Shared internal models for feedforward and feedback control of arm dynamics in non-human primates

Area of Science:

• Neuroscience
• Motor Control
• Primate Research

Background:

• Humans adapt reaching and reflexes to novel arm dynamics.
• This adaptation involves changes in both feedforward and feedback motor control.
• Understanding these mechanisms in primates is crucial for comparative neuroscience.

Purpose of the Study:

• To investigate if non-human primates (Macaca fascicularis) exhibit similar adaptive learning of arm dynamics as humans.
• To examine how altered intersegmental dynamics affect motor control in monkeys.
• To explore the transfer of learning to both predictive (feedforward) and reactive (feedback) responses.

Main Methods:

• Two monkeys were trained using an exoskeleton for single-joint elbow reaching and to respond to mechanical perturbations.
• Intersegmental arm dynamics were manipulated by fixing or freeing the shoulder joint during movements.
• Shoulder muscle activity, kinematic reach errors, and feedback responses to perturbations were measured.

Main Results:

• Monkeys showed reduced shoulder muscle activity when shoulder torques were eliminated (fixed shoulder).
• Releasing the shoulder resulted in kinematic aftereffects (reach errors), indicating adaptation to altered dynamics.
• Learning transferred to feedback responses, with reduced shoulder activity during perturbations after adaptation.

Conclusions:

• Old-world monkeys demonstrate adaptive learning of arm dynamics, mirroring human capabilities.
• This learning impacts both feedforward and feedback motor control mechanisms.
• Findings in non-human primates provide a foundation for studying the neural underpinnings of motor adaptation and control.