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Paranoia is one of the most unpleasant “side effects” of marijuana. It’s also a key experience shared by marijuana smokers and people with schizophrenia. But exactly how does smoking a joint cause the feeling that dark forces are conspiring to do you wrong?

New research in rats may help explain the source of this distress. The study, led by Steven Laviolette at the University of Western Ontario in Canada, involved training rats to fear the scent of either almond or peppermint. The scents were delivered to rats in a cage either with black-and-white striped walls or with black polka dots on a gray background. (The rats were not pre-tested for their taste in interior design.) One scent was accompanied by an electric shock to the rodents’ feet, while the other scent was not.

At the same time, researchers experimented with the activity of the CB1 receptors in a certain region of the rats’ brains. These cannabinoid receptors are activated by the main psychoactive component of marijuana, THC. In some rats, the scientists blocked CB1-receptor activity; in others, they used a marijuana-like drug to enhance it.

When scientists blocked the CB1 receptors in a region called the basolateral amygdala — which is involved in the processing of fear and emotion — the rats that got strong electric shocks did not learn to fear the associated scent or the cage in which they received it. After getting shocked, they were just as happy as unaffected rats to explore the cage and smell the scent.

When rats were given a drug that enhanced cannabinoid-receptor activity, however, even receiving a minor shock was enough to cause them to freeze with fear when they were later exposed to the cage and its related scent. Without the marijuana-like drug, small shocks did not have the same effect.

The findings, published in the Journal of Neuroscience, suggest that activity in the basolateral amygdala is involved in marijuana-induced paranoia (the state of becoming afraid of things that wouldn’t normally trigger fear). That means marijuana is actually enhancing a type of learning about fear, leading the brain to jump to conclusions about mild experiences involving particular places or things, and to perceive them as scarier and more strongly connected than they are.

This increased fear-based learning helps explain why stoners tend to see patterns in events that aren’t real, such as conspiracies. (Of course, to be fair, the rats in this experiment were justifiably paranoid: they were being experimented on!)

Interestingly, the researchers also found that they could prevent the enhanced fear learning in rats given the marijuana-like drug by inactivating activity in a region called the prefrontal cortex before exposing them to the shocks. The prefrontal cortex is a higher-level brain area involved in executive functions like planning, decision-making and controlling responses and impulses. In humans, this could potentially explain why telling yourself or being told, “Chill out, you’re just high,” can help. (This may not work if the police actually are coming to arrest you.)

The researchers point out that both of the brain regions studied are implicated in the pathology of schizophrenia, and that understanding their interconnections could lead to better treatments for the disorder.

“We know there are abnormalities in both the amygdala and prefrontal cortex in patients who have schizophrenia, and we now know these same brain areas are critical to the effects of marijuana and other cannabinoid drugs on emotional processing,” said Laviolette in a statement.