Temporal Effects of Environmental Enrichment-Mediated Functional Improvement After Experimental Traumatic Brain Injury in Rats

Background. Environmental enrichment (EE) enhances motor and cognitive performance after traumatic brain injury (TBI). However, whether the EE-mediated benefits are time dependent and task specific is unclear. A preliminary study, in which only half of the possible temporal manipulations were evaluated, revealed that the beneficial effects of enrichment were only observed when provided concurrently with specific training (ie, motor or cognitive), suggesting task-specific dependence. Objective. To further assess the effects of time of initiation and duration of EE on neurobehavioral recovery after TBI by evaluating and directly comparing all the temporal permutations. Methods. Anesthetized adult male rats received either a cortical impact or sham injury and were then randomly assigned to 8 groups receiving continuous or early and delayed EE with either 1 or 2 weeks of exposure. Functional outcome was assessed with established motor (beam-balance/walk) and cognitive (Morris water maze) tests on postinjury days 1 to 5 and 14 to 18, respectively. Results. Motor ability was enhanced in the TBI groups that received early EE (ie, during testing) versus standard housing. In contrast, acquisition of spatial learning was facilitated in the groups receiving delayed EE (ie, during training). Conclusions. These data support the conclusion from the previous study that EE-mediated functional improvement after TBI is contingent on task-specific neurobehavioral experience and extends those preliminary findings by demonstrating that the duration of enriched exposure is also important for functional recovery.