Paranoid or Placid? Scans Show Pot’s Effect on Brain

FRIDAY, Jan. 6 (HealthDay News) — Smoking marijuana can mean
different things to different people — for some, anxiety and paranoia can
set in, while others mellow out.

Now, a unique brain scan study suggests two ingredients in pot may work
independently to achieve these effects.

British scientists who watched the effects of the two marijuana
ingredients — Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) —
on the brains of 15 young men say the research shows how the drug can
either ease or agitate the mind.

“People have polarized views about marijuana,” said study lead author
Dr. Sagnik Bhattacharyya, a researcher in the department of psychosis
studies at the Institute of Psychiatry, King’s College London. “Some
consider it to be essentially harmless but potentially useful as a
treatment in a number of medical conditions, and others link it to
potentially severe public health consequences in terms of mental health.
This study explains why the truth is somewhere in between.”

The findings were published in the January issue of Archives of
General Psychiatry
.

According to Bhattacharyya‘s team, it’s long been noted that cannabis
can prompt the onset of psychotic symptoms, such as paranoia and/or
delusional thinking, among otherwise healthy people.

“A number of studies have (also) clearly shown that regular marijuana
or cannabis use in vulnerable individuals is associated with increased
risk of developing psychotic disorders such as schizophrenia, where one
loses contact with reality,” Bhattacharyya said.

Just how this occurs in the brain wasn’t understood.

In the new study, the researchers used functional MRI brain imaging on
15 healthy men, roughly 27 years old on average and described as
“occasional cannabis users.”

On three occasions under fMRI monitoring, the men received one of three
identical-looking gelatin capsules: one containing 10 milligrams (mg) of
the marijuana ingredient THC (deemed to be a “modest” dose); another
containing 600 mg of CBD; and a third filled with flour.

Testing was conducted in a highly controlled and monitored environment,
in which no marijuana was actually smoked.

The fMRI scans (which track brain activity in real time) were conducted
one and two hours after capsule administration. During the scans, the men
engaged in simple visual-cognition tasks (such as pressing buttons to
reflect the direction of a series of flashing arrows). Psychopathological
assessments were conducted throughout the brain imaging process.

The team found that THC and CBD appeared to affect the brain in
different and opposite ways.

Ingesting THC brought about irregular activity in two regions of the
brain (the striatum and the lateral prefrontal cortex) that are key to the
way people perceive their surroundings. THC seemed to boost the brain’s
responses to otherwise insignificant stimuli, while reducing response to
what would typically be seen as significant or salient.

In other words, under the influence of THC, healthy individuals might
give far more importance to details in their environment than they would
have without the chemical in their brain.

THC also prompted a significant uptick in paranoid and delusional
thinking, the authors said, and the more that “normal” brain responses
were set off-kilter, the more severe the paranoid or even psychotic
reaction.

The effect of the other main pot ingredient, CBD, was nearly the
opposite, however.

Ingesting the CBD capsule appeared to prompt brain activity linked to
appropriate responses to significant stimuli in the environment,
the team reported.

According to Bhattacharyya, this suggests that, on balance, marijuana
may play both a good and bad role in the context of psychosis.

The study also suggests that CBD, at least, may “have potential use for
the treatment of psychosis,” he said, even as marijuana’s other principle
ingredient, THC, raises the risk for developing psychotic
complications.

Dr. Joseph Coyle, a professor of psychiatry and neuroscience at Harvard
Medical School in Boston, said the current work goes a long way toward
“connecting all the dots” when it comes to understanding the marijuana
experience.

“What we’re talking about here is the kind of perception, in this case
prompted by marijuana, that leads a person to think that other people who
are just talking in the subway are all actually talking about him,” he
noted. “Or people who are just tipping their hat for no reason are
actually doing so specifically about him. And so this paper strikes me as
important, because it actually looks at this kind of increased anxiety and
increased hyper-alertness which are major factors in psychosis — and then
finds out what’s going on in the brain among people who experience
them.

“So I think this provides another brick in the foundation when talking
about direct causality,” he said. “It links the psychological state
marijuana brings about with a specific psychophysical response in the
brain. And that’s very, very interesting.”

More information

There’s more on marijuana at the U.S.
National Institute on Drug Abuse
.

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