“Given prior reports of adverse effects of cannabis use on working memory, an executive function with a protracted developmental course during adolescence, we examined associations between developmental patterns of cannabis use and adult working memory (WM) processes.

Within repeated cannabis users, greater levels of total cannabis use were associated with performance-related increases in dorsolateral prefrontal cortex (DLPFC) activation during maintenance.

Surprisingly, however, at the group level, cannabis users generally performed better than participants who reported never using cannabis (faster RT, higher accuracy).”

https://www.ncbi.nlm.nih.gov/pubmed/29253654

https://www.sciencedirect.com/science/article/pii/S1053811917310637

“Why Pot Smokers Scored Higher Than Nonsmokers on This Memory Test. Among a sample of 28-year-olds who took a working-memory test while undergoing an MRI brain scan, individuals who started smoking marijuana in adolescence performed just as well or even better than individuals who never smoked cannabis, the study found.” https://www.livescience.com/61574-adolescent-cannabis-use-memory-study.html