Control of Head Movement.

Control of Head Movement Edited by Peterson BW, Richmond 19, New York, NY 10016, Oxford University Press, 1988, cloth, 322 pp, illus, $47.95

Head movement is a complex motor behavior that has never attracted much scientific attention. However, it is a topic of utmost importance in physical therapy, particularly to those physical therapists who are involved with children who are neurologically involved or developmentally delayed. In the past, most scientific consideration of head movement was incidental to research on oculomotor control, vestibular function, or the control of posture and gait. In 1986, however, a symposium brought together scientists of many different backgrounds to address the control of head movement.

This text was derived from the proceedings of the symposium. The editors point out, however, that the chapters are not simply a collection of the proceedings. The original works were reworked by the authors and editors to harmonize the scope and style of each chapter. It was the editors' intent to create a book that would serve as a comprehensive review of the field and that could be read by anyone with a broad background in the life sciences.

Some chapters are oriented strongly toward history. Others are concerned with fields so new that the information is only a few years old. The chapters are ordered so that the peripheral organization of the head-movement system is considered first and the nature of the different neural pathways and control mechanisms is discussed later. The major emphasis is placed on the physiologic mechanisms responsible for head movement.

In the first chapter, the joints and muscles of the neck are explored. The structure and analysis of the cervical joints is detailed with information both about human beings and about animals. The same treatment is accorded the neck and musculature. Analysis of head movement shows that the role played by a single muscle depends on its direction of pull, its biomechanical properties, its fiber-type composition, and its relationship with different cervical joints.

A chapter is included on the biomedical modeling of the human head and neck that is relevant and understandable even for those whose biomedical and mathematical expertise is rusty. The entire chapter devoted to cervical motoneurons may seem a bit esoteric on the surface; nevertheless, the author identifies several features of neck motor nuclei and motoneuron morphology that may have important implications for the control of head movement. Another chapter relating to peripheral components of head control addresses the sensory receptors in muscles and joints. These inputs may provide a detailed matrix of information that will help produce a three-dimensional picture of events.

Much emphasis is given to central projections of peripheral afferents, segmental organization of the upper cervical cord, and cervicocollic and cervico-ocular reflexes. Two chapters are devoted to the spinal circuitry and supraspinal control of the tonic neck reflexes. Not surprisingly, several chapters address the actions of the vestibular system in reflex stabilization of the head.

Chapters on eye-head coordination in gaze control and the control of head movement during visual orientation provide important discourse on the interaction of vision with other sensory inputs and muscular actions during active head turns, gaze shift, and final gaze position. The final chapter includes the discussion of some clinical disorders of head movement, such as athetosis or spasmodic torticollis (which interferes primarily with the postural carriage of the head). Also discussed are tics and choreic movements, which interrupt or caricature the normal movements that occur during orienting behaviors.

This is a readable text despite the spate of technical details. The book would be an excellent resource for the physical therapist who has an interest in head control and in particular an interest in the detailed scientific background related to it. It is definitely a reference text and should not be considered a classroom text for entry-level students. There is no magic insight into the difficulty of correcting head-control problems in patients who have cerebral palsy; however, the rich details should provide a greater understanding of the mechanisms involved, which may lead to the development of interventions.