Musculoskeletal kinematics during voluntary head tracking movements in primate

In this study we examined connections between vertebral motion and patterns of muscle activation during voluntary head tracking movements. A Rhesus (Macaca mulatto) monkey was trained to produce sinusoidal tracking movements of the head in the sagittal plane while seated. Radio-opaque markers were placed in the cervical vertebrae, and intramuscular patch electrodes were implanted to record from eight neck muscles. Videofluoroscopic images of cervical vertebral motion, and EMG (electromyographic) responses were simultaneously recorded. Experimental results demonstrated that head and vertebrae moved synchronously and that motion occurred primarily at skull-C-1, C-6-C-7 and C-7-T-1. Our findings illustrate that although the biomechanical constraints of each species may limit the number of solutions available, it is the task requirements that appear to govern CNS (central nervous system) selection of movement behaviors.