Skeletal Geometry Underlying Head Movements a

The relationship between eye and head movements has been studied in recent years utilizing a number of methodological approaches. Behavioral studies and electromyographic recordings have revealed a tonic eye-head coupling in the rabbit,' the and the m0nkey.4.~ However, little attention has been devoted to the general question of the posture underlying eye-head coordination. The complexity of the vertebral arrangement in the cervical vertebral column and the necessity of assuming that-at least in the vertical plane-the elements of the head-neck system move around several frequency-dependent centers of rotation6 prompted us to reevaluate the skeletal geometry underlying head movements. As a general hypothesis, Bernstein' suggested that certain preferred axes for motor activity may have become prevalent in order to coordinate multiarticular systems, each of them having several degrees of freedom. This hypothesis formed the basis of an X-ray cinematography study on head movements during orienting behavior in different vertebrates. In the first section of this paper, we shall introduce the stereotyped resting posture adopted by seven of nine studied vertebrate species. These results have already been published elsewhere* and will be summarized here briefly to the extent necessary to follow the subsequent two sections. In the second section we shall propose that the number of degrees of freedom of the articulations of the cervical vertebral column is reduced as a result of the geometry of the skeletal system described in the first section. This reduction probably contributes to the fact that orienting movements when studied by cineradiography are in fact stereotyped and confined to certain planes of space, corroborating Bernstein's' hypothesis. Finally, in the third section, we shall try to demonstrate that these results are of consequence in understanding the pathology of postural control. We shall take as an example the postural syndrome observed in guinea pigs following hemilabyrinthectomy.

[1]  A. Berthoz,et al.  Frequency analysis of vestibular influence on extensor motoneurons. I. Response to tilt in forelimb extensors. , 1971, Brain research.

[2]  E Bizzi,et al.  Two modes of active eye-head coordination in monkeys. , 1972, Brain research.

[3]  I. Curthoys,et al.  The effect of visual deprivation on vestibular compensation in the guinea pig , 1986, Brain Research.

[4]  Y. Uchino,et al.  Axon collaterals of anterior semicircular canal-activated vestibular neurons and their coactivation of extraocular and neck motoneurons in the cat , 1984, Neuroscience Research.

[5]  R H Schor,et al.  Spatial organization of neck and vestibular reflexes acting on the forelimbs of the decerebrate cat. , 1986, Journal of neurophysiology.

[6]  J. Fuller,et al.  Linkage of eye and head movements in the alert rabbit , 1980, Brain Research.

[7]  Y. Uchino,et al.  Saccular and utricular input to cat neck motoneurons. , 1977, Journal of neurophysiology.

[8]  H Shimazu,et al.  RETICULOVESTIBULAR ORGANIZATION PARTICIPATING IN GENERATION OF HORIZONTAL FAST EYE MOVEMENT * , 1981, Annals of the New York Academy of Sciences.

[9]  N. A. Bernshteĭn.  The co-ordination and regulation of movements , 1967 .

[10]  K P Schaefer,et al.  On the organization of neuronal circuits involved in the generation of the orientation response (visual graspreflex). , 1975, Fortschritte der Zoologie.

[11]  G. Beer.  PRESIDENTIAL ADDRESS: How Animals hold their Heads. , 1947 .

[12]  V. J. Wilson,et al.  Connections between semicircular canals and neck motorneurons in the cat. , 1974, Journal of neurophysiology.

[13]  D. W. Jensen.  Reflex control of acute postural asymmetry and compensatory symmetry after a unilateral vestibular lesion , 1979, Neuroscience.

[14]  R. Baker,et al.  Morphological and physiological identification of excitatory pontine reticular neurons projecting to the cat abducens nucleus and spinal cord , 1980, Brain Research.

[15]  W. Cruce,et al.  Evolution of Motor Systems: The Reticulospinal Pathways , 1984 .

[16]  D. L. Meyer,et al.  Compensation of Vestibular Lesions , 1974 .

[17]  I. Curthoys,et al.  The orientation of the semicircular canals in the guinea pig. , 1975, Acta oto-laryngologica.

[18]  A Berthoz,et al.  HORIZONTAL EYE MOVEMENT SIGNALS IN SECOND‐ORDER VESTIBULAR NUCLEI NEURONS IN THE CAT * , 1981, Annals of the New York Academy of Sciences.

[19]  N. Ishizuka,et al.  Axonal branches and terminations in the cat abducens nucleus of secondary vestibular neurons in the horizontal canal system , 1980, Neuroscience Letters.

[20]  A. Berthoz,et al.  Neuronal mechanisms underlying eye-head coordination. , 1986, Progress in brain research.