Unless otherwise mandated, neuroscientific research on mice is done with ~7-week old animals. There is a sort-of mantra that at this age their skulls stop growing.
However, recently, I noticed a rather robust difference in how I have to place ~4-month old mice in a scanner versus 7-week old ones. I am pretty sure this is due to skull size, since I am fixing all my animals relative to the ear canal, and there should be no fat/hair accumulation in the inner ear. Also, if there would be, I am quite certain I would feel it.
This made me try to look up the source of the 7-week recommendation, but up until now I found nothing. Do you know whether it is correct that the mouse skull "stops growing" at 7 weeks of age, and if so, what studies support this observation?