Chapter 17. Learning and Memory
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By JOHN ROGERS LOS ANGELES (AP) — The founder of a Los Angeles-based nonprofit that provides free music lessons to low-income students from gang-ridden neighborhoods began to notice several years ago a hopeful sign: Kids were graduating high school and heading off to UCLA, Tulane and other big universities. That’s when Margaret Martin asked how the children in the Harmony Project were beating the odds. Researchers at Northwestern University in Illinois believe that the students’ music training played a role in their educational achievement, helping as Martin noticed 90 percent of them graduate from high school while 50 percent or more didn’t from those same neighborhoods. A two-year study of 44 children in the program shows that the training changes the brain in ways that make it easier for youngsters to process sounds, according to results reported in Tuesday’s edition of The Journal of Neuroscience. That increased ability, the researchers say, is linked directly to improved skills in such subjects as reading and speech. But, there is one catch: People have to actually play an instrument to get smarter. They can’t just crank up the tunes on their iPod. Nina Kraus, the study’s lead researcher and director of Northwestern’s auditory neuroscience laboratory, compared the difference to that of building up one’s body through exercise. ‘‘I like to say to people: You’re not going to get physically fit just watching sports,’’ she said.
Memory can be boosted by using a magnetic field to stimulate part of the brain, a study has shown. The effect lasts at least 24 hours after the stimulation is given, improving the ability of volunteers to remember words linked to photos of faces. Scientists believe the discovery could lead to new treatments for loss of memory function caused by ageing, strokes, head injuries and early Alzheimer's disease. Dr Joel Voss, from Northwestern University in Chicago, said: "We show for the first time that you can specifically change memory functions of the brain in adults without surgery or drugs, which have not proven effective. "This non-invasive stimulation improves the ability to learn new things. It has tremendous potential for treating memory disorders." The scientists focused on associative memory, the ability to learn and remember relationships between unrelated items. An example of associative memory would be linking someone to a particular restaurant where you both once dined. It involves a network of different brain regions working in concert with a key memory structure called the hippocampus, which has been compared to an "orchestra conductor" directing brain activity. Stimulating the hippocampus caused the "musicians" – the brain regions – to "play" more in time, thereby tightening up their performance. A total of 16 volunteers aged 21-40 took part in the study, agreeing to undergo 20 minutes of transcranial magnetic stimulation (TMS) every day for five days. © 2014 Guardian News and Media Limited
Keyword: Learning & Memory
Link ID: 20015 - Posted: 08.30.2014
by Michael Slezak It's odourless, colourless, tasteless and mostly non-reactive – but it may help you forget. Xenon gas has been shown to erase fearful memories in mice, raising the possibility that it could be used to treat post-traumatic stress disorder (PTSD) if the results are replicated in a human trial next year. The method exploits a neurological process known as "reconsolidation". When memories are recalled, they seem to get re-encoded, almost like a new memory. When this process is taking place, the memories become malleable and can be subtly altered. This new research suggests that at least in mice, the reconsolidation process might be partially blocked by xenon, essentially erasing fearful memories. Among other things, xenon is used as an anaesthetic. Frozen in fear Edward Meloni and his colleagues at Harvard Medical School in Boston trained mice to be afraid of a sound by placing them in a cage and giving them an electric shock after the sound was played. Thereafter, if the mice heard the noise, they would become frightened and freeze. Later, the team played the sound and then gave the mice either a low dose of xenon gas for an hour or just exposed them to normal air. Mice that were exposed to xenon froze for less time in response to the sound than the other mice. © Copyright Reed Business Information Ltd.
Keyword: Learning & Memory
Link ID: 20014 - Posted: 08.30.2014
By PAM BELLUCK Memories and the feelings associated with them are not set in stone. You may have happy memories about your family’s annual ski vacation, but if you see a tragic accident on the slopes, those feelings may change. You might even be afraid to ski that mountain again. Now, using a technique in which light is used to switch neurons on and off, neuroscientists at the Massachusetts Institute of Technology appear to have unlocked some secrets about how the brain attaches emotions to memories and how those emotions can be adjusted. Their research, published Wednesday in the journal Nature, was conducted on mice, not humans, so the findings cannot immediately be translated to the treatment of patients. But experts said the experiments may eventually lead to more effective therapies for people with psychological problems such as depression, anxiety or post-traumatic stress disorder. “Imagine you can go in and find a particular traumatic memory and turn it off or change it somehow,” said David Moorman, an assistant professor of psychological and brain sciences at the University of Massachusetts Amherst, who was not involved in the research. “That’s still science fiction, but with this we’re getting a lot closer to it.” The M.I.T. scientists labeled neurons in the brains of mice with a light-sensitive protein and used pulses of light to switch the cells on and off, a technique called optogenetics. Then they identified patterns of neurons activated when mice created a negative memory or a positive one. A negative memory formed when mice received a mild electric shock to their feet; a positive one was formed when the mice, all male, were allowed to spend time with female mice. © 2014 The New York Times Company
by Penny Sarchet Memory is a fickle beast. A bad experience can turn a once-loved coffee shop or holiday destination into a place to be avoided. Now experiments in mice have shown how such associations can be reversed. When forming a memory of a place, the details of the location and the associated emotions are encoded in different regions of the brain. Memories of the place are formed in the hippocampus, whereas positive or negative associations are encoded in the amygdala. In experiments with mice in 2012, a group led by Susumo Tonegawa of the Massachusetts Institute of Technology managed to trigger the fear part of a memory associated with a location when the animals were in a different location. They used a technique known as optogenetics, which involves genetically engineering mice so that their brains produce a light-sensitive protein in response to a certain cue. In this case, the cue was the formation of the location memory. This meant the team could make the mouse recall the location just by flashing pulses of light down an optical fibre embedded in the skull. The mice were given electric shocks while their memories of the place were was being formed, so that the animals learned to associate that location with pain. Once trained, the mice were put in a new place and a pulse of light was flashed into their brains. This activated the neurons associated with the original location memory and the mice froze, terrified of a shock, demonstrating that the emotion associated with the original location could be induced by reactivating the memory of the place. © Copyright Reed Business Information Ltd.
Learning is easier when it only requires nerve cells to rearrange existing patterns of activity than when the nerve cells have to generate new patterns, a study of monkeys has found. The scientists explored the brain’s capacity to learn through recordings of electrical activity of brain cell networks. The study was partly funded by the National Institutes of Health. “We looked into the brain and may have seen why it’s so hard to think outside the box,” said Aaron Batista, Ph.D., an assistant professor at the University of Pittsburgh and a senior author of the study published in Nature, with Byron Yu, Ph.D., assistant professor at Carnegie Mellon University, Pittsburgh. The human brain contains nearly 86 billion neurons, which communicate through intricate networks of connections. Understanding how they work together during learning can be challenging. Dr. Batista and his colleagues combined two innovative technologies, brain-computer interfaces and machine learning, to study patterns of activity among neurons in monkey brains as the animals learned to use their thoughts to move a computer cursor. “This is a fundamental advance in understanding the neurobiological patterns that underlie the learning process,” said Theresa Cruz, Ph.D., a program official at the National Center for Medical Rehabilitations Research at NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). “The findings may eventually lead to new treatments for stroke as well as other neurological disorders.”
|By Michael Leon I had been working quite happily on the basic biology of the brain when a good friend of mine called for advice about his daughter, who had just been diagnosed with autism. I could hear the anguish and fear in his voice when he asked me whether there was anything that could be done to make her better. I told him about the standard-care therapies, including Intensive Behavioral Intervention, Early Intensive Behavioral Intervention, Applied Behavior Analysis, and the Early Start Denver Model (ESDM). These therapies also are expensive, time-consuming and have variable outcomes, with the best outcomes seen for ESDM. There are, however, few ESDM therapists, and the cost of such intensive therapy can be quite high. Moreover, my friend’s daughter was already past the age of the oldest children in the study that demonstrated the efficacy of ESDM. My feeling was that there was a good chance that there was an effective therapy for her using a simple, inexpensive at-home approach involving daily exposure to a wide variety of sensory stimulation. This is a partial list of the disorders whose symptoms can be greatly reduced, or even completely reversed, with what is known as “environmental enrichment”: Autism Stroke Seizures Brain damage Neuronal death during aging ADHD Prenatal alcohol syndrome Lead exposure Multiple sclerosis Addiction Schizophrenia Memory loss Huntington’s disease Parkinson’s disease Alzheimer’s disease Down syndrome Depression But why haven’t you heard about this? The reason is that all of these disorders that have been successfully treated only in animal models of these neurological problems. However, the effects seen in lab animals can be dramatic. © 2014 Scientific American,
|By Roni Jacobson Children are notoriously unreliable witnesses. Conventional wisdom holds that they frequently “remember” things that never happened. Yet a large body of research indicates that adults actually generate more false memories than children. Now a new study finds that children are just as susceptible to false memories as adults, if not more so. Scientists may simply have been using the wrong test. Traditionally, researchers have explored false memories by presenting test subjects with a list of associated words (for instance, “weep,” “sorrow” and “wet”) thematically related to a word not on the list (in this case, “cry”) and then asking them what words they remember. Adults typically mention the missing related word more often than children do—possibly because their life experiences enable them to draw associations between concepts more readily, says Henry Otgaar, a forensic psychologist at Maastricht University in the Netherlands and co-author of the new paper, published in May in the Journal of Experimental Child Psychology. Instead of using word lists to investigate false memories, Otgaar and his colleagues showed participants pictures of scenes, including a classroom, a funeral and a beach. After a short break, they asked those participants whether they remembered seeing certain objects in each picture. Across three experiments, seven- and eight-year-old children consistently reported seeing more objects that were not in the pictures than adults did. © 2014 Scientific American
|By Jason G. Goldman When you do not know the answer to a question, say, a crossword puzzle hint, you realize your shortcomings and devise a strategy for finding the missing information. The ability to identify the state of your knowledge—thinking about thinking—is known as metacognition. It is hard to tell whether other animals are also capable of metacognition because we cannot ask them; studies of primates and birds have not yet been able to rule out simpler explanations for this complex process. Scientists know, however, that some animals, such as western scrub jays, can plan for the future. Western scrub jays, corvids native to western North America, are a favorite of cognitive scientists because they are not “stuck in time”—that is, they are able to remember past events and are known to cache their food in anticipation of hunger, according to psychologist Arii Watanabe of the University of Cambridge. But the question remained: Are they aware that they are planning? Watanabe devised a way to test them. He let five birds watch two researchers hide food, in this case a wax worm. The first researcher could hide the food in any of four cups lined up in front of him. The second had three covered cups, so he could place the food only in the open one. The trick was that the researchers hid their food at the same time, forcing the birds to choose which one to watch. If the jays were capable of metacognition, Watanabe surmised, the birds should realize that they could easily find the second researcher's food. The wax worm had to be in the singular open cup. They should instead prefer keeping their eyes on the setup with four open cups because witnessing where that food went would prove more useful in the future. And that is exactly what happened: the jays spent more time watching the first researcher. The results appeared in the July issue of the journal © 2014 Scientific American,
by Sarah Zielinski PRINCETON, N.J. — Learning can be a quick shortcut for figuring out how to do something on your own. The ability to learn from watching another individual — called social learning — is something that hasn’t been documented in many species outside of primates and birds. But now a lizard can be added to the list of critters that can learn from one another. Young eastern water skinks were able to learn by watching older lizards, Martin Whiting of Macquarie University in Sydney reported August 10 at the Animal Behavior Society meeting at Princeton University. The eastern water skink, which reaches a length of about 30 centimeters, can be found near streams and waterways in eastern Australia. The lizards live up to eight years, and while they don’t live in groups, they often see each other in the wild. That could provide an opportunity for learning from each other. Whiting and his colleagues worked with 18 mature (older than 5 years) and 18 young (1.5 to 2 years) male skinks in the lab. The lizards were placed in bins with a barrier in the middle that was either opaque or transparent. In the first of two experiments, the skinks were given a yellow-lidded container with a mealworm inside. They had to learn to open the lid to get the food. In that task, skinks that could see a demonstrator through a transparent barrier were no better at opening the lid than those who had to figure it out on their own. After watching a demonstrator lizard (top row), the skink in the other half of the tub was supposed to have learned that a mealworm was beneath the blue lid. The skink in the middle arena, however, failed the task when he opened the white lid first.D.W.A. Noble et al/Biology Letters 2014 © Society for Science & the Public 2000 - 2013.
by Bethany Brookshire Every day sees a new research article on addiction, be it cocaine, heroin, food or porn. Each one takes a specific angle on how addiction works in the brain. Perhaps it’s a disorder of reward, with drugs hijacking a natural system that is meant to respond to food, sex and friendship. Possibly addiction is a disorder of learning, where our brains learn bad habits and responses. Maybe we should think of addiction as a combination of an environmental stimulus and vulnerable genes. Or perhaps it’s an inappropriate response to stress, where bad days trigger a relapse to the cigarette, syringe or bottle. None of these views are wrong. But none of them are complete, either. Addiction is a disorder of reward, a disorder of learning. It has genetic, epigenetic and environmental influences. It is all of that and more. Addiction is a display of the brain’s astounding ability to change — a feature called plasticity — and it showcases what we know and don’t yet know about how brains adapt to all that we throw at them. “A lot of people think addiction is what happens when someone finds a drug to be the most rewarding thing they’ve ever experienced,” says neuroscientist George Koob, director of the National Institute on Alcohol Abuse and Alcoholism in Bethesda, Md. “But drug abuse is not just feeling good about drugs. Your brain is changed when you misuse drugs. It is changed in ways that perpetuate the problem.” The changes associated with drug use affect how addicts respond to drug cues, like the smell of a cigarette or the sight of a shot of vodka. Drug abuse also changes how other rewards, such as money or food are processed, decreasing their relative value. © Society for Science & the Public 2000 - 2013
By DOUGLAS QUENQUA A tiny part of the brain keeps track of painful experiences and helps determine how we will react to them in the future, scientists say. The findings could be a boon to depression treatments. The habenula (pronounced ha-BEN-you-la), a part of the brain less than half the size of a pea, has been shown in animal studies to activate during painful or unpleasant episodes. Using M.R.I.s to produce powerful brain scans, researchers at University College London tracked the habenulas in subjects who were hooked up to electric shock machines. The subjects were presented with a series of photographs, some of which were followed by increasingly strong shocks. Soon, when the subjects were shown pictures associated with shocks, their habenulas would light up. “The habenula seems to track the associations with electric shocks becoming stronger and stronger,” said Jonathan Roiser, a neuroscientist at the college and an author of the study, published in The Proceedings of the National Academy of Sciences. The habenula appeared to have an effect on motivation, too. The subjects had been asked to occasionally press a button, just to show they were awake. They were much slower to do so when their habenula was active. In fact, the more slowly they responded, the more reliably their habenulas tracked associations with shocks. In animals, the habenula has been shown to suppress production of dopamine, a chemical that drives motivation. Perhaps, the researchers say, an overactive habenula can cause the feelings of impending doom and low motivation common in people with depression. © 2014 The New York Times Company
|By Annie Sneed It's easy to recall events of decades past—birthdays, high school graduations, visits to Grandma—yet who can remember being a baby? Researchers have tried for more than a century to identify the cause of “infantile amnesia.” Sigmund Freud blamed it on repression of early sexual experiences, an idea that has been discredited. More recently, researchers have attributed it to a child's lack of self-perception, language or other mental equipment required to encode memories. Neuroscientists Paul Frankland and Sheena Josselyn, both at the Hospital for Sick Children in Toronto, do not think linguistics or a sense of self offers a good explanation, either. It so happens that humans are not the only animals that experience infantile amnesia. Mice and monkeys also forget their early childhood. To account for the similarities, Frankland and Josselyn have another theory: the rapid birth of many new neurons in a young brain blocks access to old memories. In a new experiment, the scientists manipulated the rate at which hippocampal neurons grew in young and adult mice. The hippocampus is the region in the brain that records autobiographical events. The young mice with slowed neuron growth had better long-term memory. Conversely, the older mice with increased rates of neuron formation had memory loss. Based on these results, published in May in the journal Science, Frankland and Josselyn think that rapid neuron growth during early childhood disrupts the brain circuitry that stores old memories, making them inaccessible. Young children also have an underdeveloped prefrontal cortex, another region of the brain that encodes memories, so infantile amnesia may be a combination of these two factors. © 2014 Scientific American
|By Jillian Rose Lim and LiveScience People who don't get enough sleep could be increasing their risk of developing false memories, a new study finds. In the study, when researchers compared the memory of people who'd had a good night's sleep with the memory of those who hadn't slept at all, they found that, under certain conditions, sleep-deprived individuals mix fact with imagination, embellish events and even "remember" things that never actually happened. False memories occur when people's brains distort how they remember a past event — whether it's what they did after work, how a painful relationship ended or what they witnessed at a crime scene. Memory is not an exact recording of past events, said Steven Frenda, a psychology Ph.D. student at the University of California, Irvine, who was involved in the study. Rather, fresh memories are constructed each time people mentally revisit a past event. During this process, people draw from multiple sources — like what they've been told by others, what they've seen in photographs or what they know as stereotypes or expectations, Frenda said. The new findings "have implications for people's everyday lives —recalling information for an exam, or in work contexts, but also for the reliability of eyewitnesses who may have experienced periods of restricted or deprived sleep," said Frenda, who noted that chronic sleep deprivation is on the rise. In a previous study, Frenda and his colleagues observed that people with restricted sleep (less than 5 hours a night) were more likely to incorporate misinformation into their memories of certain photos, and report they had seen video footage of a news event that didn't happen. In the current study, they wanted to see how a complete lack of sleep for 24 hours could influence a person's memory. © 2014 Scientific American
By DOUGLAS QUENQUA Like Pavlov’s dogs, most organisms can learn to associate two events that usually occur together. Now, a team of researchers says they have identified a gene that enables such learning. The scientists, at the University of Tokyo, found that worms could learn to avoid unpleasant situations as long as a specific insulin receptor remained intact. Roundworms were exposed to different concentrations of salt; some received food during the initial exposure, others did not. Later, when exposed to various concentrations of salt again, the roundworms that had been fed during the first stage gravitated toward their initial salt concentrations, while those that had been starved avoided them. But the results changed when the researchers repeated the experiment using worms with a defect in a particular receptor for insulin, a protein crucial to metabolism. Those worms could not learn to avoid the salt concentrations associated with starvation. “We looked for different forms of the receptor and found that a new one, which we named DAF-2c, functions in taste-aversion learning,” said Masahiro Tomioka, a geneticist at the University of Tokyo and an author of the study, which was published in the journal Science. “It turned out that only this form of the receptor can support learning” in roundworms. While human insulin receptors bear some resemblance to those of a roundworm, more study is needed to determine if it plays a similar role in memory and decision-making, Dr. Tomioka said. But studies have suggested a link between insulin levels and Alzheimer’s disease in humans. © 2014 The New York Times Company
By HENRY L. ROEDIGER III TESTS have a bad reputation in education circles these days: They take time, the critics say, put students under pressure and, in the case of standardized testing, crowd out other educational priorities. But the truth is that, used properly, testing as part of an educational routine provides an important tool not just to measure learning, but to promote it. In one study I published with Jeffrey D. Karpicke, a psychologist at Purdue, we assessed how well students remembered material they had read. After an initial reading, students were tested on some passages by being given a blank sheet of paper and asked to recall as much as possible. They recalled about 70 percent of the ideas. Other passages were not tested but were reread, and thus 100 percent of the ideas were re-exposed. In final tests given either two days or a week later, the passages that had been tested just after reading were remembered much better than those that had been reread. What’s at work here? When students are tested, they are required to retrieve knowledge from memory. Much educational activity, such as lectures and textbook readings, is aimed at helping students acquire and store knowledge. Various kinds of testing, though, when used appropriately, encourage students to practice the valuable skill of retrieving and using knowledge. The fact of improved retention after a quiz — called the testing effect or the retrieval practice effect — makes the learning stronger and embeds it more securely in memory. This is vital, because many studies reveal that much of what we learn is quickly forgotten. Thus a central challenge to learning is finding a way to stem forgetting. © 2014 The New York Times Company
Keyword: Learning & Memory
Link ID: 19861 - Posted: 07.21.2014
Emily A. Holmes, Michelle G. Craske & Ann M. Graybiel How does one human talking to another, as occurs in psychological therapy, bring about changes in brain activity and cure or ease mental disorders? We don't really know. We need to. Mental-health conditions, such as post-traumatic stress disorder (PTSD), obsessive–compulsive disorder (OCD), eating disorders, schizophrenia and depression, affect one in four people worldwide. Depression is the third leading contributor to the global burden of disease, according to the World Health Organization. Psychological treatments have been subjected to hundreds of randomized clinical trials and hold the strongest evidence base for addressing many such conditions. These activities, techniques or strategies target behavioural, cognitive, social, emotional or environmental factors to improve mental or physical health or related functioning. Despite the time and effort involved, they are the treatment of choice for most people (see ‘Treating trauma with talk therapy’). For example, eating disorders were previously considered intractable within our life time. They can now be addressed with a specific form of cognitive behavioural therapy (CBT)1 that targets attitudes to body shape and disturbances in eating habits. For depression, CBT can be as effective as antidepressant medication and provide benefits that are longer lasting2. There is also evidence that interpersonal psychotherapy (IPT) is effective for treating depression. Ian was filling his car with petrol and was caught in the cross-fire of an armed robbery. His daughter was severely injured. For the following decade Ian suffered nightmares, intrusive memories, flashbacks of the trauma and was reluctant to drive — symptoms of post-traumatic stress disorder (PTSD). © 2014 Nature Publishing Group,
By Emily Anthes The women that come to see Deane Aikins, a clinical psychologist at Wayne State University, in Detroit, are searching for a way to leave their traumas behind them. Veterans in their late 20s and 30s, they served in Iraq and Afghanistan. Technically, they’d been in non-combat positions, but that didn’t eliminate the dangers of warfare. Mortars and rockets were an ever-present threat on their bases, and they learned to sleep lightly so as not to miss alarms signaling late-night attacks. Some of the women drove convoys of supplies across the desert. It was a job that involved worrying about whether a bump in the road was an improvised explosive device, or if civilians in their path were strategic human roadblocks. On top of all that, some of the women had been sexually assaulted by their military colleagues. After one woman was raped, she helped her drunk assailant sneak back into his barracks because she worried that if they were caught, she’d be disciplined or lose her job. These traumas followed the women home. Today, far from the battlefield, they find themselves struggling with vivid flashbacks and nightmares, tucking their guns under their pillows at night. Some have turned to alcohol to manage their symptoms; others have developed exhausting routines to avoid any people or places that might trigger painful memories and cause them to re-live their experiences in excruciating detail. © 2014 Nautilus,
Fearful memories can be dampened by imagining past traumas in a safe setting. The "extinction" of fear is fragile, however, and surprising or unexpected events can cause fear memories to return. Inactivating brain areas that detect novelty prevents relapse of unwanted fear memories. Traumatic and emotional experiences often lead to debilitating mental health disorders, including post-traumatic stress disorder (PTSD). In the clinic, it is typical to use behavioral therapies such as exposure therapy to help reduce fear in patients suffering from traumatic memories. Using these approaches, patients are asked to remember the circumstances and stimuli surrounding their traumatic memory in a safe setting in order to "extinguish" their fear response to those events. While effective in many cases, the loss of fear and anxiety achieved by these therapies is often short-lived—fear returns or relapses under a variety of conditions. Many years ago, the famous Russian physiologist Ivan Pavlov noted that simply exposing animals to novel or unexpected events could cause extinguished responses (such as salivary responses to sounds) to return. Might exposure to novelty also cause extinguished fear responses to return? In a recent study (Maren, 2014), rats first learned that an innocuous tone predicted an aversive (but mild) electric shock to their feet. The subsequent fear response to the tone was then extinguished by presenting the stimulus to the animals many times without the shock. After the fear response to the tone was reduced with the extinction procedure, they were then presented with the tone in either a new location (a novel test box) or in a familiar location, but in the presence of an unexpected sound (a noise burst). In both cases, fear to the tone returned as Pavlov predicted: the unexpected places and sounds led to a disinhibition of fear—in other words, fear relapsed. © 2014 Publiscize
Obese women may have a "food learning impairment" that could explain their attitude to food, research from Yale School of Medicine suggests. Tests on groups of obese and healthy-weight people found that the obese women performed worst when asked to remember a sequence of food picture cards. Writing in Current Biology, Yale researchers tested 135 men and women. The findings could lead to new ways to tackle obesity, the study says. Study author Ifat Levy, assistant professor at Yale School of Medicine, said the difference in the performance of the obese women compared with the other groups was "really striking" and "significant". The tests looked at an individual's ability to learn and predict the appearance of pictures of food or money on coloured cards. The participants were told they would be given whatever appeared on these "reward" cards. In the first phase, the reward cards always followed a particular coloured card in a sequence. Later, the order was changed and the reward cards appeared following a different coloured card. During this time, participants were asked to predict the likelihood of a reward card appearing as the cards were shown one by one. The results showed that obese women performed worst because they overestimated how often the pictures of food, including pretzels or chocolate, appeared. Even after researchers had accounted for other factors, there was still a large difference in their learning performance. Prof Levy said: "This is not a general learning impairment, as obese women had no problem learning when the reward was money rather than food. BBC © 2014