Afferent Control Of Posture And Locomotion

Afferent Control of Posture and Locomotion

R. B. Stein Department of Physiology, University of Alberta, Edmonton, Canada The impetus for this volume and the conference that gave rise to it was the feeling that studies on motor control had reached a turning point. In recent years, studies on motor units and muscle receptors have become increasingly detailed. Attempts to integrate these studies into quantitative models for the spinal control of posture have appeared and preliminary attempts have been made to include the most direct supraspinal pathways into these models (see for example the chapters by Nashner and Melvill Jones et al. in this volume). Thus, we felt that the time was ripe to summarize these developments in a way which might be useful not only to basic medical scientists, but also to clinicians dealing with disorders of motor control, and to bioengineers attempting to build devices to assist or replace normal control. Over the past few years, computer methods have also made possible increasingly detailed studies of mammalian locomotion, and improved physiological and pharmacological studies have appeared. There seems to be almost universal agreement now that the patterns for locomotion are generated in the spinal cord, and that they can be generated with little, if any, phasic sensory information (see chapters by Grillner and Miller et al. ). This concludes a long controversy on whether chains of reflexes or central circuits generate stepping patterns. The nature of the pattern generators in mammals remains obscure, but invertebrate studies on locomotion have recently made striking advances.

This collection of contributions on the subject of the neural mechanisms of sensorimotor control resulted from a conference held in Cairns, Australia, September 3-6, 2001. While the three of us were attending the International Union of Physiological Sciences (IUPS) Congress in St Petersburg, Russia, in 1997, we discussed the implications of the next Congress being awarded to New Zealand. We agreed to organise a satellite to this congress in an area of mutual interest -the neuroscience of movement and sensation. Australia has a long-standing and enviable reputation in the field of neural mechanisms of sensorimotor control. Arguably this reached its peak with the award of a Nobel Prize to Sir John Eccles in 1963 for his work on synaptic transmission in the central nervous system. Since that time, the subject of neuroscience has progressed considerably. One advance is the exploitation of knowledge acquired from animal experiments to studies on conscious human subjects. In this development, Australians have achieved international prominence, particularly in the areas of kinaesthesia and movement control. This bias is evident in the choice of subject matter for the conference and, subsequently, this book. It was also decided to assign a whole section to muscle mechanics, a subject that is often left out altogether from conferences on motor control. Cairns is a lovely city and September is a good time to visit it.

This volume publishes the review articles presented by the invited speakers at the Satellite Meeting to the Barany Society Meeting held in Bologna, Italy during June 1987. The subject matter in this book is divided into seven main sections. The first three present basic neuroanatomical and neurophysiological aspects of vestibulospinal reflexes and document the neck afferent and visual influences on these reflexes. The following sections deal with the control of locomotion, posture, and eye-head-trunk coordination by vestibulospinal signals. The final section provides current knowledge on the processes underlying compensation of vestibulospinal deficits. An overall review precedes each main section so that the reader is informed as to which questions are still controversial and require further investigation. In this way a basis is provided for those needing a current account of the field of vestibulospinal reflexes. Due to the extensive length of the contents, only the number of articles presented per session is listed below.

Reflex Control of Posture and Movement

Brain Mechanisms for the Integration of Posture and Movement

Neuromechanics is a new, quickly growing field of neuroscience research that merges neurophysiology, biomechanics and motor control and aims at understanding living systems and their elements through interactions between their neural and mechanical dynamic properties. Although research in Neuromechanics is not limited by computational approaches, neuromechanical modeling is a powerful tool that allows for integration of massive knowledge gained in the past several decades in organization of motion related brain and spinal cord activity, various body sensors and reflex pathways, muscle mechanical and physiological properties and detailed quantitative morphology of musculoskeletal systems. Recent work in neuromechanical modeling has demonstrated advantages of such an integrative approach and led to discoveries of new emergent properties of neuromechanical systems. Neuromechanical Modeling of Posture and Locomotion will cover a wide range of topics from theoretical studies linking the organization of reflex pathways and central pattern generating circuits with morphology and mechanics of the musculoskeletal system (Burkholder; Nichols; Shevtsova et al.) to detailed neuromechanical models of postural and locomotor control (Bunderson; Edwards, Marking et al., Ting). Furthermore, uniquely diverse modeling approaches will be presented in the book including a theoretical dynamic analysis of locomotor phase transitions (Spardy and Rubin), a hybrid computational modeling that allows for in vivo interactions between parts of a living organism and a computer model (Edwards et al.), a physical neuromechanical model of the human locomotor system (Lewis), and others.

This book dealing with stance and motion was planned in June 1986 at a meeting held in Moscow and Leningrad between a group of Soviet and French scientists interested in motor control. This meeting took place in the framework of an exchange program between the USSR Academy of Seiences and the French Centre National de la Recherche Scientifique. It was very successful event and was greatly appreciated by all those who attended it. Several participants put forward the proposal that the possibility of publishing a book was worth exploring. What were the reasons for publishing a book on stance and motion ? The interest aroused in the participants by each others contributions was not a sufficiently decisive argument. It was feit, however, that a large proportion of the orginal material presented at the meeting, especially in the field of posture and locomotion but also on other aspects covered by the book could be presented in a summarized form which should appeal to a larger audience because the facts and hypotheses they contained especially those from the Soviet participants, were not very familiar among international circles, and that many scientists would appreciate having a single volume containing a survey ofthe current state of research in this field. This was also the opinion of Plenum Press, who agreed to publish the book. Each participant at the meeting submitted a paper which was examined by two referees before being accepted.

From recent developments in the rapidly growing area of neuroscience it has become increasingly clear that a simplistic description of brain function as a broad collection of simple input-output relations is quite inadequate. Introspection already tells us that our motor behavior is guided by a complex interplay between many inputs from the outside world and from our internal "milieu," internal models of ourselves and the outside world, memory content, directed attention, volition, and so forth. Also, our motor activity normally involves more than a circumscribed group of muscles, even if we intend to move only one effector organ. For example, a reaching movement or a reorientation of a sensory organ almost invariably requires a pattern of preparatory or assisting activities in other parts of the body, like the ones that maintain the body's equilibrium. The present volume is a summary of the papers presented at the symposium "Sensory Interaction in Posture and Movement Control" that was held at Smolenice Castle near Bratislava, Slovakia, as a Satellite Symposium to the ENA Meeting 1994 in Vienna. The focus of this meeting was not only restricted to the "classical" sensory interactions such as between vestibular and visual signals, or between otolith and semicircular canal inputs. Rather, the symposium tried to consider also the interplay between perception and action, between reflexive and volitional motor acts as well as between sensory driven or self-initi ated motor acts and reafferent inputs.