When the synthetic cannabinoid HU-210 was injected into mice, it caused proliferation of neurons in the hippocampus, a brain area essential for learning and memory. Because HU-210 decreases the release of the inhibitory neurotransmitter GABA, the new cells did not differentiate. This provides a biological explanation for part of the experience of getting high; the THC in marijuana causes an excess of new cells that do not form organized connections.
It is interesting to note that our current understanding of depression involves the reduction of neurogenesis in the hippocampus (1); without new cells you cannot create new ways of thinking. It has been found that exercise increases neurogenesis (2) . In a society that where a person spends most of their day sitting in a car or in front of a computer, is mental stagnation really a surprise? So exercise, smoke pot, do new things, and watch you mental architecture morph into new shapes and patterns!