ROLE OF EYE AND NECK PROPRIOCEPTIVE MECHANISMS IN BODY ORIENTATION AND MOTOR COORDINATION

Abstract

Proprioceptive mechanisms activated by receptors situated in the extra-ocular muscles, ciliary muscles of accommodation and the first 3 cervical vertebrae of monkeys and baboons have been abolished singly and in combination, and the resultant effects on motor coordination have been studied and recorded with a moving film camera. Surgical detachment of all 6 extraocular muscles of one eye and application of homatropin drops to abolish the power of accommodation did not result in any defect in motor coordination as measured with a pegboard, ladder and swing arrangement. Ten animals were subjected to anesthetic block of the C 1,2,3 dorsal roots and this was repeated on 9 of the animals. All animals demonstrated severe defects in balance and orientation. During walking, the animals were unable to walk in a straight line toward their objective but often staggered and swayed, frequently bumping into nearby objects. They also demonstrated a "floppiness" in the rear portion of their bodies, occasional head wobbling, and broad base standing suggestive of cerebellar ataxia. When reaching for objects upon which they had fixed their gaze, they often missed the object completely and had to reach a 2nd or even 3rd time. There were no signs of muscle weakness. Various controls were employed, and these indicated that the anesthetic only affected the Cl,2,3 dorsal roots. The widespread deficits in balance and orientation with the resultant motor incoordination, were very similar to the defects which are displayed by bilaterally labyrinthectomized animals. Indeed it is now clear in regard to overall body balance and orientation that it is as important to be informed of the position of the head on the body, which is the province of the neck proprioceptors, as it is to know the position and acceleration of the head in space, which is the duty of the vestibular structures; and impairment of either mechanism will produce major defects in body balance and orientation which are similar in form and magnitude.