LSD affects (?)

This is about how LSD affects people - physically. My friend claims that LSD causes hallucinations by causing the brain to swell and press against the cranium. This pressure is what causes the hallucination.

The web sites that I have looked up (via google) said that it works by removing some chemicals from the seratergic cycle. But they are not too sure how it all works.

So my question is, which version is correct, and where did the pressing on the skull causing hallucinations come from? (my guess concussion). Or are both of these wrong? I have no real way of finding out otherwise.
Thanks in advance
FloChi

The vaults of Erowid http://www.erowid.org/psychoactives/psychoactives.shtml
Has a pretty good article on the mechanism of LSD
http://www.cs.hmc.edu/~ivl/writing/non_fiction/lsd/
The exact mechanism by which it produces visual hallucinations is not known.

Your friends peculiar story about brain swelling causing visual hallucinations make stem from the observation that pressing on the the eyeballs, or stimulating the optic nerve electrically, induces phosphemes.

LSD probably works primarily as a catalyst, especially as a mimic of some natural catalyst. Damn little of it actually gets to the brain: the doses are small to begin with (effective doses beginning as low as 20 micrograms) and LSD being not particularly efficient at permeating the blood-brain barrier.

It only causes the brain to swell metaphorically.

“Visual hallucinations” tend to be of three main types:
a) an inability to distinguish between moving and non-moving surfaces at certain focal lengths. Most commonly, things look like something on their surface is crawling or wriggling from 2-5 feet distance. If you look right at something, it is the parts of the object you aren’t directly staring at that will seem to be in motion as if covered several inches deep in fuzzy caterpillars crawling over each other.

b) massive metaphorical symbolism. The three planes you see taking off from the regional airport as you ride by on the bus are interpreted in light of your musings on how the big city is a dehumanizing hive and we have turned ourselves from mammals into insects. The next face you see seems to have taken on rather insectile characteristics, their jaws moving like insects’ mandibles. You see faint translucent green and gold insectile antennae that wave as if connected to their eyebrows.

c) sensory signal leak. The F# diminished chord that Roger Waters keeps returning to hangs a neon blue sheet over the speaker every time he plays it. The rapid synthesizer loop makes a red snake slinking across the carpet with a black band at every percussive snare beat. Not only that, you can feel the rubbery texture of those snare beats in the pit of your stomach. Your friend says something and the room lightens up and flickers like a tape recorder’s signal meter in time with the rhythm of his voice. You really like the soapy-cinnamon smell of conversation and the way it mixes with the color of the rubbery sensation of the snare drum.

I’m not saying no one ever sees purple dancing elephants on LSD, or never see a staircase where there is actually only empty space outside the window, but mostly “hallucination” is a misrepresentation of the experience.

::thinking I need to score some::

DAMN STRAIGHT!!

oh, and I think your descriptions are dead on.

jb