Paranoid or Placid? Brain Scans Show Pot's Effect on Mind.

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."