Environmental enrichment as a viable neurorehabilitation strategy for experimental traumatic brain injury

Abstract

Environmental enrichment (EE) emerged as a robust independent variable capable of influencing behavioral outcome in experimental studies after the fortuitous observation by renowned neuropsychologist Donald O. Hebb that rats raised as pets in his home performed markedly better on problem-solving tasks than those kept in the laboratory. In the subsequent years, numerous studies ensued demonstrating that EE was also capable of inducing neuroplasticity in normal (i.e., noninjured) rats. These behavioral and neural alterations provided the impetus for investigating EE as a potential therapy for traumatic brain injury (TBI), which, over the past two decades, has resulted in several reports. Hence, the aim of this review is to integrate the findings and present the current state of EE as a viable neurorehabilitation strategy for TBI. Using the specific key term searches "traumatic brain injury" and "environmental enrichment" or "enriched environment," 30 and 30 experimental TBI articles were identified by PubMed and Scopus, respectively. Of these, 27 articles were common to both search engines. An additional article was found on PubMed using the key terms "enriched environment" and "fluid percussion." A review of the bibliographies in the 34 articles did not yield additional citations. The overwhelming consensus of the 34 publications is that EE benefits behavioral and histological outcome after brain injury produced by various models. Further, the enhancements are observed in male and female as well as adult and pediatric rats and mice. Taken together, these cumulative findings provide strong support for EE as a generalized and robust preclinical model of neurorehabilitation. However, to further enhance the model and to more accurately mimic the clinic, future studies should continue to evaluate EE during more rehabilitation-relevant conditions, such as delayed and shorter time periods, as well as in combination with other therapeutic approaches, as we have been doing for the past few years.

FIG. 1.

Photograph of our environmental enrichment (EE) cage with multiple levels and wide array of sensory stimuli (e.g., balls, ramps, tubes, and nesting materials). In our laboratory, 10–12 rats, which include both traumatic brain injury and sham controls, are housed together to ensure equal conditions. For studies investigating continuous EE, rats were only removed briefly for behavioral assessments, weighing, and, if applicable, drug administrations. Together, these components make up the “typical” EE. However, it should be noted that EE cage setups differ from laboratory to laboratory in terms of the number of rats housed together, the design of the cages, and the complexity of the cage contents.