Infant lesion effect: II. Sparing and recovery of function after spinal cord damage in newborn and adult cats.

Considerable disagreement exists concerning the degree to which sparing and/or recovery of function occurs following CNS damage at birth rather than in adulthood. To study this question, the spinal cord was hemisected in neonatal and adult cats and the motor behavior of the two groups was compared when the neonatal operates matured and the adult operates recovered. Quantitative analysis of the motor behavior indicated that the effects were not uniform: in some aspects of motor behavior sparing of function was found in neonatal operates; in others, the adult operates displayed performance which was superior to the neonatal group. Both groups exhibited considerable recovery of locomotor function, but adult operates showed greater accuracy of limb placement during locomotion. Furthermore, the neonatal group had some deficits in locomotion and postural reflexes which were not seen at all in adult operates. There were, however, examples of greater recovery in neonatal operates, e.g. in ipsilateral hopping responses and in the reduced hypermetria of the proprioceptive placing reflexes. True sparing of function was manifested by the presence of tactile placing in neonatal operates which was always abolished permanently in adult operates. The characteristics of the performance suggested that although sparing of function had obviously occurred, the response had never matured fully. These results taken together indicate that the relationship between age at the time damage occurs and ultimate outcome in terms of motor behavior is complex: different motor patterns respond differently to the same lesion. True sparing of function may be restricted to motor patterns which are not directly affected by the lesion because they have not yet developed when the lesion is made.