Neuroscience

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Posts tagged hippocampus

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What happened when? How the brain stores memories by time Before I left the house this morning, I let the cat out and started the dishwasher. Or was that yesterday? Very often, our memories must distinguish not just what happened and where, but when an event occurred — and what came before and after. New research from the University of California, Davis, Center for Neuroscience shows that a part of the brain called the hippocampus stores memories by their “temporal context” — what happened before, and what came after. "We need to remember not just what happened, but when," said graduate student Liang-Tien (Frank) Hsieh, first author on the paper published March 5 in the journal Neuron. The hippocampus is thought to be involved in forming memories. But it’s not clear whether the hippocampus stores representations of specific objects, or if it represents them in context. Hsieh and Charan Ranganath, professor in the Department of Psychology and the Center for Neuroscience, looked for hippocampus activity linked to particular memories. First, they showed volunteers a series of pictures of animals and objects. Then they scanned the volunteers’ brains as they showed them the same series again, with questions such as, “is this alive?” or “does this generate heat?” The questions prompted the volunteers to search their memories for information. When the images were shown in the same sequence as before, the volunteers could anticipate the next image, making for a faster response. From brain scans of the hippocampus as the volunteers were answering questions, Hsieh and Ranganath could identify patterns of activity specific to each image. But when they showed the volunteers the same images in a different sequence, they got different patterns of activity. In other words, the coding of the memory in the hippocampus was dependent on its context, not just on content. "It turns out that when you take the image out of sequence, the pattern disappears," Ranganath said. "For the hippocampus, context is critical, not content, and it’s fairly unique in how it pulls things together." Other parts of the brain store memories of objects that are independent of their context, Ranganath noted. "For patients with memory problems this is a big deal," Ranganath said. "It’s not just something that’s useful in understanding healthy memory, but allows us to understand and intervene in memory problems."

What happened when? How the brain stores memories by time

Before I left the house this morning, I let the cat out and started the dishwasher. Or was that yesterday? Very often, our memories must distinguish not just what happened and where, but when an event occurred — and what came before and after. New research from the University of California, Davis, Center for Neuroscience shows that a part of the brain called the hippocampus stores memories by their “temporal context” — what happened before, and what came after.

"We need to remember not just what happened, but when," said graduate student Liang-Tien (Frank) Hsieh, first author on the paper published March 5 in the journal Neuron.

The hippocampus is thought to be involved in forming memories. But it’s not clear whether the hippocampus stores representations of specific objects, or if it represents them in context.

Hsieh and Charan Ranganath, professor in the Department of Psychology and the Center for Neuroscience, looked for hippocampus activity linked to particular memories. First, they showed volunteers a series of pictures of animals and objects. Then they scanned the volunteers’ brains as they showed them the same series again, with questions such as, “is this alive?” or “does this generate heat?”

The questions prompted the volunteers to search their memories for information. When the images were shown in the same sequence as before, the volunteers could anticipate the next image, making for a faster response.

From brain scans of the hippocampus as the volunteers were answering questions, Hsieh and Ranganath could identify patterns of activity specific to each image. But when they showed the volunteers the same images in a different sequence, they got different patterns of activity.

In other words, the coding of the memory in the hippocampus was dependent on its context, not just on content.

"It turns out that when you take the image out of sequence, the pattern disappears," Ranganath said. "For the hippocampus, context is critical, not content, and it’s fairly unique in how it pulls things together."

Other parts of the brain store memories of objects that are independent of their context, Ranganath noted.

"For patients with memory problems this is a big deal," Ranganath said. "It’s not just something that’s useful in understanding healthy memory, but allows us to understand and intervene in memory problems."

Filed under memory hippocampus memory formation perirhinal cortex neuroscience science

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Outside the body our memories fail us

New research from Karolinska Institutet and Umeå University in Sweden demonstrates for the first time that there is a close relationship between body perception and the ability to remember. For us to be able to store new memories from our lives, we need to feel that we are in our own body. According to researchers, the results could be of major importance in understanding the memory problems that psychiatric patients often exhibit.

The memories of what happened on the first day of school are an example of an episodic memory. How these memories are created and how the role that the perception of one’s own body has when storing memories has long been inconclusive. Swedish researchers can now demonstrate that volunteers who experience an exciting event whilst perceiving an illusion of being outside their own body exhibit a form of memory loss.

“It is already evident that people who have suffered psychiatric conditions in which they felt that they were not in their own body have fragmentary memories of what actually occurred”, says Loretxu Bergouignan, principal author of the current study. “We wanted to see how this manifests itself in healthy subjects.”

The study, which is published in the scientific journal PNAS, involved a total of 84 students reading about and undergoing four oral questioning sessions. To make these sessions extra memorable, an actor (Peter Bergared) took up the role of examiner – a (fictional) very eccentric professor at Karolinska Institutet. Two of the interrogations were perceived from a first person perspective from their own bodies in the usual way, while the participants in the other two sessions experienced a created illusion of being outside their own body. In both cases, the participants wore virtual reality goggles and earphones. One week later, they either underwent memory testing where they had to recall the events and provide details about what had happened, in which order, and what they felt, or they had to try to remember the events while they underwent brain imaging with functional magnetic resonance imaging (fMRI).

It then turned out that the participants remembered the ‘out-of-body’ interrogations significantly worse than those experienced from the normal ‘In body’ perspective. This was the case despite the fact that they responded equally well to the questions from each situation and also indicated that they experienced the same level of emotion. The fMRI scans further revealed a crucial difference in activity in the portion of the temporal lobe – the hippocampus – that is known to be central for episodic memories.

“When they tried to remember what happened during the interrogations experienced out-of-body, activity in the hippocampus was eliminated, unlike when they remembered the other situations. However, we could see activity in the frontal lobe cortex, so they were really making an effort to remember”, says professor Henrik Ehrsson, the research group leader behind the study. 

The researchers’ interpretation of the results is that there is a close relationship between body experience and memory. Our brain constantly creates the experience of one’s own body in space by combining information from multiple senses: sight, hearing, touch, and more. When a memory is created, it is the task of the hippocampus to link all the information found in the cerebral cortex into a unified memory for further long-term storage. During the experience of being outside one’s body, this memory storage process is disturbed, whereupon the brain creates fragmentary memories instead.

“We believe that this new knowledge may be important for future research on memory disorders in a number of psychiatric conditions such as post-traumatic stress disorder, borderline personality disorder and certain psychoses where patients have dissociative experiences,” says Loretxu Bergouignan.

(Source: news.cision.com)

Filed under hippocampus frontal lobe body perception memory neuroimaging neuroscience science

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Researchers Pinpoint Brain Region Essential for Social Memory Columbia University Medical Center (CUMC) researchers have determined that a small region of the hippocampus known as CA2 is essential for social memory, the ability of an animal to recognize another of the same species. A better grasp of the function of CA2 could prove useful in understanding and treating disorders characterized by altered social behaviors, such as autism, schizophrenia, and bipolar disorder. The findings, made in mice, were published on Feb. 23, 2014, in the online edition of Nature. Scientists have long understood that the hippocampus—a pair of seahorse-shaped structures in the brain’s temporal lobes—plays a critical role in our ability to remember the who, what, where, and when of our daily lives. Recent studies have shown that different subregions of the hippocampus have different functions. For instance, the dentate gyrus is critical for distinguishing between similar environments, while CA3 enables us to recall a memory from partial cues (e.g., Proust’s famous madeleine). The CA1 region is critical for all forms of memory. “However, the role of CA2, a relatively small region of the hippocampus sandwiched between CA3 and CA1, has remained largely unknown,” said senior author Steven A. Siegelbaum, PhD, professor of neuroscience and pharmacology, chair of the Department of Neuroscience, a member of the Mortimer B. Zuckerman Mind Brain Behavior Institute and Kavli Institute for Brain Science, and a Howard Hughes Medical Institute Investigator. A few studies have suggested that CA2 might be involved in social memory, as this region has a high level of expression of a receptor for vasopressin, a hormone linked to sexual motivation, bonding, and other social behaviors. To learn more about this part of the hippocampus, the researchers created a transgenic mouse in which CA2 neurons could be selectively inhibited in adult animals. Once the neurons were inhibited, the mice were given a series of behavioral tests. “The mice looked quite normal until we looked at social memory,” said first author Frederick L. Hitti, an MD-PhD student in Dr. Siegelbaum’s laboratory, who developed the transgenic mouse. “Normally, mice are naturally curious about a mouse they’ve never met; they spend more time investigating an unfamiliar mouse than a familiar one. In our experiment, however, mice with an inactivated CA2 region showed no preference for a novel mouse versus a previously encountered mouse, indicating a lack of social memory.” In two separate novel-object recognition tests, the CA2-deficient mice showed a normal preference for an object they had not previously encountered, showing that the mice did not have a global lack of interest in novelty. In another experiment, the researchers tested whether the animals’ inability to form social memories might have to do with deficits in olfaction (sense of smell), which is crucial for normal social interaction. However, the mice showed no loss in ability to discriminate social or non-social odors. In humans, the importance of the hippocampus for social memory was famously illustrated by the case of Henry Molaison, who had much of his hippocampus removed by surgeons in 1953 in an attempt to cure severe epilepsy. Molaison (often referred to as HM in the scientific literature) was subsequently unable to form new memories of people. Scientists have observed that lesions limited to the hippocampus also impair social memory in both rodents and humans. “Because several neuropsychiatric disorders are associated with altered social behaviors, our findings raise the possibility that CA2 dysfunction may contribute to these behavioral changes,” said Dr. Siegelbaum. This possibility is supported by findings of a decreased number of CA2 inhibitory neurons in individuals with schizophrenia and bipolar disorder and altered vasopressin signaling in autism. Thus, CA2 may provide a new target for therapeutic approaches to the treatment of social disorders.
Researchers Pinpoint Brain Region Essential for Social Memory

Columbia University Medical Center (CUMC) researchers have determined that a small region of the hippocampus known as CA2 is essential for social memory, the ability of an animal to recognize another of the same species. A better grasp of the function of CA2 could prove useful in understanding and treating disorders characterized by altered social behaviors, such as autism, schizophrenia, and bipolar disorder. The findings, made in mice, were published on Feb. 23, 2014, in the online edition of Nature.

Scientists have long understood that the hippocampus—a pair of seahorse-shaped structures in the brain’s temporal lobes—plays a critical role in our ability to remember the who, what, where, and when of our daily lives. Recent studies have shown that different subregions of the hippocampus have different functions. For instance, the dentate gyrus is critical for distinguishing between similar environments, while CA3 enables us to recall a memory from partial cues (e.g., Proust’s famous madeleine). The CA1 region is critical for all forms of memory.

“However, the role of CA2, a relatively small region of the hippocampus sandwiched between CA3 and CA1, has remained largely unknown,” said senior author Steven A. Siegelbaum, PhD, professor of neuroscience and pharmacology, chair of the Department of Neuroscience, a member of the Mortimer B. Zuckerman Mind Brain Behavior Institute and Kavli Institute for Brain Science, and a Howard Hughes Medical Institute Investigator. A few studies have suggested that CA2 might be involved in social memory, as this region has a high level of expression of a receptor for vasopressin, a hormone linked to sexual motivation, bonding, and other social behaviors.

To learn more about this part of the hippocampus, the researchers created a transgenic mouse in which CA2 neurons could be selectively inhibited in adult animals. Once the neurons were inhibited, the mice were given a series of behavioral tests. “The mice looked quite normal until we looked at social memory,” said first author Frederick L. Hitti, an MD-PhD student in Dr. Siegelbaum’s laboratory, who developed the transgenic mouse. “Normally, mice are naturally curious about a mouse they’ve never met; they spend more time investigating an unfamiliar mouse than a familiar one. In our experiment, however, mice with an inactivated CA2 region showed no preference for a novel mouse versus a previously encountered mouse, indicating a lack of social memory.”

In two separate novel-object recognition tests, the CA2-deficient mice showed a normal preference for an object they had not previously encountered, showing that the mice did not have a global lack of interest in novelty. In another experiment, the researchers tested whether the animals’ inability to form social memories might have to do with deficits in olfaction (sense of smell), which is crucial for normal social interaction. However, the mice showed no loss in ability to discriminate social or non-social odors.

In humans, the importance of the hippocampus for social memory was famously illustrated by the case of Henry Molaison, who had much of his hippocampus removed by surgeons in 1953 in an attempt to cure severe epilepsy. Molaison (often referred to as HM in the scientific literature) was subsequently unable to form new memories of people. Scientists have observed that lesions limited to the hippocampus also impair social memory in both rodents and humans.

“Because several neuropsychiatric disorders are associated with altered social behaviors, our findings raise the possibility that CA2 dysfunction may contribute to these behavioral changes,” said Dr. Siegelbaum. This possibility is supported by findings of a decreased number of CA2 inhibitory neurons in individuals with schizophrenia and bipolar disorder and altered vasopressin signaling in autism. Thus, CA2 may provide a new target for therapeutic approaches to the treatment of social disorders.

Filed under hippocampus social memory schizophrenia autism social interaction dentate gyrus psychology neuroscience science

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Figure 1: Typical slow gamma (left), fast gamma (center) and theta (right) brain-wave patterns measured during voluntary actions in rats. Banding together to control movement Synchrony is critical for the proper functioning of the brain. Synchronous firing of neurons within regions of the brain and synchrony between brain waves in different regions facilitate information processing, yet researchers know very little about these neural codes. Now, new research led by Tomoki Fukai of the RIKEN Brain Science Institute reveals how one region of the brain uses multiple brain-wave frequency bands to control movement. Control of movement requires activation of numerous muscle groups in correct sequence, a function achieved by the motor cortex. To investigate the contribution of brain waves to this process, Fukai and his colleagues inserted multi-channel electrodes into the motor cortex of rats to record brain-wave patterns as the animals learned to push, hold and then pull a lever to obtain a food reward. They also developed a machine-learning technique to extract spike sequences of individual neurons from the recorded waves.  Fukai and his colleagues found that brain waves of different frequencies appeared during distinct stages of the movements. Fast gamma waves, with frequencies of around 100 hertz, were most prominent when the rats pushed or pulled the lever, whereas slow gamma waves, with frequencies of 25–40 hertz, peaked when the rats held the lever to prepare for the next pull. Theta waves (4–10 hertz) peaked while the rats held the lever, and the initiation of the pulling movement coincided with a specific phase of these oscillations (Fig. 1). Both frequencies of gamma waves were coupled to the theta waves such that the peaks of all three brain-wave frequencies occurred at the same time. The activity of different types of nerve cells in different layers of the motor cortex was also synchronized with specific brain-wave frequencies. Importantly, cells encoding different stages of the sequential movements fired in distinct phases of the theta waves.  The results suggest that theta waves play an important role in coordinating the neuronal activity underlying the planning and execution of voluntary movement. Theta waves are known to be important for the processing of spatial information in the hippocampus, but this is the first time that a similar code has been observed in the motor cortex. “We are currently using machine-learning techniques to study how phase-locked spikes in different layers of the motor cortex encode motor information,” says Fukai. “We are also studying whether a similar oscillatory coordination takes place in the prefrontal cortex during decision-making.”

Figure 1: Typical slow gamma (left), fast gamma (center) and theta (right) brain-wave patterns measured during voluntary actions in rats.

Banding together to control movement

Synchrony is critical for the proper functioning of the brain. Synchronous firing of neurons within regions of the brain and synchrony between brain waves in different regions facilitate information processing, yet researchers know very little about these neural codes. Now, new research led by Tomoki Fukai of the RIKEN Brain Science Institute reveals how one region of the brain uses multiple brain-wave frequency bands to control movement.

Control of movement requires activation of numerous muscle groups in correct sequence, a function achieved by the motor cortex. To investigate the contribution of brain waves to this process, Fukai and his colleagues inserted multi-channel electrodes into the motor cortex of rats to record brain-wave patterns as the animals learned to push, hold and then pull a lever to obtain a food reward. They also developed a machine-learning technique to extract spike sequences of individual neurons from the recorded waves. 

Fukai and his colleagues found that brain waves of different frequencies appeared during distinct stages of the movements. Fast gamma waves, with frequencies of around 100 hertz, were most prominent when the rats pushed or pulled the lever, whereas slow gamma waves, with frequencies of 25–40 hertz, peaked when the rats held the lever to prepare for the next pull. Theta waves (4–10 hertz) peaked while the rats held the lever, and the initiation of the pulling movement coincided with a specific phase of these oscillations (Fig. 1).

Both frequencies of gamma waves were coupled to the theta waves such that the peaks of all three brain-wave frequencies occurred at the same time. The activity of different types of nerve cells in different layers of the motor cortex was also synchronized with specific brain-wave frequencies. Importantly, cells encoding different stages of the sequential movements fired in distinct phases of the theta waves. 

The results suggest that theta waves play an important role in coordinating the neuronal activity underlying the planning and execution of voluntary movement. Theta waves are known to be important for the processing of spatial information in the hippocampus, but this is the first time that a similar code has been observed in the motor cortex.

“We are currently using machine-learning techniques to study how phase-locked spikes in different layers of the motor cortex encode motor information,” says Fukai. “We are also studying whether a similar oscillatory coordination takes place in the prefrontal cortex during decision-making.”

Filed under motor cortex hippocampus brainwaves theta waves neuroscience science

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Mechanism behind the activation of dormant memory cells discovered The electrical stimulation of the hippocampus in in-vivo experiments activates precisely the same receptor complexes as learning or memory recall. This has been discovered for the first time and the finding has now been published in the highly respected journal “Brain Structure Function”. “This may form the basis for the use of medications aimed at powering up dormant or less active memory cells,” says Gert Lubec, Head of Fundamental Research / Neuroproteomics at the University Department of Paediatrics and Adolescent Medicine at the MedUni Vienna.  “This discovery has far-reaching consequences both for the molecular understanding of memory formation and the understanding of the clinical electrical stimulation, which is already possible, of areas of the brain for therapeutic purposes,” says the MedUni Vienna researcher.  Similar principles are currently already being used in the field of deep brain stimulation. With this technology, an implanted device delivers electronic impulses to the patient’s brain. This physical stimulation allows neuronal circuits to be influenced that control both behaviour and memory. The latest findings very much form part of the highly controversial subject of “cognitive enhancement”. Scientists are currently discussing the possibility of improving mental capacity through the use of drugs - including in healthy subjects of all age groups, but especially in patients with age-related impairments of cognitive processes. With regard to the study design, two electrodes were implanted into the brain in an animal model. One transferred electrical impulses to stimulate the hippocampus, while the other transferred the electrical signals away. “These electrical potentials are the electrical equivalent of memory and are known as LTP (Long Term Potentiation),” explains Lubec. The generation of LTP in an in-vivo experiment was accompanied by specific changes in the receptor complexes - the same receptor complexes that are also activated during learning and memory formation.

Mechanism behind the activation of dormant memory cells discovered

The electrical stimulation of the hippocampus in in-vivo experiments activates precisely the same receptor complexes as learning or memory recall. This has been discovered for the first time and the finding has now been published in the highly respected journal “Brain Structure Function”. “This may form the basis for the use of medications aimed at powering up dormant or less active memory cells,” says Gert Lubec, Head of Fundamental Research / Neuroproteomics at the University Department of Paediatrics and Adolescent Medicine at the MedUni Vienna. 

“This discovery has far-reaching consequences both for the molecular understanding of memory formation and the understanding of the clinical electrical stimulation, which is already possible, of areas of the brain for therapeutic purposes,” says the MedUni Vienna researcher.  Similar principles are currently already being used in the field of deep brain stimulation. With this technology, an implanted device delivers electronic impulses to the patient’s brain. This physical stimulation allows neuronal circuits to be influenced that control both behaviour and memory.

The latest findings very much form part of the highly controversial subject of “cognitive enhancement”. Scientists are currently discussing the possibility of improving mental capacity through the use of drugs - including in healthy subjects of all age groups, but especially in patients with age-related impairments of cognitive processes.

With regard to the study design, two electrodes were implanted into the brain in an animal model. One transferred electrical impulses to stimulate the hippocampus, while the other transferred the electrical signals away. “These electrical potentials are the electrical equivalent of memory and are known as LTP (Long Term Potentiation),” explains Lubec. The generation of LTP in an in-vivo experiment was accompanied by specific changes in the receptor complexes - the same receptor complexes that are also activated during learning and memory formation.

Filed under deep brain stimulation hippocampus memory formation memory neurons LTP neuroscience science

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A circuit for change To answer the seemingly simple question “Have I been here before?” we must use our memories of previous experiences to determine if our current location is familiar or novel. In a new study published in the Journal of Neuroscience researchers from the RIKEN Brain Science Institute have identified a region of the hippocampus, called CA2, which is sensitive to even small changes in a familiar context. The results provide the first clue to the contributions of CA2 to memory and may help shed light on why this area is often found to be abnormal in the schizophrenic brain. Change comes in many flavors; if we move to a new country, city or house it is easy to recognize the novelty of the environment, but if we come home to find the furniture rearranged or a new piece of art on the wall, this recognition may be much slower. Scientists believe this is because memory formation requires comparing current information with previous experience and the larger the overlap, the more difficult the distinction. It has long been known that the hippocampus is a region of the brain crucial for this type of memory, however the identification of neurons responsible for this comparison has remained elusive. In this study Marie Wintzer, Roman Boehringer, Denis Polygalov and Thomas McHugh used genetically modified mice and advanced cell imaging techniques to demonstrate that while the entire hippocampus is capable of detecting large changes in context, the small and often overlooked CA2 region is exquisitely sensitive to small changes. Mice were familiarized with one context and then placed either in a much different context or back in the original with small alterations, such as several new small objects. By detecting the expression of activity induced genes Wintzer and colleagues were able to demonstrate that just a few new objects in the otherwise unchanged context completely altered the pattern of active cells specifically in CA2. Mice that had been genetically engineered to lack this CA2 response explored the new context much less than their normal siblings. “CA2 has often been overlooked or simply grouped together with its more prominent neighbors, but these data suggest it’s unique and important for recognizing and reacting to changes in our environments” explains Dr. McHugh, the leader of the study. Compared to rodents, human CA2 is proportionally larger, but still as mysterious. One intriguing finding has been that early in the onset of schizophrenia and bipolar disorder there is a loss of inhibitory neurons specifically in CA2. In addition to the memory problems that accompany these diseases, patients often exhibit a hyper-sensitivity to changes in environment and routine. This study suggests there may be a functional relationship between this sensitivity and CA2 dysfunction, hinting at a new circuit to target in our attempts to understand the function of both the normal and diseased brain.

A circuit for change

To answer the seemingly simple question “Have I been here before?” we must use our memories of previous experiences to determine if our current location is familiar or novel. In a new study published in the Journal of Neuroscience researchers from the RIKEN Brain Science Institute have identified a region of the hippocampus, called CA2, which is sensitive to even small changes in a familiar context. The results provide the first clue to the contributions of CA2 to memory and may help shed light on why this area is often found to be abnormal in the schizophrenic brain.

Change comes in many flavors; if we move to a new country, city or house it is easy to recognize the novelty of the environment, but if we come home to find the furniture rearranged or a new piece of art on the wall, this recognition may be much slower. Scientists believe this is because memory formation requires comparing current information with previous experience and the larger the overlap, the more difficult the distinction. It has long been known that the hippocampus is a region of the brain crucial for this type of memory, however the identification of neurons responsible for this comparison has remained elusive.

In this study Marie Wintzer, Roman Boehringer, Denis Polygalov and Thomas McHugh used genetically modified mice and advanced cell imaging techniques to demonstrate that while the entire hippocampus is capable of detecting large changes in context, the small and often overlooked CA2 region is exquisitely sensitive to small changes.

Mice were familiarized with one context and then placed either in a much different context or back in the original with small alterations, such as several new small objects. By detecting the expression of activity induced genes Wintzer and colleagues were able to demonstrate that just a few new objects in the otherwise unchanged context completely altered the pattern of active cells specifically in CA2. Mice that had been genetically engineered to lack this CA2 response explored the new context much less than their normal siblings.

“CA2 has often been overlooked or simply grouped together with its more prominent neighbors, but these data suggest it’s unique and important for recognizing and reacting to changes in our environments” explains Dr. McHugh, the leader of the study.

Compared to rodents, human CA2 is proportionally larger, but still as mysterious. One intriguing finding has been that early in the onset of schizophrenia and bipolar disorder there is a loss of inhibitory neurons specifically in CA2. In addition to the memory problems that accompany these diseases, patients often exhibit a hyper-sensitivity to changes in environment and routine. This study suggests there may be a functional relationship between this sensitivity and CA2 dysfunction, hinting at a new circuit to target in our attempts to understand the function of both the normal and diseased brain.

Filed under hippocampus memory schizophrenia neurons CA2 psychology neuroscience science

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How Your Memory Rewrites the Past

Your memory is a wily time traveler, plucking fragments of the present and inserting them into the past, reports a new Northwestern Medicine® study. In terms of accuracy, it’s no video camera.

Rather, the memory rewrites the past with current information, updating your recollections with new experiences. 

Love at first sight, for example, is more likely a trick of your memory than a Hollywood-worthy moment.

“When you think back to when you met your current partner, you may recall this feeling of love and euphoria,” said lead author Donna Jo Bridge, a postdoctoral fellow in medical social sciences at Northwestern University Feinberg School of Medicine. “But you may be projecting your current feelings back to the original encounter with this person.”

The study is published Feb. 5 in the Journal of Neuroscience.

This the first study to show specifically how memory is faulty, and how it can insert things from the present into memories of the past when those memories are retrieved. The study shows the exact point in time when that incorrectly recalled information gets implanted into an existing memory.

To help us survive, Bridge said, our memories adapt to an ever-changing environment and help us deal with what’s important now.

“Our memory is not like a video camera,” Bridge said. “Your memory reframes and edits events to create a story to fit your current world. It’s built to be current.”

All that editing happens in the hippocampus, the new study found. The hippocampus, in this function, is the memory’s equivalent of a film editor and special effects team.

For the experiment, 17 men and women studied 168 object locations on a computer screen with varied backgrounds such as an underwater ocean scene or an aerial view of Midwest farmland. Next, researchers asked participants to try to place the object in the original location but on a new background screen. Participants would always place the objects in an incorrect location.

For the final part of the study, participants were shown the object in three locations on the original screen and asked to choose the correct location. Their choices were: the location they originally saw the object, the location they placed it in part 2 or a brand new location.

“People always chose the location they picked in part 2,” Bridge said. “This shows their original memory of the location has changed to reflect the location they recalled on the new background screen. Their memory has updated the information by inserting the new information into the old memory.”

Participants took the test in an MRI scanner so scientists could observe their brain activity. Scientists also tracked participants’ eye movements, which sometimes were more revealing about the content of their memories – and if there was conflict in their choices — than the actual location they ended up choosing.   

The notion of a perfect memory is a myth, said Joel Voss, senior author of the paper and an assistant professor of medical social sciences and of neurology at Feinberg.

“Everyone likes to think of memory as this thing that lets us vividly remember our childhoods or what we did last week,” Voss said. “But memory is designed to help us make good decisions in the moment and, therefore, memory has to stay up-to-date. The information that is relevant right now can overwrite what was there to begin with.”

Bridge noted the study’s implications for eyewitness court testimony. “Our memory is built to change, not regurgitate facts, so we are not very reliable witnesses,” she said.

A caveat of the research is that it was done in a controlled experimental setting and shows how memories changed within the experiment. “Although this occurred in a laboratory setting, it’s reasonable to think the memory behaves like this in the real world,” Bridge said.

(Source: northwestern.edu)

Filed under memory hippocampus brain activity neuroimaging psychology neuroscience science

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Imaging Technique Shows Brain Anatomy Change in Women with Multiple Sclerosis, Depression

A multicenter research team led by Cedars-Sinai neurologist Nancy Sicotte, MD, an expert in multiple sclerosis and state-of-the-art imaging techniques, used a new, automated technique to identify shrinkage of a mood-regulating brain structure in a large sample of women with MS who also have a certain type of depression.

image

In the study, women with MS and symptoms of “depressive affect” – such as depressed mood and loss of interest – were found to have reduced size of the right hippocampus. The left hippocampus remained unchanged, and other types of depression – such as vegetative depression, which can bring about extreme fatigue – did not correlate with hippocampal size reduction, according to an article featured on the cover of the January 2014 issue of Human Brain Mapping.

The research supports earlier studies suggesting that the hippocampus may contribute to the high frequency of depression in multiple sclerosis. It also shows that a computerized imaging technique called automated surface mesh modeling can readily detect thickness changes in subregions of the hippocampus. This previously required a labor-intensive manual analysis of MRI images.

Sicotte, the article’s senior author, and others have previously found evidence of tissue loss in the hippocampus, but the changes could only be documented in manual tracings of a series of special high-resolution MRI images. The new approach can use more easily obtainable MRI scans and it automates the brain mapping process.

“Patients with medical disorders – and especially those with inflammatory diseases such as MS – often suffer from depression, which can cause fatigue. But not all fatigue is caused by depression. We believe that while fatigue and depression often co-occur in patients with MS, they may be brought about by different biological mechanisms. Our studies are designed to help us better understand how MS-related depression differs from other types, improve diagnostic imaging systems to make them more widely available and efficient, and create better, more individualized treatments for our patients,” said Sicotte, director of Cedars-Sinai’s Multiple Sclerosis Program and the Neurology Residency Program. She received a $506,000 grant from the National Multiple Sclerosis Society last year to continue this research.

(Source: newswise.com)

Filed under brain imaging MS depression hippocampus neuroimaging neuroscience science

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Can Fish Oil Help Preserve Brain Cells? People with higher levels of the omega-3 fatty acids found in fish oil may also have larger brain volumes in old age equivalent to preserving one to two years of brain health, according to a study published in the January 22, 2014, online issue of Neurology®, the medical journal of the American Academy of Neurology. Shrinking brain volume is a sign of Alzheimer’s disease as well as normal aging. For the study, the levels of omega-3 fatty acids EPA+DHA in red blood cells were tested in 1,111 women who were part of the Women’s Health Initiative Memory Study. Eight years later, when the women were an average age of 78, MRI scans were taken to measure their brain volume. Those with higher levels of omega-3s had larger total brain volumes eight years later. Those with twice as high levels of fatty acids (7.5 vs. 3.4 percent) had a 0.7 percent larger brain volume. “These higher levels of fatty acids can be achieved through diet and the use of supplements, and the results suggest that the effect on brain volume is the equivalent of delaying the normal loss of brain cells that comes with aging by one to two years,” said study author James V. Pottala, PhD, of the University of South Dakota in Sioux Falls and Health Diagnostic Laboratory, Inc., in Richmond, Va. Those with higher levels of omega-3s also had a 2.7 percent larger volume in the hippocampus area of the brain, which plays an important role in memory. In Alzheimer’s disease, the hippocampus begins to atrophy even before symptoms appear.

Can Fish Oil Help Preserve Brain Cells?

People with higher levels of the omega-3 fatty acids found in fish oil may also have larger brain volumes in old age equivalent to preserving one to two years of brain health, according to a study published in the January 22, 2014, online issue of Neurology®, the medical journal of the American Academy of Neurology. Shrinking brain volume is a sign of Alzheimer’s disease as well as normal aging.

For the study, the levels of omega-3 fatty acids EPA+DHA in red blood cells were tested in 1,111 women who were part of the Women’s Health Initiative Memory Study. Eight years later, when the women were an average age of 78, MRI scans were taken to measure their brain volume.

Those with higher levels of omega-3s had larger total brain volumes eight years later. Those with twice as high levels of fatty acids (7.5 vs. 3.4 percent) had a 0.7 percent larger brain volume.

“These higher levels of fatty acids can be achieved through diet and the use of supplements, and the results suggest that the effect on brain volume is the equivalent of delaying the normal loss of brain cells that comes with aging by one to two years,” said study author James V. Pottala, PhD, of the University of South Dakota in Sioux Falls and Health Diagnostic Laboratory, Inc., in Richmond, Va.

Those with higher levels of omega-3s also had a 2.7 percent larger volume in the hippocampus area of the brain, which plays an important role in memory. In Alzheimer’s disease, the hippocampus begins to atrophy even before symptoms appear.

Filed under omega-3 alzheimer's disease dementia hippocampus memory brain cells neuroscience science

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A time for memories

Neuroscientists from the University of Leicester, in collaboration with the Department of Neurosurgery at the University California Los Angeles (UCLA), are to reveal details of how the brain determines the timing at which neurons in specific areas fire to create new memories.

This research exploits the unique opportunity of recording multiple single-neurons in patients suffering from epilepsy refractory to medication that are implanted with intracranial electrodes for clinical reasons.

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The study, which is to be published in the academic journal Current Biology, is the result of collaboration between Professor Rodrigo Quian Quiroga and Dr Hernan Rey at the Centre for Systems Neuroscience at the University of Leicester and Professor Itzhak Fried at UCLA.

The work follows up on the group’s research into what was dubbed the ‘Jennifer Aniston neurons’ – neurons in the hippocampus and its surrounding areas within the brain that specifically fire in an ‘abstract’ manner when we see or hear a certain concept  - such as a person, an animal or a landscape - that we recognise.

Professor Quian Quiroga said: “The firing of these neurons is relatively very late after the moment of seeing the picture, or hearing the person’s name, but is still very precise. These neurons also fire only when the pictures are consciously recognised and remain silent when they are not.

“Our research shows that there is a specific brain response that marks the timing of the firing of these neurons. This response shortly precedes the neuron’s firing and is only present for the consciously recognised pictures - being absent if the pictures were not recognised.

“This brain response thus reflects an activation that provides a temporal window for processing consciously perceived stimuli in the hippocampus and surrounding cortex. Given the proposed role of these neurons in memory formation, we argue that the brain response we found is a gateway for processing consciously perceived stimuli to form or recall memories.”

Dr Hernan Rey, first author of the study, added: “This time-keeping may indeed be critical for synchronizing and combining multisensory information involving different processing times. This, in turn, helps in creating a unified conceptual representation that can be used for memory functions.”

Professor Quian Quiroga’s work is specifically concerned with examining how information about the external world - what we see, hear and touch - is represented by neurons in the brain and how this leads to the creation of our own internal representations and memories.

For example, we can easily recognize a person in a fraction of a second, even when seen from different angles, with different sizes, colours, contrasts and under strikingly different conditions. But how neurons in the brain are capable of creating such an ‘abstract’ representation, disregarding basic visual details, is only starting to be known.

(Source: www2.le.ac.uk)

Filed under neurons memory memory formation hippocampus neuroscience science

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