It’s a similar story among other rare cases found to have HSAM by McGaugh’s lab,the only centre in the world that diagnoses it. “These people have otherwise ordinary memories,” McGaugh says. “But they can remember 30 years ago the way you or I remember yesterday – the mundane as well as the important.”

“These people can remember 30 years ago the way you or I remember yesterday – the mundane as well as the important.”

He had no idea such feats were possible until a woman namedJill Price emailed him in 2000 asking for help with her “forgetting problem”. McGaugh recalls the “big fat” history book he whipped out to quiz her on random events in her lifetime. As testing intensified,he even asked her if she could name the date of every Easter for the past 20 years. She could. Events didn’t have to be significant to her. She remembered when crooner Bing Crosby died (October 14,1977) because the news had been on the radio on her way to soccer practice as an 11-year-old. “Whereas that’s important to me,” says McGaugh. “He’s of my era – but even I don’t remember the date.”

More people with this ability began to surface. Louise Owen,a New York violinist,could tell McGaugh every day it had rained in her city during the month of January some 20 years earlier. The actress Marilu Henner,who met McGaugh as part of a 60 Minutes special on his research in 2010,organised her clothes and shoes in order of date last worn.

“It came as a huge surprise to me,” McGaugh says. Apart from one obscure case he found from the 19th century,no one had heard of this before.

After Price’s HSAM was confirmed as a new condition,and the60 Minutesprogram aired,hundreds of emails began flooding in to McGaugh from people who thought they or someone they knew might have it. He set up phone screening,testing people on random dates and events as he had Price,and then inviting high-performers (“the bona fides”) to his lab for more extensive testing,where personal recollections were sometimes vetted against records and family. Sharrock was one of those invited (and diagnosed) after her parents saw the program. She was 21 by then.

“And we’d never known what was wrong with me,” she says. “We knew I couldn’t forget,I couldn’t let things go,but we’d always put that down to my OCD.”

What’s it like to remember everything?

Tiring,says Sharrock,who has to sleep with classical music drowning out the constant stream of flashbacks. They arrive in no particular order,in vivid detail. The sun hitting a blade of grass on the sidewalk might transport her back to her first day of school – and the nerves clenching in her belly. There’s emotion,the ghost of a child’s tantrum or excitement,anxiety,grief. “I can be in a restaurant and all of a sudden I’m crying.”

Of course,it comes in handy,too. Try winning an argument with Sharrock about the past. She always knows when a faulty appliance is still under warranty. Her memory is so vivid that if she’s eating something bland she can recall a favourite meal –perhaps Black Forest cake – to taste instead. When we speak,she’s excited to be travelling in Wellington in New Zealand for the first time:a memory-free zone. But she smiles as she remembers meeting others with HSAM at McGaugh’s lab in California. Many of them had also been crossing off each day on the calendar from a young age,a way of anchoring themselves in linear order. Some also understood Sharrock’s strange feeling of going back in time,not forward,whenever the new year ticks over to January 1. “There were so many things like that,they’d go,‘Oh,I do that too,’ as if it was normal.”

“Say a memory of being in a cafe ... a song playing in the background will come back or the perfume of the person in front of me ordering.”

While Robinson confesses she’s ceased to be amazed by Sharrock after so long studying her,it’s the richness of Sharrock’s memories that is particularly striking. “She almost has a network for every memory,where you and I would only have a fraction of that.”

Some others with HSAM,including Marilu Henner,have also described an almost video-like recall. But,McGaugh notes,they can still make mistakes. Even their memories aren’t perfect.

As well as autism and obsessive-compulsive disorder,Sharrock has synesthesia,where one sense comes through alongside another,say a sound with a particular colour. (“I always taste yoghurt when I hear the word chalk.”) This may account for some of the richness of her recollections,Robinson says.

But Sharrock also says her memories becomestronger over time. “The senses,the noises,around me come back even if I didn’t really take note of them then. So,say a memory of being in a cafe,just a typical day,but a song playing in the background will come back or the perfume of the person in front of me ordering.”

Are memories interrupting her now,as we speak? “Yes,” she says,likening it to specks flickering before her vision. “It’s annoying. But I’m used to it.” She practises mindfulness to stay in the moment,plays the video game Minecraft,building virtual cities,and learns languages as a distraction. She’s also writing a memoir – from birth to her 30th birthday. The hardest part has been editing out the mundane memories from the noteworthy.

Still,McGaugh says when he’s asked those with HSAM if they’d rather not have their super memory,the answer’s always no. “In fact,they feel sorry for me,they tease me,like,‘You can’t do that?’” he laughs,his own memory still sharp at 91.

What might cause super memory? And can you train yours?

On scans,the brains of people with HSAM look normal. Everything is the typical size. “What we haven’t measured yet is whether Becky has stronger connections between[certain areas],” says Robinson of her research on Sharrock. Scientists in Italy are also exploring brain activity in people with HSAM,says McGaugh,to try to understand what might underpin it.

One theory suggests that people prone to fantasy encode information more strongly in their memories,perhaps even going back more often during daydreams to cement those connections.Mental rehearsal of events and activities has been shown to strengthen their hold in our minds.

The secret of memory athletes is itself visualisation,Konrad says. Our brains are good at encoding stories – the more bizarre the better. Remember our fact that turtles use Earth’s magnetic field like a GPS? Remarkable already,perhaps. But try picturing a leathery pirate turtle setting sail on a giant magnet,and you’re unlikely to forget that trivia nugget any time soon. Even better,imagine a story set somewhere you know well,like your house. Perhaps Captain Loggerhead is voyaging from your bathtub. But his first mate has been left behind and his tears are turning into salt mountains filling up your kitchen sink (to help you remember turtles excrete salt through their eyes). This bizarre daydream is a memory palace. Konrad visits his own often,weaving a story involving snowmen at the front door and high court judges criticising his coat rack – to remember the order of a deck of cards,for example. (“The judge is always the king of clubs for me.” )

In the lab,Konrad and his colleagues have shown that such memory hacks can help store information directly in long-term memory,not just short. Areas related to it light up on MRI scans when memory athletes use their tricks to recall random strings of information but not when they rely just on their regular working memory.

The kooky stories spun by memory athletes take serious concentration to conjure.

Still,it’s unlikely those with HSAM are just doing this all the time,unconsciously. The kooky stories spun by memory athletes take serious concentration to conjure. At championships,they sit spread out wearing thick noise-cancelling headphones,eyes focused,like people sitting exams. But when Sharrock’s attention is measured in the lab,it’s average,and those with HSAM do not report particularly wild imaginations. (Robinson and her team have already examined whether Sharrock can better imagine the future as well as the past. But those results look average so far.)

“This taps into similar memory systems,” says Konrad. “But they can’t remember passwords or names like[mnemonists] can. That’s why I’m interested to train them in what we do.” Competitive memorisers will forget what they’ve learned through their memory palace in a few days,but would someone with HSAM remember it forever?

Still,there is one major clue to the HSAM puzzle:those with hyper recall all seem to have higher rates of obsessiveness too and,often,anxiety. Though some are very functional and outgoing,as a group,McGaugh says they tend to score well above average for OCD tendencies. People suffering from OCD dwell on memories,too,but researchers are not sure if HSAM’s super recall causes obsessiveness or if the parts of the brain involved in OCD also help activate the HSAM. (Jill Price took detailed journals for example. But Sharrock,who also suffers from anxiety and obsessiveness,does not journal.) Either way,experts doubt it is the whole story.

Robinson suspects the answer may lie in the sensory richness of Sharrock’s recollections,the way she encodes memories. “And that could help us with people with[poor memories] like dementia,” she says. “It’s not going to give us a pill to stop it. But it might give us pathways to strengthen memories.”

Sharrock,who submits enthusiastically to testing,recalls her step-grandfather’s descent into Alzheimer’s,how old memories began to surface in vivid detail even as his short-term memory failed. “All of a sudden he was talking about his grade one class as a boy,which girls had their tonsils out,and what the salesman was wearing at the local toy shop,what was on the shelf behind him ... When he got the diagnosis,he was so scared.” She says helping people like him would bring meaning to her own at times chaotic life.

But does photographic memory exist?

The Hollywood idea of a perfect memory makes for convenient plotting,as our heroes call up swaths of text or other clues at key moments from just a glance. But to date,there’s no verified evidence such people exist (thoughStromeyer has stood by his 1970 paper on the mysterious Elizabeth).

One person who may come close isStephen Wiltshire,a gifted London artist with autism. He can sketch sprawling cityscapes in minute detail many hours or days after taking brief helicopter rides overhead to survey them. The windows of the Empire State Building. The entire grid of Sydney. Wiltshire can recreate it all,often for an audience or video recording.

McGaugh hasn’t studied Wiltshire himself,but admits he’s fascinated. “He has what seems to be a real photographic memory. It’s mind-blowing.”

Still,even Wiltshire’s memory is not thought to beperfect. (And his work is not the product of mere recall,but artistry,too.) Certainly,science suggests you need to focus on something to remember it. The brain doesn’t process all sensory information in one snap,as with a photograph. (Wiltshire has spoken of methodically scanning a cityscape to remember it.)

He wonders if there are more out there – people with astounding recall.

Suspected cases of photographic memory have generally not had close study. In the 1950s,it was reported that Aboriginal artist Winnie Bamara could also look at a scene and replicate it in detail later. Kim Peek,the savant who inspired the filmRain Man,is said to have memorised every page of the thousands of books he speed-read. As a memory researcher,Robinson is sometimes contacted by people who claim to have photographic memories,or HSAM,as well as those who struggle to make episodic memories at all. She’s met another savant who could recreate buildings and landscapes on the page remarkably accurately,but “it came at a major cost to his other abilities”. “He couldn’t process faces or words properly.”

Some experts wonder if certain people are better tuned in to detail. “There’s one idea that if you focus on the details,you don’t have the gestalt,the whole,” explains Robinson.

Or is it just that an artistic prodigy such as Wilshire will notice what the rest of us might miss if scanning a city skyline – in the way that NBA starLeBron James’ impressive ability to recount play-by-play moments of a basketball game could come down to his sporting expertise. “I had a patient only yesterday tell me they had a photographic memory,” says Robinson. “But I don’t think it exists in quite the[Hollywood] form.”

Even one of the most studied cases,S,the Russian journalist once told off for never taking notes at work who was then extensively tested by neurologist Alexander Luria,used memory techniques.

Some people really do have a kind of supercharged working memory,though,known as eidetic memory. That’s when images are preserved in the mind’s eye longer and more vividly than usual (up to a few minutes). This ability is very rare and,even then,mostly found in children. You cantake the same kind of magic eye puzzleElizabeth did (in a far simpler form) online to test your “afterimage”. It’s thought to be controlled by the part of the brain processing visual information more than our memory hardware itself.

But Konrad cites the world memory championships as anecdotal proof that true photographic memory doesn’t exist. Wouldn’t someone who could take detailed mental snapshots have swept in by now to claim the prize money? “It would be easy for them to beat us,” he laughs. Once in a while,a competitor will arrive with claims of a photographic memory. “And they are sometimes better at recalling details,but they usually don’t even score a point.”

Meanwhile,McGaugh is still in touch with many of his HSAM cohort (“They’ve been sort of like extended family.”) But he wonders if there are more out there – people less able to apply their experiences to testable calendar dates but with nonetheless astounding recall. “This is a huge puzzle that’ll be solved by my scientific grandchildren.” Memory is,after all crucial to our survival. “All animals,as far as we know,have memory. Even fruit flies. So to see variations is very exciting. Without memory,we wouldn’t be us.”

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