Chapter 17. Learning and Memory
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Douwe Draaisma When we sleep, wrote English psychiatrist Havelock Ellis over a hundred years ago, we enter a ‘dim and ancient house of shadow’. We wander through its rooms, climb staircases, linger on a landing. Towards morning we leave the house again. In the doorway we look over our shoulders briefly and with the morning light flooding in we can still catch a glimpse of the rooms where we spent the night. Then the door closes behind us and a few hours later even those fragmentary memories we had when we woke have been wiped away. That is how it feels. You wake up and still have access to bits of the dream. But as you try to bring the dream more clearly to mind, you notice that even those few fragments are already starting to fade. Sometimes there is even less. On waking you are unable to shake off the impression that you have been dreaming; the mood of the dream is still there, but you no longer know what it was about. Sometimes you are unable to remember anything at all in the morning, not a dream, not a feeling, but later in the day you experience something that causes a fragment of the apparently forgotten dream to pop into your mind. No matter what we may see as we look back through the doorway, most of our dreams slip away and the obvious question is: why? Why is it so hard to hold on to dreams? Why do we have such a poor memory for them? In 1893, American psychologist Mary Calkins published her ‘Statistics of Dreams’, a numerical analysis of what she and her husband dreamed about over a period of roughly six weeks. They both kept candles, matches, pencil and paper in readiness on the bedside table. But dreams are so fleeting, Calkins wrote, that even reaching out for matches was enough to make them disappear. Still with an arm outstretched, she was forced to conclude that the dream had gone. © 2015 Salon Media Group, Inc
|By Michele Solis An individual with obsessive-compulsive disorder (OCD) is overcome with an urge to engage in unproductive habits, such as excessive hand washing or lock checking. Though recognizing these behaviors as irrational, the person remains trapped in a cycle of life-disrupting compulsions. Previous studies found that OCD patients have abnormalities in two different brain systems—one that creates habits and one that plays a supervisory role. Yet whether the anomalies drive habit formation or are instead a consequence of doing an action over and over remained unclear. To resolve this question, a team at the University of Cambridge monitored brain activity while people were actually forming new habits. Lapses in supervision are to blame, the researchers reported in a study published online in December 2014 in the American Journal of Psychiatry. They scanned 37 people with OCD and 33 healthy control subjects while they learned to avoid a mild shock by pressing on a foot pedal. Pressing the pedal became a habit for everyone, but people with OCD continued to press even when the threat of shock was over. Those with OCD showed abnormal activity in the supervisory regions important for goal-directed behavior but not in those responsible for habit formation. The finding suggests that shoring up the goal-directed systems through cognitive training might help people with OCD. The growing understanding of OCD's roots in the brain may also help convince individuals to engage in standard habit-breaking treatments, which expose a person to a trigger but prevent his or her typical response. “It's hard for people to not perform an action that their whole body is telling them to do,” says first author Claire Gillan, now at New York University. “So if you have an awareness that the habit is just a biological slip, then it makes OCD a lot less scary and something you can eventually control.” © 2015 Scientific American
Neuroscientists have discovered brain circuitry for encoding positive and negative learned associations in mice. After finding that two circuits showed opposite activity following fear and reward learning, the researchers proved that this divergent activity causes either avoidance or reward-driven behaviors. Funded by the National Institutes of Health, they used cutting-edge optical-genetic tools to pinpoint these mechanisms critical to survival, which are also implicated in mental illness. “This study exemplifies the power of new molecular tools that can push and pull on the same circuit to see what drives behavior,” explained Thomas R. Insel, M.D., director of NIH’s National Institute of Mental Health (NIMH). “Improved understanding of how such emotional memory works holds promise for solving mysteries of brain circuit disorders in which these mechanisms are disrupted.” NIMH grantee Kay Tye, Ph.D. External Web Site Policy, Praneeth Namburi and Anna Beyeler, Ph.D., of the Massachusetts Institute of Technology (MIT), Cambridge, and colleagues, report their findings April 29, 2015 in the journal Nature. Prior to the new study, scientists suspected involvement of the circuits ultimately implicated, but were stumped by a seeming paradox. A crossroads of convergent circuits in an emotion hub deep in the brain, thebasolateral amygdala, seem to be involved in both fear and reward learning, but how one brain region could orchestrate such opposing behaviors – approach and avoidance – remained an enigma. How might signals find the appropriate path to follow at this fork in the road?
Pete Etchells Over the past few years, there seems to have been a insidious pandemic of nonsense neuroscientific claims creeping into the education system. In 2013, the Wellcome Trust commissioned a series of surveys of parents and teachers, asking about various types of educational tools or teaching methods, and the extent to which they believe they have a basis in neuroscience. Worryingly, 76% of teachers responded that they used learning styles in their teaching, and a further 19% responded that they either use, or intend to use, left brain/right brain distinctions to help inform learning methods. Both of these approaches have been thoroughly debunked, and have no place in either neuroscience or education. In October last year, I reported on another study that showed that in the intervening time, things hadn’t really improved – 91% of UK teachers in that survey believed that there were differences in the way that students think and learn, depending on which hemisphere of the brain is ‘dominant’. And despite lots of great attempts to debunk myths about the brain, they still seem to persist and take up residence as ‘commonplace’ knowledge, being passed onto children as if they are fact. When I wrote about an ATL proposal to train teachers in neuroscience – a well-intended idea, but ultimately grounded in nonsense about left brain/right brain myths – I commented at the end that we need to do more to bring teachers and neuroscientists together, to discuss whether neuroscience has a relevant role in informing the way we teach students. Now, a new initiative funded by the Wellcome Trust is aiming to just that. © 2015 Guardian News and Media Limited
By Felicity Muth One of the first things I get asked when I tell people that I work on bee cognition (apart from ‘do you get stung a lot?’) is ‘bees have cognition?’. I usually assume that this question shouldn’t be taken literally otherwise it would mean that whoever was asking me this thought that there was a possibility that bees didn’t have cognition and I had just been making a terrible mistake for the past two years. Instead I guess this question actually means ‘please tell me more about the kind of cognitive abilities bees have, as I am very much surprised to hear that bees can do more than just mindlessly sting people’. So, here it is: a summary of some of the more remarkable things that bees can do with their little brains. In the first part of two articles on this topic, I introduce the history and basics of bee learning. In the second article, I go on to discuss the more advanced cognitive abilities of bees. The study of bee cognition isn’t a new thing. Back in the early 1900s the Austrian scientist Karl von Frisch won the Nobel Prize for his work with honeybees (Apis mellifera). He is perhaps most famous for his research on their remarkable ability to communicate through the waggle dance but he also showed for the first time that honeybees have colour vision and learn the colours of the flowers they visit. Appreciating how he did this is perhaps the first step to understanding everything we know about bee cognition today. Before delving into the cognitive abilities of bees it’s important to think about what kinds of abilities a bee might need, given the environment she lives in (all foraging worker bees are female). Bees are generalists, meaning that they don’t have to just visit one particular flower type for food (nectar and pollen), but can instead visit hundreds of different types. However, not all flowers are the same. © 2015 Scientific American,
By Alix Spiegel In 1979, when Jim Stigler was still a graduate student at the University of Michigan, he went to Japan to research teaching methods and found himself sitting in the back row of a crowded fourth-grade math class. “The teacher was trying to teach the class how to draw three-dimensional cubes on paper,” Stigler explains, “and one kid was just totally having trouble with it. His cube looked all cockeyed, so the teacher said to him, ‘Why don’t you go put yours on the board?’ So right there I thought, ‘That’s interesting! He took the one who can’t do it and told him to go and put it on the board.’ ” Stigler knew that in American classrooms, it was usually the best kid in the class who was invited to the board. And so he watched with interest as the Japanese student dutifully came to the board and started drawing, but still couldn’t complete the cube. Every few minutes, the teacher would ask the rest of the class whether the kid had gotten it right, and the class would look up from their work, and shake their heads no. And as the period progressed, Stigler noticed that he — Stigler — was getting more and more anxious. In Japanese classrooms, teachers consciously design tasks that are slightly beyond the capabilities of the students they teach, so the students can actually experience struggling with something just outside their reach. “I realized that I was sitting there starting to perspire,” he says, “because I was really empathizing with this kid. I thought, ‘This kid is going to break into tears!’ ” © 2015 KQED Inc.
Keyword: Learning & Memory
Link ID: 20820 - Posted: 04.20.2015
By Nicholas Bakalar Breathing problems during sleep may be linked to early mental decline and Alzheimer’s disease, a new study suggests. But treating apnea with a continuous positive airway pressure machine can significantly delay the onset of cognitive problems. In a group of 2,470 people, average age 73, researchers gathered information on the incidence of sleep apnea, a breathing disorder marked by interrupted breathing and snoring, and the incidence of mild cognitive impairment and Alzheimer’s disease. After adjusting for a range of variables, they found that people with disordered breathing during sleep became cognitively impaired an average of about 10 years sooner than those without the disorder. But compared with those whose sleep disorder was untreated, those using C.P.A.P. machines delayed the appearance of cognitive impairment by an average of 10 years — making their age of onset almost identical to those who had no sleep disorder at all. The lead author, Dr. Ricardo S. Osorio, a research professor of psychiatry at New York University, said the analysis, published online in Neurology, is an observational study that does not prove cause and effect. “But,” he added, “we need to increase the awareness that sleep disorders can increase the risk for cognitive impairment and possibly for Alzheimer’s. Whether treating sleep disorders truly slows the decline is still not known, but there is some evidence that it might.” © 2015 The New York Times Company
Jon Hamilton There's new evidence that the brain's activity during sleep isn't random. And the findings could help explain why the brain consumes so much energy even when it appears to be resting. "There is something that's going on in a very structured manner during rest and during sleep," says Stanford neurologist Dr. Josef Parvizi, "and that will, of course, require energy consumption." For a long time, scientists dismissed the brain's electrical activity during rest and sleep as meaningless "noise." But then studies using fMRI began to reveal patterns suggesting coordinated activity. To take a closer look, Parvizi and a team of researchers studied three people awaiting surgery for epilepsy. These people spent several days with electrodes in their brains to help locate the source of their seizures. And that meant Parvizi's team was able to monitor the activity of small groups of brain cells in real time. "We wanted to know exactly what's going on during rest," Parvizi says, "and whether or not it reflects what went on during the daytime when the subject was not resting." In the study published online earlier this month in Neuron, the team first studied the volunteers while they were awake and answering simple questions like: Did you drive to work last week? "In order to answer yes or no, you retrieve a lot of facts; you retrieve a lot of visualized memories," Parvizi says. © 2015 NPR
By Megan Griffith-Greene The idea of playing a game to make you sharper seems like a no-brainer. That's the thinking behind a billion-dollar industry selling brain training games and programs designed to boost cognitive ability. But an investigation by CBC's Marketplace reveals that brain training games such as Lumosity may not make your brain perform better in everyday life. Lumosity Brain training games, such as Lumosity, are a billion-dollar industry. Many people are worried about maintaining their brain health and want to prevent a decline in their mental abilities. (CBC) Almost 15 per cent of Canadians over the age of 65 are affected by some kind of dementia. And many people of all ages are worried about maintaining their brain health and possibly preventing a decline in their mental abilities. "I don't think there's anything to say that you can train your brain to be cognitively better in the way that we know that we can train our bodies to be physically better," neuroscientist Adrian Owen told Marketplace co-host Tom Harrington. To test how effective the games are at improving cognitive function, Marketplace partnered with Owen, who holds the Canada Excellence Research Chair in Cognitive Neuroscience and Imaging at the Brain and Mind Institute at Western University. A group of 54 adults, including Harrington, did the brain training at least three times per week for 15 minutes or more over a period of between two and a half and four weeks. The group underwent a complete cognitive assessment at the beginning and end of the training to see if there had been any change as the result of the training program. ©2015 CBC/Radio-Canada.
Cari Romm “As humans, we can identify galaxies light-years away. We can study particles smaller than an atom,” President Barack Obama said in April 2013, “But we still haven’t unlocked the mystery of the three pounds of matter that sits between our ears.” The observation was part of the president’s announcement of the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative, an effort to fast-track the development of new technology that will help scientists understand the workings of the human brain and its diseases. With progress, though, comes a whole new set of ethical questions. Can drugs used to treat conditions like ADHD, for example, also be used to make healthy people into sharper, more focused versions of themselves—and should they? Can a person with Alzheimer’s truly consent to testing that may help scientists better understand their disease? Can brain scans submitted as courtroom evidence reveal anything about a defendant’s intent? Can a person with Alzheimer’s truly consent to testing that may help scientists better understand their disease? To address these questions, the Presidential Commission for the Study of Bioethical Issues, an independent advisory group, recently released the second volume of a report examining the issues that may arise as neuroscience advances. The commission outlined three areas it deemed particularly fraught: cognitive enhancement, consent, and the use of neuroscience in the legal system. © 2015 by The Atlantic Monthly Group
Alison Abbott Historian of psychology Douwe Draaisma knows well how to weave science, history and literature into irresistible tales. Forgetting, his latest collection of essays around the theme of memory, is — like his successful Nostalgia Factory (Yale University Press, 2013) — hard to put down. His vivid tour through the history of memory-repression theories brings home how dangerous and wrong, yet persistent, were the ideas of Sigmund Freud and his intellectual heirs. Freud thought that traumatic memories and shameful thoughts could be driven from the consciousness, but not forgotten. They would simmer in the unconscious, influencing behaviour. He maintained that forcing them out with psychoanalysis, and confronting patients with them, would be curative. Draaisma relates the case of an 18-year-old whom Freud dubbed Dora, diagnosed in 1900 with 'hysteria'. Dora's family refused to believe that the husband of her father's mistress had made sexual advances to her. Among other absurdities, Freud told Dora that her nervous cough reflected her repressed desire to fellate the man. Dora broke off the therapy, which Freud saw as proof of his theory. He thought that patients will naturally resist reawakening painful thoughts. What Dora did not buy, plenty of others did. Psychoanalysis boomed, becoming lucrative. Its principles were adopted in the 1990s by an unlikely alliance of lawyers and some feminists, who argued that repressed memories of childhood abuse could be recovered with techniques such as hypnosis, and used as evidence in court. Many judges went along with it; the rush of claims cast a shadow over genuine cases of abuse, Draaisma points out. We now know from studies of post-traumatic stress disorder that traumatic memories are impossible to repress. They flood into the conscious mind in horrifying flashbacks. © 2015 Macmillan Publishers Limited
Keyword: Learning & Memory
Link ID: 20747 - Posted: 04.02.2015
|By Dwayne Godwin and Jorge Cham Our minds are veritable memory machines. © 2015 Scientific American
Keyword: Learning & Memory
Link ID: 20734 - Posted: 03.31.2015
|By Roni Jacobson As intangible as they may seem, memories have a firm biological basis. According to textbook neuroscience, they form when neighboring brain cells send chemical communications across the synapses, or junctions, that connect them. Each time a memory is recalled, the connection is reactivated and strengthened. The idea that synapses store memories has dominated neuroscience for more than a century, but a new study by scientists at the University of California, Los Angeles, may fundamentally upend it: instead memories may reside inside brain cells. If supported, the work could have major implications for the treatment of post-traumatic stress disorder (PTSD), a condition marked by painfully vivid and intrusive memories. More than a decade ago scientists began investigating the drug propranolol for the treatment of PTSD. Propranolol was thought to prevent memories from forming by blocking production of proteins required for long-term storage. Unfortunately, the research quickly hit a snag. Unless administered immediately after the traumatic event, the treatment was ineffective. Lately researchers have been crafting a work-around: evidence suggests that when someone recalls a memory, the reactivated connection is not only strengthened but becomes temporarily susceptible to change, a process called memory reconsolidation. Administering propranolol (and perhaps also therapy, electrical stimulation and certain other drugs) during this window can enable scientists to block reconsolidation, wiping out the synapse on the spot. The possibility of purging recollections caught the eye of David Glanzman, a neurobiologist at U.C.L.A., who set out to study the process in Aplysia, a sluglike mollusk commonly used in neuroscience research. Glanzman and his team zapped Aplysia with mild electric shocks, creating a memory of the event expressed as new synapses in the brain. The scientists then transferred neurons from the mollusk into a petri dish and chemically triggered the memory of the shocks in them, quickly followed by a dose of propranolol. © 2015 Scientific American
by Michael Slezak What were we talking about? Oh yes, brain-training programmes may be useful for helping inattentive people focus on tasks in their daily life. At least, that's the implication of an analysis looking at one particular programme. It's the latest salvo in a field that has seen the battles lines drawn between those who believe there is no compelling scientific evidence that training the brain to do a specific task better can offer wider cognitive improvements, and those that think it can work in some cases. The party line is that brain training improves only that which it exercises, says Jared Horvath from the University of Melbourne in Australia. "What this means is, if the training programme uses a working memory game, you get better at working memory games and little else." But an analysis by Megan Spencer-Smith of Monash University in Melbourne, Australia, and Torkel Klingberg at the Karolinska Institute in Stockholm, Sweden, claims to show that there are benefits for daily life – at least for people with attention deficit hyperactivity disorder or other problems related to attentiveness. They focused on a programme called Cogmed, which Klingberg has helped develop, and combined the results of several smaller studies. Cogmed is designed to improve how much verbal or visual information you can temporarily remember and work with. © Copyright Reed Business Information Ltd.
By PAM BELLUCK What happens to forgotten memories — old computer passwords, friends’ previous phone numbers? Scientists have long held two different theories. One is that memories do not diminish but simply get overshadowed by new memories. The other is that older memories become weaker, that pulling to mind new passwords or phone numbers degrades old recollections so they do not interfere. The difference could be significant. If old memories stay strong and are merely papered over by new ones, they may be easier to recover. That could be positive for someone trying to remember an acquaintance’s name, but difficult for someone trying to lessen memories of abuse. It could suggest different strategies for easing traumatic memories, evaluating witness testimony about crimes, or helping students study for tests. Now, a study claims to provide evidence of memory’s weakening by showing that people’s ability to remember something and the pattern of brain activity that thing generates both appear to diminish when a competing memory gets stronger. Demonstrating sophisticated use of brain scans in memory research, authors of the study, published Monday in the journal Nature Neuroscience, appear to have identified neural fingerprints of specific memories, distinguishing brain activity patterns produced when viewing a picture of a necklace, say, from a picture of binoculars or other objects. The experiment, conducted by scientists in Birmingham and Cambridge, England, involved several stages with 24 participants first trained to associate words to two unrelated black and white pictures from lists of famous people, ordinary objects or scenes. © 2015 The New York Times Company
Keyword: Learning & Memory
Link ID: 20695 - Posted: 03.17.2015
By BENEDICT CAREY Behind all those canned compliments for older adults — spry! wily! wise! — is an appreciation for something that scientists have had a hard time characterizing: mental faculties that improve with age. Knowledge is a large part of the equation, of course. People who are middle-aged and older tend to know more than young adults, by virtue of having been around longer, and score higher on vocabulary tests, crossword puzzles and other measures of so-called crystallized intelligence. Still, young adults who consult their elders (mostly when desperate) don’t do so just to gather facts, solve crosswords or borrow a credit card. Nor, generally, are they looking for help with short-term memory or puzzle solving. Those abilities, called fluid intelligence, peak in the 20s. No, the older brain offers something more, according to a new paper in the journal Psychological Science. Elements of social judgment and short-term memory, important pieces of the cognitive puzzle, may peak later in life than previously thought. The postdoctoral fellows Joshua Hartshorne of M.I.T. and Laura Germine of Harvard and Massachusetts General Hospital analyzed a huge trove of scores on cognitive tests taken by people of all ages. The researchers found that the broad split in age-related cognition — fluid in the young, crystallized in the old — masked several important nuances. “This dichotomy between early peaks and later peaks is way too coarse,” Dr. Hartshorne said. “There are a lot more patterns going on, and we need to take those into account to fully understand the effects of age on cognition.” The new paper is hardly the first challenge to the scientific literature on age-related decline, and it won’t be the last. A year ago, German scientists argued that cognitive “deficits” in aging were caused largely by the accumulation of knowledge — that is, the brain slows down because it has to search a larger mental library of facts. That idea has stirred some debate among scientists. Experts said the new analysis raised a different question: Are there distinct, independent elements of memory and cognition that peak at varying times of life? © 2015 The New York Times Company
By Maggie Fox Teenagers who use marijuana heavily grow up to have poor memories and also have brain abnormalities, a new study shows. The study cannot say which came first — the brain structure differences or the pot use. But it suggests there could be long-term effects of heavy marijuana use. A team at Northwestern University looked at 97 volunteers with and without mental illness. The dope smokers said they'd used marijuana daily starting at age 16 or 17, and said they had not used other drugs. The daily marijuana users had an abnormally shaped hippocampus and performed about 18 percent more poorly on long-term memory tasks, the researchers reported in the journal Hippocampus. The hippocampus is a part of the brain used in storing long-term memory. "The memory processes that appear to be affected by cannabis are ones that we use every day to solve common problems and to sustain our relationships with friends and family," said Dr. John Csernansky, who worked on the study. Previous research by the same Northwestern team showed heavy pot smokers had poor short-term and working memory and abnormally shaped brain structures including the striatum, globus pallidus and thalamus. "It is possible that the abnormal brain structures reveal a pre-existing vulnerability to marijuana abuse," Matthew Smith, who led the study, said in a statement.
By Douglas Starr In 1906, Hugo Münsterberg, the chair of the psychology laboratory at Harvard University and the president of the American Psychological Association, wrote in the Times Magazine about a case of false confession. A woman had been found dead in Chicago, garroted with a copper wire and left in a barnyard, and the simpleminded farmer’s son who had discovered her body stood accused. The young man had an alibi, but after questioning by police he admitted to the murder. He did not simply confess, Münsterberg wrote; “he was quite willing to repeat his confession again and again. Each time it became richer in detail.” The young man’s account, he continued, was “absurd and contradictory,” a clear instance of “the involuntary elaboration of a suggestion” from his interrogators. Münsterberg cited the Salem witch trials, in which similarly vulnerable people were coerced into self-incrimination. He shared his opinion in a letter to a Chicago nerve specialist, which made the local press. A week later, the farmer’s son was hanged. Münsterberg was ahead of his time. It would be decades before the legal and psychological communities began to understand how powerfully suggestion can shape memory and, in turn, the course of justice. In the early nineteen-nineties, American society was recuperating from another panic over occult influence; Satanists had replaced witches. One case, the McMartin Preschool trial, hinged on nine young victims’ memories of molestation and ritual abuse—memories that they had supposedly forgotten and then, after being interviewed, recovered. The case fell apart, in 1990, because the prosecution could produce no persuasive evidence of the victims’ claims. A cognitive psychologist named Elizabeth Loftus, who had consulted on the case, wondered whether the children’s memories might have been fabricated—in Münsterberg’s formulation, involuntarily elaborated—rather than actually recovered.
Keyword: Learning & Memory
Link ID: 20679 - Posted: 03.12.2015
Mo Costandi Neuroscientists in France have implanted false memories into the brains of sleeping mice. Using electrodes to directly stimulate and record the activity of nerve cells, they created artificial associative memories that persisted while the animals snoozed and then influenced their behaviour when they awoke. Manipulating memories by tinkering with brain cells is becoming routine in neuroscience labs. Last year, one team of researchers used a technique called optogenetics to label the cells encoding fearful memories in the mouse brain and to switch the memories on and off, and another used it to identify the cells encoding positive and negative emotional memories, so that they could convert positive memories into negative ones, and vice versa. The new work, published today in the journal Nature Neuroscience, shows for the first time that artificial memories can be implanted into the brains of sleeping animals. It also provides more details about how populations of nerve cells encode spatial memories, and about the important role that sleep plays in making such memories stronger. Karim Benchenane of the French National Centre for Scientific Research (CNRS) in Paris and his colleagues implanted electrodes into the brains of 40 mice, targeting the medial forebrain bundle (MFB), a component of the reward circuitry, and the CA1 region of the hippocampus, which contains at least three different cell types that encode the memories needed for spatial navigation. © 2015 Guardian News and Media Limited
by Penny Sarchet For some of us, it might have been behind the bikeshed. Not so the African cotton leafworm moth (Spodoptera littoralis), which can choose any one of a vast number of plant species to mate on. But these moths remember their first time, returning to the same species in search of other mates. In the wild, this moth feeds and mates on species from as many as 40 different plant families. That much choice means there's usually something available to eat, but selecting and remembering the best plants is tricky. So, recalling what you ate as a larva, or where you first copulated, may help narrow down which plants provide better quality food or are more likely to attract other potential mates. Magali Proffit and David Carrasco of the Swedish University of Agricultural Sciences in Alnarp and their colleagues have discovered that this moth's first mating experience shapes its future preferences. These moths have an innate preference for cotton plants over cabbage. But when the researchers made them mate for the first time on cabbage, the moths later showed an increased preference for mating or laying eggs on this plant. Further experiments revealed that moths didn't just favour plants they were familiar with, even in combination with a sex pheromone – mating had to be involved. © Copyright Reed Business Information Ltd.