ABSTRACT
Underlying all behavioral development is the maturation of the nervous system. The repertory of patterned reflexes that is present in the newborn is based on changes in the structure of the nervous system that have been going on long before birth. The gradual weakening and eventual disappearance of these phylogenetic reflexes coincide with the descent of moderating and controlling influences from the supra-segmental hierarchical structures. “The direction of development is cephalocaudad. The first movable parts to come under volitional control are those nearest the brain, namely, the eyes. Thence forward, progressively downward and distally into the extremities, controlled movements occur until mastery is established over the skeletal musculature and even over emotional expression. Meanwhile, growing awareness and accumulating experience are making sensory reception increasingly meaningful and elevating it to the level of perception.… The persistence of certain phylogenetic reflexes beyond the time that they should have disappeared is a sign of delayed encephalization of behavior or of damage to the central nervous system” (Di Leo, 1967). Among the reflexes destined to extinction during the normal course of development are the Moro, tonic-neck reflex, indiscriminate sucking, automatic hand grasp and toe grasp, and Babinski.
