Meta level concept versus classic reflex concept for the control of posture and movement

摘要

The control of posture is traditionally thought to be based upon simple sensory feedback mechanisms known as the postural reflexes. The reflexes consist of highly stereotype postural reactions which are observed in response to sensory stimuli. This concept received support from basic research in that electrophysiological and anatomical studies demonstrated neuronal connections between the corresponding sensors, their central relays and motor output centres. Postural reflexes can be evoked not only in primitive animals, but also in mammals and man. This applies, however, only as long as the central nervous system of mammals and man is still in an immature state, or if it is damaged during later life. In the intact and adult individual, in contrast, the postural responses are no longer stereotype and therefore cannot be termed reflexes. Yet, they still represent highly automatized reactions and certain body postures adopted during spontaneous behaviour are reminiscent of the reflexes (38). It is generally believed that the postural reflexes come under the control of higher brain centres soon after birth with maturation of the brain. This would then allow volition and cognition to control the postural mechanisms. How this control is achieved is still an enigma, however. A simple and straight forward assumption would be a control that modulates the gain of the reflexes-an often adopted notion. The present study suggests an alternative.