Hello and welcome to BW forums
There are usually a couple of reasons why babies wake at 40 mins. Either they have not learned yet to fall to sleep independently which means when they come out of one sleep cycle they do not know how to transition to the next sleep cycle without help. The other common reason, if they are already an independent sleeper, is that the A time is a bit too short (it can also be too long but that usually shows as naps shorter than you describe).
Is your LO sleep trained? Did you use the BW method of shush/pat? Or are you trying to sleep train at the moment?
If you can record the exact times of your EASY and post them here we could have a look and see if a tweak on teh routine could help get better naps. When you post your EASY this format is helpful:
WU (wake up) 7
E 7
A 1hr 15
S 8.15 - 8.55am (40 min) tried to resettle
S 9.25 - 11.25 (2hr) woke happy
E 11.25
A 1hr 15
...and so on. Include
BT (bed time)
DF (dream feed if you do one)
NW (waking for no feed)
NF (waking for feed)
WU (next day wake up time)
Try not to worry about brain development. Babies do need sleep, yes, but you are doing all you can to help him sleep and you are not purposely keeping him up or not offering naps. He will be fine. They say the brighter kids need less sleep than the norm so you never know the short naps could be an indication of a fabulous brain!
These early months are tough. I felt like I was feeding and getting by LO to his bed all day long. It gets easier though. Try not to worry and rest whenever you possibly can.
If you can answer those questions above and post your EASY times we can probably offer more support.