Here I presented evidence how lack of enrichment impacts brain. I did not paint the rodent brain - it's a human brain so people recognise what it's about right away.

The studies I talk about investigate the impact of enrichment, and they compare enriched groups to non-enriched. The level of enrichment differs between studies. Non-enriched include some bedding and a couple of items like a hide and a tunnel - what people usually buy in a pet store.

Enriched habitats differ between studies, so I advise you read the one you want to know about.