VERTEBRAL ORIENTATIONS AND MUSCLE ACTIVATION PATTERNS DURING CONTROLLED HEAD MOVEMENTS IN CATS

The focus of these experiments was to determine the relationships betw een head movement, neck muscle activation patterns, and the positions and movements of the cervical vertebrae. One standing cat and one pron e cat were trained to produce voluntary sinusoidal movements of the he ad in the sagittal plane. Video-opaque markers were placed on the cerv ical vertebrae, and intramuscular patch electrodes implanted in four m uscles of the head and neck. Cinefluoroscopic images of cervical verte bral motion and electromyographic responses were simultaneously record ed. Analysis of the spinal movement revealed that the two cats used di fferent strategies to keep their heads aligned with the tracker. In th e standing cat, vertebral motion described a more circular are, compar ed to a forward diagonal in the prone cat. Intervertebral motion was l imited, but more acute angles appeared between the vertebrae of the pr one lying than of the standing animal. Data revealed that the central nervous system could control several axes of motion to keep the cervic al spine matched to the moving stimulus. Phase relations between the s inusoidal motion of the vertebral column, peak activation of the neck muscles, and that of the stimulus were examined, and several different control strategies were observed both between and within animals. The results suggest that the central nervous system engages in multiple s trategies of musculo-skeletal coordination to achieve a single movemen t outcome.