What Weed and Cocaine Do to Memory

"Your memory is really your identity. Your own history, your own desires, your own fears.”

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Aug 8 2018, 5:34pm

It’s well accepted that marijuana is associated with changes in memory, and the more you use, the more it could impede your ability to remember.

But “memory” is not just one thing, or one process. Some studies have looked at how marijuana affects your ability to remember words or information, while a new study in the Journal of Psychopharmacology looked at the effects of marijuana on a kind of "future memory" called episodic foresight.

Episodic foresight is the ability to mentally time travel into the future and pre-experience a new, future event that will happen to you, lead author Kim Mercuri, a clinical psychologist at Australian Catholic University, tells me.

It might seem strange to use the word “memory” to describe thoughts of the future. But researchers who study memory do so because of the realization that the purpose of memory is not to nostalgically remember sleep-away camp or your graduation. We remember to create a database of experiences so that we can prepare for future events. Moshe Bar, a professor of cognitive neuroscience and the director of the Gonda Multidisciplinary Brain Research Center, who was not involved in the new study, says that the brain is a very predictive organ, and it uses your past to anticipate the future.

To have episodic foresight, or mental “time travel,” you first need to have episodic memory, named such because it has to do with remembering episodes. “It's personal,” Bar says. “It's autobiographical. It's about your specific breakfast or your specific conversation last night.”

This is different from semantic memory, which he says would be like asking me to describe “breakfast.” I might say scrambled eggs and toast, based on my memories of what a general breakfast is. But if he asked me about my own breakfast this morning, my answer would be completely different: I had a smoothie bowl topped with granola. It’s something specific to me, a specific episode that’s mine.

Bar says that there have been cases where one type of memory, semantic or episodic, is impaired but not the other. This implies that, while there’s probably overlap, they are at least partially distinguished from each other. Episodic memories, Bar thinks, carry more significance. “That's kind of part of your identity,” he says. “I usually say when I give talks that it sounds like cliché but your memory is really your identity. Your own history, your own desires, your own fears.”

Mercuri tells me that previous research has shown that marijuana use can impair episodic memory. And if episodic foresight is created from the database of episodic memories—could it be affected by cannabis too?

Studies have shown that when you ask people to remember events from their past, or imagine things that could happen into the future, similar parts of the brain are involved. And in people with amnesia, who have lost their ability to remember their past, they also can’t imagine themselves in the future. Given that relationship, Kim and her colleagues decided to ask how marijuana impacted episodic foresight.

The new paper looked at 57 cannabis users, 23 who said they used it recreationally, and 34 regularly, and compared them to 57 controls. The recreational cannabis users reported marijuana use “weekly or less,” while the regular-users reported smoking at least three times per week.

All the participants of the study were asked to describe past and potential future events in response to cue words like, birthday, vacation, nightmare, taxi, or bench. There were a mixture of positive, negative, and neutral cue words. Later, the number of personal details each person generated was counted and they found that the regular cannabis users weren’t as able as the other groups to come up with details about themselves when asked to imagine future scenarios.
Their results, Mercuri says, shows that more marijuana use leads to more impairment of episodic memory and episodic foresight.

“Episodic memory is considered a building block, or the scaffolding to create a future event, to mentally time travel,” Mercuri says. “In order to go forward, you need to go back.”

Mercuri thinks their findings offer even more evidence to the connection between cannabis use and memory function. “It strengthens that argument that cannabis is targeting our memory centers,” Mercuri says.

Researchers have previously observed reductions in grey matter in regular long-term cannabis smokers and other brain changes in areas of the brain like the hippocampus and amygdala. But interestingly, a lot of cannabis research isn’t consistent. Some studies have found changes in the brain related to cannabis use, but not any behavioral deficits, and others don’t show any changes at all.

Continuing to study this might help reveal where in the brain these different memory processes take place. In a paper from 2014, Mercuri and colleagues found that opiate users were worse also at episodic foresight, but performed the same as controls when asked to recall past events. “There are greater densities of cannabinoid receptors in areas responsible for memory recall, potentially rendering regular cannabis users particularly vulnerable to episodic memory disruption,” their new study offers as a potential hypothesis.

If a drug can lower our ability to look into the future, can a different one enhance it? In the same issue of the journal, another study asked just that question about cocaine. Nadia Hutten, the first author and a neuropsychologist at Maastricht University, says that one of reasons they looked into this was that stimulants are often used as cognitive enhancers by college students. They were curious: Does it actually improve your memory? They found a single dose of cocaine could enhance something called prospective memory, another future-forward type of memory.

There are slight differences between episodic foresight and prospective memory. Hutten tells me that prospective memory is about remembering activities and actions in the future at their appropriate time or in the right context. Like, remembering that you have a doctor’s appointment in the afternoon, or which groceries you need when you’re at the store. Whereas episodic foresight is imagining a future event, prospective memory is remembering to do something.


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“The really neat thing about prospective memory is that I would say it's one of the modes of future thinking that we engage in that really has immediate consequences,” Karl Szpunar, an assistant professor at the University of Illinois at Chicago and the head of the UIC memory lab, says. “So usually, when we think about our future, it's something that's much more distant. Whereas with prospective memory, if I forget to tell my colleague something I really need to tell them when I see them at a meeting later on, then that could have consequences.”

In Hutten's study, people were either given a placebo, marijuana, or cocaine and asked to do a prospective memory activity. They were asked to do one task, while holding another in their mind, and only performing it when prompted later. They found that the people on cocaine were better at this than the other two groups.

Szpunar, who wasn't involved in the research, tells me he’s not sure the task in the study really got at prospective memory. He thinks the people might have been prompted too quickly to be using memory, and instead were testing their vigilance, or ability to pay attention. “Prospective memory is usually: There's this one thing you need to remember to do, and you sort of stop thinking about it, and then at some point, it pops back to into mind," he says.

Bar tells me he didn't have a problem with the task, and Hutten says that they measured attention and arousal independently, finding that the enhancement they saw couldn't be completely explained by how well someone was paying attention. Some or most of the enhancement, she says, must be from a direct effect of the cocaine on prospective memory.

What's important to note about Hutten's study is that it looked at the effects of a single dose of cocaine, and they measured people while still under the influence. Many studies show that people who use cocaine and other stimulants show deficits in many areas of memory, even prospective memory. “It might be that regular cocaine use leads to impairment in the long run,” Hutten says. “In addition, it might be that the cocaine use among the participant samples are different. It will be interesting to examine: When does the enhancing effects of cocaine turn into an impairment?”

She says she's hoping to study further how exactly the single dose of cocaine enhanced memory: Was it the creation of the memory itself? The retrieval of memory? She says they don't know, but what they find might generalize to interactions of drugs and other types of memory too.

Mercuri thinks that understanding drugs’ effects on these future kinds of memory is important beyond basic science. Prospective memory will ensure that you don't forget something on your to-do list, but there’s reason to believe that something like episodic foresight has even greater survival value. If you can mentally rehearse situations before they happen, you can make better choices.

Mercuri works with addiction, and she says a big part of treatment is focused on planning the future: How a person will say no to drugs when they encounter them out in the community, or making goals for the future. She says that knowing about marijuana's effect on this ability to make future personal plans can help drive treatment.

“We can make the goal setting quite close to the here and now,” she says. “What can you do now to make later better? Versus, focusing on a goal for later on. This type of information does help tailor the way we work as clinicians in terms of preparing clients to work with their goals, and hopefully bettering later outcomes.”

It reminds Szpunar of a related field of research called temporal discounting, which is choosing a more immediate reward, and discounting a better one because it’s in the future. For example, if I say to you: I’ll give you ten dollars now, or 100 dollars next week, you’d probably wait until next week. But if I said, do you want 10 dollars now, or 100 dollars in three months, Szpunar tells me there are some people who would take the money now rather than wait.

This plays out in more subtle ways all the time, like in our health. Are you going to eat those two slices of pizza at 2 AM, or are you going to hold off because you have a goal weight for yourself in the future? Are you going to smoke those cigarettes, or not, because you want to be healthy in 30 years? And it translates to many other areas of life besides health. Being future oriented is predictive of job success, marriage success, and Szpunar says that “in life, people who are more future oriented just seem to do better.”

Lots of people don’t think about the long-term future. But there’s work showing that if you get people to imagine what their distant futures will be like, it helps them to behave in more future-oriented ways. This ties back into the cannabis study findings because, “if there are certain drugs that impair our ability to imagine the future, then they might get in the way of helping people to become more future oriented,” he says. “We know future thinking can make us more future oriented, but if we're taking certain drugs that can prevent us from being able to imagine the future in a lot of detail, then maybe it won't work as well for some people as compared to others.”

Cannabis is also being explored medically for many disorders, and Mercuri says it’s important to know all the cognitive side effects so people can be aware how it might affect their decision making or memory. “There are so many potential benefits because of the molecular structure of cannabis but there are parts of it that aren't very good," she says. "Isolating what is beneficial without the potential cognitive cost; I think there's still a lot of work that's got to be done there.”

This isn’t trivial stuff, Bar tells me. Episodic foresight is a fundamental, crucial part of daily life. “It is not something exotic that the brain does once in a blue moon,” Bar says. “Every decision— and we make hundreds or thousands of decisions a day—involves some kind of foresight, some kind of simulation about the future. Even simpler ones, like what to have for lunch.”

It is possible that studying the deleterious effects of drugs on these memory types could help us figure out exactly how they work in the brain, since we know roughly where the drugs bind and interact. Hearing how beneficial this kind of memory is, I’m left wondering: If we could figure out the episodic foresight or memory networks, could or should we—hypothetically—make it stronger? And gain even more ability of the process that helps us imagine the future?

Like most things, too much can be just as harmful as too little. Think about what the experience of constantly imagining yourself in the future would be like. You can think about your future too much and then it goes from being adaptive, to developing into anxiety-related disorders, says Szpunar. “I think that's one thing that people are very interested in is what is that balance?" He says. "Why is it that some people use it in a very adaptive way and for other people it's sort of serves as a road block to leading an adaptive life?”

It reminds me about the current fixation on mindfulness, which tells us to stay focused on the present and not consider what’s going to happen next. I have OCD, and I can say with certainty that I could use a break from constantly envisioning myself in future scenarios, and what will happen in them.

“The answer to anything we research is that it probably depends, and that's what we're sort of trying to figure out is what are the contingencies in day to day life that make it depend?" Szpunar says. "When is it good to be in the present? When is it good to be in the future? And how much does it matter in terms of how good you are at switching between those different perspectives?”

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