(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)

Synchronous oscillations in the short-term memory

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.

Important advance in brain mapping and memory

“When a tiger starts to move towards you, you need to know whether it is something you are actually seeing or whether it’s just something that you remember or have imagined,” says Prof. Julio Martinez-Trujillo of McGill’s Department of Physiology. The researcher and his team have discovered that there is a clear frontier in the brain between the area that encodes information about what is immediately before the eyes and the area that encodes the abstract representations that are the product of our short-term memory or imagination. It is an important advance in brain mapping and opens the doors to further research in the area of short-term memory.

These finding, which are described in an article just published in Nature Neuroscience, resolve a question that has occupied neuroscientists for years. Namely that of how and where exactly in the brain the visual information coming from our eyes is first transformed into short-term memories. “We found that while one area in the brain processes information about what we are currently seeing, an area right beside it stores the information in short-term memory,” says McGill PhD student Diego Mendoza-Halliday, first author of the article.  “What is so exciting about this finding is that until now, no one knew the place where visual information first gets transformed into short-term memory.”

The researchers arrived at this conclusion by measuring the neuronal activity in these two areas in the brains of macaques as they first looked at, and then after a short time (1.2 - 2 seconds) remembered, a random sequence of dots moving across a computer screen like rainfall. What surprised Martinez-Trujillo and his team was how clearly demarcated the divide was between the activities and functions of the two brain areas, and this despite the fact that they lie side-by-side.

“It is rare to find this kind of sharp boundary in biological systems of any kind,” says Martinez-Trujillo. “Most of the time, when you look at the function of different brain areas, there is more of a transitional zone, more grey and not such a clear border between black and white. I think the evolutionary reason for this clear frontier is that it helped us to survive in dangerous situations.”

The discovery comes after five years spent by Martinez-Trujillo and his team doing research in the area. Despite this fact, he acknowledges that there was a certain amount of serendipity, and a lot of technological help involved in being able to capture a signal that travels for 3 milliseconds and fires synapses in neurons that lie right beside one another.

Martinez-Trujillo and his team continue to work on mapping the receptors and connectivity between these two areas of the brain. But what is most important for him is to try and relate this discovery to schizophrenia and other diseases that involve hallucinations, and in order to do so he is working with a psychiatrist at Montreal’s Douglas Hospital.

(Image: Bigstock)

Stress hormone linked to short-term memory loss as we age

A new study at the University of Iowa reports a potential link between stress hormones and short-term memory loss in older adults.

The study, published in the Journal of Neuroscience, reveals that having high levels of cortisol—a natural hormone in our body whose levels surge when we are stressed—can lead to memory lapses as we age.

Short-term increases in cortisol are critical for survival. They promote coping and help us respond to life’s challenges by making us more alert and able to think on our feet. But abnormally high or prolonged spikes in cortisol—like what happens when we are dealing with long-term stress—can lead to negative consequences that numerous bodies of research have shown to include digestion problems, anxiety, weight gain, and high blood pressure.

In this study, the UI researchers linked elevated amounts of cortisol to the gradual loss of synapses in the prefrontal cortex, the region of the brain that houses short-term memory. Synapses are the connections that help us process, store, and recall information. And when we get older, repeated and long-term exposure to cortisol can cause them to shrink and disappear.

“Stress hormones are one mechanism that we believe leads to weathering of the brain,” says Jason Radley, assistant professor in psychology at the UI and corresponding author on the paper. Like a rock on the shoreline, after years and years it will eventually break down and disappear.

While previous studies have shown cortisol to produce similar effects in other regions of the aging brain, this was the first study to examine its impact on the prefrontal cortex.

And although preliminary, the findings raise the possibility that short-memory decline in aging adults may be slowed or prevented by treatments that decrease levels of cortisol in susceptible individuals, says Radley. That could mean treating people who have naturally high levels of cortisol—such as those who are depressed—or those who experience repeated, long-term stress due to traumatic life events like the death of a loved one.

According to Radley and Rachel Anderson, the paper’s lead author and a second year-graduate student in psychology at the UI, short-term memory lapses related to cortisol start around age 65. That’s about the equivalent of 21 month-old rats, which the pair studied to make their discovery.

The UI scientists compared the elderly rats to four-month old rats, which are roughly the same age as a 20 year-old person. The young and elderly groups were then separated further according to whether the rats had naturally high or naturally low levels of corticosterone—the hormone comparable to cortisol in humans.

The researchers subsequently placed the rats in a T-shaped maze that required them to use their short-term memory. In order to receive a treat, they needed to recall which direction they had turned at the top of the T just 30, 60, or 120 seconds ago and then turn the opposite way each time they ran the maze.

Though memory declined across all groups as the time rats waited before running the maze again increased, older rats with high corticosterone levels consistently performed the worst. They chose the correct direction only 58 percent of the time, compared to their older peers with low corticosterone levels who chose it 80 percent of the time.

When researchers took tissue samples from the rats’ prefrontal cortexes and examined them under a microscope, they found the poor performers had smaller and 20 percent fewer synapses than all other groups, indicating memory loss.

In contrast, older rats with low corticosterone levels showed little memory loss and ran the maze nearly as well as the younger rats, who were not affected by any level of corticosterone—low or high.

Still, researchers say it’s important to remember that stress hormones are only one of a host of factors when it comes to mental decline and memory loss as we age.

Chewing gum helps you concentrate for longer

Chewing gum can help you stay focused for longer on tasks that require continuous monitoring.

This is the finding of new research by Kate Morgan and colleagues from Cardiff University published in the British Journal of Psychology.

Previous research has shown that chewing gum can improve concentration in visual memory tasks. This study focussed on the potential benefits of chewing gum during an audio memory task.

Kate Morgan, author of the study explained: “It’s been well established by previous research that chewing gum can benefit some areas of cognition. In our study we focussed on an audio task that involved short-term memory recall to see if chewing gum would improve concentration; especially in the latter stages of the task.”

The study involved 38 participants being split in to two groups. Both groups completed a 30 minute audio task that involved listening to a list of numbers from 1-9 being read out in a random manner. Participants were scored on how accurately and quickly they were able to detect a sequence of odd-even-odd numbers, such as 7-2-1. Participants also completed questionnaires on their mood both before and after the task.

The results showed that participants who chewed gum had quicker reaction times and more accurate results than the participants who didn’t chew gum. This was especially the case towards the latter parts of the task.

Kate explained: “Interestingly participants who didn’t chew gum performed slightly better at the beginning of the task but were overtaken by the end. This suggests that chewing gum helps us focus on tasks that require continuous monitoring over a longer amount of time.”

The study was discussed in Radio Four Today programme.

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How chronic pain disrupts short term memory

A group of Portuguese researchers from IBMC and FMUP at the University of Porto has found the reason why patients with chronic pain often suffer from impaired short –term memory. The study, to be published in the Journal of Neuroscience, shows how persistent pain disrupts the flow of information between two brain regions crucial to retain temporary memories.

Chronic pain suffers often complain of short term memory’s problems. The neural mechanisms why this occurs are however not understood. Recent studies in animals showed that pain can disturb several cognitive processes as well as change the brain pathways for how we think and feel. Of the many cognitive disturbances observed the most important include problems in spatial memory, recognition memory, attention and even emotional and non-emotional decisions.

In the new article the team of researchers from the University of Porto led by Vasco Gallardo describes in a rat model of neuropathic pain how a neuronal circuit crucial for the processing of short-term memory is affected by pain. The circuit, established between the prefrontal cortex and the hippocampus, is essential for encoding and retaining temporary memories on spatial information. The researchers used multi-electrodes implanted in the brain to record neuronal activity during a behaviour dependent of spatial memory - the animals were trained in a maze where they had to choose between two alternative paths and then asked to recall their chosen path.

The results show that after a painful injury there is a significant reduction in the amount of information that passes through the circuit. This could mean a loss of ability to process information on spatial localization memory, or that those regions critical to memory are now “overwhelmed” by the painful stimuli disrupting the flow of information for memory.

According to Vasco Gallardo, the team ” has already demonstrated that peripheral nerve injury induces an instability in the spatial coding capacity of hippocampus neurons “, where is seen “a clear reduction in their capacity to encode information on the location of the animal.”

So to the author “this new work contributes to the demonstration that chronic pain induces alterations in the function of brain circuits that are not directly connected to tactile or painful processes”. So as a result of chronic pain it is seen that “are also affected neuronal circuits linked to the processing of memories and emotions, what might mean a need for larger and more integrative strategies in the treatment of painful pathologies”, says the researcher.

Four is the “magic” number

According to psychological lore, when it comes to items of information the mind can cope with before confusion sets in, the “magic” number is seven. But a new analysis by a leading Australian psychiatrist challenges this long-held view, suggesting the number might actually be four.

In 1956, American psychologist George Miller published a paper in the influential journal Psychological Review arguing the mind could cope with a maximum of only seven chunks of information. The paper, “The Magical Number Seven, Plus or Minus Two. Some Limits on Our Capacity for Processing Information”, has since become one of the most highly cited psychology articles and has been judged by the Psychological Review as its most influential paper of all time.

But UNSW professor of psychiatry Gordon Parker says a re-analysis of the experiments used by Miller shows he missed the correct number by a wide mark. Writing in the journal Acta Psychiatrica Scandinavica, Scientia Professor Parker says a closer look at the evidence shows the human mind copes with a maximum of four ‘chunks’ of information, not seven.

“So to remember a seven numeral phone number, say 6458937, we need to break it into four chunks: 64. 58. 93. 7.   Basically four is the limit to our perception.

“That’s a big difference for a paper that is one of the most highly referenced psychology articles ever – nearly a 100 percent discrepancy,” he suggests.

Professor Parker says the success of the original paper lies “more in its multilayered title and Miller’s evocative use of the word ‘magic’,” than in the science.

Professor Parker says 50 years after Miller there is still uncertainty about the nature of the brain’s storage capacity limits: “There may be no limit in storage capacity per se but only a limit to the duration in which items can remain active in short-term memory”. “Regardless, the consensus now is that humans can best store only four chunks in short-term memory tasks,” he says.

Making a Game Out of Improving the ‘Sticky’ Brain

UCSF neuroscientists have found that by training on attention tests, people young and old can improve brain performance and multitasking skills.

Anyone who tries to perform two tasks at once is likely to do worse on both. Why that is so at the neurological level has largely been terra incognita. But research now is starting to reveal the impact of multitasking on short-term memory and attention.

Adam Gazzaley, MD, PhD, associate professor of neurology, physiology and psychiatry, and researchers at the UCSF Neuroscience Imaging Center use EEG, MRI and other non-invasive tools to study cognitive processes while people try their best on drills that test short-term memory.

Brain’s Code for Visual Working Memory Deciphered in Monkeys

The brain holds in mind what has just been seen by synchronizing brain waves in a working memory circuit, an animal study supported by the National Institutes of Health suggests. The more in-sync such electrical signals of neurons were in two key hubs of the circuit, the more those cells held the short-term memory of a just-seen object.

Charles Gray, Ph.D., of Montana State University, Bozeman, a grantee of NIH’s National Institute of Mental Health (NIMH), and colleagues, report their findings Nov. 1, 2012, online, in the journal Science Express.

“This work demonstrates, for the first time, that there is information about short term memories reflected in in-sync brainwaves,” explained Gray.

“The Holy Grail of neuroscience has been to understand how and where information is encoded in the brain. This study provides more evidence that large scale electrical oscillations across distant brain regions may carry information for visual memories,” said NIMH director Thomas R. Insel, M.D.

Prior to the study, scientists had observed synchronous patterns of electrical activity between the two circuit hubs after a monkey saw an object, but weren’t sure if the signals actually represent such short-term visual memories in the brain. Rather, it was thought that such neural oscillations might play the role of a traffic cop, directing information along brain highways.

The Fabric for Weaving Memory

The details of memory formation are still largely unknown. It has, however, been established that the two kinds of memory – long term and short term – use different mechanisms. When short-term memory is formed, certain proteins in the nerve cells (neurons) of the brain are transiently modified. To establish long-term memory, the cells have to synthesize new protein molecules. This has been shown in experiments with animals. When drugs were used to block protein synthesis, the treated animals were not able to form long-term memory.

The precise mechanism by which the newly synthesized proteins regulate memory formation is still poorly understood. They are thought to strengthen existing connections between neurons, as well as establish new connections. Both processes are required for long-term memory formation.

A nerve cell in the brain makes connections with tens of thousands of other nerve cells through so-called synapses. When memory is formed, only specific synapses, which are activated by a specific experience are modified. The mechanism of how the synthesis of new proteins can be restricted to these activated synapses has been unclear. Neurobiologists have postulated the existence of “synaptic tags”. One of the candidates is a family of proteins known to regulate local protein synthesis, the CPEB family of proteins. These proteins have been known for some time to perform important tasks during embryonic development, and recently have been identified in neuronal synapses.

In 2007, Krystyna Keleman, a neuroscientist at the Research Institute of Molecular Pathology (IMP) in Vienna, was able to show that fruit flies require CPEB proteins for long-term memory formation.

To study memory formation, the researchers at the IMP looked at the sexual behavior of flies. After copulation, female flies loose interest in the courtship advances of males. Male flies must learn – by trial and error – that only virgin females are receptive. The key to telling them apart is their smell.