Archaeologists recently found a 2,700-year-old pot stash,
so we know humans have been smoking weed for thousands of years. But it
was only about 20 years ago that neuroscientists began to understand
how it affects our brains.
Scientists have known for a while that the active ingredient in cannabis
was a chemical called delta-9-tetrahydrocannabinol, or THC for short.
Ingesting or smoking THC has a wide range of effects, from the
psychoactive "getting high" to the physiological relief of pain and
swelling. It also acts as both a stimulant and depressant. How could one
substance do all that?
Meet the cannabinoid receptor
In the 1980s and 90s, researchers identified cannabinoid receptors,
long, ropy proteins that weave themselves into the surfaces of our cells
and process THC. They also process other chemicals, many of them
naturally occurring in our bodies. Once we'd discovered these receptors,
we knew exactly where THC was being processed in our bodies and brains,
as well as what physical systems it was affecting. Scattered throughout
the body, cannabinoid receptors come in two varieties, called CB1 and
CB2 - most of your CB1 receptors are in your brain, and are responsible
for that "high" feeling when you smoke pot. CB2 receptors, often
associated with the immune system, are found all over the body. THC
interacts with both, which is why the drug gives you the giggles and
also (when interacting with the immune system) reduces swelling and
pain.
Cannabinoid receptors evolved in sea squirts about 500 million years
ago; humans and many other creatures inherited ours from a distant
ancestor we share with these simple sea creatures. THC binds to
receptors in animals as well as humans, with similar effects.
Tasty, tasty, tasty
Cannabis notoriously makes people hungry - even cancer patients who had lost all desire to eat. One study showed
that cancer patients who thought food smelled and tasted awful suddenly
regained an ability to appreciate food odors after ingesting a THC
compound. There are CB1 receptors in your hypothalamus, a part of your
brain known to regulate appetite, and your body's own cannabinoids
usually send the "I'm hungry" message to them. But when you ingest THC,
you artificially boost the amount of cannabinoids sending that message
to your hypothalamus, which is why you get the munchies.
Understanding this process has actually led to a new body of research into safe diet drugs that would block those cannabinoid receptors.
That way, your hypothalamus wouldn't receive signals from your body
telling it to eat, and would reduce hunger cravings in dieters. What you're forgetting
What's
happening in your brain when smoking pot makes you forget what you're
saying in the middle of saying it? According to the book Marijuana and Medicine (National Academies Press):
One
of the primary effects of marijuana in humans is disruption of
short-term memory. That is consistent with the abundance of CB1
receptors in the hippocampus, the brain region most closely associated
with memory. The effects of THC resemble a temporary hippocampal lesion.
That's right - smoking a joint creates the effect of temporary brain damage.
What
happens is that THC shuts down a lot of the normal neuroprocessing that
goes on in your hippocampus, slowing down the memory process. So
memories while stoned are often jumpy, as if parts are missing. That's
because parts literally are missing: Basically you are saving a lot less
information to your memory. It's not that you've quickly forgotten
what's happened. You never remembered it at all. A bit of the old timey wimey
Cannabis also distorts your sense of time. THC affects your brain's
dopamine system, creating a stimulant effect. People who are stoned
often report feeling excited, anxious, or energetic as a result. Like
other stimulants, this affects people's sense of time. Things seem to
pass quickly because the brain's clock is sped up. At the same time, as
we discussed earlier (if you can remember), the drug slows down your
ability to remember things. That's because it interferes with the
brain's acetylcholine system, which is part of what helps you store
those memories in your hippocampus. You can see that system's pathway
through the brain in red in the illustration at left.source : http://io9.gizmodo.com/5794209/what-cannabis-actually-does-to-your-brain
