Chapter 17. Learning and Memory
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By Uri Bram Early-life exposure to pathogenic bacteria can induce a lifelong imprinted olfactory memory in C. elegans through two distinct neural circuits, according to a study published today (February 11) in Cell. Researchers from Rockefeller University in New York City have shown that early-life pathogen exposure leads the nematode to have a lifelong aversion to the specific associated bacterial odors, whereas later-in-life exposure spurs only transient aversion. “This study is very exciting,” said Yun Zhang of Harvard who studies learning in C. elegans but was not involved in the present work. “Imprinting is a form of learning widely observed in many animals [but] finding this in C. elegans is very meaningful because this nematode is genetically tractable, and its small nervous system is well described.” A classic example of imprinting is how geese form attachments to the first moving object they see after birth; Nobel laureate Konrad Lorenz famously showed that the “moving object” could be himself instead of a mother goose. During the critical period at the start of life, animals often have unusual abilities to create and maintain long-term memories. For the present study, Rockefeller’s Xin Jin and colleagues described a form of aversive imprinting in their C. elegans: newly hatched nematodes exposed to Pseudomonas aeruginosa PA14 or toxin-emitting Escherichia coli BL21 established a long-term olfactory aversion to it. Animals that experienced the pathogen immediately after hatching were able to synthesize and maintain the aversive memory for the whole of their four-day lifespans, while animals trained in adulthood only retained the aversive memory for up to 24 hours. © 1986-2016 The Scientist
By Julia Shaw The approach to Valentine's Day is a reminder that we humans are so intrigued by the idea of love that we have made it into something to celebrate in it’s own right. Love is something amazing. Love is something special. But what are the implications of love for our memories? Remember those “your brain on drugs” awareness posters? You can essentially substitute “love” for “drugs” and the same warnings apply. Scientists have found that being in love actually makes you activate some of the same brain regions as when you take addictive drugs, like ecstasy or cocaine. Neuroscientist Kayo Takahashi and his team have described passionate love as an “all-encompassing experience” which has “disorienting effects” and is generally considered “highly pleasurable”. While you probably don’t need a bunch of scientists to tell you that, you probably do need them to explain what that actually means in the brain. In 2015 Kayo and his team were keen on exploring the role of one particular culprit of the feel-good effects of love, the neurotransmitter dopamine. Among many other effects, dopamine generally makes us feel pleasure. Kayo and his team looked into the brains of people who were in the early stages of romantic relationships, and they found that when shown pictures of their romantic partners, participants experienced a flood of dopamine to parts of their brains. As it turns out, brains need to release dopamine in order to store long-term memories. © 2016 Scientific American
By PAM BELLUCK The risk of developing dementia is decreasing for people with at least a high school education, according to an important new study that suggests that changes in lifestyle and improvements in physical health can help prevent or delay cognitive decline. The study, published Wednesday in The New England Journal of Medicine, provides the strongest evidence to date that a more educated population and better cardiovascular health are contributing to a decline in new dementia cases over time, or at least helping more people stave off dementia for longer. The findings have implications for health policy and research funding, and they suggest that the long-term cost of dementia care may not be as devastatingly expensive as policy makers had predicted, because more people will be able to live independently longer. There are wild cards that could dampen some of the optimism. The study participants were largely white and suburban, so results may not apply to all races and ethnicities. Still, a recent study showed a similar trend among African-Americans in Indianapolis, finding that new cases of dementia declined from 1992 to 2001. The 2001 participants had more education, and although they had more cardiovascular problems than the 1992 participants, those problems were receiving more medical treatment. Another question mark is whether obesity and diabetes, which increase dementia risk, will cause a surge in dementia cases when the large number of overweight or diabetic 40- and 50-year-olds become old enough to develop dementia. © 2016 The New York Times Company
It’s well known that some people report that their mood is influenced by the seasons. But can the time of year affect other cognitive functions? To find out, Gilles Vandewalle and colleagues at the University of Liege in Belgium scanned the brains of 28 volunteers while they performed attention and working memory tests at different times of the year. To ensure the results were influenced by the seasons rather than the environmental conditions on the test day, the participants were confined to a lab for 4.5 days prior to the test, exposed to a constant light level and temperature. Although their test scores didn’t change with the seasons, activity in some brain areas showed a consistent seasonal pattern among the volunteers: brain activity peaked in the summer on the attention task and in the autumn on the memory task. Many seasonally changing factors could regulate such a pattern, including day length (known as photoperiod), temperature, humidity, social interaction and physical activity. Since these weren’t all controlled for in the study, it’s impossible to say what is responsible for the seasonal changes seen. “In our data it seems that photoperiod, or the rate of change of photoperiod, was more likely to explain what we were seeing. But we can’t exclude all the others,” says Vandewalle. The results suggest that over the course of a year, the brain might work in different ways to compensate for seasonal factors that could affect its function, enabling it to maintain a stable performance. Vandewalle speculates that these mechanisms might not work as well in some people, for example, those vulnerable to the winter blues. © Copyright Reed Business Information Ltd.
By Jeneen Interlandi The human brain’s memory-storage capacity is an order of magnitude greater than previously thought, researchers at the Salk Institute for Biological Studies reported last week. The findings, recently detailed in eLife, are significant not only for what they say about storage space but more importantly because they nudge us toward a better understanding of how, exactly, information is encoded in our brains. The question of just how much information our brains can hold is a longstanding one. We know that the human brain is made up of about 100 billion neurons, and that each one makes 1,000 or more connections to other neurons, adding up to some 100 trillion in total. We also know that the strengths of these connections, or synapses, are regulated by experience. When two neurons on either side of a synapse are active simultaneously, that synapse becomes more robust; the dendritic spine (the antenna on the receiving neuron) also becomes larger to support the increased signal strength. These changes in strength and size are believed to be the molecular correlates of memory. The different antenna sizes are often compared with bits of computer code, only instead of 1s and 0s they can assume a range of values. Until last week scientists had no idea how many values, exactly. Based on crude measurements, they had identified just three: small, medium and large. But a curious observation led the Salk team to refine those measurements. In the course of reconstructing a rat hippocampus, an area of the mammalian brain involved in memory storage, they noticed some neurons would form two connections with each other: the axon (or sending cable) of one neuron would connect with two dendritic spines (or receiving antennas) on the same neighboring neuron, suggesting that duplicate messages were being passed from sender to receiver. © 2016 Scientific American
Keyword: Learning & Memory
Link ID: 21866 - Posted: 02.06.2016
Heidi Ledford Difficulty with concentration, memory and other cognitive tasks is often associated with depression. In the past quarter of a century, a wave of drugs has transformed the treatment of depression. But the advances have struggled to come to grips with symptoms that often linger long after people start to feel better: cognitive problems such as memory loss and trouble concentrating. On 3 February, the US Food and Drug Administration (FDA) will convene a meeting of its scientific advisers to discuss whether such cognitive impairments are components of the disorder that drugs might be able to target — or just a result of depressed mood. The discussion will help the agency to decide whether two companies that sell the antidepressant vortioxetine should be allowed to label it as a treatment for the cognitive effects. A ‘yes’ could spur drug developers to invest in ways to test cognitive function during their antidepressant trials. Psychiatrists have long noted that some people with depression also struggle to concentrate and to make decisions. The question has been whether such difficulties are merely an offshoot of altered mood and would thus clear up without specific treatment, says Diego Pizzagalli, a neuroscientist at McLean Hospital, an affiliate of Harvard Medical School in Belmont, Massachusetts. But some patients who report improved mood after treatment still struggle with cognitive deficits — so psychiatrists sometimes prescribe concentration-enhancing drugs that are approved to treat attention deficit hyperactivity disorder to people with depression. © 2016 Nature Publishing Group
Fears over surveillance seem to figure large in the bird world, too. Ravens hide their food more quickly if they think they are being watched, even when no other bird is in sight. It’s the strongest evidence yet that ravens have a “theory of mind” – that they can attribute mental states such as knowledge to others. Many studies have shown that certain primates and birds behave differently in the presence of peers who might want to steal their food. While some researchers think this shows a theory of mind, others say they might just be reacting to visual cues, rather than having a mental representation of what others can see and know. Through the peephole Thomas Bugnyar and colleagues at the University of Vienna, Austria, devised an experiment to rule out the possibility that birds are responding to another’s cues. The setup involved two rooms separated by a wooden wall, with windows and peepholes that could be covered. First, a raven was given food with another raven in the next room, with the window open or covered, to see how quickly it caches its prize. With the window open, the birds hid their food more quickly and avoided going back to conceal it further. Then individual ravens were then trained to use the peephole to see where humans were putting food in the other room. The idea here was to allow the bird to realise it could be seen through the peephole. © Copyright Reed Business Information Ltd.
Nell Greenfieldboyce The state of New Jersey has been trying to help jurors better assess the reliability of eyewitness testimony, but a recent study suggests that the effort may be having unintended consequences. That's because a new set of instructions read to jurors by a judge seems to make them skeptical of all eyewitness testimony — even testimony that should be considered reasonably reliable. Back in 2012, New Jersey's Supreme Court did something groundbreaking. It said that in cases that involve eyewitness testimony, judges must give jurors a special set of instructions. The instructions are basically a tutorial on what scientific research has learned about eyewitness testimony and the factors that can make it more dependable or less so. "The hope with this was that jurors would then be able to tell what eyewitness testimony was trustworthy, what sort wasn't, and at the end of the day it would lead to better decisions, better court outcomes, better justice," says psychologist David Yokum. Yokum was a graduate student at the University of Arizona, doing research on decision-making, when he and two colleagues, Athan Papailiou and Christopher Robertson, decided to test the effect of these new jury instructions, using videos of a mock trial that they showed to volunteers. © 2016 npr
Keyword: Learning & Memory
Link ID: 21828 - Posted: 01.27.2016
James Gorman Spotted hyenas are the animals that got Sarah Benson-Amram thinking about how smart carnivores are and in what ways. Dr. Benson-Amram, a researcher at the University of Wyoming in Laramie, did research for her dissertation on hyenas in the wild under Kay E. Holekamp of Michigan State University. Hyenas have very complicated social structures and they require intelligence to function in their clans, or groups. But the researchers also tested the animals on a kind of intelligence very different from figuring out who ranks the highest: They put out metal boxes that the animals had to open by sliding a bolt in order to get at meat inside. Only 15 percent of the hyenas solved the problem in the wild, but in captivity, the animals showed a success rate of 80 percent. Dr. Benson-Amram and Dr. Holekamp decided to test other carnivores, comparing species and families. They and other researchers presented animals in several different zoos with a metal puzzle box with a treat inside and recorded the animals’ efforts. They tested 140 animals in 39 species that were part of nine families. They reported their findings on Monday in the Proceedings of the National Academy of Sciences. They compared the success rates of different families with absolute brain size, relative brain size, and the size of the social groups that the species form in the wild. Just having a bigger brain did not make difference, but the relative size of the brain, compared with the size of the body, was the best indication of which animals were able to solve the problem of opening the box. © 2016 The New York Times Company
by Graham McDougall, Jr., behavioral scientist at U. of Alabama Chemo brain is a mental cloudiness reported by about 30 percent of cancer patients who receive chemotherapy. Symptoms typically include impairments in attention, concentration, executive function, memory and visuospatial skills. Since the 1990s researchers have tried to understand this phenomenon, particularly in breast cancer patients. But the exact cause of chemo brain remains unclear. Some studies indicate that chemotherapy may trigger a variety of related neurological symptoms. One study, which examined the effects of chemotherapy in 42 breast cancer patients who underwent a neuropsychological evaluation before and after treatment, found that almost three times more patients displayed signs of cognitive dysfunction after treatment as compared with before (21 versus 61 percent). A 2012 review of 17 studies considering 807 breast cancer patients found that cognitive changes after chemotherapy were pervasive. Other research indicates that the degree of mental fogginess that a patient experiences may be directly related to how much chemotherapy that person receives: higher doses lead to greater dysfunction. There are several possible mechanisms to explain the cognitive changes associated with chemotherapy treatments. The drugs may have direct neurotoxic effects on the brain or may indirectly trigger immunological responses that may cause an inflammatory reaction in the brain. Chemotherapy, however, is not the only possible culprit. Research also shows that cancer itself may cause changes to the brain. In addition, it is possible that the observed cognitive decline may simply be part of the natural aging process, especially considering that many cancer patients are older than 50 years. © 2016 Scientific American,
By Emily Underwood Roughly half of Americans use marijuana at some point in their lives, and many start as teenagers. Although some studies suggest the drug could harm the maturing adolescent brain, the true risk is controversial. Now, in the first study of its kind, scientists have analyzed long-term marijuana use in teens, comparing IQ changes in twin siblings who either used or abstained from marijuana for 10 years. After taking environmental factors into account, the scientists found no measurable link between marijuana use and lower IQ. “This is a very well-conducted study … and a welcome addition to the literature,” says Valerie Curran, a psychopharmacologist at the University College London. She and her colleagues reached “broadly the same conclusions” in a separate, nontwin study of more than2000 British teenagers, published earlier this month in the Journal of Psychopharmacology, she says. But, warning that the study has important limitations, George Patton, a psychiatric epidemiologist at the University of Melbourne in Australia, adds that it in no way proves that marijuana—particularly heavy, or chronic use —is safe for teenagers. Most studies that linked marijuana to cognitive deficits, such as memory loss and low IQ, looked at a single “snapshot” in time, says statistician Nicholas Jackson of the University of Southern California in Los Angeles, lead author of the new work. That makes it impossible to tell which came first: drug use or poor cognitive performance. “It's a classic chicken-egg scenario,” he says. © 2016 American Association for the Advancement of Science.
Laura Sanders Pain can sear memories into the brain, a new study finds. A full year after viewing a picture of a random, neutral object, people could remember it better if they had been feeling painful heat when they first saw it. “The results are fun, they are interesting and they are provocative,” says neuroscientist A. Vania Apkarian of Northwestern University in Chicago. The findings “speak to the idea that pain really engages memory.” Neuroscientists G. Elliott Wimmer and Christian Büchel of University Medical Center Hamburg-Eppendorf in Germany reported the results in a paper online at BioRxiv.org first posted December 24 and revised January 6. The findings are under review at a journal, and Wimmer declined to comment on the study until it is accepted for publication. Wimmer and Büchel recruited 31 brave souls who agreed to feel pain delivered by a heat-delivering thermode on their left forearms. Each person’s pain sensitivity was used to calibrate the amount of heat they received in the experiment, which was either not painful (a 2 on an 8-point scale) or the highest a person could endure multiple times (a full 8). While undergoing a functional MRI scan, participants looked at a series of pictures of unremarkable household objects, such as a camera, sometimes feeling pain and sometimes not. Right after seeing the images, the people took a pop quiz in which they answered whether an object was familiar. Pain didn’t influence memory right away. Right after their ordeal, participants remembered about three-quarters of the previously seen objects, regardless of whether pain was present, the researchers found. © Society for Science & the Public 2000 - 2015.
By Emily Underwood Lumos Labs, the company that produces the popular “brain-training” program Lumosity, yesterday agreed to pay a $2 million settlement to the Federal Trade Commission (FTC) for running deceptive advertisements. Lumos had claimed that its online games can help users perform better at work and in school and stave off cognitive deficits associated with serious diseases such as Alzheimer’s, traumatic brain injury, and post-traumatic stress. The $2 million settlement will be used to compensate Lumosity consumers who were misled by false advertising, says Michelle Rusk, a spokesperson with FTC in Washington, D.C. The company will also be required to provide an easy way to cancel autorenewal billing for the service, which includes online and mobile app subscriptions, with payments ranging from $14.95 monthly to lifetime memberships for $299.95. Before consumers can access the games, a pop-up screen will alert them to FTC’s order and allow them to avoid future billing, Rusk says. The action is part of a larger crackdown on companies selling products that purportedly enhance memory or provide some other cognitive benefit, Rusk says. For some time now, FTC has been “concerned about some of the claims we’re seeing out there,” particularly those from companies like Lumos that suggest their games can reduce the effects of conditions such as dementia, she says. After evaluating the literature on Lumos's products, and the broader research on the benefits of brain-training games, “our assessment was they didn’t have adequate science for the claims that they’re making,” she says. © 2016 American Association for the Advancement of Science
Patricia Neighmond Losing your ability to think and remember is pretty scary. We know the risk of dementia increases with age. But if you have memory lapses, you probably needn't worry. There are pretty clear differences between signs of dementia and age-related memory loss. After age 50, it's quite common to have trouble remembering the names of people, places and things quickly, says Dr. Kirk Daffner, chief of the division of cognitive and behavioral neurology at Brigham and Women's Hospital in Boston. The brain ages just like the rest of the body. Certain parts shrink, especially areas in the brain that are important to learning, memory and planning. Changes in brain cells can affect communication between different regions of the brain. And blood flow can be reduced as arteries narrow. Simply put, this exquisitely complex organ just isn't functioning like it used to. Forgetting the name of an actor in a favorite movie, for example, is nothing to worry about. But if you forget the plot of the movie or don't remember even seeing it, that's far more concerning, Daffner says. When you forget entire experiences, he says, that's "a red flag that something more serious may be involved." Forgetting how to operate a familiar object like a microwave oven or forgetting how to drive to the house of a friend you've visited many times before can also be signs something is wrong. © 2016 npr
By R. Douglas Fields We all heard the warning as kids: “That TV will rot your brain!” You may even find yourself repeating the threat when you see young eyes glued to the tube instead of exploring the real world. The parental scolding dates back to the black-and-white days of I Love Lucy, and today concern is growing amid a flood of video streaming on portable devices. But are young minds really being harmed? With brain imaging, the effects of regular TV viewing on a child's neural circuits are plain to see. Studies suggest watching television for prolonged periods changes the anatomical structure of a child's brain and lowers verbal abilities. Behaviorally, even more detrimental effects may exist: although a cause-and-effect relation is hard to prove, higher rates of antisocial behavior, obesity and mental health problems correlate with hours in front of the set. Now a new study hits the pause button on this line of thinking. The researchers conclude that the entire body of research up to now has overlooked an important confounding variable, heredity, that could call into question the conventional wisdom that TV is bad for the brain. Further study will be needed to evaluate this claim, but the combined evidence suggests we need a more nuanced attitude toward our viewing habits. To understand the argument against television, we should rewind to 2013, when a team ofresearchers at Tohoku University in Japan, led by neuroscientist Hikaru Takeuchi, first published findings from a study in which the brains of 290 children between the ages of five and 18 were imaged. The kids' TV viewing habits, ranging from zero to four hours each day, were also taken into account. © 2016 Scientific American
By Karen Weintraub Mild cognitive impairment, or M.C.I., is not a disease in itself. Rather, it is a clinical description based on performance on a test of memory and thinking skills. Depending on its cause, mild cognitive impairment is potentially reversible. Poor performance on a cognitive test could be caused by certain medications, sleep apnea, depression or other problems, said Dr. Alvaro Pascual-Leone, a professor of neurology at Harvard Medical School and Beth Israel Deaconess Medical Center. In those cases, when the underlying disease is treated, cognitive abilities can bounce back. But in about half of people with M.C.I. – doctors are not sure of the exact number — memory problems are the first sign of impending Alzheimer’s disease. If M.C.I. progresses to Alzheimer’s, there is no recovery. Alzheimer’s is marked by an inexorable decline that is always fatal, although the path from the first signs of cognitive impairment to death may take three to 15 years, said Dr. David Knopman, a professor of neurology at the Mayo Clinic in Rochester, Minn. As many as 20 percent to 30 percent of those with M.C.I. who score below but near the cutoff for normal can cross back above in a subsequent cognitive test – perhaps because they are having a better day, he said. But someone whose score is borderline is at higher risk of developing Alzheimer’s than someone who scores higher, said Dr. Knopman, also vice chair of the medical and scientific advisory council of the Alzheimer’s Association. Doctors may be hesitant to label someone with early Alzheimer’s, which can be difficult to diagnose in the early stages, so they often call it mild cognitive impairment instead, said Dr. John C. Morris, a professor of neurology and the director of the Knight Alzheimer's Disease Research Center at Washington University School of Medicine in St. Louis. © 2015 The New York Times Company
Need to remember something important? Take a break. A proper one – no TV or flicking through your phone messages. It seems that resting in a quiet room for 10 minutes without stimulation can boost our ability to remember new information. The effect is particularly strong in people with amnesia, suggesting that they may not have lost the ability to form new memories after all. “A lot of people think the brain is a muscle that needs to be continually stimulated, but perhaps that’s not the best way,” says Michaela Dewar at Heriot-Watt University in Edinburgh, UK. New memories are fragile. They need to be consolidated before being committed to long-term storage, a process thought to happen while we sleep. But at least some consolidation may occur while we’re awake, says Dewar – all you need is a timeout. In 2012, Dewar’s team showed that having a rest helps a person to remember what they were told a few minutes earlier. And the effect seems to last. People who had a 10-minute rest after hearing a story remembered 10 per cent more of it a week later than those who played a spot-the-difference game immediately afterwards. “We dim the lights and ask them to sit in an empty, quiet room, with no mobile phones,” says Dewar. When asked what they had been thinking about afterwards, most volunteers said they had let their minds wander. Now Dewar, along with Michael Craig at the University of Edinburgh and their colleagues, have found that spatial memories can also be consolidated when we rest. © Copyright Reed Business Information Ltd.
By John Bohannon In July 1984, a man broke into the apartment of Jennifer Thompson, a 22-year-old in North Carolina, and threatened her with a knife. She negotiated, convincing him to not kill her. Instead, he raped her and fled. Just hours later, a sketch artist worked with Thompson to create an image of the assailant's face. Then the police showed her a series of mug shots of similar-looking men. Thompson picked out 22-year-old Ronald Cotton, whose photograph was on file because of a robbery committed in his youth. When word reached Cotton that the police were looking for him, he walked into a precinct voluntarily. He was eventually sentenced to life in prison based on Thompson's testimony. Eleven years later, after DNA sequencing technology caught up, samples taken from Thomson's body matched a different man who finally confessed. Cotton was set free. When Thompson first identified Cotton by photo, she was not convinced of her choice. "I think this is the guy," she told the police after several minutes of hesitation. As time went on, she grew surer. By the time Thompson faced Cotton in court a year later, her doubts were gone. She confidently pointed to him as the man who raped her. Because of examples like these, the U.S. justice system has been changing how eyewitnesses are used in criminal cases. Juries are told to discount the value of eyewitness testimony and ignore how confident the witnesses may be about whom they think they saw. Now, a new study of robbery investigations suggests that these changes may be doing more harm than good. © 2015 American Association for the Advancement of Science
Keyword: Learning & Memory
Link ID: 21715 - Posted: 12.22.2015
Megan Scudellari In 1997, physicians in southwest Korea began to offer ultrasound screening for early detection of thyroid cancer. News of the programme spread, and soon physicians around the region began to offer the service. Eventually it went nationwide, piggybacking on a government initiative to screen for other cancers. Hundreds of thousands took the test for just US$30–50. LISTEN James Harkin, a researcher for the British TV trivia show QI, talks to Adam Levy about how he finds facts and myths for the show — and then runs a mini-quiz to see whether the Podcast team can discern science fact from science fiction 00:00 Across the country, detection of thyroid cancer soared, from 5 cases per 100,000 people in 1999 to 70 per 100,000 in 2011. Two-thirds of those diagnosed had their thyroid glands removed and were placed on lifelong drug regimens, both of which carry risks. Such a costly and extensive public-health programme might be expected to save lives. But this one did not. Thyroid cancer is now the most common type of cancer diagnosed in South Korea, but the number of people who die from it has remained exactly the same — about 1 per 100,000. Even when some physicians in Korea realized this, and suggested that thyroid screening be stopped in 2014, the Korean Thyroid Association, a professional society of endocrinologists and thyroid surgeons, argued that screening and treatment were basic human rights. © 2015 Nature Publishing Group,
Human memory is about to get supercharged. A memory prosthesis being trialled next year could not only restore long-term recall but may eventually be used to upload new skills directly to the brain – just like in the film The Matrix. The first trials will involve people with epilepsy. Seizures can sometimes damage the hippocampus, causing the brain to lose its ability to form long-term memories. To repair this ability, Theodore Berger at the University of Southern California and his colleagues used electrodes already implanted in people’s brains as part of epilepsy treatment to record electrical activity associated with memory. The team then developed an algorithm that could predict the neural activity thought to occur when a short-term memory becomes a long-term memory, as it passes through the hippocampus. Early next year, Berger’s team will use this algorithm to instruct the electrodes to predict and then mimic the activity that should occur when long-term memories are formed. “Hopefully, it will repair their long-term memory,” says Berger. Previous studies using animals suggest that the prosthesis might even give people a better memory than they could expect naturally. A similar approach could eventually be used to implant new memories into the brain. Berger’s team recorded brain activity in a rat that had been trained to perform a specific task. The memory prosthesis then replicated that activity in a rat that hadn’t been trained. The second rat was able to learn the task much faster than the first rat – as if it already had some memory of the task. © Copyright Reed Business Information Ltd.