A CRITICAL MATURATIONAL PERIOD OF REDUCED BRAIN VULNERABILITY TO DEVELOPMENTAL INJURY I - BEHAVIORAL-STUDIES IN CATS

Groups of cats with resection of the neocortex of the left cerebral he misphere at postnatal (P) ages (in days) 5-15 (PIG), 30 (P30), 60 (P60 ), 90 (P90), 120 (P120), and in adulthood, were compared using a compr ehensive battery of 16 neurobehavioral tests administered when they we re at least 6 months post-lesion. For all behaviors, except 3 (includi ng the paw contact placing reaction which never recovered), the perfor mance was significantly better for the cats lesioned between P10 and P 30 compared to cats lesioned at older ages. For 10 of the behaviors, t he transition from age-at-lesion P30 to P60 was rather abrupt and char acterized by a significant increment in impairments. However, cats wit h the resection at ages P90 and P120 still showed some behavioral adva ntage over the adult-lesioned animals. Overall, for most of the behavi ors tested, there was a significant linear trend for an increase in th e magnitude of impairments across the entire age-at-lesion range. We p reviously reported that cats with a unilateral frontal cortical lesion sustained during the late fetal life showed substantial behavioral im pairments, while animals with a similar resection sustained early post natally exhibited minimal abnormalities. These findings, together with the present results, indicate that the long-term behavioral outcome o f neocortical injury is best when the lesion is sustained during a dis crete period of the life of the cat: This period extends from about fe tal age 55 days (the oldest lesion age in our fetal studies) to about P60, as shown in the present paper. For these reasons, we propose that there is a Critical Maturational Period (CMP) for optimal post injury brain and behavioral restoration. We hypothesize that this span of re duced vulnerability is linked to specific developmental morphological events which occur during the same time period. Since, as discussed, s uch ontogenetic events also occur in other mammal species (albeit at d ifferent chronological ages), we further propose that the timing of th e CMP as delineated in cats, can be extrapolated to other higher mamma ls species including humans. (C) 1998 Elsevier Science B.V.