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October 26, 2021
What Were We Talking About? How Cannabis Affects Short- & Long-Term Memory

BY BEN THOMAS | Original illustration for Ember by Zac Fay

For some people, forgetfulness is part of the fun of being stoned. In the euphoria of a good buzz, it’s hard not to crack up as everyone in the room responds to “wait, what?” with “I forgot” for the tenth time. Besides, maybe life’s better when we don’t try to remember so much pointless stuff.

But what about the stuff that isn’t pointless? As funny as forgetting can be, sometimes it’s scary to think about all the great memories we may be losing forever—not to mention the ones so lost that we’ve forgotten we even forgot them!

How do our memories change when we’re high? Can we do anything to recover memories we’ve lost? The answers reveal some intriguing truths about how our brains’ memory systems work—and how cannabis interacts with them.

Memory that works (mostly)

Working memory is often described as our “memory of the present.” While this might sound like a weird idea, it reflects a key reality about how our brains work: we’re not wired to multitask. When we think we’re multitasking, we’re really just shifting our attention from one thing, to the next thing, then back to the first thing, in very quick succession—creating the illusion that we’re focusing on multiple things at once.

What happens to the words, sights, sounds and other information we sense “in the background” while our attention jumps around? That info gets stored in the brain’s working memory system, ready for instant retrieval—like copy-pasted text. 

In fact, your brain literally does copy-paste colors and textures onto out-of-focus areas of your visual field. You can see this for yourself by staring at the central red dot in this picture while slowly counting to 30. The blue circle will disappear, replaced by the white background, which your brain has copy-pasted to fill the space. Your working memory recalls the circle is there, but your visual system can’t see it because it’s in your blind spot—so it makes an incorrect guess about what’s there, creating a conflict between what you see and what you remember.

Most people’s working memory can hold about three to five items (such as numbers, names, or shapes) at once. However, decades of neuroscience studies have shown that cannabis measurably reduces the number of words, visual images, and object locations people can keep in mind. One reason for this is that delta-9-THC creates a lot of staticky neural “noise”—making our brains work harder to focus, remember, and ignore distractions.

But that’s just forgetfulness in the present moment, which may not be such a big deal. What about memories of the recent past?

Just for the short term

The distinction between working memory and short-term memory isn’t always clear; in fact, neuroscientists continue to argue about whether they’re two different storage systems at all. Even so, we’re obviously able to recall more than the three to five items our working memory can hold—and we can (usually) remember experiences we’re not actively holding in working memory, like the opening scenes of a movie we’re watching. 

This appears to indicate that our working memory system has a mental scratchpad of its own, where it keeps track of sights, sounds, words and ideas we might need to recall within the next few minutes or hours. Most of these memories will eventually get lost—but neuroscience shows that “rehearsing” a short-term memory helps it stick around longer, and may even initiate the process of saving it to long-term storage.

Short-term memories aren’t really “saved” the way a digital file gets saved—instead, they’re continually “played” in synchronized dances of neural activity. When THC creates neural noise, that delicate dance turns into a memory mosh pit. CBD adds to the confusion by inhibiting the release of gamma-aminobutyric acid (GABA), a neurotransmitter chemical that plays a crucial role in memory by helping keep neurons’ signaling in sync.

In other words, if we frame working memory and short-term memory as two distinct systems (which, again, not all neuroscientists agree on), then cannabis seems to disrupt them both for similar reasons. Lifelong daily cannabis users, in particular, exhibit much poorer short-term memory recall than people who just toke up once or twice on the weekends—hinting that many of these symptoms may be avoidable for those who keep their THC loads light.

But what happens when our brains transfer a short-term memory into long-term storage? Is cannabis more of a help or a hindrance there?

Your brain’s survivable media

If a short-term memory stands out as particularly important—by being attached to an intense emotion, or by getting replayed a lot—then it’s likely to end up converted into a long-term memory. During rapid eye movement (REM) and slow-wave sleep (SWS), your brain consolidates significant memories into permanent records, like compressing files on a hard drive to free up space.

Long-term memory consolidation involves many brain areas, including the prefrontal cortex (PFC) and the amygdala, all working in concert with the hippocampus, which plays an especially crucial role. The hippocampus also seems to help “decompress” certain types of memories when we recall them. In fact, a person with a severely damaged hippocampus can’t form new memories at all — trapping them in a “permanent present” with no past.

Although a powerful sativa high can create the feeling of being trapped in an eternal moment, cannabis doesn’t damage the hippocampus quite that badly. However—as will come as a shock to absolutely no one—heavy cannabis users do have very bad long-term memories. Over time, daily doses of THC actually reduce the hippocampus’s size by 15 percent or more. Cannabis also damages neural tissue in the hippocampus, and in other brain areas involved in long-term memory; particularly among younger users.

Still, this cannabis cloud may have a silver lining: CBD improves blood flow to the hippocampus in older people, and can even trigger the formation of brand-new neurons. Cannabinoids have also been shown to reduce the formation of neural plaque in the brains of Alzheimer’s patients—and a new wave of neuroscience studies suggest that THC and CBD may help fight dementia even more effectively when used in combination.

In short, cannabis seems to become better for your memory as you get older, particularly if you use it in moderation. For younger people, on the other hand, just one month of cannabis abstinence results in significantly improved short-term and long-term memory recall. But this, too, is an encouraging sign: it reminds us that our brains are constantly learning and changing—and when we treat them kindly, even damaged memory systems can quickly bounce back to health.

Ben Thomas is a journalist and novelist who's lived in 40+ countries. He specializes in telling stories from the frontiers of science, history, culture and the cosmos—and the points where all these fields intersect.

These statements have not been evaluated by the Food and Drug Administration. Products are not intended to diagnose, treat, cure, or prevent any disease.
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