[robotnik]

Stress can inhibit neurogenesis (among other things) in the hippocampus, as the article states. Is it possible that HIIT was not as beneficial for the rodents, because they were, unlike the moderate exercisers, forced to exercise? Being forced to exercise intensely might have been the real source of stress.

[jjallen]

Having a weight strapped to your tail could definitely be stressful too.

[thesz]

For humans it is different.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3772595/ - brain derived neurotrophic factor (BDNF) serum level increase for what can be considered high intensity exercise.

http://www.medscape.com/viewarticle/723059 - resistance training induce BDNF release, from all of the body. BDNF can cross brain-blood barrier.

Rodents are easy to experiment with, but quite distant from humans in actual metabolism.

[bonniemuffin]

This struck me as the most important potential difference -- that the moderate-intensity rats were able to make choices about when and how to exercise, while the HIIT rats had exercise forced upon them.

It reminds me of Rat Park -- when you stress out rats by treating them poorly, all you end up measuring is the effect of misery on rat physiology.