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Splitting Hairs – The Role of New Adult Brain Cells

§ July 10th, 2009 § Filed under brain research, neuroscience, plasticity § No Comments

A study published in the July 10, 2009, issue of the journal Science shows that new brain cells help us find our way around.

According to senior author Fred Gage of the Salk Institute new brain cells “help us to distinguish between memories that are closely related in space.”

“Adding new neurons could be a very problematic process if they don’t integrate properly into the existing neural circuitry,” says Gage. “There must be a clear benefit to outweigh the potential risk.”

Most neurogenesis happens in the hippocampus, a small horn-shaped region in the brain’s interior. The hippocampus prepares information for recall and then send it off for storage. Experiences involving time, emotion, intent, touch, smell etc., arise in the cortex and gets channeled to the hippocampus.

Previous studies had indicated that new neurons contributed to learning and memory but the details were unclear.

The dentate gyrus divides and distributes incoming signals. This process, known as pattern separation, increases the number of active cells by a factor of ten. To find out whether the brain was using new cells to aid in pattern separation, the study team devised two sets of experiments:

1. To find food presented relative to the location of an earlier meal within an eight-spoke radial maze. “Mice without neurogenesis had no trouble finding the new location as long as it was far enough from the original location,” says Clelland, “but couldn’t differentiate between the two when they were close to each other.”

2. To differentiate close points on a touch screen. Again, mice in which neurogenesis had been curtailed could not discriminate between closely set points on the screen, but had no trouble recalling spatial information in general.

“Neurogenesis helps us to make finer distinctions and appears to play a very specific role in forming spatial memories,” says Clelland. Adds Gage, “There is value in knowing something about the relationship between separate events and the closer they get the more important this information becomes.”

Obviously, it is very unlikely that new cells only assist with pattern separation.  For instance, the researchers also discovered that “newborn neurons actually form a link between individual elements of episodes occurring closely in time,” says Gage.

Gage and his team will go on to investigate whether neurons also enable the encoding of relationships of time and context.

Anxiety Linked to Brain Chemical

§ May 14th, 2009 § Filed under brain research, depression, neuroscience, plasticity § No Comments

Scientists have linked low levels of a particular brain growth factor (fibroblast growth factor 2) to a disposition toward anxiety.  The University of Michigan study on rats appears in the May 13 issue of The Journal of Neuroscience. Since FGF2 increases the survival rate of new brain cells, the findings also highlight the role of neurogenesis, or cell birth and integration in the adult brain, in reducing anxiety. These findings may offer new possibilities for the treatment of anxiety and potentially depression.

Previous human studies led by the senior author, Huda Akil, PhD, at the University of Michigan and team at the Pritzker Consortium, showed that people with severe depression had low levels of FGF2, but couldn’t say whether low FGF2 levels caused the disease or were caused by it.

Javier Perez, PhD, also at the University of Michigan, bred rats for high or low anxiety for over 19 generations. The researchers found lower FGF2 levels in rats bred for high anxiety compared to those bred for low anxiety.

The study also found that providing a more stimulating and interesting environment for the rats increased FGF2 levels and reduced anxiety.  They also found that FGF2 treatment alone reduced anxiety behaviors in the high-anxiety rats.

“We have discovered that FGF2 has two important new roles: it’s a genetic vulnerability factor for anxiety and a mediator for how the environment affects different individuals. This is surprising, as FGF2 and related molecules are known primarily for organizing the brain during development and repairing it after injury,” Perez said.

The findings further indicate that FGF2 may in part reduce anxiety because it increases the survival of new cells in the hippocampus. Previous research has suggested that depression decreases the production and incorporation of new brain cells (neurogenesis). High-anxiety rats produced the same number of new brain cells as low-anxiety rats, but more of these new cells died off. FGF2 treatment and environmental enrichment each restored brain cell survival.

“This discovery may pave the way for new, more specific treatments for anxiety that will not be based on sedation — like currently prescribed drugs — but will instead fight the real cause of the disease,” said Pier Vincenzo Piazza, MD, PhD, Director of the Neurocentre Magendie an INSERM/University of Bordeaux institution in France, an expert on the role of neurogenesis in addiction and anxiety (not involved in the current study).

What Happens To Those New Brain Cells?

§ May 7th, 2009 § Filed under brain research, neuroscience, plasticity § No Comments

Pasteur Institute

Pasteur Institute

A study by the Pasteur Institute shows that new brain cells respond more readily to stimulation and more readily “learn” new skills and information. This enhanced plasticity lasts for about twelve weeks, at which point they become only as plastic as existing brain cells.

This discovery could explain the failure of therapeutic strategies based on grafts, which deliver large quantities of new neurons that then lose their special properties very quickly.

Scientists have also demonstrated that, two weeks after their formation, only 50% of these new cells succeed in integrating into neuronal circuits – an essential condition for their survival.

In the 1990s, grafts for patients suffering from Parkinson’s disease brought about only a temporary recovery of motor ability. If new neurons demonstrate significant properties only for a few weeks, attempts at recovering certain cerebral functions by relying solely on the grafting of cells can never be successful. It would be better to look towards stimulating the brain’s natural capacity to produce neurons continuously.


- Neurogenesis promotes synaptic plasticity in the adult olfactory bulb, Nature Neurosciences, published online on May 3d, 2009.

Antoine Nissant, Cedric Bardy, Hiroyuki Katagiri, Kerren Murray & Pierre-Marie Lledo
Institut Pasteur, Perception and Memory unit, CNRS, URA 2182, 25 rue du Dr. Roux, F-75724 Paris Cedex 15, France.

-  Mouret A, Gheusi G, Gabellec MM, de Chaumont F, Olivo-Marin JC et Lledo P-M. Learning and survival of newly generated neurons: when time matters. J. Neurosci. 28, 11511-16, 2008

Proteins (Shank & Homer) In Process of Brain Plasticity

§ May 5th, 2009 § Filed under brain research, plasticity § No Comments

A Tour of MIT's Picower Institute

A Tour of MIT's Picower Institute

Researchers from MIT’s Picower Institute for Learning and Memory have identified two proteins – dubbed Shank and Homer – that work together to control the formation and pruning of synaptic connections as the brain both forms connections and lets them go.

A better understanding of this mechanism may lead to a better understanding of how to treat brain disorders such as autism, mental retardation, and Fragile X syndrome. Researchers believe these conditions are tied to abnormalities in synapses.

“Increase in the size of synapses and memory formation are closely linked,” said Mariko Hayashi, a Picower Institute research affiliate and co-author of the  study. “Synapses get larger when we learn something and smaller when we forget something or unused connections are pruned. This happens in infants’ growing brains and in learning and memory during adulthood. ”

Read the full MIT article.

Neurons That Know Words

§ April 30th, 2009 § Filed under brain research, neuroscience, plasticity § No Comments

As reported in today’s issue of Neuron, researchers from the department of neuroscience at Georgetown University Medical Center have identified neurons that show a preference for complete, real words. They found them in the brain’s “visual word form” area.

Maximilian Riesenhuber

Maximilian Riesenhuber

“Although some theories of reading, as well as some neuropsychological and experimental data, have argued for the existence of a neural representation for whole real words, experimental evidence for such a representation has been elusive,” said Dr. Maximilian Riesenhuber.

As with other recent studies the researchers used real-time brain scans of participants to detect activation of specific regions of the brain as they completed tasks involving real words and nonsense words.

The left visual word form area consistently displayed a highly selective preference for real words over jibberish.

According to Riesenhuber, “These results are not just relevant for theories of reading and reading acquisitions, but also for our understanding of the mechanisms underlying experience-driven cortical plasticity in general.”

By which I suppose he means that our brains most likely develop specific and highly targeted responses to information that makes sense and has meaning.

“It will be interesting in future studies to investigate how the specificity of the representation in the VWFA changes during development, and how it might differ in individuals with reading disorders,” he added.

Brain Training Helps Stroke Victims See Again

§ April 1st, 2009 § Filed under brain research, neuroscience, plasticity § No Comments

Stroke Victim Retrains Sight

Stroke Victim Retrains Sight

A study by Scientists at the University of Rochester Eye Institute has shown that patients can recover sight loss caused by a stroke. The patients engaged in intensive prolonged visual brain training, stimulating neuroplastic change.

“We were very surprised when we saw the results from our first patients,” said Krystel Huxlin, Ph.D., the neuroscientist and associate professor who led the study of seven patients. “This is a type of brain damage that clinicians and scientists have long believed you simply can’t recover from. It’s devastating, and patients are usually sent home to somehow deal with it the best they can.”

A stroke affects the brain not the eyes, visual information still reaches the brain but the brain cannot construct images from it. The team used this “blindsight” – unprocessed visual information that still reaches the brain.

“The question is whether we can we recruit other, healthy regions of the brain to benefit the person’s vision. Can we train those brain regions so hard and stimulate the brain to such a degree that this visual information is brought to consciousness, so the person is aware of what they’re seeing?” said Huxlin.

The four women and three men in the study in their 30s through their 80s had suffered substantial damage to the primary visual cortex.

The team focused on motion perception, critical for most everyday tasks, aiming to see whether they could stimulate the brain’s middle temporal region, healthy in the participants,  to take on some of the tasks normally handled by the visual cortex.

The five participants who performed the training and completed the experiment had significantly improved vision. They were able to see in ways they weren’t able to before the experiment began. A few found the experiment life-changing – a couple of participants are driving again, for instance, or have gained the confidence to go shopping and exercise frequently.

Following the dancing dots that can’t be “seen”

Participants fix their gaze on a small black square in the middle of a computer screen.

Every few seconds, a group of about 100 small dots appears within a circle on the screen, somewhere in the person’s damaged visual field – when the patients stare at the square, they don’t initially see the dots. The dots twinkle into existence, appear to move as a group either to the left or the right, then disappear after about one-half second. Then the patient has to choose whether the dots are moving left or right. A chime indicates whether he or she chose correctly, providing feedback that lets the brain know whether it made the right choice and speeding up learning.

But how do patients choose if they can’t consciously see the dots?

“The patients can’t see the dots, but they’re aware that there is something happening that they can’t quite see. They might say, ‘I know that there’s something there, but I can’t make any sense of it,’” said Huxlin, who is also a faculty member in the departments of Ophthalmology, Neurobiology and Anatomy, Brain and Cognitive Sciences, and in the Center for Visual Science.

But the brain is able to make some sense of it all, even though the patient is unaware that he or she is seeing anything. When forced to make a choice, patients typically start out with a success rate of around 50 percent by guessing. Over a period of days, weeks or months, that number goes to 80 or 90 percent, as the brain learns to “see” a new area, and the visual information moves from blindsight to consciousness. Patients eventually become aware of the dots and their movement.

As patients improve, researchers move the dots further and further into what was the patient’s blind area, as a way to challenge the brain, to coax it to see a new area.

“Basically, it’s exercising the visual part of the brain every day,” said Huxlin. “It’s very hard work, very grueling. By forcing patients to choose, you’re helping the brain re-develop.”

The patients in the study did about 300 tests at a time, which translated roughly to sitting in front of a computer for 15 to 30 minutes once or twice a day, every day, for nine to 18 months. It’s an exhausting task, especially for someone whose brain is working extra-hard to accomplish it.

Working with Huxlin on the work were Tim Martin, Ph.D., post-doctoral research associate; Kristin Kelly, formerly a technical associate and now a medical student; former graduate student Meghan Riley; neuro-ophthalmologist Deborah Friedman, M.D.; neurologist W. Scott Burgin, M.D.; and Mary Hayhoe, Ph.D., formerly of the Department of Brain and Cognitive Sciences at the University of Rochester, and now at the University of Texas at Austin. The University of Rochester has filed a patent on the technology.

Brain Activity And First Impressions

§ March 10th, 2009 § Filed under brain research, neuroscience, plasticity § No Comments

(This is proving to be a bonanza day for new research.)

Scientists from NYU and Harvard devised a rather unwieldy sounding study that nevertheless produced compelling indications that there’s a lot going on in our heads when we meet someone for the first time. The team provided subjects with written profiles and pictures of fictitious individuals, each seeded with “trait” information that would commonly inspire some kind of judgment. They used neuroimaging to record what was happening in the subjects brains as they reached their first impressions about the characters.

The neuroimaging results showed significant activity in two regions of the brain: The amygdala, a small structure in the medial temporal lobe previously linked to emotional learning about inanimate objects and social evaluations based on trust or race group. And the posterior cingulate cortex (PCC), linked to economic decision-making and assigning subjective value to rewards.

“Even when we only briefly encounter others, brain regions that are important in forming evaluations are engaged, resulting in a quick first impression,” said NYU’s Dr. Elizabeth Phelps.

NYU’s Dr. Daniela Schiller, the study’s lead author, concluded, “When encoding everyday social information during a social encounter, these regions sort information based on its personal and subjective significance, and summarize it into an ultimate score–a first impression.”

Brain Plasticity – Proof of Long Term Rewiring

§ March 10th, 2009 § Filed under brain research, neuroscience, plasticity § No Comments

Scientists in Tübingen, Germany have proven for the first time that widely-distributed networks of nerves in the brain can fundamentally reorganize as required…

A team from the Max Planck Institute for Biological Cybernetics in Tübingen demonstrated long term reorganization in activities of large parts of the brain. By stimulating nerve cells in the hippocampus and measuring changes with functional magnetic resonance tomography (FMRt) and electrophysiology, the team tracked reorganization in large populations of nerve cells in the forebrain (active in memory and spatial awareness). This is the first experimental proof that large parts of the brain change when we learn. (Current Biology, March 10, 2009)

Before and after images of activity in the brain following plastic change

Before and after images of activity in the brain following plastic change

Link to longer story on InSciences.

Brain Plasticity And Chronic Stress

§ February 26th, 2009 § Filed under depression, plasticity § 1 Comment

As a reminder that plastic change can be harmful as well as helpful to our mental health, scientists have identified what looks to be a process of long term damage caused by chronic stress.

“Stress and depression are known to cause a reversible retraction of dendrites in certain brain cells, particularly in the hippocampus, that McEwen and colleagues refer to as “adaptive plasticity.” The new research suggests that an increase in KA1, caused by the corticosteroid response in rats, may trigger this retraction. The finding follows recent work by Rockefeller’s Sidney Strickland, head of the Laboratory of Neurobiology and Genetics, that showed that KA1 production explodes in the hippocampus during simulated stroke in mice, driving a cell-death cascade that begins when part of the brain is deprived of blood. Combined, the work suggests that the relatively understudied KA1 subunit plays an important role in a key area of the brain in both causing damage in an uncontrolled trauma such as a stroke and in protecting the brain from damage under the more controlled circumstances of chronic stress.

“McEwen and colleagues have shown that healthy brains are remarkably resilient in the face of stress — brains replace their retracted neurons once the stress is removed. Perhaps, the researchers say, the same will prove true for depression. “One of the great hopes is that these changes in the hippocampus that happen with prolonged depression may not be signs of permanent irreversible damage but they may actually be signs of plasticity that we can treat with appropriate medications and also behavioral therapies,” McEwen says.”

Brain Training – What Use New Neurons?

§ February 23rd, 2009 § Filed under brain research, neuroscience, plasticity § No Comments

Tracey J. Shors

Tracey J. Shors

In a fascinating article in Scientific American’s Mind section Tracey J. Shors, a professor in the department of psychology and the Center for Collaborative Neuroscience at Rutgers University, explains how new brain cells typically die off unless the brain is stimulated to put them to use. Shors and fellow scientists found that demanding and challenging cognitive tasks engage the brain in such a way that it assimilates the new brain cells, strengthening problem solving ability.

“Presumably the added cells, once they mature, are used to fine-tune or boost problem-solving skills that already exist.”

Shors introduces the subject with a paragraph supporting brain training.

I like scientific findings that concur with what one would think should sensibly happen — i.e., the finding that taxing the brain will strengthen cognition seems evolutionarily right.

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