Abstract
Erect posture in man is a recent affordance from an evolutionary perspective. About eight million years ago, the stock from which modern humans derived split off from the ape family, and from around sixty-thousand years ago, modern man developed. Upright gait and manipulations while standing pose intricate cybernetic problems for postural control. The trunk, having an older evolutionary history than the extremities, is innervated by medially descending motor systems and extremity muscles by the more recent, laterally descending systems. Movements obviously require concerted actions from both systems. Research in rats has demonstrated the interdependencies between postural control and the development of fluent walking. Only 15 days after birth, adult-like fluent locomotion emerges and is critically dependent upon postural development. Vesttibular deprivation induces a retardation in postural development and, consequently, a retarded development of adult-like locomotion. The cerebellum obviously has an important role in mutual adjustments in postural control and extremity movements, or, in coupling the phyiogenetic older and newer structures. In the human, the cerebellum develops partly after birth and therefore is vulnerable to adverse perinatal influences. Such vulnerability seems to justify focusing our scientific research efforts onto the development of this structure.
Highlights
Erect posture in man is a recent affordance from an evolutionary perspective
Deficient postural control in human infants is considered an important factor in several developmental disorders concerning motor control (Aicardi & Bax 1992), and for that reason, this aspect has been in the center of interests of rehabilitation therapists, pediatric neurologists and neurobiologists, for example
When considering postural control from a neurophysiological point of view, it is important to realize that this control as such is an abstraction from motor control
Summary
"Posture" might be defined as the position of the body in relation to the gravitational vector and of the body-segments in relation to each other, both in static and in dynamical conditions (e.g., Gramsbergen, 1998). A similar example is the visual system in man, in which the fovea, projecting via the geniculate nucleus to the visual cortex, is fully integrated with the subcortical retino-tectal system active in directing gaze (Deacon, 1992) The latter system (involving peripheral retinal fields, tecto-spinal, and tectobulbar projections) developed early in evo-lution, whereas acuity and color vision (depending upon tightly packed cones in the fovea and on cortical circuitry) has developed only recently. Differences between older and newer elements can remain apparent, generally by their circuitries and localization, often by their develop-mental pathways and sometimes by differential vulnerabilities to trauma This is the background for considering in this essay some evolutionary aspects of postural control and movements
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