Well written in terms that even a layman could read it! Thank you.
Bonnie Malone Houghton

Honestly, I don’t know. The brain has a set of natural “cannabis” receptors (endocabbinoids) that are activated by marijuana. They are everywhere. Almost certainly they are found on dopamine neurons, or on other neurons that control the release of dopamine.

So the loss of “motivation” could be a direct action on those natural receptors; or could indeed be an indirect action of changing the dopamine soup. Or likely many other possibilities!