A recent article (A. Rubio-Araiz et al., Mol Cell Neurosci
:374-80) says that neural stem cells (the cells in your brain that create new neurons continually, even in adults) can be induced to proliferate using agonists of CB1 or CB2. CB1 and CB2 are the "cannibinoid" receptors, which respond to the active compounds in cannibis (pot). Proliferating neural stem cells leads to having more neurons in your brain.
Thus, it appears that pot actually does
expand your mind...
On the other hand, the CB1 receptors appear to be involved in the circuit that causes memories to be forgotten. I'm sure this comes as no surprise