The
neurochemistry of LSD - A technical explanation
for nontechnical readers.
The primary effect of LSD occurs at receptors
intended to respond to
serotonin (kudos
to
enth for touching on this in the most
detail so far). Serotonin (aka
5-HT, 5-hydroxy
tryptophan) exists as an evolutionarily new
addition to our
brains. All the highest systems
make heavy use of it, including our
frontal lobe
(and specifically, the
prefrontal cortex) that
seems to give us an edge (
intelligence-wise)
over every other animal on Earth. It also has
effects outside the brain, which happens to
(partially) explain why LSD causes things like
jaw clenching and
nystagmus. Believe it or
not, LSD has
more effect on
smooth muscle
tissue than it does in the brain.
To get right to the point, LSD acts as a
5-HT
2 partial
agonist (the
"
2" just designates a particular
type of postsynaptic
receptor).
This results in a decrease in the amount of
serotonin that gets dumped into a
synapse,
but at the same time LSD produces some degree of
effect similar to serotonin itself.
Of course, keep in mind that the previous paragraph
only describes the best current theory, in that it
most fully accounts for LSD's effects at the local
level of an actual synapse. A good site with some
alternative theories as to its actual action in
a
serotonergic synapse lives at
"http://www.cs.hmc.edu/~ivl/writing/non_fiction/lsd/".
(I apologize for the external link, but I have
yet to find a better site discussing the specifics,
including competing theories, of the activity of
LSD at the
synaptic level).
So what does serotonin actually
do...
It acts to
prevent the postsynaptic cell
from firing (ie, it acts as an "
inhibitory"
neurotransmitter). So, decreasing serotonin
release into a synapse increases the rate of
firing of the postsynaptic cell. Thus, LSD
"speeds up" the outer layer of the brain. This
doesn't mean you
think faster (and
certainly not "better"), just differently.
Now that you have that down...
LSD also acts at
noradrenergic synapses, though
its effect on such sites has received
far
less research than its effects on serotonergic
receptors. I'll focus on the main system affected
here, rather than the specific receptors, for that
reason.
The
Locus Coeruleus, which communicates primarily
using
norepinepherine (thus the connection with LSD)
acts as the "gate" for letting sensory input get
through to the parts of us we consider "us" .
most of the time, it filters out the
vast
majority of information we receive, but LSD forces
it open, so we become aware of countless features
of our environment we normally don't notice. On
the down side, LSD also garbles the transmission,
leading to the cross-
modal experiences one
can sometimes experience while
tripping (such as
"hearing" a color, a classic effect of LSD that most
users describe as not really occuring to such an
obvious degree).
To summarize, LSD temporarily modifies the way
we consciously process information. At the
same time, it gives us conscious access to
immensely more information, though not reliably
true information, than we normally perceive.