Posts tagged memory
Posts tagged memory
Just look into the light: not quite, but researchers at the UC Davis Center for Neuroscience and Department of Psychology have used light to erase specific memories in mice, and proved a basic theory of how different parts of the brain work together to retrieve episodic memories.
Optogenetics, pioneered by Karl Diesseroth at Stanford University, is a new technique for manipulating and studying nerve cells using light. The techniques of optogenetics are rapidly becoming the standard method for investigating brain function.
Kazumasa Tanaka, Brian Wiltgen and colleagues at UC Davis applied the technique to test a long-standing idea about memory retrieval. For about 40 years, Wiltgen said, neuroscientists have theorized that retrieving episodic memories — memories about specific places and events — involves coordinated activity between the cerebral cortex and the hippocampus, a small structure deep in the brain.
"The theory is that learning involves processing in the cortex, and the hippocampus reproduces this pattern of activity during retrieval, allowing you to re-experience the event," Wiltgen said. If the hippocampus is damaged, patients can lose decades of memories.
But this model has been difficult to test directly, until the arrival of optogenetics.
Wiltgen and Tanaka used mice genetically modified so that when nerve cells are activated, they both fluoresce green and express a protein that allows the cells to be switched off by light. They were therefore able both to follow exactly which nerve cells in the cortex and hippocampus were activated in learning and memory retrieval, and switch them off with light directed through a fiber-optic cable.
They trained the mice by placing them in a cage where they got a mild electric shock. Normally, mice placed in a new environment will nose around and explore. But when placed in a cage where they have previously received a shock, they freeze in place in a “fear response.”
Tanaka and Wiltgen first showed that they could label the cells involved in learning and demonstrate that they were reactivated during memory recall. Then they were able to switch off the specific nerve cells in the hippocampus, and show that the mice lost their memories of the unpleasant event. They were also able to show that turning off other cells in the hippocampus did not affect retrieval of that memory, and to follow fibers from the hippocampus to specific cells in the cortex.
"The cortex can’t do it alone, it needs input from the hippocampus," Wiltgen said. "This has been a fundamental assumption in our field for a long time and Kazu’s data provides the first direct evidence that it is true."
They could also see how the specific cells in the cortex were connected to the amygdala, a structure in the brain that is involved in emotion and in generating the freezing response.
Studying rats as model subjects, scientists found that adolescents were at an increased risk of suffering negative health effects from sugar-sweetened beverage consumption.
Adolescent rats that freely consumed large quantities of liquid solutions containing sugar or high-fructose corn syrup (HFCS) in concentrations comparable to popular sugar-sweetened beverages experienced memory problems and brain inflammation, and became pre-diabetic, according to a new study from USC. Neither adult rats fed the sugary drinks nor adolescent rats who did not consume sugar had the same issues.
“The brain is especially vulnerable to dietary influences during critical periods of development, like adolescence,” said Scott Kanoski, corresponding author of the study and an assistant professor at the USC Dornsife College of Letters, Arts and Sciences.
Kanoski collaborated with USC’s Ted Hsu, Vaibhav Konanur, Lilly Taing, Ryan Usui, Brandon Kayser, and Michael Goran. Their study, which tested a total of 76 rats, was published online by the journal Hippocampus on Sept. 23.
About 35 to 40 percent of the rats’ caloric intake was from sugar or HFCS. For comparason, added sugars make up about 17 percent of the total caloric intake of teens in the U.S. on average, according to the CDC.
The rats were then tested in mazes that probe their spatial memory ability. Adolescent rats that had consumed the sugary beverages, particularly HFCS, performed worse on the test than any other group – which may be the result of the neuroinflammation detected in the hippocampus, Kanoski said.
The hippocampus is a part of the temporal lobe located deep within the brain that controls memory formation. People with Alzheimer’s Disease and other dementias often suffer damage to the hippocampus.
“Consuming a diet high in added sugars not only can lead to weight gain and metabolic disturbances, but can also negatively impact our neural functioning and cognitive ability.” Kanoski said. Next, Kanoski and his team plant to see how different monosaccharides (simple sugars) and HFCS affect the brain.
(Image caption: 3D image of the hippocampus of a rat. Credit: M. Pyka)
People who wish to know how memory works are forced to take a glimpse into the brain. They can now do so without bloodshed: RUB researchers have developed a new method for creating 3D models of memory-relevant brain structures. They published their results in the trade journal “Frontiers in Neuroanatomy”.
Sea Horse gave the hippocampus the name
The way neurons are interconnected in the brain is very complicated. This holds especially true for the cells of the hippocampus. It is one of the oldest brain regions and its form resembles a sea horse (hippocampus in Latin). The hippocampus enables us to navigate space securely and to form personal memories. So far, the anatomic knowledge of the networks inside the hippocampus and its connection to the rest of the brain has left scientists guessing which information arrived where and when.
Signals spread through the brain
Accordingly, Dr Martin Pyka and his colleagues from the Mercator Research Group have developed a method which facilitates the reconstruction of the brain’s anatomic data as a 3D model on the computer. This approach is quite unique, because it enables automatic calculation of the neural interconnection on the basis of their position inside the space and their projection directions. Biologically feasible network structures can thus be generated more easily than it used to be the case with the method available to date. Deploying 3D models, the researchers use this technique to monitor the way neural signals spread throughout the network time-wise. They have, for example, found evidence that the hippocampus’ form and size could explain why neurons in those networks fire in certain frequencies.
Information become memories
In future, this method may help us understand how animals, for example, combine various information to form memories within the hippocampus, in order to memorise food sources or dangers and to remember them in certain situations.
The more curious we are about a topic, the easier it is to learn information about that topic. New research publishing online October 2 in the Cell Press journal Neuron provides insights into what happens in our brains when curiosity is piqued. The findings could help scientists find ways to enhance overall learning and memory in both healthy individuals and those with neurological conditions.
"Our findings potentially have far-reaching implications for the public because they reveal insights into how a form of intrinsic motivation—curiosity—affects memory. These findings suggest ways to enhance learning in the classroom and other settings," says lead author Dr. Matthias Gruber, of University of California at Davis.
For the study, participants rated their curiosity to learn the answers to a series of trivia questions. When they were later presented with a selected trivia question, there was a 14 second delay before the answer was provided, during which time the participants were shown a picture of a neutral, unrelated face. Afterwards, participants performed a surprise recognition memory test for the faces that were presented, followed by a memory test for the answers to the trivia questions. During certain parts of the study, participants had their brains scanned via functional magnetic resonance imaging.
The study revealed three major findings. First, as expected, when people were highly curious to find out the answer to a question, they were better at learning that information. More surprising, however, was that once their curiosity was aroused, they showed better learning of entirely unrelated information (face recognition) that they encountered but were not necessarily curious about. People were also better able to retain the information learned during a curious state across a 24-hour delay. “Curiosity may put the brain in a state that allows it to learn and retain any kind of information, like a vortex that sucks in what you are motivated to learn, and also everything around it,” explains Dr. Gruber.
Second, the investigators found that when curiosity is stimulated, there is increased activity in the brain circuit related to reward. “We showed that intrinsic motivation actually recruits the very same brain areas that are heavily involved in tangible, extrinsic motivation,” says Dr. Gruber. This reward circuit relies on dopamine, a chemical messenger that relays messages between neurons.
Third, the team discovered that when curiosity motivated learning, there was increased activity in the hippocampus, a brain region that is important for forming new memories, as well as increased interactions between the hippocampus and the reward circuit. “So curiosity recruits the reward system, and interactions between the reward system and the hippocampus seem to put the brain in a state in which you are more likely to learn and retain information, even if that information is not of particular interest or importance,” explains principal investigator Dr. Charan Ranganath, also of UC Davis.
The findings could have implications for medicine and beyond. For example, the brain circuits that rely on dopamine tend to decline in function as people get older, or sooner in people with neurological conditions. Understanding the relationship between motivation and memory could therefore stimulate new efforts to improve memory in the healthy elderly and to develop new approaches for treating patients with disorders that affect memory. And in the classroom or workplace, learning what might be considered boring material could be enhanced if teachers or managers are able to harness the power of students’ and workers’ curiosity about something they are naturally motivated to learn.
The Georgia Tech research isn’t the first to find that exercise can improve memory. But the study, which was just published in the journal Acta Psychologica, took a few new approaches. While many existing studies have demonstrated that months of aerobic exercises such as running can improve memory, the current study had participants lift weights just once two days before testing them. The Georgia Tech researchers also had participants study events just before the exercise rather than after workout. They did this because of extensive animal research suggesting that the period after learning (or consolidation) is when the arousal or stress caused by exercise is most likely to benefit memory.
The study began with everyone looking at a series of 90 photos on a computer screen. The images were evenly split between positive (i.e. kids on a waterslide), negative (mutilated bodies) and neutral (clocks) pictures. Participants weren’t asked to try and remember the photos. Everyone then sat at a leg extension resistance exercise machine. Half of them extended and contracted each leg at their personal maximum effort 50 times. The control group simply sat in the chair and allowed the machine and the experimenter to move their legs. Throughout the process, each participant’s blood pressure and heart rate were monitored. Every person also contributed saliva samples so the team could detect levels of neurotransmitter markers linked to stress.
The participants returned to the lab 48 hours later and saw a series of 180 pictures – the 90 originals were mixed in with 90 new photos. The control group recalled about 50 percent of the photos from the first session. Those who exercised remembered about 60 percent.
“Our study indicates that people don’t have to dedicate large amounts of time to give their brain a boost,” said Lisa Weinberg, the Georgia Tech graduate student who led the project.
Although the study used weight exercises, Weinberg notes that resistance activities such as squats or knee bends would likely produce the same results. In other words, exercises that don’t require the person to be in good enough to shape to bike, run or participate in prolonged aerobic exercises.
While all participants remembered the positive and negative images better than the neutral images, this pattern was greatest in the exercise participants, who showed the highest physiological responses. The team expected that result, as existing research on memory indicates that people are more likely to remember emotional experiences especially after acute (short-term) stress.
But why does it work? Existing, non-Georgia Tech human research has linked memory enhancements to acute stress responses, usually from psychological stressors such as public speaking. Other studies have also tied specific hormonal and norepinephrine releases in rodent brains to better memory. Interestingly, the current study found that exercise participants had increased saliva measures of alpha amylase, a marker of central norepinephrine.
“Even without doing expensive fMRI scans, our results give us an idea of what areas of the brain might be supporting these exercise-induced memory benefits,” said Audrey Duarte, an associate professor in the School of Psychology. “The findings are encouraging because they are consistent with rodent literature that pinpoints exactly the parts of the brain that play a role in stress-induced memory benefits caused by exercise.”
The collaborative team of psychology and applied physiology faculty and students plans to expand the study in the future, now that the researchers know resistance exercise can enhance episodic memory in healthy young adults.
“We can now try to determine its applicability to other types of memories and the optimal type and amount of resistance exercise in various populations,” said Minoru Shinohara, an associate professor in the School of Applied Physiology. “This includes older adults and individuals with memory impairment.”
Vitamin D in diet might ease effects of age on memory
If you don’t want to dumb down with age, vitamin D may be the meal ticket.
A boosted daily dosage of the vitamin over several months helped middle-aged rats navigate a difficult water maze better than their lower-dosed cohorts, according to a study published online Monday in the journal Proceedings of the National Academy of Sciences.
The supplement appears to boost the machinery that helps recycle and repackage signaling chemicals that help neurons communicate with one another in a part of the brain that is central to memory and learning.
"This process is like restocking shelves in grocery stores," said study co-author Nada Porter, a biomedical pharmacologist at the University of Kentucky College of Medicine.
RMIT University researchers have brought ultra-fast, nano-scale data storage within striking reach, using technology that mimics the human brain.
The researchers have built a novel nano-structure that offers a new platform for the development of highly stable and reliable nanoscale memory devices.
The pioneering work will feature on a forthcoming cover of prestigious materials science journal Advanced Functional Materials (11 November).
Project leader Dr Sharath Sriram, co-leader of the RMIT Functional Materials and Microsystems Research Group, said the nanometer-thin stacked structure was created using thin film, a functional oxide material more than 10,000 times thinner than a human hair.
“The thin film is specifically designed to have defects in its chemistry to demonstrate a ‘memristive’ effect – where the memory element’s behaviour is dependent on its past experiences,” Dr Sriram said.
“With flash memory rapidly approaching fundamental scaling limits, we need novel materials and architectures for creating the next generation of non-volatile memory.
“The structure we developed could be used for a range of electronic applications – from ultrafast memory devices that can be shrunk down to a few nanometers, to computer logic architectures that replicate the versatility and response time of a biological neural network.
“While more investigation needs to be done, our work advances the search for next generation memory technology can replicate the complex functions of human neural system – bringing us one step closer to the bionic brain.”
The research relies on memristors, touted as a transformational replacement for current hard drive technologies such as Flash, SSD and DRAM. Memristors have potential to be fashioned into non-volatile solid-state memory and offer building blocks for computing that could be trained to mimic synaptic interfaces in the human brain.
(Image caption: In the two brain regions IPF (lateral prefrontal cortex) and V4, a region of the visual system, the brain activity oscillates in a specific frequency range. Credit: © Stefanie Liebe, MPI for biological Cybernetics)
School children and university students are often big fans of the short-term memory – not least when they have to cram large volumes of information on the eve of an exam. Although its duration is brief, short term memory is a complex network of neurons in the brain that includes different brain regions. To store the information, these regions must work together. Researchers from the Max Planck Institute for Biological Cybernetics in Tübingen have now discovered that the participating regions must be active at the same time to enable us to form short-term memories of things that happen.
When we see something, signals from the eyes are processed in areas of the cerebral cortex located at the back of the head. For short-term memory, in contrast, regions in the front part of the cerebral cortex must be active. In order for us to remember something we have seen briefly, these far-apart regions of the brain must collate their information.
How this works can only be examined in apes. Scientists from Nikos Logothetis’s Department at the Max Planck Institute for Biological Cybernetics in Tübingen measured the electrical activity in an optic region and in the front area of the brain while the animals had to remember different images.
In the process, the scientists observed electrical vibrations, known as theta-band oscillations, in the two regions of brain. Surprisingly, these oscillations did not arise independently, but were synchronous. The more synchronously active the regions, the better the animals were able to remember an image.
Accordingly, the functioning of short-term memory can be envisaged as two revolving doors: While the memory is at work, the two doors move in time with each other and, in this way, facilitate the more effective exchange of information.
The study shows how important synchronised brain oscillations are for the communication between the different regions of the brain. Almost all higher intellectual capacities result from the complex interplay of specialised neuronal networks in different parts of the brain.
New research by scientists at the University of Kentucky’s Sanders-Brown Center on Aging suggests that people who notice their memory is slipping may be on to something.
The research, led by Richard Kryscio, Ph.D., chair of the Department of of Biostatistics and associate director of the Alzheimer’s Disease Center at UK, appears to confirm that self-reported memory complaints are strong predictors of clinical memory impairment later in life.
Kryscio and his group asked 531 people with an average age of 73 and free of dementia if they had noticed any changes in their memory in the prior year. The participants were also given annual memory and thinking tests for an average of 10 years. After death, participants’ brains were examined for evidence of Alzheimer’s disease.
During the study, 56 percent of the participants reported changes in their memory, at an average age of 82. The study found that participants who reported changes in their memory were nearly three times more likely to develop memory and thinking problems. About one in six participants developed dementia during the study, and 80 percent of those first reported memory changes.
"What’s notable about our study is the time it took for the transition from self-reported memory complaint to dementia or clinical impairment — about 12 years for dementia and nine years for clinical impairment — after the memory complaints began," Kryscio said. "That suggests that there may be a significant window of opportunity for intervention before a diagnosable problem shows up."
Kryscio points out that while these findings add to a growing body of evidence that self-reported memory complaints can be predictive of cognitive impairment later in life, there isn’t cause for immediate alarm if you can’t remember where you left your keys.
"Certainly, someone with memory issues should report it to their doctor so they can be followed. Unfortunately, however, we do not yet have preventative therapies for Alzheimer’s disease or other illnesses that cause memory problems."
The research, which was supported by grants from the National Institutes of Health, the National Institute on Aging, and the National Center for Advancing Translational Sciences, was published in the Sept. 24, 2014, online issue of Neurology.
Xanthohumol, a type of flavonoid found in hops and beer, has been shown in a new study to improve cognitive function in young mice, but not in older animals.
The research was just published in Behavioral Brain Research by scientists from the Linus Pauling Institute and College of Veterinary Medicine at Oregon State University. It’s another step toward understanding, and ultimately reducing the degradation of memory that happens with age in many mammalian species, including humans.
Flavonoids are compounds found in plants that often give them their color. The study of them – whether in blueberries, dark chocolate or red wine - has increased in recent years due to their apparent nutritional benefits, on issues ranging from cancer to inflammation or cardiovascular disease. Several have also been shown to be important in cognition.
Xanthohumol has been of particular interest because of possible value in treating metabolic syndrome, a condition associated with obesity, high blood pressure and other concerns, including age-related deficits in memory. The compound has been used successfully to lower body weight and blood sugar in a rat model of obesity.
The new research studied use of xanthohumol in high dosages, far beyond what could be obtained just by diet. At least in young animals, it appeared to enhance their ability to adapt to changes in the environment. This cognitive flexibility was tested with a special type of maze designed for that purpose.
“Our goal was to determine whether xanthohumol could affect a process we call palmitoylation, which is a normal biological process but in older animals may become harmful,” said Daniel Zamzow, a former OSU doctoral student and now a lecturer at the University of Wisconsin/Rock County.
“Xanthohumol can speed the metabolism, reduce fatty acids in the liver and, at least with young mice, appeared to improve their cognitive flexibility, or higher level thinking,” Zamzow said. “Unfortunately it did not reduce palmitoylation in older mice, or improve their learning or cognitive performance, at least in the amounts of the compound we gave them.”
Kathy Magnusson, a professor in the OSU Department of Biomedical Sciences, principal investigator with the Linus Pauling Institute and corresponding author on this study, said that xanthohumol continues to be of significant interest for its biological properties, as are many other flavonoids.
“This flavonoid and others may have a function in the optimal ability to form memories,” Magnusson said. “Part of what this study seems to be suggesting is that it’s important to begin early in life to gain the full benefits of healthy nutrition.”
It’s also important to note, Magnusson said, that the levels of xanthohumol used in this study were only possible with supplements. As a fairly rare micronutrient, the only normal dietary source of it would be through the hops used in making beer, and “a human would have to drink 2000 liters of beer a day to reach the xanthohumol levels we used in this research.”
In this and other research, Magnusson’s research has primarily focused on two subunits of the NMDA receptor, called GluN1 and GluN2B. Their decline with age appears to be related to the decreased ability to form and quickly recall memories.
In humans, many adults start to experience deficits in memory around the age of 50, and some aspects of cognition begin to decline around age 40, the researchers noted in their report.