How long does it take for environmental enrichment to show effects?

From funnyvet.
From funnyvet.

Environmental enrichment is a powerful way to give a boost to neurogenesis and alleviate some anxiety and depression symptoms. For the laboratory rodents, who spend their lives in cages with water and food access, environmental enrichment can refer to as little as a toy or two or as much as large room colonies with different size tubes, different levels to explore, nesting materials, plenty of toys with various shapes, textures, and colors, exercise wheels, and even the occasional fruit or peanut butter snack. But for how long does a mouse need to be exposed to enrichment to show cognitive and emotional improvement?

Leger et al. (2015) ran several anxiety, depression, and long-term memory tests in mice who have been exposed to environmental enrichment for 24 h, 1, 3, or 5 weeks. Although 24 h exposure was enough to improve memory, only after 3-week exposure some anxiety behaviors were attenuated. No effect on depressive behaviors or coticosterone levels, which may be due to that particular strain of mouse (several other studies found that environmental enrichment ameliorates depressive symptoms in other mice strains and rats). The 3-week exposure also increased the levels of serotonin in the frontal cortex. Only after 5-eweek exposure there was a significant survival rate of the hippocampal new cells. Of note, these were normal mice, i.e. they were not suffering from any disorder prior to exposure.

Mice raised in an impoverished environment (a) show less dendrite growth (c) than do mice raised in an enriched environment (b, d). Copyright: BSCS.
Mice raised in an impoverished environment (a) show less dendrite growth (c) than do mice raised in an enriched environment (b, d). Copyright: BSCS.

The findings give us a nice timeline for environmental enrichment to show its desired effects. But… if there are differences in the timeline and effects of environmental enrichment exposure from mouse strain to mouse strain, then what can we say for humans? Probably not much, unfortunately. As the ad nauseam overused phrase goes at the end of so many papers, ‘more research is needed to elucidate this problem’.

Reference: Leger M, Paizanis E, Dzahini K, Quiedeville A, Bouet V, Cassel JC, Freret T, Schumann-Bard P, & Boulouard M. (Nov 2015, Epub 5 Jun 2014). Environmental Enrichment Duration Differentially Affects Behavior and Neuroplasticity in Adult Mice. Cerebral Cortex, 25(11):4048-61. doi: 10.1093/cercor/bhu119. Article | FREE PDF

By Neuronicus, 1 November 2015

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