|Growing Neurons (source)|
They also tested whether neurogenesis was modulated by exercise. And it was. Mice who had access to a running wheel in their cage grew about the same number of cells during the night, but grew more cells during the day. So much so that the difference between night and day disappeared.
|Tamai et al.,, 2008 Figs 1B and 2D|
So exercise helped new cells grow, but without exercise more cells grew during the night time. Now all this use of the phrase 'night time' might make you think that this neural growth is happening during sleep.
|After a long night of wheel running, Jasper succumbs to a restful days sleep. (source)|
But it's not. Mice are nocturnal. They sleep during the day and are wide awake at night. The paper shows that almost all the running that occurs on the running wheel happens at night. So the enhanced cell growth is happening when the mice are active. Why exercising at night causes cells to grow during the day is interesting, but the authors offer no mechanism for why that might be happening.
Tamai S, Sanada K, & Fukada Y (2008). Time-of-day-dependent enhancement of adult neurogenesis in the hippocampus. PloS one, 3 (12) PMID: 19048107