In a recent study, more than four million Canadians reported using pot.
Yet few of us know what it does in our brains to make us high.
In a recent study, more than four million Canadians reported using pot.
Yet few of us know what it does in our brains to make us high.
Inside the brain, signals pass between cells called neurons. These signals become thoughts, memories, emotions and reactions to the world.
A signal is passed on when an electric charge travels through a neuron and releases chemicals called neurotransmitters.
Neurotransmitters flow across a gap called a synapse, causing the next neuron to fire and send the message, or stay dormant.
A change in neurotransmitters can influence our thoughts, moods, sensations and access to memory.
Using pot can result in those kinds of changes.
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The major active ingredient in cannabis, tetrahydrocannabinol (THC), resembles chemicals produced naturally in the brain, called cannabinoids.
Anandamide is one of the cannabinoids produced by the body.
It affects our energy, appetite, mood and perception of time.
Because THC resembles anandamide, it can disrupt the typical operation of the brain.
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Anandamide helps keep brain function balanced and regulated.
After a neuron fires, the second neuron sends anandamide back to receptors on the first neuron.
That response creates a rest period between neurons.
If another electrical impulse happens now, fewer neurotransmitters will be released.
The second neuron will not fire.
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THC takes over the regulation that is usually handled by anandamide. Here's how it happens.
Once the job is done, anandamide breaks down quickly.
When a person smokes or eats cannabis, THC connects to the same neural receptors that anandamide uses.
But THC enters the system at greater amounts, and lasts much longer.
THC temporarily overwhelms our self-regulating system.
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The "high" of THC comes from a chemical called dopamine. Dopamine is released by the brain to reward us for behaviour that, historically, has improved our chance of survival.
For example, through most of human history, food has been scarce. Our brains would reward us with a dopamine rush when we ate high-calorie food.
This reward system uses anandamide to release dopamine in small amounts.
Ingesting THC causes the brain to release much more, and THC lasts longer than anandamide.
It tricks our ancient survival system into creating a feeling of well-being.
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Studies in animals suggest that dopamine-producing neurons are controlled by the neurotransmitters glutamate and gamma-aminobutyric acid (GABA).
Imagine these neurotransmitters as traffic lights.
Glutamate would be the green light and GABA the red light.
Both chemicals act together to keep dopamine production regulated, just as lights would manage the flow of traffic.
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As we have seen before, THC takes the place of chemicals like anandamide, which usually keeps dopamine regulated.
THC inhibits the production of GABA. Fewer “stop” signals are transmitted to the dopamine neuron.
Ultimately, more glutamate builds up, amplifying the "go" signal.
The dopamine neuron can then run free, producing more dopamine, and a sense of pleasure.
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Only to a point. The brain is a self-tuning instrument that always seeks balance.
If excessive dopamine levels continue, dopamine receptors in the brain may temporarily close off.
This could explain why heavy cannabis users experience less reward from pleasurable things when they aren’t high.
They may find themselves smoking more pot to get the same high, and enjoying themselves less when they are sober.
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THC also interferes with our internal clock.
A study that used magnetic resonance imaging (MRI) found that volunteers on THC had altered blood flow to their cerebellum, which is thought to manage our sense of time.
In a balanced brain, when a sensation or impulse has been received, the transmission ends and the brain goes on with other things.
It’s possible that THC disrupts that self-moderation. We experience things differently because our internal clock is running faster, and external time appears to slow down or stop.
Rather than experiencing the thrill of music, ideas and sensations as usual, a person who is high may experience them more intensely.
A feedback loop occurs because there is no self-moderation prompting the brain to move on.
Later, when the effects of THC wear off, what seemed to be an epic idea or song returns to just being average.
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Distortions in the perception of time are not the only reason why a bag of chips may suddenly become irresistable, even though you just ate an hour ago.
The nucleus accumbens and hypothalamus are two areas of the brain that monitor our nutritional needs and feeding schedule.
They are sensitive to anandamide. Not surprisingly, the addition of THC hijacks the regular operation of these systems.
Regardless of the last time we ate, they kick into action, making the idea of food much more attractive.
The result we experience isn't hunger, as it is generally understood.
We experience a compelling increase in the anticipated pleasure of eating.
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Enhanced sensations from any drug can also cause unpleasant effects if the user is not in a comfortable, controlled environment.
In most people, THC creates a feeling of well-being and mild euphoria.
But if you are uneasy before you consume a mind-altering drug, those feelings can also be amplified.
For example, THC might make an average guitar solo seem epic, but it might also cause a sound in the next room to set off fears of a home invasion.
Whether a person experiences anxiety or pleasure after ingesting THC may have to do with the dosage and their individual sensitivity, based on the distribution of cannabinoid receptors in their brain.
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As you might have guessed by now, there is a brain centre for anxiety. The amygdala regulates fear and other emotional responses.
Remember glutamate and GABA, the green and red stoplights of our neural activity?
The current theory is that a low dose of THC will inhibit the release of glutamate in the amygdala. GABA builds up, calming activity.
A high dose of THC will inhibit GABA neurons. Glutamate builds up, activating the amygdala.
The glutamate/GABA balance is thought to be the switch that flips between a pot experience that is pleasant and unpleasant.
But these theories are based on animal research. Study of human subjects may lead to new theories.
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Pot users have long been stereotyped as having reduced mental abilities. When cannabis was illegal, it was difficult to study the effect of THC on a large number of human subjects, but several effects have been proven.
Coordination, reaction time, concentration and decision-making abilities are all affected by THC.
Mood-altering drugs can be dangerous for people with a personal or family history of schizophrenia or bipolar disorder.
Studies on humans show that THC intoxication causes a measurable difficulty in accessing verbal memories.
When they are high, pot users may be unable to find the word they want to express a certain thought.
Studies link this outcome to the presence of THC in the brain. Once the THC breaks down, that tongue-tied state passes.
The larger question is whether THC use results in the impairment of cognitive performance after the intoxication wears off.
Now that pot is legal, better studies are planned to answer that question.
In the meantime, several of Canada's health associations have collaborated on this 10-point list of ways to use pot more safely.
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Editing: Christine Birak, Andre Mayer | Design and Development: Richard Grasley, Dwight Friesen, CBC News Labs | Consultants: Dr. Andra Smith, Dr. Romina Mizrahi, Dr. Rebecca Haines-Saah and Dr. Matthew N. Hill