http://slatestarcodex.com/2017/10/25/against-rat-park/ has links, e.g.:

http://sci-hub.io/10.2466/pr0.1996.78.2.391

https://www.ncbi.nlm.nih.gov/pubmed/2616610

But there are other studies linked that seem to confirm it.

https://www.ncbi.nlm.nih.gov/pubmed/3696469

https://www.ncbi.nlm.nih.gov/pubmed/18463628

Not sure where that leaves us.