Chapter 17. Learning and Memory
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By LUKE DITTRICH ‘Can you tell me who the president of the United States is at the moment?” A man and a woman sat in an office in the Clinical Research Center at the Massachusetts Institute of Technology. It was 1986, and the man, Henry Molaison, was about to turn 60. He was wearing sweatpants and a checkered shirt and had thick glasses and thick hair. He pondered the question for a moment. “No,” he said. “I can’t.” The woman, Jenni Ogden, was a visiting postdoctoral research fellow from the University of Auckland, in New Zealand. One of the greatest thrills of her time at M.I.T. was the chance to have sit-down sessions with Henry. In her field — neuropsychology — he was a legendary figure, something between a rock star and a saint. “Who’s the last president you remember?” “I don’t. ... ” He paused for a second, mulling over the question. He had a soft, tentative voice, a warm New England accent. “Ike,” he said finally. Dwight D. Eisenhower’s inauguration took place in 1953. Our world had spun around the sun more than 30 times since, though Henry’s world had stayed still, frozen in orbit. This is because 1953 was the year he received an experimental operation, one that destroyed most of several deep-seated structures in his brain, including his hippocampus, his amygdala and his entorhinal cortex. The operation, performed on both sides of his brain and intended to treat Henry’s epilepsy, rendered him profoundly amnesiac, unable to hold on to the present moment for more than 30 seconds or so. That outcome, devastating to Henry, was a boon to science: By 1986, Patient H.M. — as he was called in countless journal articles and textbooks — had become arguably the most important human research subject of all time, revolutionizing our understanding of how memory works. © 2016 The New York Times Company
Keyword: Learning & Memory
Link ID: 22519 - Posted: 08.04.2016
by Helen Thompson Pinky and The Brain's smarts might not be so far-fetched. Some mice are quicker on the uptake than others. While it might not lead to world domination, wits have their upside: a better shot at staying alive. Biologists Audrey Maille and Carsten Schradin of the University of Strasbourg in France tested reaction time and spatial memory in 90 African striped mice (Rhabdomys pumilio) over the course of a summer. For this particular wild rodent, surviving harsh summer droughts means making it to mating season in the early fall. The team saw some overall trends: Females were more likely to survive if they had quick reflexes, and males were more likely to survive if they had good spatial memory. Cognitive traits like reacting quickly and remembering the best places to hide are key to eluding predators during these tough times but may come with trade-offs for males and females. The results show that an individual mouse’s cognitive strengths are linked to its survival odds, suggesting that the pressure to survive can shape basic cognition, Maille and Schradin write August 3 in Biology Letters. |© Society for Science & the Public 2000 - 2016
Meghan Rosen Exercise may not erase old memories, as some studies in animals have previously suggested. Running on an exercise wheel doesn’t make rats forgetprevious trips through an underwater maze, Ashok Shetty and colleagues report August 2 in the Journal of Neuroscience. Exercise or not, four weeks after learning how to find a hidden platform, rats seem to remember the location just fine, the team found. The results conflict with two earlier papers that show that running triggers memory loss in some rodents by boosting the birth of new brain cells. Making new brain cells rejiggers memory circuits, and that can make it hard for animals to remember what they’ve learned, says Paul Frankland, a neuroscientist at the Hospital for Sick Children in Toronto. He has reported this phenomenon in mice, guinea pigs and degus (SN: 6/14/14, p. 7). Maybe rats are the exception, he says, “but I’m not convinced.” In 2014, Frankland and colleagues reported that brain cell genesis clears out fearful memories in three different kinds of rodents. Two years later, Frankland’s team found similar results with spatial memories. After exercising, mice had trouble remembering the location of a hidden platform in a water maze, the team reported in February in Nature Communications. Again, Frankland and colleagues pinned the memory wipeout on brain cell creation — like a chalkboard eraser that brushes away old information. The wipe seemed to clear the way for new memories to form. Shetty, a neuroscientist at Texas A&M Health Science Center in Temple, wondered if the results held true in rats, too. “Rats are quite different from mice,” he says. “Their biology is similar to humans.” |© Society for Science & the Public 2000 - 2016. All rights reserved.
Keyword: Learning & Memory
Link ID: 22510 - Posted: 08.03.2016
By Bahar Gholipour After reflexively reaching out to grab a hot pan falling from the stove, you may be able to withdraw your hand at the very last moment to avoid getting burned. That is because the brain's executive control can step in to break a chain of automatic commands. Several new lines of evidence suggest that the same may be true when it comes to the reflex of recollection—and that the brain can halt the spontaneous retrieval of potentially painful memories. Within the brain, memories sit in a web of interconnected information. As a result, one memory can trigger another, making it bubble up to the surface without any conscious effort. “When you get a reminder, the mind's automatic response is to do you a favor by trying to deliver the thing that's associated with it,” says Michael Anderson, a neuroscientist at the University of Cambridge. “But sometimes we are reminded of things we would rather not think about.” Humans are not helpless against this process, however. Previous imaging studies suggest that the brain's frontal areas can dampen the activity of the hippocampus, a crucial structure for memory, and therefore suppress retrieval. In an effort to learn more, Anderson and his colleagues recently investigated what happens after the hippocampus is suppressed. They asked 381 college students to learn pairs of loosely related words. Later, the students were shown one word and asked to recall the other—or to do the opposite and to actively not think about the other word. Sometimes between these tasks they were shown unusual images, such as a peacock standing in a parking lot. © 2016 Scientific American
Keyword: Learning & Memory
Link ID: 22500 - Posted: 08.01.2016
By Richard Kemeny Sleep is essential for memory. Mounting evidence continues to support the notion that the nocturnal brain replays, stabilizes, reorganizes, and strengthens memories while the body is at rest. Recently, one particular facet of this process has piqued the interest of a growing group of neuroscientists: sleep spindles. For years these brief bursts of brain activity have been largely ignored. Now it seems that examining these neuronal pulses could help researchers better understand—perhaps even treat—cognitive impairments. Sleep spindles are a defining characteristic of stage 2 non-rapid eye movement (NREM) sleep. These electrical bursts between 10-16 Hz last only around a second, and are known to occur in the human brain thousands of times per night. Generated by a thin net of neurons enveloping the thalamus, spindles appear across several regions of the brain, and are thought to perform various functions, including maintaining sleep in the face of disturbances in the environment. It appears they are also a fundamental part of the process by which the human brain consolidates memories during sleep. A memory formed during the day is stored temporarily in the hippocampus, before being spontaneously replayed during the night. Information about the memory is distributed out and integrated into the neocortex through an orchestra of slow-waves, spindles, and rapid hippocampal ripples. Spindles, it seems, could be a guiding force—providing the plasticity and coordination needed for this delicate, interregional transfer of information. © 1986-2016 The Scientist
By Gretchen Reynolds Learning requires more than the acquisition of unfamiliar knowledge; that new information or know-how, if it’s to be more than ephemeral, must be consolidated and securely stored in long-term memory. Mental repetition is one way to do that, of course. But mounting scientific evidence suggests that what we do physically also plays an important role in this process. Sleep, for instance, reinforces memory. And recent experiments show that when mice and rats jog on running wheels after acquiring a new skill, they learn much better than sedentary rodents do. Exercise seems to increase the production of biochemicals in the body and brain related to mental function. Researchers at the Donders Institute for Brain, Cognition and Behavior at Radboud University in the Netherlands and the University of Edinburgh have begun to explore this connection. For a study published this month in Current Biology, 72 healthy adult men and women spent about 40 minutes undergoing a standard test of visual and spatial learning. They observed pictures on a computer screen and then were asked to remember their locations. Afterward, the subjects all watched nature documentaries. Two-thirds of them also exercised: Half were first put through interval training on exercise bicycles for 35 minutes immediately after completing the test; the others did the same workout four hours after the test. Two days later, everyone returned to the lab and repeated the original computerized test while an M.R.I. machine scanned their brain activity. Those who exercised four hours after the test recognized and recreated the picture locations most accurately. Their brain activity was subtly different, too, showing a more consistent pattern of neural activity. The study’s authors suggest that their brains might have been functioning more efficiently because they had learned the patterns so fully. But why delaying exercise for four hours was more effective than an immediate workout remains mysterious. By contrast, rodents do better in many experiments if they work out right after learning. © 2016 The New York Times Company
Keyword: Learning & Memory
Link ID: 22486 - Posted: 07.28.2016
By Sharon Begley, STAT For the first time ever, researchers have managed to reduce people’s risk for dementia — not through a medicine, special diet, or exercise, but by having healthy older adults play a computer-based brain-training game. The training nearly halved the incidence of Alzheimer’s disease and other devastating forms of cognitive and memory loss in older adults a decade after they completed it, scientists reported on Sunday. If the surprising finding holds up, the intervention would be the first of any kind — including drugs, diet, and exercise — to do that. “I think these results are highly, highly promising,” said George Rebok of the Johns Hopkins Bloomberg School of Public Health, an expert on cognitive aging who was not involved in the study. “It’s exciting that this intervention pays dividends so far down the line.” The results, presented at the Alzheimer’s Association International Conference in Toronto, come from the government-funded ACTIVE (Advanced Cognitive Training for Independent and Vital Elderly) study. Starting in 1998, ACTIVE’s 2,832 healthy older adults (average age at the start: 74) received one of three forms of cognitive training, or none, and were evaluated periodically in the years after. In actual numbers, 14 percent of ACTIVE participants who received no training had dementia 10 years later, said psychologist Jerri Edwards of the University of South Florida, who led the study. Among those who completed up to 10 60-to-75-minute sessions of computer-based training in speed-of-processing — basically, how quickly and accurately they can pay attention to, process, and remember brief images on a computer screen — 12.1 percent developed dementia. Of those who completed all 10 initial training sessions plus four booster sessions a few years later, 8.2 percent developed dementia. © 2016 Scientific American
By Tim Page When I returned to California, I brought my diaries into the back yard every afternoon and read them through sequentially, with the hope of learning more about the years before my brain injury. I remembered much of what I’d done professionally, and whatever additional information I needed could usually be found on my constantly vandalized Wikipedia page. Here was the story of an awkward, imperious child prodigy who made his own films and became famous much too early; a music explainer who won a Pulitzer Prize; a driven and obsessive loner whose fascinations led to collaborations with Glenn Gould, Philip Glass and Thomas Pynchon. In 2000, at age 45, I was diagnosed with Asperger’s syndrome. In retrospect, the only surprise is that it took so long. But the diaries offered a more intimate view. Reading them was slow going, and I felt as though my nose was pressed up against the windowpane of my own life. The shaggy-dog accretion of material — phone numbers, long-ago concert dates, coded references to secret loves — all seemed to belong to somebody else. My last clear memory was of a muggy, quiet Sunday morning in July, three months earlier, as I waited for a train in New London, Conn. It was 11:13 a.m., and the train was due to arrive two minutes later. I was contented, proud of my punctuality and expecting an easy ride to New York in the designated “quiet car,” with just enough time to finish whatever book I was carrying. There would be dinner in Midtown with a magical friend, followed by overnight family visits in Baltimore and Washington, and then a flight back to Los Angeles and the University of Southern California, at which point a sabbatical semester would be at an end.
By Tanya Lewis Scientists have made significant progress toward understanding how individual memories are formed, but less is known about how multiple memories interact. Researchers from the Hospital for Sick Children in Toronto and colleagues studied how memories are encoded in the amygdalas of mice. Memories formed within six hours of each other activate the same population of neurons, whereas distinct sets of brain cells encode memories formed farther apart, in a process whereby neurons compete with their neighbors, according to the team’s study, published today (July 21) in Science. “Some memories naturally go together,” study coauthor Sheena Josselyn of the Hospital for Sick Children told The Scientist. For example, you may remember walking down the aisle at your wedding ceremony and, later, your friend having a bit too much to drink at the reception. “We’re wondering about how these memories become linked in your mind,” Josselyn said. When the brain forms a memory, a group of neurons called an “engram” stores that information. Neurons in the lateral amygdala—a brain region involved in memory of fearful events—are thought to compete with one another to form an engram. Cells that are more excitable or have higher expression of the transcription factor CREB—which is critical for the formation of long-term memories—at the time the memory is being formed will “win” this competition and become part of a memory. © 1986-2016 The Scientist
Keyword: Learning & Memory
Link ID: 22467 - Posted: 07.23.2016
By TRIP GABRIEL DO you remember June 27, 2015? If you knew you had been on a sailboat, and that the weather was miserable, and that afterward you had a beer with the other sailors, would you expect to recall — even one year later — at least a few details? I was on that boat, on a blustery Saturday on Long Island Sound. But every detail is missing from my memory, as if snipped out by an overzealous movie editor. The earliest moment I recall from the day is lying in an industrial tube with a kind of upturned colander over my face, fighting waves of claustrophobia. My mind was densely fogged, but I understood that I was in an M.R.I. machine. Someone was scanning my brain. Other hazy scenes followed: being wheeled into a hospital room. My wife, Alice, hovering in the background. A wall clock that read minutes to midnight, an astonishing piece of information. What had happened to the day? Late that night, alone in the room, I noticed two yellow Post-its on the bedside table in Alice’s writing: “You have a condition called transient global amnesia. It will last Hours not DAYS. You’re going to be fine. Your CT scan was clear. You sailed today and drove yourself home,” the note read in part. I had never heard of transient global amnesia, a rare condition in which you are suddenly unable to recall recent events. Its causes are unknown. Unlike other triggers of memory loss, like a stroke or epileptic seizures, the condition is considered harmless, and an episode does not last long. “We don’t understand why it happens,” a neurologist would later tell me. “There are a million theories.” © 2016 The New York Times Company
Keyword: Learning & Memory
Link ID: 22456 - Posted: 07.19.2016
Helen Haste The American psychologist and educationist Jerome Bruner, who has died aged 100, repeatedly challenged orthodoxies and generated novel directions. His elegant, accessible writing reached wide audiences. His colleague Rom Harré described his lectures as inspiring: “He darted all over the place, one topic suggested another and so on through a thrilling zigzag.” To the charge that he was always asking impossible questions, Jerry replied: “They are pretty much impossible, but the search for the impossible is part of what intelligence is about.” He was willing to engage with controversy, both on academic issues and in education politics. Blind at birth because of cataracts, Jerry gained his sight after surgery at the age of two. He credited this for his sense that we actively interpret and organise our world rather than passively react to it – a theme that he continued to develop in different ways. His first work lay in perception, when he resumed research at Harvard after the second world war. He found that children’s judgments of the size of coins and coin-like disks varied: poorer children overestimated the size of the coins. This contributed to the emerging “new look” movement in psychology, involving values, intentions and interpretation in contrast to the then dominant behaviourist focus on passive learning, reward and punishment. His professorship at Harvard came in 1952, and by the middle of the decade a computer metaphor began to influence psychology – the “cognitive revolution”. With Jacqueline Goodnow and George Austin, Jerry published A Study of Thinking (1956). © 2016 Guardian News and Media Limited
By Andy Coghlan There once was a brainy duckling. It could remember whether shapes or colours it saw just after hatching were the same as or different to each other. The feat surprised the researchers, who were initially sceptical about whether the ducklings could grasp such complex concepts as “same” and “different”. The fact that they could suggests the ability to think in an abstract way may be far more common in nature than expected, and not just restricted to humans and a handful of animals with big brains. “We were completely surprised,” says Alex Kacelnik at the University of Oxford, who conducted the experiment along with his colleague Antone Martinho III. Kacelnik and Martinho reasoned that ducklings might be able to grasp patterns relating to shape or colour as part of the array of sensory information they absorb soon after hatching. Doing so would allow them to recognise their mothers and siblings and distinguish them from all others – abilities vital for survival. In ducklings, goslings and other species that depend for survival on following their mothers, newborns learn quickly – a process called filial imprinting. Kacelnik wondered whether this would enable them to be tricked soon after hatching into “following” objects or colours instead of their natural mother, and recognising those same patterns in future. © Copyright Reed Business Information Ltd.
By Tanya Lewis In recent years, research on mammalian navigation has focused on the role of the hippocampus, a banana-shaped structure known to be integral to episodic memory and spatial information processing. The hippocampus’s primary output, a region called CA1, is known to be divided into superficial and deep layers. Now, using two-photon imaging in mice, researchers at Columbia University in New York have found these layers have distinct functions: superficial-layer neurons encode more-stable maps, whereas deep-layer brain cells better represent goal-oriented navigation, according to a study published last week (July 7) in Neuron. “There are lots of catalogued differences in sublayers of pyramidal cells” within the hippocampus, study coauthor Nathan Danielson of Columbia told The Scientist. “The question is, are the principle cells in each subregion doing the same thing? Or is there a finer level of granularity?” For that past few decades, scientists have been chipping away at an explanation of the brain’s “inner GPS.” The 2014 Nobel Prize in Physiology or Medicine honored the discovery of so-called place cells and grid cells in the hippocampus, which keep track of an individual’s location and coordinates in space, respectively. Since then, studies have revealed that neurons in different hippocampal regions have distinct genetic, anatomical, and physiological properties, said Attila Losonczy of Columbia, Danielson’s graduate advisor and a coauthor on the study. © 1986-2016 The Scientist
Keyword: Learning & Memory
Link ID: 22437 - Posted: 07.14.2016
Not much is definitively proven about consciousness, the awareness of one’s existence and surroundings, other than that it’s somehow linked to the brain. But theories as to how, exactly, grey matter generates consciousness are challenged when a fully-conscious man is found to be missing most of his brain. Several years ago, a 44-year-old Frenchman went to the hospital complaining of mild weakness in his left leg. It was discovered then that his skull was filled largely by fluid, leaving just a thin perimeter of actual brain tissue. And yet the man was a married father of two and a civil servant with an IQ of 75, below-average in his intelligence but not mentally disabled. Doctors believe the man’s brain slowly eroded over 30 years due to a build up of fluid in the brain’s ventricles, a condition known as “hydrocephalus.” His hydrocephalus was treated with a shunt, which drains the fluid into the bloodstream, when he was an infant. But it was removed when he was 14 years old. Over the following decades, the fluid accumulated, leaving less and less space for his brain. While this may seem medically miraculous, it also poses a major challenge for cognitive psychologists, says Axel Cleeremans of the Université Libre de Bruxelles.
By Gretchen Reynolds To strengthen your mind, you may first want to exert your leg muscles, according to a sophisticated new experiment involving people, mice and monkeys. The study’s results suggest that long-term endurance exercise such as running can alter muscles in ways that then jump-start changes in the brain, helping to fortify learning and memory. I often have written about the benefits of exercise for the brain and, in particular, how, when lab rodents or other animals exercise, they create extra neurons in their brains, a process known as neurogenesis. These new cells then cluster in portions of the brain critical for thinking and recollection. Even more telling, other experiments have found that animals living in cages enlivened with colored toys, flavored varieties of water and other enrichments wind up showing greater neurogenesis than animals in drab, standard cages. But animals given access to running wheels, even if they don’t also have all of the toys and other party-cage extras, develop the most new brain cells of all. These experiments strongly suggest that while mental stimulation is important for brain health, physical stimulation is even more potent. But so far scientists have not teased out precisely how physical movement remakes the brain, although all agree that the process is bogglingly complex. Fascinated by that complexity, researchers at the National Institutes of Health recently began to wonder whether some of the necessary steps might be taking place far from the brain itself, and specifically, in the muscles, which are the body part most affected by exercise. Working muscles contract, burn fuel and pump out a wide variety of proteins and other substances. The N.I.H. researchers suspected that some of those substances migrated from the muscles into the bloodstream and then to the brain, where they most likely contributed to brain health. © 2016 The New York Times Company
Keyword: Learning & Memory
Link ID: 22429 - Posted: 07.13.2016
By Clare Wilson It is one of life’s great enigmas: why do we sleep? Now we have the best evidence yet of what sleep is for – allowing housekeeping processes to take place that stop our brains becoming overloaded with new memories. All animals studied so far have been found to sleep, but the reason for their slumber has eluded us. When lab rats are deprived of sleep, they die within a month, and when people go for a few days without sleeping, they start to hallucinate and may have epileptic seizures. One idea is that sleep helps us consolidate new memories, as people do better in tests if they get a chance to sleep after learning. We know that, while awake, fresh memories are recorded by reinforcing connections between brain cells, but the memory processes that take place while we sleep have remained unclear. Support is growing for a theory that sleep evolved so that connections in the brain can be pruned down during slumber, making room for fresh memories to form the next day. “Sleep is the price we pay for learning,” says Giulio Tononi of the University of Wisconsin-Madison, who developed the idea. Now we have the most direct evidence yet that he’s right. Tononi’s team measured the size of these connections or synapses in brain slices taken from mice. The synapses in samples taken at the end of a period of sleep were 18 per cent smaller than those in samples taken from before sleep, showing that the synapses between neurons are weakened during slumber. © Copyright Reed Business Information Ltd.
By Andy Coghlan It could be that romantic restaurant, or your favourite park bench. A specific part of the brain seems to be responsible for learning and remembering the precise locations of places that are special to us, research in mice has shown for the first time. Place cells are neurons that help us map our surroundings, and both mice and humans have such cells in the hippocampus – a brain region vital for learning, memory and navigation. Nathan Danielson at Columbia University in New York and his colleagues focused on a part of the hippocampus that feeds signals to the rest of the brain, called CA1. They found that in mice, the CA1 layer where general environment maps are learned and stored is different to the one for locations that have an important meaning. Treadmill test They discovered this by recording brain activity in the two distinct layers of CA1, using mice placed on a treadmill. The treadmill rotated between six distinctive surface materials – including silky ribbons, green pom-pom fabric and silver glitter masking tape. At all times, the mice were able to lick a sensor to try to trigger the release of drinking water. During the first phase of the experiment, however, the sensor only worked at random times. The mice formed generalised maps of their experience on the multi-surfaced treadmill, and the team found that these were stored in the superficial layer of CA1. © Copyright Reed Business Information Ltd.
Keyword: Learning & Memory
Link ID: 22414 - Posted: 07.09.2016
By Louise Whiteley It’s an appealing idea: the notion that understanding the learning brain will tell us how to maximise children’s potential, bypassing the knotty complexities of education research. But promises to replace sociological complexity with biological certainty should always be treated with caution. Hilary and Steven Rose are deeply sceptical of claims that neuroscience can inform education and early intervention policy, and deeply concerned about the use of such claims to support neoliberal agendas. They argue that focusing on the brain encourages a focus on the individual divorced from their social context, and that this is easily aligned with a view of poor achievement as a personal moral failing, rather than a practical consequence of poverty and inequality. Whether or not you end up cheerleading for the book’s political agenda, its deconstruction of faulty claims about how neuroscience translates into the classroom is relevant to anyone interested in education. The authors tear apart the scientific logic of policy documents, interrogate brain-based interventions and dismantle prevalent neuro-myths. One of the book’s meatiest chapters deals with government reports advocating early intervention to increase “mental capital”, and thus reduce the future economic burden of deprived, underachieving brains. As we discover, the neuroscientific foundations of these reports are shaky. For instance, they tend to assume that the more synaptic connections between brain cells the better, and that poor environment in a critical early period permanently reduces the number of synapses. This makes early intervention focusing on the individual child and “poor parenting” seem like the obvious solution. But pruning of synapses is just as important to brain development, and learning involves the continual forming and reforming of synaptic connections. More is not necessarily better. And while an initial explosion in synapses can be irreversibly disrupted by extreme neglect, the evidence just isn’t there yet for extrapolating this to the more common kinds of childhood deprivation that such reports address.
Laura Sanders Feeling good may help the body fight germs, experiments on mice suggest. When activated, nerve cells that help signal reward also boost the mice’s immune systems, scientists report July 4 in Nature Medicine. The study links positive feelings to a supercharged immune system, results that may partially explain the placebo effect. Scientists artificially dialed up the activity of nerve cells in the ventral tegmental area — a part of the brain thought to help dole out rewarding feelings. This activation had a big effect on the mice’s immune systems, Tamar Ben-Shaanan of Technion-Israel Institute of Technology in Haifa and colleagues found. A day after the nerve cells in the ventral tegmental area were activated, mice were infected with E. coli bacteria. Later tests revealed that mice with artificially activated nerve cells had less E. coli in their bodies than mice without the nerve cell activation. Certain immune cells seemed to be ramped up, too. Monocytes and macrophages were more powerful E. coli killers after the nerve cell activation. If a similar effect is found in people, the results may offer a biological explanation for how positive thinking can influence health. |© Society for Science & the Public 2000 - 2016
Jon Hamilton Researchers have identified a substance in muscles that helps explain the connection between a fit body and a sharp mind. When muscles work, they release a protein that appears to generate new cells and connections in a part of the brain that is critical to memory, a team reports Thursday in the journal Cell Metabolism. The finding "provides another piece to the puzzle," says Henriette van Praag, an author of the study and an investigator in brain science at the National Institute on Aging. Previous research, she says, had revealed factors in the brain itself that responded to exercise. The discovery came after van Praag and a team of researchers decided to "cast a wide net" in searching for factors that could explain the well-known link between fitness and memory. They began by looking for substances produced by muscle cells in response to exercise. That search turned up cathepsin B, a protein best known for its association with cell death and some diseases. Experiments showed that blood levels of cathepsin B rose in mice that spent a lot of time on their exercise wheels. What's more, as levels of the protein rose, the mice did better on a memory test in which they had to swim to a platform hidden just beneath the surface of a small pool. The team also found evidence that, in mice, cathepsin B was causing the growth of new cells and connections in the hippocampus, an area of the brain that is central to memory. But the researchers needed to know whether the substance worked the same way in other species. So they tested monkeys, and found that exercise did, indeed, raise circulating levels of cathepsin in the blood. © 2016 npr