I don’t know if you’ll see this as ‘proof’ – but this is a pretty comprehensive study of the effects of cannabinoids on the brain, including behavioural neurotoxicity, neurochemistry, electrophysiological effects, cerebral blood flow studies, positron emission tomography studies, and brain morphology – brain morphology being the one we’re interested in here.

The study is published here: http://www.healthconnect.gov.au/internet/wcms/publishing.nsf/Content/health-pubs-drug-cannab2-ch75.htm

However, it’s long, and if you don’t feel like reading the whole thing as I just did, here are the relevant bits.

“A series of studies from the same laboratory (Harper et al, 1977; Myers and Heath, 1979; Heath et al, 1980 discussed below) reported widening of the synaptic cleft, clumping of synaptic vesicles in axon terminals, and an increase in intranuclear inclusions in the septum, hippocampus and amygdala.”

Another study had different results:

“Most recently, Slikker and colleagues (1992) reported the results of their neurohistochemical and electronmicroscopic evaluation of the rhesus monkeys whose dosing regime, behavioural and histochemical data were reported above. They failed to replicate earlier findings: no effects of drug exposure were found on the total area of hippocampus, or any of its subfields; there were no differences in hippocampal volume, neuronal size, number, length or degree of branching of CA3 pyramidal cell dendrites. Nor were there effects on synaptic length or width, but there were trends toward increased synaptic density (the number of synapses per cubic mm), increased soma size, and decreased basilar dendrite number in the CA3 region with marijuana treatment.”

So there you go. One study says yes, the other says not that but some other synaptic weirdness (which IMO could have a similiar effect to widening in the context of my original comment). And of course, this was all with rhesus monkeys not people.

@Jon: Yup, the experience of your friend is definitely the kind of thing I’m getting at.

@tatjna: Yup, machine learning has drawn LOTS from biological systems, such as the brain, ant colonies, bird flight/swarm behaviour, evolution. Plus because the machine learning systems can run much quicker (but with many assumptions of course) it allows stuff learnt from machine learning to be applied back to biology.

I also agree that drugs are not necessary for self-improvement or spiritual development, but that they can invoke unexpected experiences that influence the rest of someone’s life.

Re: THC widening synapse gaps… I think this probably would allow new pathways to form easier, but it’d also probably disrupt weak connections, or connections that have just formed.

Anyway, what I wanted to say was that one of the things that marijuana (thc) apparently does is widen the gap in the synapses – which I’ve always held would lend itself to the formation of new neural pathways.

I also believe that there is no ‘spiritual development’ that can be achieved with drugs, that can’t also be achieved without them, but that some people with no desire to engage in spiritual development have achieved ‘spiritua’l experiences unexpectedly while on drugs, that have changed their lives.

I’m sure other people are different to me though