constitute a class of psychoactive drugs with unique effects on
consciousness. Psychedelic means "mind-manifesting"
and refers to the ability of these drugs to illuminate normally
hidden aspects of mind or psyche. Native American shamans consumed
psychedelic plants such as the peyote cactus (contains mescaline),
psilocybe "magic" mushrooms (contains psilocybin), or
the brew called ayahuasca (contains DMT and harmaline) in order
to communicate with God or the spirit realm.
The most potent
psychedelic is the semi-synthetic ergot derivative lysergic acid
diethylamide (LSD), which has detectable effects at microscopic
doses. This drug was discovered by the Swiss chemist Albert Hofmann
in 1943. While handling vials containing the chemical, he accidentally
absorbed some of it through his skin, and later experienced a
strange state of consciousness. Suspecting that LSD was the cause,
Hofmann decided to test the drug on himself, starting with what
he thought would be a small and probably ineffective dose - only
¼ of a milligram. However, for LSD this is a rather large
dose. Hofmann’s ensuing “trip” was overwhelmingly intense and
he assumed he was either dying or going insane (Hofmann, 1981).
Hofmann recovered and a period of scientific research on LSD began.
first thought LSD induced a “model psychosis” that might shed
light on the nature of schizophrenia.However,
as the psychedelic experience or “trip” does not resemble endogenous
psychoses, this interpretation was later discarded. In the 1950s
the therapeutic potential of LSD was investigated under the assumption
that LSD was a key that could unlock the secrets of the unconscious
mind. Thousands of people in the U.S., including the actor Cary
Grant, underwent “psycholytic” (“mind-loosening”) therapy under
LSD during the 1950s and early 1960s (Grinspoon & Bakalar,
1979). Other work investigated the religious aspect of high-dose
psychedelic experiences. In a 1961 experiment known as the “Miracle
of Marsh Chapel,” Boston Divinity Students were given psilocybin
or placebo in a double-blind design; most subjects in the psilocybin
group (and none in the placebo group) reported profound religious
experiences with lasting beneficial consequences (Doblin, 1991).
Scientific and clinical work with psychedelics was interrupted
when the drugs were outlawed in the U.S. in 1965 as a response
to their growing non-medical use, but in recent years, renewed
scientific interest in consciousness has led to a small revival
of psychedelic drug research.
drugs, psychedelics do not produce reliable, consistent effects
across users, or even in the same user at different times. The
most positive accounts describe mystical revelations such as gaining
direct knowledge of God or an all-encompassing cosmic unity. More
commonly reported is a kaleidoscopic display of intensely colorful
visions, ranging from continuously unfolding abstract designs
to fully formed images of animals, plants, landscapes or more
bizarre scenes. However, taking a psychedelic also entails the
risk that the user may spiral down into the black hole of a “bad
trip,” an overwhelming state of terror and psychic anguish that
can be followed by lasting PTSD-type symptoms such as flashbacks.
“Bad trips” are the main hazard of psychedelic drug use, as the
possibility of a lethal overdose is vanishingly small.
drugs are not addictive. Even enthusiastic proponents of psychedelics
take them infrequently due to the intensity of the “trip.” Animal
research indicates that Homo sapiens is the only species that
will voluntarily take a psychedelic drug again after having experienced
the effects. Although laboratory animals such as rats or monkeys
will readily self-admininister most other drugs abused by humans,
including cocaine, heroin, amphetamine, nicotine and alcohol,
they find psychedelic drugs highly aversive (Yokel, 1987).
of how these agents produce their striking alterations of consciousness
has long fascinated brain researchers. The first clue was that
LSD, psilocybin, DMT, and many other psychedelics bear a close
structural similarity to the neurotransmitter serotonin. Research
in the 1970s showed that LSD temporarily suppresses the firing
of serotonin-releasing neurons of the raphe nuclei (Rechs &
Rosecrans, 1982), a part of the brainstem reticular activating
system. These neurons send axons into widespread regions of the
cerebral cortex and limbic system, where they release serotonin
when active. Because the raphe nuclei also go silent during REM
sleep, the notion that the psychedelic state represents “dreaming
while awake” became the standard account. However, subsequent
research contradicted this interpretation by showing that LSD
and other psychedelics act postsynaptically as agonists at 5-HT2
receptors (Jacobs, 1987), the most common serotonin receptors
in the brain. The silencing
of the raphe nuclei was due to LSD’s agonist action at presynaptic
autoreceptors (inhibitory 5-HT1) on the serotonin-releasing cells.
Autoreceptors serve a negative feedback function such that the
neurotransmitter (in this case serotonin) inhibits its own release
when extracellular levels are too high. LSD thus acts like serotonin
both presynaptically and postsynaptically, inhibiting serotonin
release via inhibitory 5-HT1 autoreceptors while simultaneously
activating excitatory postsynaptic 5-HT2 receptors; only the latter
action is relevant to the psychedelic state (Feldman, Meyer &
Quenzer, 1997). This interpretation was bolstered by the finding
that serotonin antagonists can block psychedelic effects. Recent
PET scans of volunteers under the influence of psilocybin showed
hyperactivity of the frontal and occipital lobes, especially in
the right hemisphere, presumably reflecting strong activation
of excitatory 5-HT2 receptors in the cortex (Vollenweider et al.,
1997). But how and why these brain changes translate into psychedelic
experiences are questions as difficult as the mind-body problem
the brain actions of psychedelic drugs has potential implications
for theories of consciousness and the brain correlates of mystical
experiences. People who claim to have had a mystical experience
under the influence of a psychedelic give reports that are often
similar to the accounts of non-drug using religious mystics from
the major religious traditions (Pahnke & Richards, 1966).
Themes such as the unity of all sentient beings, oneness with
God and the universe, and the illusory nature of human existence
have been reported by figures as diverse as Buddha, the Christian
mystic Meister Eckhart, and psychologist turned sixties LSD guru
Timothy Leary. The psychedelic experience thus represents a unique
intersection between mind, matter, science and mysticism that
still defies explanation.
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