This isn't quite accurate.
I'll add that I don't quite get what you mean by the psychoactice agents of THC.
THC is the psychoactive component of cannabis and its effects vary from a very significant increase in psychosis to diminished cortical volume with associated cognitive and affective deficits, both which can be permanent.
The loss has only been shown in adolescence, and hence, since it is only tickness they verified, not activity, they can't know whether it is an accentuated effect of normal cortical pruning or actual cortical/functional loss. Also, non-diagnosed ADHD might also be the culprit.
Here's a research on the thickness technique VBM (Voxel-based Morphometry)
Long-Term Effects of Cannabis on Brain Structure
"However, our results cannot exclude that
abnormal pruning is due to genetic predisposition as seen in children from multiplex alcoholic families even before the beginning of any drinking behavior or in obsessive compulsive disorder (
Hill et al, 2007). Hence, a limitation of our study and a matter of debate in the literature are connected to the question of whether these brain changes are caused by cannabis use or are already present before drug use."
Neuronal pruning is not cortical loss. And they forgot to add ADHD and depression patients. (I would need to find other studies that did included the cavaet as I've read some, it's just long to sift through and haven't gone into this in over four years.
This following research was done afterwards with Functional MRI instead of analysing thickness only, you should read what it says:
Grey Matter Changes Associated with Heavy Cannabis Use: A Longitudinal sMRI Study
A small exert "and some others reporting even larger regional brain volumes in cannabis users compared to controls"
The only adult research that shows cortical loss (and not pruning) in adults, again with thickness analysis, is with patience with schizophrenia.
There is still no concensus whether cannabis is causal to schizophrenia. But when looking on research for its origin, you can read giants in the field of genetics research on diseases, like Guy Rouleau, will tell you that there is a lot of genetic modulation by the environment when it comes to schizophrenia. This means intrauterine or postnatal/formative years epigenetic effects. For now, cannabis is a lock as a facilitator for schizophrenia.
A big stumbling block of cannabis research and its effect on cortical mass is the fact that cannabis users are often diagnosed and undiagnosed ADHD individuals or individuals with undiagnosed depression. The smaller cortical regions are the same for both, hence it's hard to tell what came first. The thing is, we know what comes first. ADHD, depression and addiction have a very intimate relationship. They are very related in how they come about. Again, intrauterine and post-natal factors, which we know more about than schizophrenia. The same cortical regions that are affected by ADHD are the same as the cortical regions they notice are smaller in cannabis users. So what is it? Non-diagnosed ADHD patients maybe?
Point is, they do not know if cortical reduction (already present) is due to cannabis, or undiagnosed ADHD or depression.
What we do know about CB1 and CB2 is that they are exact matches for receptors in the endocannabinoid system in the brain (there are steps in our evolutionary history where we
probably ate cannabis plants). The endocannabinoid system, and the CB1 and CB2 receptors play a catalyst role in neurogenesis. In adults, neurogenesis is mainly concentrated on the hippocampus, which functions are long-term memory and ANS inhibitor/activator.
Cannabinoids promote embryonic and adult hippocampus neurogenesis and produce anxiolytic- and antidepressant-like effects
The role of cannabinoids in adult neurogenesis
Also, there is no proof of permanent detrimental effect from cannabis. If Phineas Gage's brain was able to redeem lossed functions over time, the impact of cannabis, especially on the Nucleus Accumbens and the cortical and dopaminergic mesolimbic pathway can be reversed even more easily than how Gage's brain readapted (without any help) and the insult/injury to Gage's brain was physical and extensive.
I wrote the previous post really quickly, I meant psychoactive agents of cannabis, which THC is a major one.