Posts tagged memory
Articles and news from the latest research reports.
Sleep Oscillations in the Thalamocortical System Induce Long-Term Neuronal Plasticity
Long-term plasticity contributes to memory formation and sleep plays a critical role in memory consolidation. However, it is unclear whether sleep slow oscillation by itself induces long-term plasticity that contributes to memory retention. Using in vivo prethalamic electrical stimulation at 1 Hz, which itself does not induce immediate potentiation of evoked responses, we investigated how the cortical evoked response was modulated by different states of vigilance. We found that somatosensory evoked potentials during wake were enhanced after a slow-wave sleep episode (with or without stimulation during sleep) as compared to a previous wake episode. In vitro, we determined that this enhancement has a postsynaptic mechanism that is calcium dependent, requires hyperpolarization periods (slow waves), and requires a coactivation of both AMPA and NMDA receptors. Our results suggest that long-term potentiation occurs during slow-wave sleep, supporting its contribution to memory.
Bumblebees are anything but bumbling: The insects quickly figure out the optimal route for visiting five far-flung flowers, a computational task that even human brains find challenging.
That result suggests that an elaborate mental map isn’t necessary to travel efficiently in unknown territory. Finding a way to mimic the bumblebee’s navigation system may allow programmers to develop robots that adeptly maneuver through unfamiliar places.
The new study, published online September 20 in PLOS Biology, pulls together several lines of previous research into one grand experiment. After training bumblebees to associate artificial flowers with a reward, scientists from the University of Sydney, Rothamsted Research in Harpenden, England and Queen Mary University of London arranged five flowers in a pentagon with sides 50 meters long. One at a time, bumblebees outfitted with a little radar antenna were released from the nest. The bees’ movements were tracked by radar, and motion-sensing cameras on the flowers recorded each visiting bee.
A computer analysis of the bees’ movements suggested that the insects were doing some quick comparing. If a bee went from flower A to B and later went from flower A to C, it would compare those routes, adding the one that was shorter to its itinerary and abandoning longer paths. The bees also made adjustments when a flower was moved to a different location. These results suggest that bees don’t need a big-picture map to search their surroundings, says team member Mathieu Lihoreau, a behavioral ecologist at the University of Sydney.
“It’s amazing that these little creatures are as flexible as they are and have evolved these solutions that make maximum use of these little brains they are carrying around,” says behavioral biologist Fred Dyer of Michigan State University in East Lansing.
Fear can be erased from the brain
Newly formed emotional memories can be erased from the human brain. This is shown by researchers from Uppsala University in a new study now being published by the academic journal Science. The findings may represent a breakthrough in research on memory and fear. Thomas Ågren, a doctoral candidate at the Department of Psychology under the supervision of Professors Mats Fredrikson and Tomas Furmark, has shown, that it is possible to erase newly formed emotional memories from the human brain.
When a person learns something, a lasting long-term memory is created with the aid of a process of consolidation, which is based on the formation of proteins. When we remember something, the memory becomes unstable for a while and is then restabilized by another consolidation process. In other words, it can be said that we are not remembering what originally happened, but rather what we remembered the last time we thought about what happened. By disrupting the reconsolidation process that follows upon remembering, we can affect the content of memory.
Remember the telephone game where people take turns whispering a message into the ear of the next person in line? By the time the last person speaks it out loud, the message has radically changed. It’s been altered with each retelling.
Turns out your memory is a lot like the telephone game, according to a new Northwestern Medicine study.
Every time you remember an event from the past, your brain networks change in ways that can alter the later recall of the event. Thus, the next time you remember it, you might recall not the original event but what you remembered the previous time. The Northwestern study is the first to show this.
“A memory is not simply an image produced by time traveling back to the original event — it can be an image that is somewhat distorted because of the prior times you remembered it,” said Donna Bridge, a postdoctoral fellow at Northwestern University Feinberg School of Medicine and lead author of the paper on the study recently published in the Journal of Neuroscience. “Your memory of an event can grow less precise even to the point of being totally false with each retrieval.”
The party drug mephedrone can cause lasting damage to the brain, according to new research led by the University of Sydney.
"Mephedrone is highly addictive in the worst possible way. Users tend to binge on massive doses of the drug over short time spans," said Craig Motbey, a PhD candidate in the University’s School of Psychology and lead author of the research published in PLOS ONE, the Public Library of Science journal, today.
"Combined with the fact mephedrone is skyrocketing in popularity worldwide, with Australia following that trend, our finding that high doses can cause ongoing cognitive impairment spells a significant risk for users."
Also known as ‘meow meow’ and ‘MCAT’, mephedrone’s immediate effect on the brain is similar to a combination of ecstasy and methamphetamine.
"You get the euphoria and touchy-feeliness of ecstasy together with the intense addictiveness of methamphetamine or cocaine," said Motbey.
The current results, based upon experiments with laboratory rats, provide evidence of mephedrone’s ability to damage memory.
CAMH illuminates roles of novel epigenetic chemical in the brain
Researchers from the Centre for Addiction and Mental Health (CAMH) have identified a new role of a chemical involved in controlling the genes underlying memory and learning.
"The brain is a plastic tissue, and we know that learning and memory require various genes to be expressed,” says CAMH Senior Scientist Dr. Art Petronis, who is a senior author on the new study. “Our research has identified how the chemical 5-hmC may be involved in the epigenetic processes allowing this plasticity.” Dr. Petronis is head of the Krembil Family Epigenetics Laboratory in CAMH’s Campbell Family Mental Health Research Institute.
5-hmC is an epigenetic modification of DNA, and was discovered in humans and mice in 2009. DNA modifications are chemical changes to DNA. They flag genes to be turned “on” - signalling the genome to make a protein - or turned “off.” As the overwhelming majority of cells in an individual contain the same genetic code, this pattern of flags is what allows a neuron to use the same genome as a blood or liver cell, but create a completely different and specialized cellular environment.
The research, published online in Nature Structural & Molecular Biology, sheds light on the role of 5-hmC. Intriguingly, it is more abundant in the brain than in other tissues in the body, for reasons not clear to date.
The CAMH team of scientists examined DNA from a variety of tissues, including the mouse and human brain, and looked at where 5-hmC was found in the genome. They detected that 5-hmC had a unique distribution in the brain: it was highly enriched in genes related to the synapse, the dynamic tips of brain cells. Growth and change in the synapse allow different brain cells to “wire” together, which allows learning and memory.
"This enrichment of 5-hmC in synapse-related genes suggests a role for this epigenetic modification in learning and memory," says Dr. Petronis.
The team further showed that 5-hmC had a special distribution even within the gene. The code for one gene can be edited and “spliced” to create several different proteins. Dr. Petronis found that 5-hmC is located at “splice junctions,” the points where the gene is cut before splicing.
"5-hmC may signal the cell’s splicing machinery to generate the diverse proteins that, in turn, give rise to the unprecedented complexity of the brain," he says.
The research team is continuing to investigate the role of 5-hmC in more detail, and to determine whether 5-hmC function is different in people with bipolar disorder and schizophrenia compared to people without these diagnoses.
This research was funded by the U.S National Institutes of Health, the Canadian Institutes of Health Research, and the Tapscott Chair in Schizophrenia Studies at the University of Toronto.
The Centre for Addiction and Mental Health (CAMH) is Canada’s largest mental health and addiction teaching hospital, as well as one of the world’s leading research centres in the area of addiction and mental health. CAMH combines clinical care, research, education, policy development and health promotion to help transform the lives of people affected by mental health and addiction issues.
(Source: Yahoo!)
Memory vs. Math: Same brain areas show inverse responses to recall and arithmetic
Scientists have historically relied on neuroimaging – but not electrophysiological – data when studying the human default mode network (DMN), a group of brain regions with lower activity during externally-directed tasks and higher activity if tasks require internal focus. Recently, however, researchers at Stanford University School of Medicine recorded electrical activity directly from a core DMN component known as the posteromedial cortex (PMC) during both internally- and externally-directed waking states – specifically, autobiographical memory and arithmetic calculation, respectively. The data they recorded showed an inverse relationship – namely, the degree activation during memory retrieval predicted the degree of suppression during arithmetic calculation – which they say provides important anatomical and temporal details about DMN function at the neural population level.
Improving Memory for Specific Events Can Alleviate Symptoms of Depression
Hear the word “party” and memories of your 8th birthday sleepover or the big bash you attended last New Year’s may come rushing to mind. But it’s exactly these kinds of memories, embedded in a specific place and time, that people with depression have difficulty recalling.
Research has shown that people who suffer from, or are at risk of, depression have difficulty tapping into specific memories from their own past, an impairment that affects their ability to solve problems and leads them to focus on feelings of distress.
In a study forthcoming in Clinical Psychological Science, a new journal of the Association for Psychological Science, psychological scientists Hamid Neshat-Doost of the University of Isfahan, Iran, Laura Jobson of the University of East Anglia, Tim Dalgleish of the Cognition and Brain Sciences Unit, Medical Research Council, Cambridge and colleagues investigated whether a particular training program, Memory Specificity Training, might improve people’s memory for past events and ameliorate their symptoms of depression.
In Iran, the researchers recruited 23 adolescent Afghani refugees who had lost their fathers in the war in Afghanistan and who showed symptoms of depression. Twelve of the adolescents were randomly assigned to participate in the memory training program and 11 were randomly assigned to a control group that received no training.
All of the adolescents completed a memory test in which they saw 18 positive, neutral, and negative words in Persian and were asked to recall a specific memory related to each word. Their responses were categorized as either a specific or a non-specific type of memory. They also completed questionnaires design to measure symptoms of depression and anxiety symptoms.
For five weeks, the adolescents assigned to the training attended a weekly 80-minute group session, in which they learned about different types of memory and memory recall, and practiced recalling specific memories after being given positive, neutral, and negative keywords.
At the end of the five weeks, both the training group and the control group were given the same memory test that they were given at the beginning of the study. And they took the memory test again as part of a follow-up visit two months later.
The adolescents who participated in the training were able to provide more specific memories after the training than those who did not receive intervention. They also showed fewer symptoms of depression than the control group at the two month follow-up. The researchers found that the relationship between participant group (training or control) and their symptoms of depression at follow-up could be accounted for by changes in specific memory recall over time.
These findings are promising because they suggest that a standalone training program that focuses on specific memory recall can actually improve depression symptoms.
Based on the results of this study, Jobson, Dalgleish, and colleagues conclude that, for individuals suffering from depression, “including a brief training component that targets memory recall as an adjunct to cognitive behavioral therapy or prior therapy may have beneficial effects on memory recall and mood.”
Stress breaks loops that hold short-term memory together
Stress has long been pegged as the enemy of attention, disrupting focus and doing substantial damage to working memory — the short-term juggling of information that allows us to do all the little things that make us productive.
By watching individual neurons at work, a group of psychologists at the University of Wisconsin-Madison has revealed just how stress can addle the mind, as well as how neurons in the brain’s prefrontal cortex help “remember” information in the first place.
Working memory is short-term and flexible, allowing the brain to hold a large amount of information close at hand to perform complex tasks. Without it, you would have forgotten the first half of this sentence while reading the second half. The prefrontal cortex is vital to working memory.
"In many respects, you’d look pretty normal without a prefrontal cortex," said Craig Berridge, UW-Madison psychology professor. "You don’t need that part of the brain to hear or talk, to keep long-term memories, or to remember what you did as a child or what you read in the newspaper three days ago."
But without your prefrontal cortex you’d be unable to stay on task or modulate your emotions well.
"People without a prefrontal cortex are very distractible," Berridge said. "They’re very impulsive. They can be very argumentative."
The neurons of the prefrontal cortex help store information for short periods. Like a chalkboard, these neurons can be written with information, erased when that information is no longer needed, and rewritten with something new.
It’s how the neurons maintain access to that short-term information that leaves them vulnerable to stress. David Devilbiss, a scientist working with Berridge and lead author on a study published today in the journal PLOS Computational Biology, applied a new statistical modeling approach to show that rat prefrontal neurons were firing and re-firing to keep recently stored information fresh.
"Even though these neurons communicate on a scale of every thousandth of a second, they know what they did one second to one-and-a-half seconds ago," Devilbiss said. "But if the neuron doesn’t stimulate itself again within a little more than a second, it’s lost that information."
Apply some stress — in the researchers’ case, a loud blast of white noise in the presence of rats working on a maze designed to test working memory — and many neurons are distracted from reminding themselves of … what was it we were doing again?
"We’re simultaneously watching dozens of individual neurons firing in the rats’ brains, and under stress those neurons get even more active," said Devilbiss, whose work was supported by the National Science Foundation and National Institutes of Health. "But what they’re doing is not retaining information important to completing the maze. They’re reacting to other things, less useful things."
Without the roar of white noise, which has been shown to impair rats in the same way it does monkeys and humans, the maze-runners were reaching their goal about 90 percent of the time. Under stress, the animals completed the test at a 65 percent clip, with many struggling enough to fall to blind chance.
Recordings of the electrical activity of prefrontal cortex neurons in the maze-running rats showed these neurons were unable to hold information key to finding the next chocolate chip reward. Instead, the neurons were frenetic, reacting to distractions such as noises and smells in the room.
The effects of stress-related distraction are well-known and dangerous.
"The literature tells us that stress plays a role in more than half of all workplace accidents, and a lot of people have to work under what we would consider a great deal of stress," Devilbiss said. "Air traffic controllers need to concentrate and focus with a lot riding on their actions. People in the military have to carry out these thought processes in conditions that would be very distracting, and now we know that this distraction is happening at the level of individual cells in the brain."
The researchers’ work may suggest new directions for treatment of prefrontal cortex dysfunction.
"Based on drug studies, it had been believed stress simply suppressed prefrontal cortex activity," Berridge said. "These studies demonstrate that rather than suppressing activity, stress modifies the nature of that activity. Treatments that keep neurons on their self-stimulating task while shutting out distractions may help protect working memory."
(Source: news.wisc.edu)