Category: Memory

 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.

In the study the researchers showed subjects a neutral picture and simultaneously administered an electric shock. In this way the picture came to elicit fear in the subjects which meant a fear memory had been formed. In order to activate this fear memory, the picture was then shown without any accompanying shock. For one experimental group the reconsolidation process was disrupted with the aid of repeated presentations of the picture. For a control group, the reconsolidation process was allowed to complete before the subjects were shown the same repeated presentations of the picture.

In that the experimental group was not allowed to reconsolidate the fear memory, the fear they previously associated with the picture dissipated. In other words, by disrupting the reconsolidation process, the memory was rendered neutral and no longer incited fear. At the same time, using a MR-scanner, the researchers were able to show that the traces of that memory also disappeared from the part of the brain that normally stores fearful memories, the nuclear group of amygdala in the temporal lobe.

'These findings may be a breakthrough in research on memory and fear. Ultimately the new findings may lead to improved treatment methods for the millions of people in the world who suffer from anxiety issues like phobias, post-traumatic stress, and panic attacks,' says Thomas Ågren.

Journal Reference:

1. T. Agren, J. Engman, A. Frick, J. Bjorkstrand, E.-M. Larsson, T. Furmark, M. Fredrikson. Disruption of Reconsolidation Erases a Fear Memory Trace in the Human Amygdala. Science, 2012; 337 (6101): 1550 DOI: 10.1126/science.1223006

The hippocampus represents an important brain structure for learning. Scientists at the Max Planck Institute of Psychiatry in Munich discovered how it filters electrical neuronal signals through an input and output control, thus regulating learning and memory processes.

Accordingly, effective signal transmission needs so-called theta-frequency impulses of the cerebral cortex. With a frequency of three to eight hertz, these impulses generate waves of electrical activity that propagate through the hippocampus. Impulses of a different frequency evoke no transmission, or only a much weaker one. Moreover, signal transmission in other areas of the brain through long-term potentiation (LTP), which is essential for learning, occurs only when the activity waves take place for a certain while. The scientists even have an explanation for why we are mentally more productive after drinking a cup of coffee or in an acute stress situation: in their experiments, caffeine and the stress hormone corticosterone boosted the activity flow.

When we learn and recall something, we have to concentrate on the relevant information and experience it again and again. Electrophysiological experiments in mice now show why this is the case. Scientists belonging to Matthias Eder´s Research Group measured the transmission of electrical impulses between neurons in the mouse hippocampus. Under the fluorescence microscope, they were able to observe in real time how the neurons forward signals.

Jens Stepan, a junior scientist at the Max Planck Institute of Psychiatry in Munich, stimulated the input region of the hippocampus the first time that specifically theta-frequency stimulations produce an effective impulse transmission across the hippocampal CA3/CA1 region. This finding is very important, as it is known from previous studies that theta-rhythmical neuronal activity in the entorhinal cortex always occurs when new information is taken up in a focused manner. With this finding, the researchers demonstrate that the hippocampus highly selectively reacts to the entorhinal signals. Obviously, it can distinguish important and, thus, potentially recollection-worth information from unimportant one and process it in a physiologically specific manner.

One possible reaction is the formation of the so-called long-term potentiation (LTP) of signal transmission at CA3-CA1 synapses, which is often essential for learning and memory. The present study documents that this CA1-LTP occurs only when the activity waves through the hippocampus take place for a certain time. Translating this to our learning behavior, to commit for instance an image to memory, we should intently view it for a while, as only then we produce the activity waves described long enough to store the image in our brain.

With this study, Matthias Eder and colleagues succeeded in closing a knowledge gap. "Our investigation on neuronal communication via the hippocampal trisynaptic circuit provides us with a new understanding of learning in the living organism. We are the first to show that long-term potentiation depends on the frequency and persistency of incoming sensory signals in the hippocampus," says Matthias Eder.

Journal Reference:

1. Jens Stepan, Julien Dine, Thomas Fenzl, Stephanie A. Polta, Gregor von Wolff, Carsten T. Wotjak, Matthias Eder. Entorhinal theta-frequency input to the dentate gyrus trisynaptically evokes hippocampal CA1 LTP. Frontiers in Neural Circuits, 2012; 6 DOI: 10.3389/fncir.2012.00064

Multiple synaptic contacts between nerve cells facilitate the creation of a new contact, as neuroscientists from the Bernstein Center Freiburg and the Forschungszentrum Jülich report in the latest issue of the journal PLoS Computational Biology. An integral mechanism of memory foundation is the formation of additional contacts between neurons in the brain. However, until now it was not known what conditions lead to the development of such synapses and how they are stabilized once created. By studying mathematical models, the scientists found a simple explanation for how and when synapses form — or disappear — in the brain.

The scientists investigated the hypothesis that synapses between nerve cells strengthen if they are active in quick succession. This consolidates memory. The team used theoretical computer models to determine what conditions need to be present for synapses to form — or disappear. Until now it was not known how it is decided on the level of individual nerve cells whether a connection with another neuron will be formed or not. The problem is that a single cell has no access to information concerning whether a synapse will contribute to the establishment of a particular memory.

Dr. Moritz Deger from the Bernstein Center Freiburg and his colleagues have found a simple mechanism which allows them to explain the formation of synapses: If one nerve cell is already connected to a second cell by several synaptic contacts, all of the contacts work together to stimulate the latter cell. This means that under these conditions the individual contacts cooperate to form synapses. But synapses will form and remain only if the neurons become active in the right order; otherwise they will disappear again. This order in cell activity must be measurable for the synaptic contacts, and indeed, physiologists have already found chemical compounds within the brain that might play this role.

As the scientists from Freiburg and Jülich report, their mathematical model can explain the frequency of synaptic connections observed in experiments. This is a strong indication that they have discovered a long-sought mechanism for memory formation.

— A target article in the Journal of Applied Research in Memory and Cognition concludes that evidence does not support the claims of Cogmed Working Memory Training. Additional experts weigh in with commentary papers in response.

Helping children achieve their full potential in school is of great concern to everyone, and a number of commercial products have been developed to try and achieve this goal. The Cogmed Working Memory Training program is such an example and is marketed to schools and parents of children with attention problems caused by poor working memory. But, does the program actually work? The target article in the September issue of Journal of Applied Research in Memory and Cognition (JARMAC) calls into question Cogmed's claims of improving working memory and addressing underachievement due to working memory constraints.

The target article authors Zach Shipstead, Kenny L. Hicks, Randall W. Engle, all from the Georgia Institute of Technology, review the research that is used to back up the claims of Cogmed. They argue that many of the problem-solving or training tasks are not related to working memory, many of the attention tasks are unrelated to problems such as ADHD, and that there is limited transfer to real-life manifestations of inattentive behavior. They conclude succinctly: "The only unequivocal statement that can be made is that Cogmed will improve performance on tasks that resemble Cogmed training."

"People deserve to hear both sides of the story before they invest money in products like Cogmed," says lead author Zach Shipstead.

Not all researchers agree with the arguments of Shipstead et al. For instance, in one of the commentaries in reply, Torkel Klingberg of the Karolinska Instituet in Sweden states that "Shipstead et al criticizes these studies with three different arguments: […] None of these arguments holds."

Two commentary authors, Charles Hulme and Monica Melby-Lervåg, who have previously questioned the evidence for Cogmed in a 2012 meta-analysis, and whose claims Cogmed directly address on their website, are firmly in support of the target article, and provide further meta-analysis in support of their shared conclusions with Shipstead et al.

— In recent years, educators have come to focus more and more on the importance of lab-based experimentation, hands-on participation, student-led inquiry, and the use of "manipulables" in the classroom. The underlying rationale seems to be that students are better able to learn when they can control the flow of their experience, or when their learning is "self-directed."

While the benefits of self-directed learning are widely acknowledged, the reasons why a sense of control leads to better acquisition of material are poorly understood.

Some researchers have highlighted the motivational component of self-directed learning, arguing that this kind of learning is effective because it makes students more willing and more motivated to learn. But few researchers have examined how self-directed learning might influence cognitive processes, such as those involved in attention and memory.

In an article published in Perspectives on Psychological Science, a journal of the Association for Psychological Science, researchers Todd Gureckis and Douglas Markant of New York University address this gap in understanding by examining the issue of self-directed learning from a cognitive and a computational perspective.

According to Gureckis and Markant, research from cognition offers several explanations that help to account for the advantages of self-directed learning. For example, self-directed learning helps us optimize our educational experience, allowing us to focus effort on useful information that we don't already possess and exposing us to information that we don't have access to through passive observation. The active nature of self-directed learning also helps us in encoding information and retaining it over time.

But we're not always optimal self-directed learners. The many cognitive biases and heuristics that we rely on to help us make decisions can also influence what information we pay attention to and, ultimately, learn.

Gureckis and Markant note that computational models commonly used in machine learning research can provide a framework for studying how people evaluate different sources of information and decide about the information they seek out and attend to. Work in machine learning can also help identify the benefits — and weaknesses — of independent exploration and the situations in which such exploration will confer the greatest benefit for learners.

Drawing together research from cognitive and computational perspectives will provide researchers with a better understanding of the processes that underlie self-directed learning and can help bridge the gap between basic cognitive research and applied educational research. Gureckis and Markant hope that this integration will help researchers to develop assistive training methods that can be used to tailor learning experiences that account for the specific demands of the situation and characteristics of the individual learner.

Researchers at Uppsala University have, together with Brazilian collaborators, discovered a new group of nerve cells that regulate processes of learning and memory. These cells act as gatekeepers and carry a receptor for nicotine, which can explain our ability to remember and sort information. The discovery of the gatekeeper cells, which are part of a memory network together with several other nerve cells in the hippocampus, reveal new fundamental knowledge about learning and memory.

The study is published today in Nature Neuroscience.

The hippocampus is an area of the brain that is important for consolidation of information into memories and helps us to learn new things. The newly discovered gatekeeper nerve cells, also called OLM-alpha2 cells, provide an explanation to how the flow of information is controlled in the hippocampus.

"It is known that nicotine improves cognitive processes including learning and memory, but this is the first time that an identified nerve cell population is linked to the effects of nicotine," says Professor Klas Kullander at Uppsala University.

Humans think, learn and memorize with the help of nerve cells sending signals between each other. Some nerve cells send signals far away to other areas of the brain, while other neurons send signals within the same area. Local nerve circuits in the hippocampus process impressions and turn some of them into memories. But how does this work? And how can nicotine improve this mechanism?

The new research study literally sheds new light on this intriguing mechanism.

"We have used a new technology called optogenetics, in which light is used to stimulate selected nerve cells. We were amazed when we discovered that light activation of the gatekeeper cells alters the flow of information in the hippocampus in the same way as nicotine does," explains coauthor Richardson Leão.

Through research on mice, the scientists showed that the gatekeeper cells connect to the principal cell of the hippocampus. Active gatekeeper cells prioritize local circuit signals arriving to the principal cell, while inactive gatekeeper cells allow inputs from long-distance targets. Nicotine activates the gatekeeper cell, thereby prioritizing the formation of memories via local inputs.

Next, the scientists want to test which types of memory and learning may be selected for by the activation of gatekeeper cells. With such knowledge, it may be possible to stimulate these nerve cells by artificial means, for example by selective nicotine-like drugs, to improve memory and learning in humans.

"Ideally, one would like to access the positive effects of nicotine on the hippocampus's ability to process information, but without creating the strong nicotine dependence that keep smokers addicted to inhaling dangerous tobacco smoke," says Klas Kullander.

Alpha waves were long ignored, but gained interest of brain researchers recently. Electrical activity of groups of brain cells results in brain waves with different amplitudes. The so-called alpha wave, a slow brain wave with a cycle of 100 milliseconds, seems to play a key role in suppressing irrelevant brain activity. The current hypothesis is that this alpha wave is associated with pulses of inhibition (every 100 ms) in the brain.

Mathilde Bonnefond and Ole Jensen (Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen) discovered that when distracting information can be anticipated in time there is an increase of the power of this alpha wave just before the distracter. Furthermore, the brain is able to precisely control the alpha wave so that the pulse of inhibition is maximal when the distracter appears. Indeed, between pulses of inhibition, there is still a window where the brain is excitable.

'It is like briefly opening a door to look what's happening outside. This enables us to detect an unexpected but important or dangerous event. But to avoid to be distracted by completely irrelevant information, it is better if the inhibition is active when a distracter is presented. It could be seen as a mechanism slamming the door of the brain on intruders'. The results are published by the scientific journal Current Biology at October 4.

The researchers designed an experiment in which timing of suppressing information was crucial for performance. The subjects were trained to do a memory task in a strict rhythm. Those subjects that were able to synchronize their alpha activity with the rhythm in which irrelevant distracters were presented had the highest score on the task. This is an unconscious process by the way. The researchers presume that the ability to adjust alpha activity to the expected distracting information might play a role when we actively sample the environment.

Experimental setup

Eighteen volunteers were tested with a non-invasive brain-wave recording technique, magneto-encephalography (MEG).The volunteers had to do a working memory task (i.e. maintaining some information in their memory over a period of a few seconds) during which the waves generated by their brain were recorded. In each trial, they had to remember four letters presented on a screen every one second.

After that, a distracter was briefly presented. The distracter was either another letter (strong distracter) or a symbol (weak distracter). Participants were asked to ignore the distracter (control experiments were ran to make sure they followed the instructions). One second after the distracter, another letter was briefly presented and the participants had to determine whether this letter was similar to one of the four letters they had to remember earlier.

The experiment consisted of blocks of trials with only one type of distracter (strong or weak) presented after the letters to remember in each trial. Very importantly, the time before the distracter was always the same so that the subjects could anticipate the timing of presentation of the distracter. The alpha waves were stronger before the strong distracters than before the weak distracters, confirming that these waves close our brain for distracting information.