I had an experience once on a synthetic cannabinoid, though I have no way to ever know what it was.
During this experience, I could view my mind like a file system on a computer (complete with a GUI) and I felt like I had access to every experience I'd ever had.
I reviewed snorkelling in the great barrier reef, various holidays and basically all my most cherished memories. But it was beyond normal recall, I was literally watching what I did, through my eyes, as if I was there again. I have no chance of re-establishing this same level of memory recall, and nothing I've tried has reproduced this effect.
My friend had a terrible time, he may have had more than I did (it was potently psychoactive), but that 'trip' sent me to one of the most euphoric states I've ever experienced - literally by becoming an accumulation of nothing but my best moments.
I tried a number of different commercial smoking blends after this, but nothing could compare. Most were absolutely fucked, I think one had some kind of synthetic ketamine derivative. Nasty.
It seems the CB2 receptor is responsible for this advanced memory phenomena, and as a wild guess I'd say the cannabinoid I had probably had a selective and/or binding nature to this receptor over CB1 (activation here has shown to impair memory by activating COX-2).
Activation of CB2 by various cannabinoids has been seen to reduce many of the toxic effects of induced Alzheimer's disease in rodent models...
In rats injected with Aβ1-40 fibrils to mimic Alzheimer's pathology, activation of CB2 (via the synthetic cannabinoid MDA7
[567]) is able to near-fully preserve memory relative to control, which is thought to be due to reduced microglial activation in the hippocampal CA area.
[555] It was also observed that CB2 activation promoted Aβ1-40 clearance in the hippocampal CA1 area as well.
[555]Treatment with MDA7 also prevented abnormalities in this region such as CB2 receptor upregulation or impaired glutaminergic signalling.
http://www.ncbi.nlm.nih.gov/pubmed/22795792
Perhaps a strain with natural CB2 selective composition could be the cause of 'memory trips', I know I've had a few with cannabis too, just not nearly to the same extent as above.