THE PUZZLE OF ENRICHMENT 

The mice were up late last night, as they should be. I could hear the squeaky, cheaply made Chinese running wheel going on and on and on and on.

The running wheel is, along with the equally ubiquitous mouse house and paper tube, among the most common of the modern lab's attempts to "enrich" the mouse environment. The purpose of such is to draw the mouse's attention away from the bars of the cage and into the the center of the cage.

The purpose of that is to foster more exploratory, "wild type" behaviour by the captives and reduce so-called "stereotypies"--repetitive, unchanging actions like bar-gnawing, cage-parimeter circling, and flipping the tv clicker endlessly through the pay-per-view selections. Enrichment has been heartily embraced by the lab animal community since various veterinary organizations recommended it and the NIH (aka "the bank") and others endorsed it. The consequence of that has been the creation of a huge industry of mouse house suppliers and enrichment researchers (Van Loo, 2004).

The motive behind this embrace comes not from some sudden bout of altruism, empathy, or fondness for little red houses, but from one thing and one thing only: the growing core of science that shows that lab animals that do not come out of an enriched environment skew the results of lab tests (Spani, 2003). A mouse from a barren environment might present a false picture of the effect of a certain neurological drug candidate, for example. And means that the results of the testing are less, let's say it, bankable.

Yet enrichment--whether in the murine lab environment or the human one--is no one-dimensional effect. As more and more studies show, it is often paradoxical. Male mice in an enriched environment may indeed show fewer stereotypies like over-grooming, but they often are more aggressive than their non-enriched peers. There is a zoomorphic of this in the person of Donald Trump, who was once dubbed by Spy magazine as "a short-fingered vulgarian." Who knew they had the fingers right too...

There are more new puzzles as well. In a series of experiments with Alzheimers mice, Jankowski (2004) showed something remarkable: Alzheimers mice in an enriched environment did not develop dementia as quickly as Alz-mice in a barren environment. But...when the mice were killed and their brains examined, there was a surprise. The amyloid plaque associated with Alzheimers was increased in the mice that had had enrichment--far more advanced than that in the barren-house mice.

What does that suggest? It may be one more doubt in the growing corpus of work that casts doubt on amyloid plaque as the initiator of Alzheimers's symptoms. The mice did not grow demented but they did have the  plaque usually associated with it. It was a mind blower--and a reminder that enrichment may cut more than one way in the realm of mice and man.