DEVELOPMENT OF RIGHTING WHEN FALLING FROM A BIPEDAL STANDING POSTURE - EVIDENCE FOR THE DISSOCIATION OF DYNAMIC AND STATIC RIGHTING REFLEXES IN RATS

Righting to prone when placed supine on the ground by rats is present at birth, albeit in incomplete form. In contrast, righting in the air when falling from the supine position does not begin to emerge until t he end of the first week and is nor, complete until the end of the thi rd week postnatally. On the ground, the animals have sensory informati on from proprioceptive-tactile sources, as well as vestibular; in the air, they have only vestibular. Thus, it is possible that the differen ce between contact righting and air righting is a reflection of the re lative difference in the maturation of tactile vs. vestibular mechanis ms. In this study, pups were tested by pushing them backwards from a b ipedal standing position. Such a concert provided proprioceptive-tacti le information during the fall. The results showed that the developmen tal onset and maturation of righting from the bipedal position resembl ed that of air righting rather than contact righting. This suggests th at the difference between air righting and contact righting is not due to differences in sensory inputs, but to differential maturation of n eural mechanisms for acceleratory (i.e., falling) vs. stationary (i.e. , lying on the ground) forms of righting. That is, the appropriate neu ral systems are organized for the type of righting, not for the sensor y systems used. Even so, some evidence is provided suggesting a develo pmental dissociation between righting from falling with vestibular inf ormation only, and with proprioceptive-tactile information in addition . Therefore, righting systems appear to need two dimensions of classif ication-one based on sensory systems involved, and the other in terms of the context of righting (i.e., falling vs. stationary).