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Out-Of-Body Experiences Make It Harder To Encode Memories

When Henrik Ehrsson tells me that his latest study is “weird”, I pay attention. This is a man, after all, who once convinced me I was the size of a doll, persuaded me that I had three arms, and ripped me out of my own body before stabbing me in the chest. Guy knows weird.

Ehrsson’s team at the Karolinska Institute in Stockholm specialises in studying our sense of self, by creating simple yet spectacular illusions that subvert our everyday experiences. For example, it seems almost trite to suggest that all of us experience our lives from within our own bodies. But with just a few rods, a virtual reality headset, and a camera, Ehrsson can give people an out-of-body experience or convince them that they’ve swapped bodies with a mannequin or another person.

These illusions tell us that our sense of self isn’t the fixed, stable, hard-wired sensation that it seems. Instead, our brain uses the information from our senses to continuously construct the feeling that we own our own bodies. Feed the senses with the wrong information, and you can make the brain believe all manner of impossible things.

Loretxu Bergouignan joined Ehrsson’s team in 2009. She had been studying memory, and she wanted to know if that brittle sense of self is important for encoding our experience. After all, we take in all the events of our lives from inside our own bodies. As Bergouignan writes, “There is always an “I” that experiences the original event, and an I that re-experiences the event during the act of remembering.” If she put someone through an out-of-body illusion, could they still make new memories? Is that first-person perspective of the world important for storing information about it?

It’s the type of experiment that fits perfectly in Ehrsson’s group, who specialise in answering questions that seem almost too weird to ask in the first place. Still, he recalls, “I thought it was a very high-risk project. But sometimes you need to try riskier projects.”

Bergouignan recruited 32 local students for a “memory experiment” and gave them materials to study beforehand. When the volunteers arrived, Bergouignan fitted them with earphones and a virtual reality headset hooked up to a camera.

Half the time, the camera sat just above their heads and gave them the view that they would normally see (A below). The rest of the time, the volunteers sat facing the camera, so they saw themselves through their headsets (B). The researchers then pushed one rod towards the camera, while synchronously tapping the volunteers on the chest with a second rod. They could see themselves being prodded from afar, but also felt the same prods on their chests. That was enough to induce an out-of-body illusion. (Having experienced this before myself, I can attest to how convincing it is!)

Once the volunteers were under, an eccentric professor—really, an actor—entered and asked them questions about the material they had learned. He was scripted to be eccentric and memorable. He punctuated his questions with random monologues, bizarre provocative statements, and personal asides. “It was like performance theatre where the actors interact with the audience in a real-world environment,” says Ehrsson.

A week later, the volunteers returned to the lab, and Bergouignan asked them about their experiences with the professor. This was the real memory test, and the results were clear. The volunteers who experienced the out-of-body illusions were uniformly worse at recalling the details of the day than those who interacted with the professor from their usual in-body perspectives.

The team repeated the experiment with a slight variation. This time, the camera was at a 30 degree angle, so the volunteers floated out of their bodies but could still see the professor’s face (C). Again, they remembered the events more poorly than their in-body peers.

ExperimentThese are fascinating results. Remember that all the volunteers go through the same events. They’re all in the same place. The professor always sticks to the same semi-structured script. And yet, the angle from which they experienced those events strongly affected their ability to remember them.

The out-of-body illusion wasn’t more distracting; under its influence, the volunteers were just as good at simple mental tasks as they normally were. And it wasn’t just bizarre and off-putting either; after all,  we’re *better* at remembering bizarre events than everyday ones. Instead, the illusion seemed to hamper memories by taking volunteers out of their normal perspectives.

Bergouignan supported this view by placing some of her volunteers in a brain-scanner. She was especially interested in their hippocampus—a seahorse-shaped region near the floor of the brain that acts as a funnel between our experiences and our memories. It binds information from our senses and emotions into cohesive forms that can be stored, and then helps to reactivate that stored information when we want to remember something.

When the in-body volunteers sat in the scanner and recalled their time with the weird professor, their hippocampus behaved in the normal way. It became more active when they first tried to remember the events, and then less active with each subsequent attempt.

But the out-of-body hippocampi did exactly the opposite. “The first time they tried to remember, there was nothing in the hippocampus. It was silent,” says Ehrsson. But the more they tried to remember, the more active the hippocampus became.

This suggests that the volunteers aren’t just remembering a little less when they’re out of their bodies. “Their hippocampus is impaired in a more profound way,” says Ehrsson. He suspects that without the first-person perspective, the hippocampus can’t encode experiences in its usual coordinated way, and volunteers end up with fragmented memories that they struggle to recall. And as they struggle, Ehrsson speculates that they could be creating false memories out of the fragments.

This is a good example of embodied cognition, where basic aspects of our bodies like sensory information can influence “higher” mental skills like our memories. “When we walk around minding our own business, we always have this sense of being located inside our bodies,” says Ehrsson. “You need to have that experience of the world to encode and recall your own memories. This has never been shown before perhaps because it’s so difficult to manipulate.”

That’s a stretch, says Howard Eichenbaum, who studies memories at Boston University. “It is well known that material learned in a particular context is better remembered in the same context than a different one… and the hippocampus plays a key role in using context to guide memory retrieval,” he says. For example, deep-sea divers are worse at remembering what happened to them underwater after they resurface. “The out-of-body effects here may be a special case of context dependent memory.”

Ehrsson acknowledges this, and wants to see if it’s possible to reverse the memory defects by putting volunteers back into the out-of-body illusion.

This could have possible applications. There are many disorders like schizophrenia or borderline disorder where people say that they feel detached from themselves. Many people with post-traumatic stress disorder (PTSD) claim that they remember experiencing traumatic events from outside of their own bodies, and struggle to remember those events clearly. Perhaps those two things are linked. “It’s not that they don’t want to remember what happened for emotional reasons,” says Ehrsson, “but it could be that the memories are damaged because they weren’t located inside themselves,” he says.

“Many such patients report that the subjective element of experience is altered, but this is difficult to verify externally,” says Brian Levine from the Baycrest in Toronto. But Ehrsson’s team have provided scientists with a way of probing these experiences, by manipulating something as inherently subjective as “self-ness”.

“They did not confirm any of their predictions in patients, though,” Levine adds. “There is a big difference between dissociations due to psychological trauma, and the dissociations induced in this experiment. So more work is need to make the connection to clinical syndromes.”

Reference: Bergouignan, Nyberg & Ehrsson. 2013. Out-of-body–induced hippocampal amnesia. PNAS http://dx.doi.org/org/10.1073/pnas.1318801111

More on Ehrsson’s work, see my Nature story: Master of illusion, and the following posts:

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Shocking Memories Away

In the spring of 1968, experimental psychologist Donald Lewis and his colleagues published a study about memory that was well before its time. The researchers first trained rats to fear a particular sound. A day later, the animals heard the same sound followed immediately by an electroconvulsive shock to the head. After getting shocked, the animals forgot their fear of the sound. The old memory was gone.

The study was remarkable for its focus on memory retrieval, rather than memory formation. See, research up until then had suggested that a memory is only unstable (and thus vulnerable to change) in the minutes or hours after it’s first created. During this period, called ‘consolidation’, the memory moves into the brain’s long-term storage and, it was thought, into a stable and fixed molecular state. “For decades people had thought that once a memory is wired in the brain it stays there forever,” says Karim Nader, a neuroscientist at McGill University in Montreal. But Lewis’s study showed that wasn’t true: When a rat recalled a stored memory, the memory somehow became unstable again, making it vulnerable to erasure.

Lewis’s study contained a revolutionary idea, but it didn’t revolutionize the memory field. It was published in a top journal, Science, and followed up immediately by another group of researchers. But as that group reported the following year, also in Science, they couldn’t replicate Lewis’s findings. Over the next few decades, a couple of other studies came out suggesting that memories become unstable during recollection, but the idea never made it into the textbooks. “Part of the field believed it, but the other part of the field just didn’t believe it,” Nader says. “And the ones who didn’t believe it were the dominant ones.”

Nader gets credit for rekindling the idea in the late 1990s, while working as a postdoc in Joe LeDoux’s lab at New York University. Nader showed that, in rats, old memories can be erased by infusing a drug into the animal’s brain as it recalls the memory. Because the drug blocked protein synthesis, this experiment was evidence that memories go through a ‘reconsolidation’ process after being recalled, and that this process requires protein synthesis (just like the initial consolidation does).

Unlike Lewis’s study, Nader’s, published in Nature in 2000, did rock the field, not least because of its clinical implications. The results opened up the possibility that the frightening memories that haunt people with post-traumatic stress disorder could be erased — even long after they are formed.

A study out today in Nature Neuroscience takes this research a big step further by demonstrating not only that memory reconsolidation happens in people, but that it can be blocked with electroconvulsive therapy, or ECT.

Marijn Kroes and his colleagues at Radboud University Nijmegen, in the Netherlands, tested the memories of 39 people with severe depression who were already undergoing ECT. This rare treatment has an interesting cultural history. “People have the One Flew Over the Cuckoo’s Nest idea of it,” Kroes says, referring to the 1975 film in which Jack Nicholson’s character is forced — wide awake, whimpering and writhing in pain — to undergo ECT at a mental institution. “Luckily it’s nothing like that.”

Today ECT is used as a last resort for people with severe depression who do not respond to antidepressants, psychotherapy, or other treatments. It’s done in a hospital room, after the patient receives muscle relaxants and general anesthesia. A brief electric current passes through the brain, inducing a seizure. For reasons no one yet knows, it usually works: ECT had an 86 percent remission rate for people with major depression, according to one study.

Kroes wanted to find out whether ECT could erase memories during active recall, as it had for the rats in Lewis’s experiment nearly 50 years ago.

All of the participants first saw two narrated slide shows, each describing a different traumatic story with 11 pictures. In one of them, for example, two sisters leave their house to visit their brother at a nearby bar. As they walk past an alley, one of the sisters is kidnapped by a man and held at knife point:


The other story is similar in structure, but shows a boy getting hit by a car and then in surgery having his feet reattached to his legs. In the words of the paper, these are “high-arousing stories with negative valence.” I’ll say.

A week after the participants watched the slide shows, the researchers showed them the first slide from one of the stories as a memory trigger. A few minutes later, some participants were given ECT. After the treatment, they were given a memory test about the details of both stories.

Participants who did not undergo ECT got about half of the questions about the triggered memory correct, compared with 40 percent of questions about the other story (which they had not seen for a week).

In stark contrast, participants who received ECT seemed to have no memory of the story they had been reminded of — they scored a 25 percent on a four-answer multiple choice test, the same as guessing at random. The same participants showed significantly better recall — 35 percent — of the second, non-triggered story. ECT, in other words, selectively erased the memories that were being actively recalled, just as it had for Lewis’s rats.

“It’s a very elegant paper, compelling data, and it’s a difficult study to do,” says Daniela Schiller, a neuroscientist at Mount Sinai School of Medicine in New York, who was not involved in the work. “It’s very impressive they managed to do that, and that they even tried.”

Schiller’s experiments have also bolstered the reconsolidation hypothesis. She has shown, for example, that if people recall a fearful memory and then go through ‘extinction learning’ — meaning that they’re shown the fearful stimulus over and over again without any pain — they can erase the emotional sting of the memory. Other groups have shown something similar by giving people propranolol, a beta-blocker, immediately after recalling a memory.

The new study adds ECT to the list. There are still a lot of questions. For example, it’s not clear how ECT is disrupting reconsolidation. Or if it’s doing it at all: The effect could be partly or wholly due to anesthesia, though the researchers say this is unlikely. Most importantly, no one knows whether the procedure would work with old, real memories, as opposed to those artificially created in the lab.

Kroes and his colleagues are planning a clinical trial in which they will use ECT to lessen traumatic memories in people with PTSD. “Just to be clear: it’s a long way from being an actual clinical application,” he says. “A lot of experimental, fundamental science is often very difficult to translate into the real world.”

I asked all of these scientists a question that I’m sure they get every week: When are we going to be able to erase whatever memories we want, like in Eternal Sunshine of the Spotless Mind?

Kroes was quick to say, and rightly so, that ECT should only be used as a serious medical treatment. “You have to have some kind of disease state,” he says.

But as far as the technology goes, and what it could do, everybody told me that there’s no reason to think that we couldn’t play out a Spotless Mind scenario in the not-too-distant future.

“I wouldn’t have said so a few years, but there’s just more and more evidence, with different types of memories, different types of manipulations, and different species,” Schiller says.

Right or wrong, there’s certainly demand for it. Nader remembers the big public response to his 2000 Nature paper. “The day after it was published, a number of women emailed Joe [LeDoux] and asked, ‘Can you get rid of the memories of my ex-husband?'”

But would he be OK with that kind of application, should the technology advance as experts expect it will? “For me,” Nader says, “I don’t think that would be the end of the world.”

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Mice Inherit Specific Memories, Because Epigenetics?

Two weeks ago I wrote about some tantalizing research coming out of the Society for Neuroscience meeting in San Diego. Brian Dias, a postdoctoral fellow in Kerry Ressler’s lab at Emory University, had reported that mice inherit specific smell memories from their fathers — even when the offspring have never experienced that smell before, and even when they’ve never met their father. What’s more, their children are born with the same specific memory.

This was a big, surprising claim, causing many genetics experts to do a double-take, as I discovered from a subsequent flurry of Tweets. “Crazy Lamarkian shit,” quipped Laura Hercher (@laurahercher), referring to Lamarckian inheritance, the largely discredited theory that says an organism can pass down learned behaviors or traits to its offspring. “My instinct is deep skepticism, but will have to wait for paper to come out,” wrote Kevin Mitchell (@WiringTheBrain). “If true, would be revolutionary.”

The paper is out today in Nature Neuroscience, showing what I reported before as well as the beginnings of an epigenetic explanation. (Epigenetics usually refers to chemical changes that affect gene expression without altering the DNA code).

Having the data in hand allowed me to fill in the backstory of the research, as well as gather more informed reactions from experts in neuroscience and in genetics. I’ve gone into a lot of detail below, but here’s the bottom line: The behavioral results are surprising, solid, and will certainly inspire further studies by many other research groups. The epigenetic data seems gauzy by comparison, with some experts saying it’s thin-but-useful and others finding it full of holes.

So what is the surprising part, again? 

If you’ve followed science news over the past decade then you’ve probably heard about epigenetics, a field that’s caught fire in the minds of scientists and the public, and understandably so. Epigenetic studies have shown that changes in an organism’s external environment — its life experiences and even its choices, if you want to get hyperbolic — can influence the expression of its otherwise inflexible DNA code. Epigenetics, in other words, is enticing because it offers a resolution to the tedious, perennial debates of nurture versus nature.

But some scientists dispute the notion that epigenetic changes have much influence on behavior (see this Nature feature for a great overview of the debate). Even more controversial is the idea that epigenetic changes can be passed down from one generation to the next, effectively giving parents a way to prime their children for a specific environment. The key question isn’t whether this so-called ‘transgenerational epigenetic inheritance’ happens — it does — but rather how it happens (and how frequently, and in what contexts and species).

That’s what Dias and Ressler wanted to investigate. Trouble is, environmental influences such as stress are notoriously difficult to measure. So the researchers focused on the mouse olfactory system, the oft-studied and well-mapped brain circuits that process smell. “We thought it would give us a molecular foothold into how transgenerational inheritance might occur,” Dias says.

The researchers made mice afraid of a fruity odor, called acetophenone, by pairing it with a mild shock to the foot. In a study published a few years ago, Ressler had shown that this type of fear learning is specific: Mice trained to fear one particular smell show an increased startle to that odor but not others. What’s more, this fear learning changes the organization of neurons in the animal’s nose, leading to more cells that are sensitive to that particular smell.

Ten days after this fear training, Dias allowed the animals to mate. And that’s where the crazy begins. The offspring (known as the F1 generation) show an increased startle to the fruity smell even when they have never encountered the smell before, and thus have no obvious reason to be sensitive to it. And their reaction is specific: They do not startle to another odor called propanol. Craziest of all, their offspring (the F2 generation) show the same increased sensitivity to acetophenone.

The scientists then looked at the F1 and F2 animals’ brains. When the grandparent generation is trained to fear acetophenone, the F1 and F2 generations’ noses end up with more “M71 neurons,” which contain a receptor that detects acetophenone. Their brains also have larger “M71 glomeruli,” a region of the olfactory bulb that responds to this smell.

“When Brian came in with the first set of data, we both just couldn’t believe it,” Ressler recalls. “I was like, ‘Well, it must just be random, let’s do it again.’ And then it just kept working. We do a lot of behavior [experiments], but being able to see structural change that correlates with behavior is really pretty astounding.”

Still, those experiments couldn’t rule out some kind of social, rather than biological transmission. Perhaps fathers exposed to the fear training treated their children differently. Or maybe mothers, sensing something odd in their mate’s behavior, treated their children differently.

To control for these possibilities, the researchers performed an in vitro fertilization (IVF) experiment in which they trained male animals to fear acetophenone and then 10 days later harvested the animals’ sperm. They sent the sperm to another lab across campus where it was used to artificially inseminate female mice. Then the researchers looked at the brains of the offspring. They had larger M71 glomeruli, just as before. (The researchers couldn’t perform behavioral tests on these animals because of laboratory regulations about animal quarantine.)

“For me it clicked when we did the IVF,” Dias says. “When the brain anatomy persisted, that to me emphasized that it’s not really a social transmission. It’s inherited.”

Other researchers also seem convinced. “It is high time public health researchers took human transgenerational responses seriously,” says Marcus Pembrey, emeritus professor of paediatric genetics at University College London, who has been championing the idea of epigenetic inheritance for over a decade. “I suspect we will not understand the rise in neuropsychiatric disorders or obesity, diabetes and metabolic disruptions generally without taking a multigenerational approach,” he says.

In an interesting historical aside, Pembrey also notes that the new study echoes an experiment that Ivan Pavlov did* 90 years ago, in which he trained mice to associate food with the sound of a bell. Pavlov “reported that successive generations took fewer and fewer training sessions before they would search for food on hearing a bell even when food was absent,” Pembrey says. Nevertheless, the idea that experience could be biologically inherited fell out of favor in the 20th century. “If alive today, Pavlov would have been delighted by the Dias and Ressler paper, first as a vindication of his own experiment and results, and second by the amazing experimental tools available to the modern scientist.”

Neuroscientists, too, are enthusiastic about what these results might mean for understanding the brain.

“To my knowledge this is the first example, in any animal, of epigenetic transmission of a simple memory for a specific perceptual stimulus,” says Tomás Ryan, a research fellow at MIT who studies how memories form in the brain. “The broader implications for the neuroscience of memory and to evolutionary biology in general could be paradigm shifting and unprecedented.”

There are still some unanswered questions, Ryan notes. For example, the researchers didn’t do a control experiment where the F0 animals are exposed to the fruity odor without the shock. So it’s unclear whether the “memory” they’re transmitting to their offspring is a fear memory, per se, or rather an increased sensitivity to an odor. This is an important distinction, because the brain uses many brain circuits outside of the olfactory bulb to encode fear memories. It’s difficult to imagine how that kind of complicated brain imprint might get passed down to the next generation.

Ressler and Dias agree, and for that reason were careful not to refer to the transmitted information as a fear memory. “I don’t know if it’s a memory,” Dias says. “It’s a sensitivity, for now.”

What’s that got to do with epigenetics?

So let’s call it a sensitivity. How could a smell sensitivity, formed in an adult animal’s olfactory bulb in its brain, possibly be transmitted to its gonads and passed on to future generations?

The researchers are nowhere near being able to answer that question, but they have some data that points to epigenetics.

There are several types of epigenetic modifications. One of the best understood is DNA methylation. There are millions of spots along the mouse genome (and the human genome), called CpG sites, where methyl groups can attach and affect the expression of nearby genes. Typically, methylation dials down gene expression.

Dias and Ressler sent sperm samples of mice that had been fear-conditioned to either acetophenone or propanol to a private company, called Active Motif, which specializes in methylation analyses. The company’s researchers (who were blinded to which samples were which) mapped out the sperm methylation patterns near two olfactory genes: Olfr151, which codes for the M71 receptor that’s sensitive to acetophenone, and Olfr6, which codes for another odor receptor that is not sensitive to either odor.

It turns out that Olfr151, but not the other gene, is significantly less methylated in sperm from animals trained to fear acetophenone than in sperm from those trained to fear propanol. Because less methylation usually means a boost in gene expression, this could plausibly explain why these animals have more M71 receptors in their brains, the researchers say.

What’s more, the same under-methylation shows up in the sperm of F1 animals whose fathers had been trained to fear acetophenone.

“It’s a very precise signal,” Ressler says. “The convergence of this data, we think, shows that this is a really profound and robust phenomenon.”

Others, though, find a number of flaws in this epigenetic explanation.

Timothy Bestor, professor of genetics and development at Columbia University, points out that methylated CpG sites only affect gene expression when they are located in the so-called gene promoter, a region about 500 bases upstream of the gene. But the Olfr151 gene doesn’t have any CpG sites in its promoter.

That means the differences in methylation reported in the paper must have occurred within the body of the gene itself. “And methylation in the gene body is common to all genes whether they’re expressed or not,” Bestor says. “I don’t see any way by which that gene could be directly regulated by methylation.”

But what would explain the methylation differences between the trained animals and controls? They’re pretty subtle, he says, and “could easily be a statistical fluke.”

Bestor was skeptical from the outset, based on the mechanics of the reproductive system alone. “There’s a real problem in how the signal could reach the germ cells,” he says.

For one thing, the seminiferous tubules, where sperm is made inside of the testes, don’t have any nerves. “So there’s no way the central nervous system could affect germ cell development.” What’s more, he says it’s not likely that acetophenone would be able to cross the blood-testis barrier, the sheet of cells that separates the seminiferous tubules from the blood.

By this point in my conversation with Bestor, I was starting to feel a bit defensive on behalf of epigenetics and all of its wonder. “Are you saying you think epigenetic inheritance is a bunch of bologna?” I asked helplessly.

“No,” he said, laughing. “It’s just not as dynamic as people think.”

What’s next?

A good next step in resolving these pesky mechanistic questions would be to use chromatography to see whether odorant molecules like acetophenone actually get into the animals’ bloodstream, Dias says. “The technology is surely there, and I think we are going to go down those routes.”

First, though, Dias and Ressler are working on another behavioral experiment. They want to know: If the F0 mice un-learn the fear of acetophenone (which can be done by repeated exposures to the smell without a shock) and then reproduce, will their children still have an increased sensitivity to it?

“We have no idea yet,” says Ressler, a practicing psychiatrist who has long been interested in the effects of post-traumatic stress disorder (PTSD). “But we think this would have tremendous implications for the treatment of adults [with PTSD] before they have children.”

It will take a lot more work before scientists come close to understanding how these data relate to human anxiety disorders. So what, after all of these words, should we take away from this study now?

Hell if I know. Here’s the most rational and conservative appraisal I can muster: Our bodies are constantly adapting to a changing world. We have many ways of helping our children make that unpredictable world slightly more predictable, and some of those ways seem to be hidden in our genome.

Anne Ferguson-Smith, a geneticist at the University of Cambridge, put it more succinctly. The study, she says, “potentially adds to the growing list of compelling models telling us that something is going on that facilitates transmission of environmentally induced traits.”

Scientists, I have to assume, will be furiously working on what that something is for many decades to come. And I’ll be following along, or trying to, with awe.

*Update, 12/1/13, 2:35pm: It seems that that Pavlov experiment may have been retracted in 1927, though I don’t know anything about that beyond what is stated here.

Style note: A few paragraphs of this post were adapted from my earlier post on this research, published November 15.

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People With Super Memories Still Prone to Misinformation

“Dear Dr. McGaugh, As I sit here trying to figure out where to begin explaining why I am writing you and your colleague (LC) I just hope somehow you can help me. I am thirty-four years old and since I was eleven I have had this unbelievable ability to recall my past…”

That was how James McGaugh first met a woman called Jill Price. Price, now 48, has a memory that’s truly as astounding as she claimed. Give her any date in her past and she’ll tell you what day it fell on, exactly what she was doing at the time, and any important events that took place. She knows that Easter Day fell on April 11 in 1993 (she had spaghetti for dinner) and on April 16 in 1995 (it was rainy). She can tell you exactly when the last episode of Dallas aired (5th March 1991) or when Challenger exploded (28 January 1986; a Tuesday). She does all of this automatically, without resorting to any memory tricks or conscious effort.

This ability is known as hyperthymesia, or highly-superior autobiographical memory (HSAM). Price was the first case to be described, in 2006, but after news of her ability broke, McGaugh’s lab was flooded by messages from hundreds of people claiming to have the same gift. Many didn’t check out; several did. HSAM is now a frequent, and often greatly exaggerated part of popular culture, featuring in shows like Unforgettable, House, and The Big Bang Theory.

Still, Price struggles to rote-learn poetry or historical dates. She can never remember what the five keys on her keyring are for. She and other people with HSAM have extraordinary autobiographical memories but in other areas, they have very ordinary weaknesses.

Now, Lawrence Patihis from University of California, Irvine has shown that people with HSAM are also vulnerable to exactly the same sorts of memory distortions that the rest of us suffer. Feed them with misinformation, and even their seemingly perfect memories can be warped and twisted. It’s pretty easy to make them think they saw words they never saw, or that they remember events that never happened.

“We didn’t know what to expect,” says Patihis. “We thought that maybe they have a new way of remembering, a new mechanism that’s different to normal people. But now, we think that they’re remembering in the same fallible, malleable way as everybody else. They’re doing something that gives them high accuracy.”

Even people who can remember what they ate for dinner thirty years ago are not immune to false memories.

We now know that every time we remember something, our memories enter a vulnerable state when they can be easily manipulated, overwritten or erased. The act of remembering isn’t like viewing a permanent recording, but like opening up a computer document—one that you can edit as well as read. This leaves us vulnerable. Present the wrong information at the right time, and you can rewrite someone’s recollections with astonishing ease—even if that someone has a super memory.

Patihis’s team, including McGaugh and memory expert Elizabeth Loftus, compared 20 people with HSAM and 38 people with normal memories. First, they asked the volunteers to remember long lists of words, which related to an absent one. For example, the list might include “rest”, “nap” and “bed”, but not “sleep”. Later, when asked to remember which words they had seen, around 70 percent of people claim that they saw “sleep”. And so do people with HSAM—they’re no better at resisting the pull of the phantom word than people with normal memories.

Next, the volunteers watched slideshows of two crimes—a man stealing a wallet, and another breaking into a car. Forty minutes later, they read 50 sentences describing each event, three of which were subtle lies—for example, “the car thief used a coat hanger”, when he actually used a credit card. The volunteers not only remembered things differently thanks to the misleading sentences, but claimed that they had actually seen the fabricated events in the slideshows. And far from being immune, the people with HSAM were actually more susceptible to the misinformation.

Finally, the volunteers answered a questionnaire about the crash of United flight 93 on September 11, 2001. The questionnaire includes some lies—for example, it mentioned that witnesses on the ground had filmed a video of the crash, when no such footage exists.

When asked later if they had seen the crash video, around 29 percent of normal people said yes but just 20 percent of people with HSAM did. They did better, but a fifth of them still made up some false memories! They weren’t relying on nebulous gut feelings, either; they provided elaborate details about the video they saw, how long it was, and what they showed. “This was a big surprise,” says Patihis. “We thought they’d have no false memories because they’re so good at news events, as part of their autobiographical memory skills.”

These flaws seem hard to square with their amazing abilities, but Patihis thinks that there’s no paradox. HSAM people are very good at remembering things that aren’t usually met with deception or contradiction. “No one comes up to them and says March 2nd, 2001 was a Monday not a Friday,” says Patihis. “In the absence of misinformation, they have fantastic autobiographical memories. When you introduce misinformation, they’d kind of the same as everyone else.”

“It is tempting to think that individuals with HSAM people may possess “photographic” memories that record exactly what happens in the same way that a camera or video recorder does,” says Daniel Schacter, a memory researcher from Harvard University. “But [this study] highlights that they do not retain a literal record of their experiences.”

But the members of Patihis’ team disagree among themselves about how to interpret the results more broadly. Some of them believe that HSAM people are such a special group that you shouldn’t generalise too much from them. Others, including Patihis, believe that everyone’s vulnerable to memory distortions.

“I can’t think of anyone who could possibly be immune,” he says. “In practical situations, like when therapists try to bring up memories, or when police do it for eyewitnesses, the basic assumption is that everyone should be vulnerable to misinformation. So, don’t give anybody misinformation.” (See Mo Costandi’s feature on Elizabeth Loftus’s work on flaws in eyewitness testimony.)

Note: There’s been a lot of talk recently about the need for larger samples and more statistical power in psychology studies. The small number of HSAM people limits how big this study can get, and the team is aware of that.  But Patihis says, “It’s not that important in this study because the results were straightforward. It would have been more of a problem if we found no false memories in one group.”

Reference: Patihis, Frend, LePorth, Petersen, Nichols, Stark, McGaugh & Loftus. 2013. False memories in highly superior autobiographical memory individuals. PNAS http://dx.doi.org/10.1073/pnas.1314373110

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Apes Remember Specific Events From Years Ago

In the climax of the Pixar film Ratatouille, a mouthful of the eponymous dish whisks food critic Anton Ego back to his happier childhood days. The scene is reminiscent of one described by Marcel Proust in Remembrance of Things Past, when the taste of a petite madeleine dipped in lime tea brings back the memory of his aunt Leonie. Many of us can recount similar moments, when a peculiar combination of sensory cues—a smell or taste or sound—transported us back to a point in our past.

Do animals share similar experiences? Do they store deep autobiographies that can be triggered by the right set of cues? According to a new experiment by Gema Martin-Ordas, Dorthe Berntsen and Josep Call, the answer is yes, a least for two species—chimpanzees and orang-utans.

In 2009, the team ushered 12 of the apes into the middle of several connected cages. In full view, they hid two tools in different boxes within the adjacent rooms. Their job was to remember where these tools were—they would need them to reach an inaccessible piece of food in a later test. They had four shots at doing this.

Over the next three years, the apes went about their lives. They ate, slept, socialised, and took part in many more studies. Then, in 2012, eleven of them were led into the same set of rooms with tool-containing boxes in the same locations. And all of them, except for one, went straight to boxes and retrieved the tools. They remembered.

Call was surprised at “how quickly they retrieved the tools as soon as we opened the doors”. They all did this on their first attempt, without prompts or trial-and-error. They didn’t know this test was coming—in 2009, even the researchers hadn’t planned to repeat their experiment three years later. And by contrast, seven individuals that weren’t part of the original experiment didn’t head for the boxes; they just explored the rooms randomly.

Here’s the amazing thing: in the intervening years, the 11 apes had been into these rooms again. They’d worked with other scientists in other studies on tool use or cooperation. Martin-Ordas’s team had even tested them in the same rooms but on different tasks. But they had apparently bound the features of the original experiment—the researchers, the location and the task—into a cohesive memory. The combination of those features, reprised in 2012, took them back to 2009, just like ratatouille or madeleines made Anton Ego and Marcel Proust feel like kids again.

In a second experiment, the team tested 10 chimps and orang-utans (including many of the same animals) on another task. This time, tools had been hidden in trays at different placed within the same rooms. They only saw this set-up once, and two weeks later, they saw it again. As before, all but one of them went straight for the tools in the first half-minute. By contrast, eleven individuals, who had no experience with the experiment, took more than 5 minutes to find the tools.

Gaps of weeks and years might not seem that long, given that we can remember events that happened decades ago. But bear in mind that as recently as the 1970s, we didn’t even know if animals had these sorts of “episodic memories”—recollections  of what, where and when.

Certainly, Canadian psychologist Endel Tulving didn’t think so, and he coined the term “episodic memories” in the first place. He believed  that such memories relied upon our language skills, and were unique to humans. He was wrong; episodic memory is one of a long line of mental abilities that were once thought to be uniquely human but are actually shared by other animals.

Nicky Clayton from the University of Cambridge has done several seminal experiments with western scrub-jays, showing that they can remember the location of food that they had previously stored, and even which hoards were freshest. Other scientists have found similar examples among great apes, hummingbirds, rats, and perhaps even honeybees. But most of these studies used delays of a week at most. By contrast, Martin-Ordas, Berntsen and Call have shown that chimps and orang-utans can retain details of what, where and when for at least three years.

“We do not know about their upper limits,” says Call. “It’s conceivable that they retain memories for much longer, and some studies are planned to assess this.”

“I am not ready to say that apes possess autobiographical memories just like we do,” he says. For example, these memories form an important part of our social lives because we can share them with each other, as I did in the opening paragraph. We don’t know if other animals do the same. “I would say that we have documented some elements of human autobiographical memories that are also present in apes, and possibly in other animals as well,” says Call.

Reference: Martin-Ordas, Berntsen & Call. 2013. Memory for Distant Past Events in Chimpanzees and Orangutans. Current Biology. http://dx.doi.org/10.1016/j.cub.2013.06.017

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When Memories are Remembered, They Can Be Rewritten

It’s not often that scientists make people watch the first episode of 24 in the name of science. It’s even rarer that they pick Jack Bauer’s exploits because they wanted to show volunteers something “more true to life”. Then again, as Jason Chan dryly says, “Some of the earlier episodes were not as far-fetched as the later ones”.

Chan’s study is the latest to show how easy it is to disrupt our memories, and supplant what we think we know with misinformation. In this case, he and colleague Jessica LaPaglia from Iowa State University showed volunteers the pilot episode of 24 and then selectively rewrote some of their memories of the show’s events. For example, some of the volunteers came to believe that an assassin (Mandy!) knocked out a flight attendant with a stun gun, when she actually used a hypodermic syringe.

It wasn’t just a simple matter of saying Mandy used a stun gun. That wouldn’t have worked. Instead, Chan and LaPaglia fed their volunteers with false information immediately after they had actively remembered what they had seen. Then, and only then, did the new memories overwrite their old ones.

The trick relies on a quirk of memory that has come to light in recent years. I’ve written about it before:

Every time we bring back an old memory, we run the risk of changing it. It’s more like opening a document on a computer – the old information enters a surprisingly vulnerable state when it can be edited, overwritten, or even deleted. It takes a while for the memory to become strengthened anew, through a process called reconsolidation. Memories aren’t just written once, but every time we remember them.

This means, somewhat ironically, that the remembering something creates a critical window in which memories can be erased or manipulated. Many scientists have done this in rodents and humans using drugs or conflicting information. But these experiments usually manipulate single simple memories, such as a drug craving or a fearful association between a colour and an electric shock.

Chan and LaPaglia have now used the reconsolidation window to change declarative memories—facts and knowledge that we consciously recall. “We have people forming a very complex memory of a story that lasts 40-50 minutes and changing specific details within that larger context,” says Chan. “This is what’s new. It’s a pretty important step for demonstrating the fundamental importance [of reconsolidation] in humans.”

After showing the pilot episode of 24 to 146 volunteers, Chan and LaPaglia asked them to either play Tetris or answer memory-testing questions about the video. Twenty minutes later, they listened to a short audio recording that supposedly recapped the episode, but that secretly changed some details—for example, swapping Mandy’s syringe for a stun gun. Five minutes later, everyone took a final true-or-false test about what they had originally seen.

In this final test, the volunteers were worse at accurately recalling details that were changed in the audio recap, but only if they had previously answered questions that made them recall the video. Those who played Tetris were unaffected.

So, taking the quiz destabilised the volunteers’ memories of what they were quizzed on, paving the way for the false recap to mess with their knowledge. This worked even when volunteers correctly remembered what happened in the episode during the first quiz—the incorrect audio still changed what they thought they knew.

Through repetitions and variations of this basic experiment, Chan and LaPaglia showed that the effect lasts a long time, even if the final test followed the audio recap by a day rather than 5 minutes. But for the trick to work, the false information needs to come quickly and be very specific. If 48 hours passed between the first quiz and the audio recap, rather than 20 minutes, the original memories stay unchanged. And if the recap involved a different scenario—say, an assassin knocking out a flight attendant in the context of drug trafficking rather than terrorism—the new info never overwrote the original memory. This explains why we’re not constantly upsetting our old memories even though we’re constantly exposed to new information.

Chan and LaPaglia also suspect that people need to believe that the new information accurately represents the old set, and not if they consciously detect a factual discrepancy. “If they think there’s misleading information in here, they’ll be much less susceptible to that effect,” says Chan.

Other studies on reconsolidation have found similar results, but this one shows that memory manipulation isn’t limited to the simple products of basic conditioning, but also more complicated bits of knowledge. It supports the work of psychologists like Elizabeth Loftus, who have shown how easy it is to implant people with false memories.

It also fits with a growing body of evidence showing that, despite what people believe, eyewitness testimony is often seriously unreliable. “Say you’ve been questioned by an investigator and you recall the event,” says Chan. “In the next 15-20 minutes, you could run into another eyewitness or overhear investigators talking to each other. Some inaccurate information could update your memory.”

More positively, the study could have implications for treating conditions that involve unwanted memories, such as phobias or post-traumatic stress disorder (PTSD). As Chan and LaPaglia, “Humans are notoriously inept at suppressing unwanted thoughts.” If we try not to think about something, we usually end up thinking about it all the more. Instead, it may be more productive to actively remember what’s troubling us and reinterpret that in a new light, relying on reconsolidation to remake the old memories in a less disqueting way.

Acceptance and commitment therapies for PTSD work along similar lines, but it’s often assumed that they help people to put the past behind them or to disconnect their experiences from negative feelings. But Chan and LaPaglia suggest that such techniques might actually be exploiting the reconsolidation effect to actually rewrite the past, rather than just severing our connections from it.

Reference: Chan & LaPaglia. 2013. Impairing existing declarative memory in humans by disrupting reconsolidation. PNAS http://dx.doi.org/10.1073/pnas.1218472110

PS: I love that reference 55 of this paper is “24 12:00 a.m.–1:00 a.m. [dvd]. Fox Television Studio, producer; 60 min, sound, color”. And reference 56 is “Neave P (2009) Tetris N-Blox (Tetris Holding, LLC, Hawaii).”

More on memory:

More on memory:

·         Rewriting fearful memories by bringing them back to mind

·         Scientists create mice that automatically label new memories for easy reactivation

·         Five myths about memory (and why they matter in court)

·         Memory improves when neurons fire in youthful surroundings

·         The extended mind – how Google affects our memories       

·         Beta-blocker drug erases the emotion of fearful memories

·         Memories can be strengthened while we sleep by providing the right triggers

·         The guardians of fear – molecules that provide safety nets for scary memories

·         Erasing a memory reveals the neurons that encode it

·         Drugs and stimulating environments reverse memory loss in brain-damaged mice

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Starving Flies Must Shut Down Long-Term Memories or Die

Here’s something that people often forget about memories—they are expensive. Whenever we create new ones, and possibly whenever we recall old memories, our brain needs to manufacture new proteins in its neurons. This consumes a lot of energy, which partly explains why the brain demands proportionally more fuel than other organ. And even if we’re short of energy, the brain gets first dibs.

But the brain can also prioritise its various jobs. By studying flies, Pierre-Yves Placais and Thomas Preat from the CNRS in Paris found that starving individuals disable the creation of unpleasant long-term memories.

Such memories might be a useful investment for the future, but the starving flies are about to die right now. Laying down expensive memories is a luxury they cannot afford, and if Placais and Preat forced them to do so, they died faster. For the flies, building certain memories actually compromised their survival—a striking reminder that the brain is subject to the same fine checks and balances that the rest of the body obeys.

Placais and Preat trained flies to associate a smell with an electric shock, and then exposed them to cycloheximide—a chemical that stops the brain from building the proteins necessary for long-term memory. If the flies had been fed, the chemical worsened their memories, as expected. But if they hadn’t eaten for 24 hours, cycloheximide did nothing. Likewise, mutant flies that find it hard to build long-term memories were worse than normal flies at learning about the electric shocks, but only if they were fed. If they were hungry, their genetic disadvantage didn’t matter.

It’s not that the hungry flies were stressed and just feeling mentally slower all round. Their condition didn’t affect another type of memory that is shorter-term, cheaper, and does not depend on making new proteins. Instead, they were responding to their hunger by adaptively shutting down one very specific type of memory.

Flies depend on two special neurons to make long-term memories, and Placais and Preat found that both of these are unusually silent when the insects are starving. The duo deliberately activated these neurons by infusing them with temperature-sensitive proteins, which made them fire at anything above 28 Celsius. When this happened, the starved flies regained the ability to make enduring memories.

But they paid a heavy cost. By forcibly bringing the flies’ disabled memories back online, Placais and Preat shortened their lives by about a third. This only happened if they were trained to link the shocks and the smells. If they were exposed to only smells, or only shocks, or given nothing at all to learn, they were fine. It was the combination of training and memory-making that doomed them.

The fruit fly Drosophila melanogaster, by George Novak

These results fit with earlier work from Swiss scientist Frederic Mery. He showed that flies that make long-term memories are more vulnerable to harsh environments, and that breeding male flies to have better long-term memory also shortens their lives. “It’s very surprising that things are apparently so clean and simple,” says Preat. “If the animal is starved, the brain blocks LTM formation; otherwise, death occurs faster.”

But of course, things aren’t quite that simple. Starving flies can still make long-term memories of pleasant experiences, such as linking smells with food. Indeed, these “appetitive memories” only seem to form if flies are hungry, which is why scientists who run experiments involving such memories have to starve their insects first. This makes sense. Flies only get the chance to build appetitive memories once they’ve actually found some food, so they can immediately pay the energetic cost of making fresh proteins. It’s only “aversive memories” of unpleasant experiences that aren’t worth creating.

Meanwhile, over in Japan, Yukinori Hirano was running a similar set of studies at the Tokyo Metropolitan Institute of Medical Science that complement but complicate the results from the French team. He found that fasting improves long-term memory in flies, but only if the insects go hungry for less than 16 hours. Any longer, and those same memories shut down, as in Placais and Preat’s experiment.

And the surprises kept coming. Hirano found that this improved long-term memory is actually different from the vanilla version that the flies normally use—it forms after a single round of training but decays after a shorter time. These two flavours of long-term memory also depend on different (if slightly overlapping) sets of molecules and neurons.

The two studies paint a complicated picture, but both support a single core theme: Flies can prioritise different types of memory depending on how hungry they are.

And the obvious million-dollar question: Does we and other mammals do the same thing? Both teams are trying to find out, but they think the answer is yes. “It’s very likely because all the basic mechanisms of brain functioning have been conserved during evolution,” says Preat.

Reference: Placais & Preat. To Favor Survival Under Food Shortage, the Brain Disables Costly Memory. http://dx.doi.org/10.1126/science.1226018

Hirano, Masuda, Naganos, Matsuno, Ueno, Miyashita, Horiuchi & Saitoe. 2013. Fasting Launches CRTC to Facilitate Long-Term Memory Formation in Drosophila. http://dx.doi.org/10.1126/science.1227170

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Scientists create mice that automatically label new memories for easy reactivation

Finding a specific memory in your brain is not easy. Is it held within a particular group of neurons? If so, which ones? Are they clustered together, or spread throughout the brain? In science-fiction, a goofy helmet and a fancy operating system is all it takes. In real life, we need a subtler and cleverer technique.

Two independent groups of scientists have devised just such a method, and used it to awaken specific memories in mice. One group even planted a slightly artificial memory. These techniques have great promise. They will allow us to study how memories are formed, how our existing memories affect the creation of new ones, and what happens during the simple act of remembering.

Scientists have long been able to reactivate old memories, but only in a crude and undirected way. Back in the 1940s, brain surgeon Wilder Penfield found that when he electrified the brains of some epileptic patients, they recalled vivid random memories. The results were scattershot, and expectedly so. Even the tiniest of electrodes will shock thousands of neurons. There’s no way of directing the electricity to the specific neurons involved in any particular memory.


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How acquiring The Knowledge changes the brains of London cab drivers

London is not a good place for fans of right angles. People who like the methodical grid system of Manhattan will whimper and cry at the baffling knot of streets of England’s capital. In this bewildering network, it’s entirely possible to take two right turns and end up in the same place. Or in Narnia. Even with a map, some people manage to get lost. And yet, there are thousands of Londoners who have committed the city’s entire layout to memory – cab drivers.

Piloting London’s distinctive black cabs (taxis to everyone else) is no easy feat. To earn the privilege, drivers have to pass an intense intellectual ordeal, known charmingly as The Knowledge. Ever since 1865, they’ve had to memorise the location of every street within six miles of Charing Cross – all 25,000 of the capital’s arteries, veins and capillaries. They also need to know the locations of 20,000 landmarks – museums, police stations, theatres, clubs, and more – and 320 routes that connect everything up.

It can take two to four years to learn everything. To prove their skills, prospective drivers make “appearances” at the licencing office, where they have to recite the best route between any two points. The only map they can use is the one in their head. They even have to narrate the details of their journey, complete with passed landmarks, road names, junctions, turns and maybe even traffic lights. Only after successfully doing this, several times over, can they earn a cab driver’s licence.

Given how hard it is, it shouldn’t be surprising that The Knowledge changes the brains of those who acquire it. And for the last 11 years, Eleanor Maguire from University College London has been studying those changes.


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Five myths about memory (and why they matter in court)

Psychology is at its most interesting to me when it demolishes what we believe to be true on the basis of common sense, and it does this with alarming regularity. Take our memories. The act of remembering is something we do all the time, so we feel we have an innate understanding of how our memory works. But it is precisely this familiarity that leads us astray. Except for moments where we forget where we placed the keys, we are not privy to the many ways in which our memories let us down. Psychological experiments, however, can make those failures clear, and they have revealed that our memories are more incomplete, inaccurate and easily changed than we would like to think.

Daniel Simons from the University of Illinois and Christopher Chabris from Union College Schenectady have done a large survey to look at our misconceptions about memory. They asked a nationally representative sample of over 1,800 Americans to say how much they agree with various statements, and compared their answers to a small group of experts – professors, polled at a psychology conference, who had been studying memory for more than 10 years. This slideshow shows what they found.

On the whole, 60 percent of people agreed with statements that the experts almost totally rejected. These misconceptions can have severe consequences, when they influence the outcomes of court cases. As Simons and Chabris write, “This discrepancy between science and popular beliefs confirms the danger of relying on intuition or common sense when evaluating claims about psychology and the mind. Accordingly, scientists should more vigorously communicate established and uncontroversial results (alongside new and surprising findings) in a way that leads to broader public understanding.”

Would you send someone to jail on the basis of video footage shot with a low-resolution camera whose lens has dirty marks around the sides and a massive hole in the middle? Probably not, and yet that is basically what eyewitness testimony is. While it looks like we see the world in vivid detail, like the display on a high-definition television, that’s largely because the information from our eyes is heavily processed by the brain. It covers the missing information in our blind spot, and smoothes over the lack of detail around the edges. It’s a filtered version of reality.

This is hardware problem, but the software has glitches too. Our view of the world is sensitive to our expectations, our desires and where we assign out attention. Simply put, we see what our brain wants us to see. The camera metaphor implies a passive process where we switch on our memory, and it dutifully records away. The reality is very different.

As we’ve seen, the memories of eyewitnesses can be fickle things. But confident eyewitnesses can sway the minds of juries. There is a grain of sense in this – look at a large group of people and they’re generally more accurate if they’re more confident in their memories. But for any individual, confidence is a poor gauge of accuracy because we all differ in how confident we are in the first place. The consequences of overly relying on the confidence of memory can be catastrophic. Eyewitness misidentifications are the single greatest reason why innocent people are convicted for crimes they did not commit.

People often imagine their memories to be like vast libraries, where information is written down, filed away, and then brought back when it’s needed (or lost in some dusty shelf). But the act of remembering is more complicated than that.

Every time we bring back an old memory, we run the risk of changing it. It’s more like opening a document on a computer – the old information enters a surprisingly vulnerable state when it can be edited, overwritten, or even deleted. It takes a while for the memory to become strengthened anew, through a process called reconsolidation. Memories aren’t just written once, but every time we remember them. This might be useful in terms of conquering traumas and phobias, but it’s much less helpful in a courtroom.

People generally believe that even if we focus our attention on a task, we will be distracted by surprising things going on around us. Time and again, Simons and Chabris have shown that this isn’t true. If you are one of the few people left who hasn’t heard of their famous illusion, try this or one of many other similar tests. On the surface, this seems to be a misconception about attention rather than memory, but obviously, we only explicitly remember things that we see in the first place.

In courtrooms, a person’s honesty can be called into question is it’s deemed that they should have noticed something obvious going on around them. Such a case happened in 1995. While chasing after a suspect, a Boston policeman called Kenneth Conley ran directly past several other officers mistakenly beating another man. Conley said he didn’t see the beating, to great disbelief. He was indicted for perjury and obstruction of justice, and sentenced to 34 months in prison. Through a staged experiment, Simons and Chabris showed that it’s entirely possible to run past a vivid beating if your mind is on other thingsThis one has few practical implications, but it is interesting nonetheless. Amnesia is often used as a convenient plot device in films and TV, where people suddenly lose all memory of their names or the past lives. This can happen – it’s called a fugue state, but it’s very rare. The film Memento has a more accurate portrayal of amnesia, or at least the variant known as “anterograde amnesia”. As in the film, people with this condition lose the ability to entrench new memories, losing new information and experiences after a short space of time. But even in this film, the hero loses a sense of his own identity, something that happens very rarely in real life.

People can also suffer from “retrograde amnesia”, where they lose older memories, particularly those that happened immediately before an accident or injury. It typically occurs alongside anterograde amnesia, and is rarer as a stand-alone condition.

Reference: :Simons, D., & Chabris, C. (2011). What People Believe about How Memory Works: A Representative Survey of the U.S. Population PLoS ONE, 6 (8) DOI: 10.1371/journal.pone.0022757

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Memory improves when neurons fire in youthful surroundings

As we get older, our memories start to fail us. The symptoms of this decline are clear, from losing track of house keys to getting easily muddled and confused. Many of these problems stem from a failure of working memory – the ability to hold pieces of information in mind, block out distractions and stay focused on our goals. Now, a team of American scientists has discovered one of the reasons behind this decline, and a way of potentially reversing it.

Our working memory depends on an area known as the prefrontal cortex or PFC, right at the front of the brain. The PFC contains a network of nerve cells called pyramidal neurons that are all connected to one another and constantly keep each other buzzing and excited – like a neural version of Twitter. This mutual stimulation is the key to our working memory. As we age, the buzz of the pyramidal neurons gets weaker, and information falls more readily from our mental grasp.

But this decline isn’t the fault of the neurons themselves. By studying monkeys, Min Wang from the Yale University School of Medicine has found that the environment around the neurons also changes with age. And by restoring that environment to a more youthful state, he managed to ease some of the age-related decline in working memory.


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The extended mind – how Google affects our memories

Information has never been easier to find or record. Within seconds, the Internet lets us find answers to questions that would have remained elusive just a few decades ago. We don’t even have to remember the answers – we can just look them up again.

Now, three psychologists have shown how our memories might react to this omnipresent store of information. They have found that when American students expect to have access to information in the future, they remember that information less well. But there’s a positive flipside: they’re also better at remembering where to find the information again.


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Single protein can strengthen old faded memories

[This is the first of three intertwined posts on PKMzeta – the molecule that keeps our memories intact]

We’re used to the idea that we become more forgetful with age. As time passes, our memories naturally fade and weaken, and that’s if we’re lucky enough to avoid traumatic accidents or diseases like Alzheimer’s. But Reut Shema, from the Weizmann Institute of Science in Israel, has found a possible way of preventing this decline, and even reversing it.

By loading the brains of rats with a protein called PKMzeta, she managed to strengthen their memories, even old and faded ones. “Multiple old memories were robustly enhanced. These results have no precedent,” says Todd Sacktor, who led the study together with Yadin Dudai.

PKMzeta is the engine of memory. This single protein behaves like a machine that constantly works to keep our memories intact. Switch it off, and we forget things permanently. It’s our lone defence against a constant tide of forgetfulness that threatens to revert our brains back to a blank slate (see “Exposing the memory engine”).


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Exposing the memory engine: the story of PKMzeta

[This is the second of three intertwined posts on PKMzeta – the molecule that keeps our memories intact]

You’ve got the phone number of a hot date – a vital piece of information that you need to keep in a safe place. You write it in a notepad, you save it on a file in your computer and you try to commit it to memory. This third method – the one involving your brain – is very different to the others.

In the other formats, stability is the norm. The ink on the paper won’t vanish (at least not for centuries). The magnetic information on the hard drive won’t spontaneously rearrange itself. Unless either material suffers physical damage, the information recorded within them will stand the test of time. In your brain, the fate of information is much less certain.

In the last decade, scientists have found that it takes active and unrelenting effort to keep our memories intact. Even long-term memories are constantly on the verge of being erased. To keep them stable, we need to continually recreate a protein called PKMzeta. This molecule is the engine of memory, constantly whirring to store information in our brains. Give the engine a boost, and old memories gain a new lease on life. Switch it off, and we forget things…. permanently.


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Todd Sacktor talks about the memory engine

[This is the third of three intertwined posts on PKMzeta – the molecule that keeps our memories intact]

Last year, I interviewed Todd Sacktor for a feature on fear and memory in Eureka, the Times’s monthly science supplement. Sacktor discovered that a protein called PKMzeta is vital for storing memory and in his latest study, he shows that adding more of this protein in the brain can strengthen even old, faded memories. (See “Single protein can strengthen old faded memories).

This post collates my two interviews with Sacktor – the first was done last year, and the second last night. The transcripts should act as a companion piece to my news story on his latest study, and my longer feature explaining the history of PKMzeta research and details about how this “memory engine” works.