Archive

Archive for the ‘Cognitive Neuroscience and Behaviour’ Category

Discovery of Gatekeeper Nerve Cells Explains the Effect of Nicotine on Learning and Memory

December 16, 2012 Leave a comment

Swedish 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 help 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. Read more…

Researchers Show that Memories Reside in Specific Brain Cells

December 16, 2012 Leave a comment

Simply activating a tiny number of neurons can conjure an entire memory.

Our fond or fearful memories — that first kiss or a bump in the night — leave memory traces that we may conjure up in the remembrance of things past, complete with time, place and all the sensations of the experience. Neuroscientists call these traces memory engrams.

But are engrams conceptual, or are they a physical network of neurons in the brain? In a new MIT study, researchers used optogenetics to show that memories really do reside in very specific brain cells, and that simply activating a tiny fraction of brain cells can recall an entire memory — explaining, for example, how Marcel Proust could recapitulate his childhood from the aroma of a once-beloved madeleine cookie.

“We demonstrate that behavior based on high-level cognition, such as the expression of a specific memory, can be generated in a mammal by highly specific physical activation of a specific small subpopulation of brain cells, in this case by light,” says Susumu Tonegawa, the Picower Professor of Biology and Neuroscience at MIT and lead author of the study reported online today in the journal Nature. “This is the rigorously designed 21st-century test of Canadian neurosurgeon Wilder Penfield’s early-1900s accidental observation suggesting that mind is based on matter.” Read more…

Why the Thrill is Gone: Scientists Identify Potential Target for Treating Major Symptom of Depression

December 16, 2012 1 comment

Stanford University School of Medicine scientists have laid bare a novel molecular mechanism responsible for the most important symptom of major depression: anhedonia, the loss of the ability to experience pleasure. While their study was conducted in mice, the brain circuit involved in this newly elucidated pathway is largely identical between rodents and humans, upping the odds that the findings point toward new therapies for depression and other disorders.

Additionally, opinion leaders hailed the study’s inventive methodology, saying it may offer a much sounder approach to testing new antidepressants than the methods now routinely used by drug developers.

While as many as one in six Americans is likely to suffer a major depression in their lifetimes, current medications either are inadequate or eventually stop working in as many as 50 percent of those for whom they’re prescribed.

“This may be because all current medications for depression work via the same mechanisms,” said Robert Malenka, MD, PhD, the Nancy Friend Pritzker Professor in Psychiatry and Behavioral Sciences. “They increase levels of one or another of two small molecules that some nerve cells in the brain use to signal one another. To get better treatments, there’s a great need to understand in greater detail the brain biology that underlies depression’s symptoms.” The study’s first author is Byung Kook Lim, PhD, a postdoctoral scholar in Malenka’s laboratory.

Malenka is senior author of the new study, published July 12 in Nature, which reveals a novel drug target by showing how a hormone known to affect appetite turns off the brain’s ability to experience pleasure when an animal is stressed. This hormone, melanocortin, signals to an ancient and almost universal apparatus deep in the brain called the reward circuit, which has evolved to guide animals toward resources, behaviors and environments — such as food, sex and warmth — that enhance their prospects for survival.

Scientists found that both chronic stress and the direct administration of melanocortin diminished the signaling strength of some synapses in the nucleus accumbens that contain receptors for melanocortin. The nucleus accumbens is labeled in this drawing of a human brain cross section. (up)

“This is the first study to suggest that we should look at the role of melanocortin in depression-related syndromes,” said Eric Nestler, MD, PhD, professor and chair of neuroscience and director of the Friedman Brain Institute at Mount Sinai School of Medicine in New York. Nestler was not involved in the study but is familiar with its contents. Read more…

Memories May Skew Visual Perception

December 16, 2012 3 comments

Taking a trip down memory lane while you are driving could land you in a roadside ditch, new research indicates.

Vanderbilt University psychologists have found that our visual perception can be contaminated by memories of what we have recently seen, impairing our ability to properly understand and act on what we are currently seeing.

“This study shows that holding the memory of a visual event in our mind for a short period of time can ‘contaminate’ visual perception during the time that we’re remembering,” Randolph Blake, study co-author and Centennial Professor of Psychology, said.

“Our study represents the first conclusive evidence for such contamination, and the results strongly suggest that remembering and perceiving engage at least some of the same brain areas.” Read more…

Researchers Explore How the Brain Perceives Direction and Location

December 16, 2012 Leave a comment

The Who asked “who are you?” but Dartmouth neurobiologist Jeffrey Taube asks “where are you?” and “where are you going?” Taube is not asking philosophical or theological questions. Rather, he is investigating nerve cells in the brain that function in establishing one’s location and direction.

Taube, a professor in the Department of Psychological and Brain Sciences, is using microelectrodes to record the activity of cells in a rat’s brain that make possible spatial navigation—how the rat gets from one place to another—from “here” to “there.” But before embarking to go “there,” you must first define “here.”

Survival Value

“Knowing what direction you are facing, where you are, and how to navigate are really fundamental to your survival,” says Taube. “For any animal that is preyed upon, you’d better know where your hole in the ground is and how you are going to get there quickly. And you also need to know direction and location to find food resources, water resources, and the like.”

Not only is this information fundamental to your survival, but knowing your spatial orientation at a given moment is important in other ways, as well. Taube points out that it is a sense or skill that you tend to take for granted, which you subconsciously keep track of. “It only comes to your attention when something goes wrong, like when you look for your car at the end of the day and you can’t find it in the parking lot,” says Taube. Read more…

Math ability requires crosstalk in the brain

September 9, 2012 Leave a comment

 

Examples of the simple numerical and arithmetic tasks used in the study. Participants were asked to judge whether the numerical operation was correct or not. Credit: Center for Vital Longevity, University of Texas at Dallas. (up)

A new study by researchers at UT Dallas’ Center for Vital Longevity, Duke University, and the University of Michigan has found that the strength of communication between the left and right hemispheres of the brain predicts performance on basic arithmetic problems. The findings shed light on the neural basis of human math abilities and suggest a possible route to aiding those who suffer from dyscalculia— an inability to understand and manipulate numbers.

It has been known for some time that the parietal cortex, the top/middle region of the brain, plays a central role in so-called numerical cognition—our ability to process numerical information. Previous brain imaging studies have shown that the right parietal region is primarily involved in basic quantity processing (like gauging relative amounts of fruit in baskets), while the left parietal region is involved in more precise numerical operations like addition and subtraction. What has not been known is whether the two hemispheres can work together to improve math performance. The new study demonstrates that they can. The findings were recently published online in Cerebral Cortex.

In the study, conducted in Dallas and led by Dr. Joonkoo Park, now a postdoctoral fellow at Duke University, researchers used functional magnetic resonance imaging, or fMRI, to measure the brain activity of 27 healthy young adults while they performed simple numerical and arithmetic tasks. In one task, participants were asked to judge whether two groups of shapes contained the same or different numbers of items. In two other tasks, participants were asked to solve simple addition and subtraction problems.

Consistent with previous studies, the researchers found that the basic number-matching task activated the right parietal cortex, while the addition and subtraction tasks produced additional activity in the left parietal cortex. But they also found something new: During the arithmetic tasks, communication between the left and right hemispheres increased significantly compared with the number-matching task. Moreover, people who exhibited the strongest connection between hemispheres were the fastest at solving the subtraction problems.

“Our results suggest that subtraction performance is optimal when there is high coherence in the neural activity in these two brain regions. Two brain areas working together rather than either region alone appears to be key” said co-author Dr. Denise C. Park, co-director of the UT Dallas Center for Vital Longevity and Distinguished University Chair in the School of Behavioral and Brain Sciences. Park (no relation to the lead author) helped direct the study along with Dr. Thad Polk, professor of psychology at the University of Michigan.

Lead author Dr. Joonkoo Park points out that the findings suggest that disrupted or inefficient neural communication between the hemispheres may contribute to the impaired math abilities seen in dyscalculia, the numerical equivalent of dyslexia. “If such a causal link exists,” he said, “one very interesting avenue of research would be to develop training tasks to enhance parietal connectivity and to test whether they improve numerical competence.”

Such a training program might help develop math ability in children and could also help older adults whose arithmetic skills begin to falter as a normal part of age-related cognitive decline.

 

Reference:

The above story is reprinted from materials provided by University of Texas at Dallas, via MedicalXpress.

Journal: Cerebral Cortex

 

Mathematics or memory? Posterior Medial Cortex Study Charts Collision Course in Brain

September 8, 2012 Leave a comment

You already know it’s hard to balance your checkbook while simultaneously reflecting on your past. Now, investigators at the Stanford University School of Medicine—having done the equivalent of wire-tapping a hard-to-reach region of the brain—can tell us how this impasse arises.

The researchers showed that groups of nerve cells in a structure called the posterior medial cortex, or PMC, are strongly activated during a recall task such as trying to remember whether you had coffee yesterday, but just as strongly suppressed when you’re engaged in solving a math problem.

The PMC, situated roughly where the brain’s two hemispheres meet, is of great interest to neuroscientists because of its central role in introspective activities.

“This brain region is famously well-connected with many other regions that are important for higher cognitive functions,” said Josef Parvizi, MD, PhD, associate professor of neurology and neurological sciences and director of Stanford’s Human Intracranial Cognitive Electrophysiology Program. “But it’s very hard to reach. It’s so deep in the brain that the most commonly used electrophysiological methods can’t access it.”

In a study to be published online Sept. 3 in Proceedings of the National Academy of Sciences, Parvizi and his Stanford colleagues found a way to directly and sensitively record the output from this ordinarily anatomically inaccessible site in human subjects. By doing so, the researchers learned that particular clusters of nerve cells in the PMC that are most active when you are recalling details of your own past are strongly suppressed when you are performing mathematical calculations. Parvizi is the study’s senior author. The first and second authors, respectively, are postdoctoral scholars Brett Foster, PhD, and Mohammed Dastjerdi, PhD.

Much of our understanding of what roles different parts of the brain play has been obtained by techniques such as functional magnetic resonance imaging, which measures the amount of blood flowing through various brain regions as a proxy for activity in those regions. But changes in blood flow are relatively slow, making fMRI a poor medium for listening in on the high-frequency electrical bursts (approximately 200 times per second) that best reflect nerve-cell firing. Moreover, fMRI typically requires pooling images from several subjects into one composite image. Each person’s brain physiognomy is somewhat different, so the blending blurs the observable anatomical coordinates of a region of interest.

Nonetheless, fMRI imaging has shown that the PMC is quite active in introspective processes such as autobiographical memory processing (“I ate breakfast this morning”) or daydreaming, and less so in external sensory processing (“How far away is that pedestrian?”). “Whenever you pay attention to the outside world, its activity decreases,” said Parvizi.

To learn what specific parts of this region are doing during, say, recall versus arithmetic requires more-individualized anatomical resolution than an fMRI provides. Otherwise, Parvizi said, “if some nerve-cell populations become less active and others more active, it all washes out, and you see no net change.” So you miss what’s really going on.

For this study, the Stanford scientists employed a highly sensitive technique to demonstrate that introspective and externally focused cognitive tasks directly interfere with one another, because they impose opposite requirements on the same brain circuitry.

The researchers took advantage of a procedure performed on patients who were being evaluated for brain surgery at the Stanford Epilepsy Monitoring Unit, associated with Stanford University Medical Center. These patients were unresponsive to drug therapy and, as a result, suffered continuing seizures. The procedure involves temporarily removing small sections of a patient’s skull, placing a thin plastic film containing electrodes onto the surface of the brain near the suspected point of origin of that patient’s seizure (the location is unique to each patient), and then monitoring electrical activity in that region for five to seven days—all of it spent in a hospital bed. Once the epilepsy team identifies the point of origin of any seizures that occurred during that time, surgeons can precisely excise a small piece of tissue at that position, effectively breaking the vicious cycle of brain-wave amplification that is a seizure.

Implanting these electrode packets doesn’t mean piercing the brain or individual cells within it. “Each electrode picks up activity from about a half-million nerve cells,” Parvizi said. “It’s more like dotting the ceiling of a big room, filled with a lot of people talking, with multiple microphones. We’re listening to the buzz in the room, not individual conversations. Each microphone picks up the buzz from a different bunch of partiers. Some groups are more excited and talking more loudly than others.”

The experimenters found eight patients whose seizures were believed to be originating somewhere near the brain’s midline and who, therefore, had had electrode packets placed in the crevasse dividing the hemispheres. (The brain’s two hemispheres are spaced far enough apart to slip an electrode packet between them without incurring damage.)

The researchers got permission from these eight patients to bring in laptop computers and put the volunteers through a battery of simple tasks requiring modest intellectual effort. “It can be boring to lie in bed waiting seven days for a seizure to come,” said Foster. “Our studies helped them pass the time.” The sessions lasted about an hour.

On the laptop would appear a series of true/false statements falling into one of four categories. Three categories were self-referential, albeit with varying degrees of specificity. Most specific was so-called “autobiographical episodic memory,” an example of which might be: “I drank coffee yesterday.” The next category of statements was more generic: “I eat a lot of fruit.” The most abstract category, “self-judgment,” comprised sentences along the lines of: “I am honest.”

A fourth category differed from the first three in that it consisted of arithmetical equations such as: 67 + 6 = 75. Evaluating such a statement’s truth required no introspection but, instead, an outward, more sensory orientation.

For each item, patients were instructed to press “1” if a statement was true, “2” if it was false.

Significant portions of the PMC that were “tapped” by electrodes became activated during self-episodic memory processing, confirming the PMC’s strong role in recall of one’s past experiences. Interestingly, true/false statements involving less specifically narrative recall—such as, “I eat a lot of fruit”—induced relatively little activity. “Self-judgment” statements—such as, “I am attractive”—elicited none at all. Moreover, whether a volunteer judged a statement to be true or false made no difference with respect to the intensity, location or duration of electrical activity in activated PMC circuits.

This suggests, both Parvizi and Foster said, that the PMC is not the brain’s “center of self-consciousness” as some have proposed, but is more specifically engaged in constructing autobiographical narrative scenes, as occurs in recall or imagination.

Foster, Dastjerdi and Parvizi also found that the PMC circuitry activated by a recall task took close to a half-second to fire up, ruling out the possibility that this circuitry’s true role was in reading or making sense of the sentence on the screen. (These two activities are typically completed within the first one-fifth of a second or so.) Once activated, these circuits remained active for a full second.

Yet all the electrodes that lit up during the self-episodic condition were conspicuously deactivated during arithmetic calculation. In fact, the circuits being monitored by these electrodes were not merely passively silent, but actively suppressed, said Parvizi. “The more a circuit is activated during autobiographical recall, the more it is suppressed during math. It’s essentially impossible to do both at once.”

Reference:

The above story is reprinted from materials provided by Stanford University Medical Center, via MedicalXpress.

Journal: Proceedings of the National Academy of Sciences