We are all collections of memories.
They dictate how we think, act
and make decisions, and even define our identity.
Yet memory, with its many virtues and flaws,
has puzzled for centuries.
How are memories made and stored in the brain?
Why do we remember some events but not others?
What do other animals remember?
And how can we improve
the flawed instrument handed to us by evolution?
In these articles of New Scientists,
authors try to answer these questions and many more,
starting with a revolutionary new understanding of memory’s purpose.
A revolution in our understanding of memory
Human memory didn't evolve so that we could
remember but to allow us to imagine what might be.
Every time we think about a possible future,
we tear up the pages of our autobiographies
and stitch together the fragments
into a montage that represents the new scenario.
This process is the key to foresight and ingenuity,
but it comes at the cost of accuracy,
as our recollections become frayed and shuffled along the way.
It's not surprising
that we confuse memories and imagination,
considering that they share so many processes.
Given the many survival benefits
of being able to imagine the future, for instance,
it is not surprising that other creatures
show a rudimentary ability to think in this way
Memory's role in planning and problem solving,
meanwhile, suggests that problems accessing the past
may lie behind mental illnesses like depression
and post-traumatic stress disorder,
offering a new approach to treating these conditions.
Equally, a growing understanding of our sense of self
can explain why we are so selective in the events
that we weave into our life story - again showing
definite parallels with the way we imagine the future.
The work might even suggest some dieting tips.
The ultimate guide to memory
(Image: van Wanten Etcetera/Souverein. Page detail: Anne Frank Fonds/Anne Frank House via Getty Images)
We are all collections of memories. They dictate how we think, act and make decisions, and even define our identity.
Yet memory, with its many virtues and flaws, has puzzled for centuries. How are memories made and stored in the brain? Why do we remember some events but not others? What do other animals remember? And how can we improve the flawed instrument handed to us by evolution?
In these articles we answer these questions and many more, starting with a revolutionary new understanding of memory’s purpose.
Yet memory, with its many virtues and flaws, has puzzled for centuries. How are memories made and stored in the brain? Why do we remember some events but not others? What do other animals remember? And how can we improve the flawed instrument handed to us by evolution?
In these articles we answer these questions and many more, starting with a revolutionary new understanding of memory’s purpose.
Remembrance of things to come
The discovery that memory evolved to allow us to predict the future rather than recall the past has some very strange implications, says David Robson
Memory: Remembrance of things to come
- New Scientist 08 October 2012 by David Robson
- Magazine issue 2885.
The discovery that memory evolved to allow us to predict the future rather than recall the past has some very strange implications
WHEN thinking about the workings of the mind, it is easy to imagine memory as a kind of mental autobiography - the private book of you. To relive the trepidation of your first day at school, say, you simply dust off the cover and turn to the relevant pages. But there is a problem with this idea. Why are the contents of that book so unreliable? It is not simply our tendency to forget key details. We are also prone to "remember" events that never actually took place, almost as if a chapter from another book has somehow slipped into our autobiography. Such flaws are puzzling if you believe that the purpose of memory is to record your past - but they begin to make sense if it is for something else entirely.
That is exactly what memory researchers are now starting to realise. They believe that human memory didn't evolve so that we could remember but to allow us to imagine what might be. This idea began with the work of Endel Tulving, now at the Rotman Research Institute in Toronto, Canada, who discovered a person with amnesia who could remember facts but not episodic memories relating to past events in his life. Crucially, whenever Tulving asked him about his plans for that evening, the next day or the summer, his mind went blank - leading Tulving to suspect that foresight was the flipside of episodic memory.
Subsequent brain scans supported the idea, suggesting that every time we think about a possible future, we tear up the pages of our autobiographies and stitch together the fragments into a montage that represents the new scenario. This process is the key to foresight and ingenuity, but it comes at the cost of accuracy, as our recollections become frayed and shuffled along the way. "It's not surprising that we confuse memories and imagination, considering that they share so many processes," says Daniel Schacter, a psychologist at Harvard University.
Over the next 10 pages, we will show how this theory has brought about a revolution in our understanding of memory. Given the many survival benefits of being able to imagine the future, for instance, it is not surprising that other creatures show a rudimentary ability to think in this way ("Do animals ever forget?"). Memory's role in planning and problem solving, meanwhile, suggests that problems accessing the past may lie behind mental illnesses like depression and post-traumatic stress disorder, offering a new approach to treating these conditions ("Boosting your mental fortress"). Equally, a growing understanding of our sense of self can explain why we are so selective in the events that we weave into our life story - again showing definite parallels with the way we imagine the future ("How the brain spins your life story"). The work might even suggest some dieting tips ("Lost in the here and now").
It is still early days, but what's clear is that we are at the beginning of a long and exciting journey. "The one thing that we really have learned is that memory is extraordinarily more complicated than anyone would have thought 10 or 20 years ago," says Tulving.
David Robson is a feature editor at New Scientist
Do animals ever forget?
From pigeons that can recognise faces to a chimp that stores rocks to throw at visitors, all animals have memories. But how similar are they to ours?
COMPARATIVE PSYCHOLOGY
Memory: Do animals ever forget?
- New Scientist 08 October 2012 by Emma Young
- Magazine issue 2885.
From pigeons that can recognise faces to a chimp that stores rocks to throw at visitors, all animals have memories. But how similar are they to ours?
EVERY morning, you take a walk in the park, bringing some bread to feed the pigeons. As the days wear on, you begin to see the birds as individuals; you even start to name them. But what do the pigeons remember of you? Do they think kindly of you as they drop off to sleep at night, or is your face a blank, indistinguishable from the others strolling through the park?
These questions may seem whimsical, but knowing what other creatures recall is crucial if we are to understand their inner lives. It turns out that the range of mnemonic feats in the wild is nearly as varied as life itself.
If you take memory to mean any ability to store and respond to past events, even the simplest organisms meet the grade. Blobs of slime mould, for instance, which can slowly crawl across a surface, seem to note the timing of changes to their climate, slowing their movement in anticipation of an expected dry spell - even when it never actually arrives.
With the emergence of the first neurons about half a billion years ago, memories became more intricate as information could be stored in the patterns of electrical connections within the nervous system (see "The making of a memory"). This type of learning may have been behind the Cambrian explosion - the sudden appearance and rapid evolution of more complex species about 530 million years ago - because it enabled animals to exploit new niches, sayEva Jablonka at Tel Aviv University and Simona Ginsburg at the Open University of Israel.
Over the following few hundred million years, increasingly advanced skills could emerge with different forces driving the evolution of each creature's mind. The result is a surprising range of mnemonic feats throughout the animal kingdom. Migratory cardinal fish, for instance, can remember where they laid their eggs during the breeding season and, after over-wintering in deep water, return to within half a metre of the same spot. Animals as diverse as lizards, bees and octopuses can learn the way out of a maze, and pigeons have anexcellent visual recognition, learning to recognise more than a thousand different images. They can even recognise individual humans and aren't fooled by a change of clothes.
Such skills, although impressive, don't match our experiences of episodic memory, in which we immerse ourselves in specific events. A pigeon might learn to associate your face with food, but it probably can't remember your last meeting in the way you might be able to recall details of your last trip to the park.
It is an important distinction, because episodic memory is thought to allow us to imagine and plan for the future. This skill, known as mental time travel, was long thought to be unique to humans, but there are now some signs that a handful of other species might also be able to escape the present.
Some of the most convincing evidence comes from Nicola Clayton and Sergio Correia at the University of Cambridge, who have shown that western scrub jays can learn from their experiences to anticipate the actions of other birds. If one bird knows that another is watching it bury its food, for instance, it will later move the stash, presumably to prevent it from being stolen. But they will only do this if they have previously stolen food themselves - suggesting that they were drawing on their memories while forming the plan. Similar studies have suggested that bonobos and orang-utans are also capable of mental time travel.
Initially, the work attracted a lot of scepticism from researchers like Michael Corballis at the University of Auckland, New Zealand, who believed that the results could be explained by a complex kind of classical conditioning, for instance. But some recent work has begun to change his mind. He points to a study of activity in the hippocampuses of rats, which suggests that they replay their movements through a maze, and may even imagine future paths that they could take. He is also impressed by Santino, a chimp at Furuvik Zoo in Sweden that collects and hides rocks to throw at visitors, using premeditation that would rely on episodic memory.
Unfortunately, so few animals have been studied that it is difficult to pinpoint exactly when this skill emerged, though the researchers suspect that it evolved separately in the different lineages, rather than emerging in one of our common ancestors.
Thomas Suddendorf at the University of Queensland in Australia is less willing to accept that animal memories rival our own. He proposes that episodic memory depends on a host of different components, and although some animals may be able to use limited foresight when it comes to food, for instance, only humans demonstrate the kind of capacity and flexibility that can allow us to imagine all kinds of futures.
"These simulations allow us to plan, prepare for and deliberately shape the future, like no other animal appears to do," Suddendorf says. Santino might be able to plan a rock attack - but he could not plan anything so conniving as a bid for freedom.
The making of a memory
When we talk about memory, we can mean many things. In the short term, we use our working memory to juggle small lists of information, such as a round of drinks. These are held in fleeting changes in the brain's electrical or chemical activity that quickly fade as the mind wanders.
Long-term memories, in contrast, can last a lifetime. They can be classed as semantic memories of facts, or episodic memories of events. Psychologists also refer to autobiographical memories, which include the episodic and semantic memories that relate to our life story.
All these different kinds of long-term memories are woven into the webs of connections between brain cells. By the creation of new receptors at the end of a neuron, by a surge in the production of a neurotransmitter, or by the forging of new ion channels that allows a brain cell to boost the voltage of its signals, the brain alters the communication between networks of cells. As a result, the same pattern of neurons will fire when we recall the memory, bringing the thought back into our consciousness. Many brain regions are involved in this process, but the hippocampus, near the base of the brain, is considered to be especially important in consolidating our memories.
Ultimately, these changes to the neural network are probably stored semi-permanently through epigenetic changes, which involve small alterations to the structure of a gene and determine its activity within the cell. Certain genes linked to the formation of memories have been shown to have fewer methyl groups attached to their DNA after learning, for instance - a clear example of an epigenetic change.
But the brain is not like a video camera. Every time we recall a memory, new proteins are made and the epigenetic markers will alter - changing it in subtle ways.
Emma Young is a writer based in Sheffield, UK
How the brain spins your life story
Our autobiography is pieced together from the many events in our lives – but we pick and choose which ones to include
Memory: How the brain spins your life story
- New Scientist 08 October 2012 by Kirsten Weir
- Magazine issue 2885.
Our autobiography is pieced together from the many events in our lives – but we pick and choose which ones to include
GRADUATION day. The first concert you attended. Your first kiss. These personal recollections stand apart from memories of shopping lists or the world's capital cities. Autobiographical memories define us; they are who we are.
Yet they are far from complete, with some periods of our lives producing heaps of recollections while others receive relatively patchy coverage. What forces lead us to remember one event but forget another? Until recently, the subject had largely been a black box to researchers, but they have now begun to make huge strides towards an understanding of the way our minds write our life story.
Our brains certainly start remembering at a young age, learning simple associations before we are born. One small study even found that newbornstend to stop crying when they hear the theme tune of a TV show their mother often watched while pregnant, perhaps because it reminds them of the comfort of the womb. But we cannot consciously remember specific events from before the age of 2 or 3, when our autobiographical memory begins to develop. Even then, we are hard-pressed to remember much from before our sixth birthday.
So far, three different factors have emerged that might explain this hazy recall. One possibility is that the neural pathways are not mature enough between the hippocampus - where memories are consolidated - and the rest of the brain, so our experiences from this period may never be cemented into long-term storage. Our burgeoning language skills also play a key role, says Martin Conway at City University London, because words provide a kind of scaffold on which we hang our memories for future retrieval. His experiments have shown that children don't tend to remember an event until they have learned the words to describe it.
A sense of our own identity is also crucial for our memory of particular experiences. In a series of experiments, Mark Howe at Lancaster University in the UK showed toddlers a toy lion, which he then placed in a drawer. A week later, those who could recognise themselves in a mirror - a sign that they had developed a sense of self - were able to recall where he had placed the stuffed toy, while toddlers who failed the mirror test drew a blank.
As we get older, our identities and recollections develop together in an intimate dance. While the events in your life shape your opinion of yourself, your personality also determines what you remember; someone who thinks they are courageous might fail to remember a time when they acted cowardly, for example. "Your sense of who you are and how you enact your personality traits is very tied up in autobiographical memory," says Robyn Fivush at Emory University in Atlanta, Georgia.
Guiding all of this are our parents, who form our identities and cement our memories with their storytelling. When families discuss personal events in an elaborate way, children develop more detailed narratives of their own by the time they reach school age than those whose parents weave less intricate stories. Psychologist Qi Wang at Cornell University in Ithaca, New York, believes this may explain the influence of culture on the way we reminisce. Chinese parents tend to focus less on individual experiences and emotions when discussing the past, with fewer details, than Americans, for instance. As a result, Wang has found that Chinese people's memories, even during adulthood, tend to be less personal, focusing instead on events of social or historical significance.
As we venture further from the safety of our parents' embrace, our autobiographical memories continue to mature. The difference is quite noticeable, says Conway; a 10-year-old cannot relay a coherent life story, but a 20-year-old can go on for hours. "Something happens over that adolescent period." But what? So far, studies to tackle that question are lacking. "There's a big lacuna between about age 7 to late adolescence where we don't really know what's going on," he says.
The cultural script
We do know, however, that we are more likely to remember events from the end of this period, in young adulthood, than from any other period in our lives. This "reminiscence bump" may be the result of anatomical changes to the still developing brain. Alternatively, it may be that our brains feel emotions more keenly during adolescence and early adulthood - and memories linked to intense feelings stick in the mind for longer.
Or perhaps it is simply down to the fact that many important landmarks in our lives - learning to drive, graduating and falling in love for the first time - tend to fall within this period. "Those distinct events are more likely to be remembered, because they're culturally marked," Fivush says.
Recent work in Denmark supports this idea. Annette Bohn and Dorthe Berntsen at Aarhus University found that when young children were asked to write their future life stories, most of the events they imagined took place in young adulthood, mirroring the reminiscence bump. So it seems that we are aware of the "cultural life script" from a young age, which may mould our recollections of events as they occur.
The finding dovetails with the idea that memory and foresight share the same machinery in the brain. A child's ability to imagine the future seems to develop in tandem with his or her autobiographical memory, for instance. Wang, meanwhile, has found that the cultural differences that shape our personal narratives can also influence our planning abilities, showing that Chinese people are less likely to give specific, personal details than Americans when they talk about events to come.
Our autobiographical memories aren't perfect, to be sure. But whether we are looking forward or gazing back into the past, our personal narratives are central to understanding our place in the world. That's a point worth remembering.
Shared recall
Autobiographical memories are, by definition, personal. But that doesn't mean they are all our own, says Amanda Barnier, a cognitive scientist at Macquarie University in Sydney, Australia. She and her colleagues interviewed couples that had been married for decades. Not surprisingly, couples who remembered together, rather than independently, were able to recall significantly more than those who took a solo approach.
Much research focuses on the downsides of this process, including the risk of false memories: it is not uncommon for people to absorb their siblings' or spouses' recollections into their own life stories, for example.
But Barnier argues that collaborative recall's benefits have long been overlooked. Understanding the cues that couples use to prompt one another could offer new ways to shore up memory in elderly people facing dementia, for instance.
"We often hear about this idea of someone losing their long-term partner, and all of a sudden they experience a rapid decline," she says. "It must be like they've lost a part of their mind."
Kirsten Weir is a writer based in Minneapolis
Boosting your mental fortress
Connecting to your past can strengthen your defences against depression and PTSD, suggesting new treatments for these disorders, says David Robson
MENTAL HEALTH
Memory: Boosting your mental fortress
- New Scientist 08 October 2012 by David Robson
- Magazine issue 2885
Connecting to your past can strengthen your defences against depression and PTSD, suggesting new treatments for these disorders
WHAT pushes someone to try to take their own life? That's what psychologist Mark Williams was trying to find out as he visited people recovering from attempted suicide in the UK's Addenbrookes Hospital in the 1980s. Williams knew he had to tread carefully: the patients had been hospitalised for an attempted overdose in the past 48 hours. "These people had done dangerous things to themselves," he recalls. "You can't ask them to do complicated tests."
Williams was there because he suspected there was something different about the long-term memories of depressed or suicidal people, and had devised a simple exercise to test his theory on the patients at Addenbrookes. Sitting at their bedside, he would read out a cue word, such as "happy" or "clumsy", before asking them to describe a past event it brought to mind. Perhaps not surprisingly, they were quicker to tell him about negative experiences than positive ones, but Williams was struck by something more subtle.
While his comparison group - other hospital patients who weren't depressed - tended to focus on specific events, the overdose patients were noticeably vaguer. One responded to the word "happy" with "the first years of my marriage", for instance; another person given the word "safe" said: "when I'm in bed". Even when Williams encouraged them to be more specific, they were less likely to dig out a single incident - such as a particular film, or an insult that had upset them.
It was as if the depressed patients were merely skimming the chapter headings of their autobiographies, without reading the text that followed. It might seem a minor detail compared with the desperation that leads to a suicide attempt. But Williams's findings, which are now supported by a host of studies from other groups, have emphasised just how important our memories are in shaping our well-being, offering a new perspective on depression and perhaps other mental illnesses too.
Holding on
According to this theory, our memories act as a kind of ballast that holds us steady during times of stress; they can suggest ways to solve problems and offer comfort when we are feeling wounded. When people find it hard to recall specific events from their past, however, they feel overwhelmed by life's challenges, which slowly pushes them into depression. "In the right circumstances, the effect can be striking," says Williams, who is now at the University of Oxford. If the theory is right, there may be new ways of treating depression that directly target the underlying memory problems.
A new approach would certainly be welcome. Depression is the commonest form of mental illness, affecting somewhere between 10 and 20 per cent of us at some point in our lives. Antidepressants help some people, particularly the most severely affected, but these drugs can bring side effects, including weight gain and loss of libido. Meanwhile, talking therapies such as cognitive behavioural therapy can be costly and often take weeks or months to make an impact.
Williams is by no means the first to suggest that memory plays a part in mental illness; Sigmund Freud once suggested that the repression of unpleasant memories from childhood could lead to hysteria. In the case of Williams's suicidal patients, however, theirs was a more general difficulty. When questioned, they painted their past in broad brush strokes - "I always enjoyed a good party" that missed the details of specific events - "my brother's 30th birthday".
Williams's paper, published in 1986 in the Journal of Abnormal Psychology, triggered a trickle, then a torrent, of similar studies. They revealed that "over-general memory", as the phenomenon came to be known, was not limited to people who had tried to commit suicide, but was linked to depression in general.
Further studies found it to be present before the low mood developed, lending weight to the idea that the memory problems led to depression and not the other way around. For instance, one team examined the memories and well-being of 74 women who had undergone IVF and failed to get pregnant. Those who had the least specific recall before the treatment were most likely to develop symptoms of depression after the disappointment. Another study, published in April, found that teenagers judged to have over-general memory were more likely to develop depression in the 12 months after they first met the researchers.
As the body of evidence supporting this idea has grown, various theories have emerged about just how memory problems could send our mood into a downward spiral. One idea is that remembering the good times is important for chasing the blues away. "Thinking of better times gives you more hope for the future," says Jennifer Sumner of Northwestern University in Evanston, Illinois. If you can't remember those sunnier days, the future may seem very dark indeed.
Given the role of memory in imagination and foresight (see "Remembrance of things to come"), poor access to our past may also impair our problem-solving skills, which are known to be weaker in depressed people. When asked how you might make friends after moving to a new neighbourhood, for example, most people can come up with good ideas, like inviting the neighbours round for drinks. Depressed people, in contrast, tend to be stumped by these questions. Importantly, people with over-general memory also seem to fare poorly at this kind of task. "When you face problems in your life, you don't have an analogy to help you solve the current situation," says Rachel Anderson at the University of Hull, UK. It is easy to imagine how, with your difficulties mounting, you may then begin to feel desperate and helpless, trapped by your circumstances with no obvious escape.
Flashbacks
That might explain her finding that people with less specific recall only develop depression when they face long-term stresses, such as ongoing quarrels with their partner; those with fewer hassles show few ill-effects.
As well as depression, over-general memories could make people more vulnerable to post-traumatic stress disorder. It may seem counter-intuitive, because PTSD involves vivid memories of a traumatic incident. But these flashbacks appear to be the exception rather than the rule as people with PTSD tend to have trouble recalling other events from their past. Once again, these difficulties seem to be present long before the onset of the disorder - firefighters with hazy recall are often the first to develop the symptoms of PTSD, for instance. Perhaps a poor memory just weakens our mental fortress - and when the defences are down, it's easier for anxiety, fear and painful flashbacks to intrude into our thoughts.
Why do people lose access to their recollections in the first place? Given the complexity of the human mind, it's probably the outcome of many interlinked processes. Williams thinks we may learn the over-general style of thinking from our parents, if they tend to talk in broad terms about the past. It could also begin as a coping mechanism, helping people to retreat from the pain of a difficult experience.
Tim Brennen at the University of Oslo in Norway probed the memories of Bosnian teenagers who had been young children during the Bosnian war in the 1990s. "They had seen people being killed, villages burnt down. They were kept in a state of terror for years," says Brennen. The teens found it harder to remember specific events in their past than their Norwegian peers.
By the time Brennen met the Bosnians in the late 2000s, many were living a relatively peaceful life and hadn't yet developed signs of mental illness as a result of their experiences, over-general memories or otherwise. That doesn't necessarily contradict the theory. As Anderson has found, the weaknesses in our defences only show during times of stress. Brennen suspects that the consequences might kick in once they face the challenges of adult life.
Although this theory of depression is gaining converts among researchers, it still has plenty of critics. Mark Howe at Lancaster University in the UK points to a contradictory study showing that depressed people simply take longer to access their recollections. If you give them enough time, they can usually summon specific incidences for a cue word, he says. Perhaps they are just less keen than other people on sharing personal recollections with a stranger. "I don't think their memory has fundamentally changed," he says.
While the theory's merits are still being debated, its proponents are already exploring whether a kind of memory training can be used to improve people's recall and so reduce their symptoms of depression. Tim Dalgleish at the MRC Cognition and Brain Sciences Unit in Cambridge, UK, for instance, has investigated a technique called Memory Specificity Training (MeST), which encourages people to practise delving into their memories. In effect, they are asked to repeat a similar version of Williams's memory test over and over again, recalling detailed specific incidents for different cue words. Crucially, the events need not have anything to do with the person's current anxieties. People can be taught MeST in groups and may only need five weekly sessions to see improvement if early results are anything to go by.
One of the first trials took place in Iran, carried out by Hamid Neshat-Doost at the University of Isfahan, who worked with Dalgleish in Cambridge before returning to his home country. It involved 23 depressed Afghani refugees, living in a community with little access to cognitive behavioural therapists. The 11 people who received five group sessions of MeST improved significantly, unlike the others, who went untreated. Importantly, those with the most improvements in their ability to recall specifics reported the greatest improvements in their mood.
Admittedly that was a small, unblinded trial and memory training would have to be compared with traditional talking therapies in a head-to-head trial before any conclusions could even begin to be drawn about their relative merits. After all, cognitive behavioural therapy is also becoming more widely and cheaply available through online programmes and group therapy. But Williams, who has worked on a similar form of memory training, says MeST could be another useful option for those who don't respond well to cognitive behavioural therapy or antidepressants. "What's nice is that it brings the patient on board in a collaborative way," he says. "It isn't stigmatising."
Sumner agrees that memory training looks promising, having tried to encourage her own patients to reminisce more specifically, with positive results. "They don't see their past and future as [uniformly] negative," she says. "It gives them something to latch on to, motivating them to make changes."
David Robson is a feature editor at New Scientist
Lost in the here and now
People who are stuck in the present reveal a strange interplay between memory and body
Memory: Lost in the here and now
- New Scientist October 2012 by Catherine de Lange
- Magazine issue 2885.
People who are stuck in the present reveal a strange interplay between memory and body
TO THE casual observer, there would have been nothing unusual about Henry Molaison as he tucked into dinner at his usual slow-and-steady pace. But to the group of psychologists at the Massachusetts Institute of Technology who were observing him, his behaviour was astonishing: just 60 seconds earlier, he had polished off an identical three-course meal. Yet Molaison was no glutton. Instead, part of his brain had been removed in an attempt to cure his epilepsy. From then on, he was unable to form new memories and became stuck in the present for perpetuity.
Scientists usually consider feelings of hunger to arise from hormonal signals in the gut, but Molaison's behaviour suggested that our memories of what we have just eaten may be more important in curbing our appetite. The idea found further support a decade later, in 1998, when Morris Moscovitch at the University of Toronto, Canada, replicated this experiment using two people with a similar memory condition. Not only did these people eat a second meal, just 15 minutes after finishing the first, but in some trials they unquestioningly ate a third.
There is always the possibility that the brain damage may have brought on complications besides the memory loss that interfered with the gut's signals to the brain, but a recent experiment by Suzanne Higgs at the University of Birmingham in the UK suggests otherwise. She tapped into "sensory specific satiety" - the familiar sensation that our liking for a given food decreases the more we eat of it, whereas a different dish will feel more appetising; it is the reason that we can find extra space for pudding. Higgs found that people with amnesia retain such preferences. After a hearty lunch of sandwiches they will prefer crisps or cookies to further sandwiches, even though they couldn't tell you what they had just eaten. She concludes that the digestive signals are reaching the brain, and that the amnesiacs' lack of memory lies behind their seemingly insatiable appetite.
Incredible endurance
The unexpected effects of memory on our feelings and behaviour might not stop with food. Diane Van Deren is one of the world's elite ultra runners. In one race this year she ran more than 1500 kilometres over 22 days. On some of those days, she ran for as long as 20 hours. Van Deren had always been good at sport, but her incredible endurance seems to be down in part to her poor short-term memory, again the result of brain surgery for epilepsy.
Often, she just cannot remember how long she has been running for, underestimating the time by as much as 8 hours. "Most people with amnesia suffer a tyranny of the present," says Adam Zeman, a neurologist studying memory and epilepsy at the University of Exeter, UK, but Van Deren's inability to remember how long she has been running seems to free her from the feelings of fatigue that plague other runners. Perhaps, while others get caught up in the details of where they have been and where they are going, Van Deren gets into a more zen-like state that lets her run for longer without feeling so much strain. Of course, it could also be that after the challenges in her life Van Deren has a higher threshold for discomfort than most people.
For the rest of us, losing track of time on a long run is difficult, but there are certainly ways in which these findings affect us all. Higgs has found that simple distractions such as watching TV can stop people from forming good memories of what they are eating. As a result, they tend to snack more after the meal than control groups who were not distracted.
Imagination can play a powerful role too. Thanks perhaps to its close link to memory, simply imagining the process of eating something can lead people to feel more satiated, causing them to eat less. Which all goes to show that in the fight against overeating, memory could be your biggest ally, even if at times it would be more palatable to forget.
Catherine de Lange is a writer based in London
Six tips to master your memory
Want to remember, or forget things, at will? These tips will show you how
Memory: Six tips to master yours
- New Scientist, 08 October 2012 by Christian Jarrett
- Magazine issue 2885.
Want to remember, or forget things, at will? These tips will show you how
MEMORY is a wonderful gift, but it's clearly one that came without a user guide. Who hasn't felt facts slip through their mind like sand through a sieve as they crammed for an exam? At other times, forgetting may be the difficulty, as we struggle to banish the memories of painful events. Thankfully, a growing understanding of the human mind offers many ways to help you make the most of your innate abilities.
1. Hit the sweet spot
When trying to memorise new material, you may find yourself staring endlessly at the page in the hope that its contents will somehow seep into your mental vault. One of the most effective ways of learning for an exam, though, is to test yourself repeatedly, which may be simpler to apply to your studies than other, more intricate methods, such as the formal mnemonic techniques used by expert memorisers (see "Secrets of a memory champion").
It's important to pace yourself, too, by revisiting material rather than cramming it all in during a single session. When doing so, you should make the most ofsweet spots in the timing of your revision. If you are studying for an exam in a week's time, for instance, you will remember more if you leave a day or sobetween your first and second passes through the material. For a test in six months, revision should come about a month into your studies.
2. Limber up
Besides keeping your body - and therefore your grey matter - in generally good shape, a bit of exercise can offer immediate benefits for anyone trying to learn new material. In one study, students taking a 10-minute walk found it much easier to learn a list of 30 nouns, compared with those who sat around, perhaps because it helped increase mental alertness.
Short, intense bursts of exercise may be the most effective. In a recent experiment, participants learning new vocabulary performed better if their studies came after two 3-minute runs, as opposed to a 40-minute gentle jog. The exercise seemed to encourage the release of neurotransmitters involved in forming new connections between brain cells.
3. Make a gesture
There are also more leisurely ways to engage your body during learning, as the brain seems to find it easier to learn abstract concepts if they can be related to simple physical sensations. As a result, various experiments have shown that acting out an idea with relevant hand gestures can improve later recall, whether you are studying new vocabulary of a foreign language or memorising the rules of physics.
It may sound dubious, but even simple eye movements might help. Andrew Parker and Neil Dagnall at Manchester Metropolitan University, UK, have foundthat subjects were better able to remember a list of words they had just studied if they repeatedly looked from left to right and back for 30 seconds straight after reading the list - perhaps because it boosts the transfer of information between the two brain hemispheres. It's worth noting, however, that this only seems to benefit right-handers. Perhaps the brains of left-handed and ambidextrous people already engage in a higher level of cross-talk, and the eye-wiggling only distracts them.
4. Engage your nose
Often it's not just facts that we would like to remember, but whole events from our past as we reminisce about the good ol' days. Such nostalgia is not just an indulgence - it has been linked to a raft of benefits, such as helping us to combat loneliness and feelings of angst. If you have trouble immersing yourself in your past, you could borrow a trick from Andy Warhol. He used to keep a well organised library of perfumes, each associated with a specific period of his life. Sniffing each bottle reportedly brought back a flood of memories from that time - giving him useful reminders whenever he wanted to reminisce. Warhol's approach finds support in a s
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