Sure would hate to live in a world where that was true.
Sad fact: marijuana thickens the cell walls to the short term memory region of your mind-- AFTER long periods of use.
It does NOT slow the mind in anyway, and some people it does not affect their memory in at all.
There is also the case of state-dependant learning, but that's another issue.
I learned the lesson of moderation and occasional use long ago.
-SW