Environmental enrichment-mediated functional improvement after experimental traumatic brain injury is contingent on task-specific neurobehavioral experience

Abstract

Environmental enrichment (EE) is superior to standard (STD) housing in promoting functional recovery after traumatic brain injury (TBI). However, whether the EE-mediated benefits after TBI are dependent on exposure to enrichment during neurobehavioral training has not been elucidated. To address this issue, isoflurane-anesthetized adult male rats received either a cortical impact or sham injury and were then randomly assigned to early EE, delayed EE, continuous EE or no EE (i.e., STD conditions). Continuous EE or no EE was initiated immediately after surgery and continued for the duration of the study. Early EE began directly after surgery, continued for 1 week, and was then followed by STD living (2 rats per cage) for the remainder of the study, while delayed EE commenced 1 week after early STD housing. Functional outcome was assessed with established motor and cognitive tests on post-injury days 1–5 and 14–18, respectively. CA1/CA3 neurons were quantified at 3 weeks. CA3 cell loss was significantly attenuated in the TBI+continuous EE group versus the TBI+no EE group. Beam-walking was facilitated in the TBI groups that received either early or continuous EE versus those receiving delayed or no EE. Cognitive training was enhanced in the TBI groups that received continuous or delayed EE versus the early EE or no EE groups. These data suggest that EE-mediated functional improvement after TBI is contingent on task-specific neurobehavioral experience.