Seminal work beginning over 50 years ago compared rats living inside standard laboratory cages with rats living as pets or under more complex environmental conditions in larger cages. These comparisons found that freer rats were better at solving problems and had heavier brains. Environmental complexity in those early experiments involved provisioning rats with both spatial heterogeneity (objects in the cages) and temporal variety (daily access to reconfigured mazes). Common “enrichment” protocols now typically involve modest changes to the cage interior and more available space. Experimental use of these protocols often shows that “enrichment” vastly increases the complexity of cellular and capillary architecture and enhances resilience to the deleterious neurological effects of genetic, surgical, and chemical manipulations, often via epigenetic mechanisms. Stepping back for a moment, we see that the term “enrichment” is a misnomer. For a mouse, the ratio between the footprint of a standard cage and the area of its natural home range is about 1 to 280,000. For a rhesus macaque, this ratio is about 1 to 7 million.
Laboratory animals can be highly responsive to drugs that turn out not to be effective in human trials. The paucity of environmental stimulation inside the cage can lead to unwanted artifacts and contribute to undue sensitivity to uncontrollable variables. Very likely, our standard cage conditions (and likely as well our various 'enriched' conditions) impose boredom on our non-human animal subjects, starving them of the spatial and temporal environmental complexity necessary for their brains to fully function and develop; they lack the freedom to make choices, to learn from trial and error, and to experience on a daily basis the consequences of their decisions.
We have made great strides in understanding behavior genetics through studies of animals in cages. The time has come to move forward. The next generation of non-human animal studies should employ semi-natural conditions where subjects have ongoing freedom to make decisions, face manageable challenges, and endure the robust variety of cognitive and affective experiences we know is necessary for healthy brain development and function. By so doing, behavioral models will achieve greater relevance to our understanding of human health and disability.
References
Lahvis G.P. 2016. Rodent models of autism, epigenetics, and the inescapable problem of animal constraint. In: Gewirtz JC, Kim YK, editors. Animal Models of Behavior Genetics. New York: Springer Nature; pp. 265–301.
Lahvis, G.P. 2017. Unbridle biomedical research from the laboratory cage. Elife; 6.
Animal models , Cognition: Education, Intelligence, Memory, Attention , Developmental Disorders (e.g. ADHD) , Positive Psychology/Wellbeing
