[thedoc (OP)]

Neil S. Briscoe  asked the Naked Scientists:
   
Just seen your tweet about "any questions on hallucinations..."

I have a friend who was on drugs (sorry, can't tell you which ones) due to an illness he was suffering. During that time, he told me that he watched a spitfire fly in and land on the shelves above his bed.

So the question is, what do drugs do to the brain that causes such odd hallucinations?

Regards
Neil

What do you think?

[cheryl j]

Thats a really interesting question, and I have no explanation other than a vague idea that neurons in, say, the visual cortex, are being made to fire when they arent being stimulated by any sensory nerve. But what is facinating is that it doesnt just result in total gibberish - like just flashing lights or random colors, but actual meaningful images. Thats pretty amazing when you think about it, but so are dreams, too.

[cheryl j]

The other thing I'd like to know is how aware are most people when they are hallucinating that it is a hallucination, and is it simply the unlikelihood of what they are seeing really being there that tells them that, or is it just "different." I've never had a hallucination, so i don't know.

[grizelda]

My own explanation is that there is a one-to-one correspondence between your emotions and your experiences (one emotion per experience, say). Since your emotions are caused by your neurotransmitter levels, having your neurotransmitter levels adjusted by medication would result in strange emotions, generating strange mental experiences (hallucinations).

[techmind]

There was an interesting Radio4 programme recently with Prof David Nutt (of ACMD fame). His research interest is in the hows and whys of hallucinogenic drugs on the brain.
See the episode for "The Life Scientific" 18 Sept 2012 here: http://www.bbc.co.uk/podcasts/series/tls
I recall the gist was that such drugs "switch off" parts of the brain that normally mediate communication between different brain areas (which normally provide checks and balances on rational thought).
Interestingly you can also experience hallucinations when on the borderline of wake/sleep, especially if you are woken in the early hours of the morning (look up some web resources on lucid dreaming, which is related). I have experienced this once: it was "interesting" and somewhat worrying at the same time - if only as it demonstrates that the line between sanity and insanity is very thin.