred in an early stage of the primate lineage. Factors affecting the ability of nonhuman primates to estimate motor costs in action selection are discussed.