[canucker2016]

from later in that article:

"Human studies have shown that long-term (>10 years) and heavy (>5 joints per day) cannabis use compared with age matched non-using controls resulted in bilaterally reduced hippocampal and amygdala volumes (p=.001) and significantly worse performance on measures of verbal learning (p<.001).14 There is evidence that recovery is possible in humans as well. ... They found that cannabis users had smaller hippocampal volumes compared to controls but the users not exposed to CBD had an even greater (11%) reduced volumes (CBD appears to be somewhat protective). In the former users the hippocampal integrity was comparable to controls. ..."

summary: THC-only users had smaller hippocampal and amygdala volumes (HAV) than THC+CBD users, while former users had HAV similar to control subjects.