From Physorg.com, Mycobacterium vaccae(a soil bacteria) was fed to mice and the mice were tested in maze runs to see if it increased learning ability. The increase in learning was only temporary, however.

They had a throw-away line about kids going outside to help with mood and learning. The implication being that outdoor activity is good for kids. But let’s get back to reality. Ingesting the bacteria lead to noticeable improvements. I think a second study should be undertaken to study farmer/gardeners/landscapers to see if there is any improvement. Especially to see a relationship between just being outdoors and actual contact with the soil.

Also something implicit with this study. That when humans started farming, we must have felt the benefits from M. vaccae. This is when we see a “great leap forward” with regard to engineering monuments, writing and the like.