Brain scans reveal the surprising secret of magic mushrooms’ hallucinogenic effect.
Psilocybin cubensis mushroomFlickr,
Kristie
Gianopulos
The geometric visuals and vivid imaginings experienced by those tripping on
mushrooms are not, as scientists had suspected, the result of increased brain
activity, according to a report out today (23 January) in Proceedings of the
National Academy of Sciences. Instead, under the influence of
psilocybin—the psychedelic component of magic mushrooms—brain activity and
connectivity decrease. The reduced connectivity might be what frees people’s
minds from normal constraints, the researchers propose.
“It was often thought to be the case that these classic hallucinogens must
increase brain function—you know, they expand awareness, expand
consciousness—but in fact what we see is decreased activity,” said Roland
Griffiths of Johns Hopkins Bayview Medical Center, who was not involved in the
study.
“I have to say this was totally unexpected,” said David Nutt of Imperial
College London, who led the study. But, he added, “when you get exactly
the opposite result to what you predict, you know it is right, because there is
no bias.”
Although humans have used magic mushrooms for centuries if not millennia,
very little is known about how they work. Soon after psychedelics gained
widespread popularity in the 1950s and 60s, “the drugs were criminalized and the
research into their beneficial uses was suppressed,” explained Rick Doblin of
the Multidisciplinary Association for Psychedelic Studies, which partly funded
the study.
Because of psilocybin’s illegality, organizing and performing the new study
was a regulatory ordeal, said Nutt. “You have to go through lots of hoops and
get special licenses. You’ve got to have special cupboards and fridges to hold
it… it’s a real rigmarole.”
There was also the ethical concern that the volunteers might experience a
so-called bad trip. Although psilocybin is generally associated with feelings of
euphoria and human connectedness, it can sometimes cause anxiety. Should this
have happened, Nutt explained, the person would have been kept safe, calmed
down, and if necessary, given Valium. To lessen the chance of a bad experience,
all 30 volunteers were chosen on the basis that they had taken hallucinogens at
least once before and so would know what to expect.
It was worth all the effort, said Nutt. Psychedelics offer not only insight
into the biology of human perception and cognition, but may also be of
therapeutic use. And, as it happened, he added, “they all had a good
experience—some had very good experiences, some had experiences they said were
very meaningful and altered the way they thought about life.”
Nutt and his team administered psilocybin to the volunteers by a slow—one
minute long—injection while their brains were scanned by functional magnetic
resonance imaging (fMRI). “We wanted to know exactly what happens when you make
that transition from the normal state to the psychedelic state,” he
explained.
The first 15 volunteers had their brains scanned by arterial spin labeling
(ASL), an fMRI technique that examines blood flow. After seeing widespread
decreases in flow, the researchers were so surprised they scanned a further 15
volunteers by blood-oxygen level dependent (BOLD) fMRI, which more directly
measures metabolism. Both gave strikingly similar results.
Brain blood flow and activity were particularly decreased in the medial
prefrontal cortex—a region involved in emotions, learning, memory, and executive
function—and the posterior cingulate cortex, the function of which is less
clear.
The team also used the fMRI data to look at functional connectivity between
these two regions over time, and found that their deactivation was linked.
“Assessing circuitry in terms of connectivity is a more sophisticated and
informative approach to understanding function, so I think that is the real
strength of their work,” said Mark Geyer of the University of San Diego,
California, who did not participate in the study.
The two regions are connected by the default mode network (DMN), which
integrates brain functions including sensations, memories, and ambitions. “It’s
kind of who you are and how you see the world,” said Nutt. The DMN might also
act as a cognitive constraining mechanism—to filter and make sense of
information. Reduced DMN activity, therefore, might enable an unconstrained mode
of cognition, such as that experienced on a magic mushroom trip.
Interestingly, DMN activity is hyperactive in people with depression,
suggesting that psilocybin may be effective as a depression treatment.
Taking a hallucinogen to deal with depression might not appeal to everyone.
But for those willing to give it a try, the hope is that the need for all
medication might be reduced or even eradicated. “Psilocybin would only be given
a few times under supervision of a therapist…with the hope that at the end of
the process you are no longer dependent on a daily medication,” explained
Doblin. “It would be like opening a door and showing them that there is another
way of being,” said Nutt.
R.L. Carhart-Harris et al., “Neural correlates of the psychedelic
state as determined by fMRI studies with psilocybin,” Proceedings of the
National Academy of Sciences, doi/10.1073/pnas.1119598109,
2012.
Source: TheScientist
Posted by
Robert Karl Stonjek
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