The Effects of Environmental Living Conditions on Adult Neurogenesis and Behavior

Abstract

It has been shown in rodent model systems that living in an ‘enriched’ environment in the laboratory can enhance brain plasticity. However, no previous studies have examined the effects on brain plasticity of living in a truly naturalistic setting. In part one of this study, we investigated whether living outside at the Stony Ford Field Center would affect neuronal growth in the hippocampus of adult mice and found that within just two weeks, a substantial increase in the number of immature neurons could be detected compared to mice living in a laboratory setting. To further explore the effects on neurogenesis of living in a naturalistic environment, but in a more controlled fashion, a second study was performed to investigate the effects on brain plasticity of adult rats living in a visible burrow system. Unlike previous ‘enriched’ controlled laboratory studies, this latter study included mixed sex cohorts of rats to promote competition among the males and provide opportunities for sexual activity. Though there was no effect of enrichment on neurogenesis, sexual activity, dominance, and neurogenesis measures were compared, revealing that dominance behaviors were associated with adult neurogenesis. Additionally, there was an association between sexual encounters and dominance behavior in male rats. This association suggests that sexual experience may increase adult neurogenesis, an association that has been reported in previous studies. Taken together, these studies suggest that multiple factors in an enriched environment are capable of increasing adult neurogenesis.