Posts tagged memory

Article Date: 20 Feb 2012 - 2:00 PST

New connections between brain cells emerge in clusters in the brain as animals learn to perform a new task, according to a study published in Nature on February 19 (advance online publication). Led by researchers at the University of California, Santa Cruz, the study reveals details of how brain circuits are rewired during the formation of new motor memories.

The researchers studied mice as they learned new behaviors, such as reaching through a slot to get a seed. They observed changes in the motor cortex, the brain layer that controls muscle movements, during the learning process. Specifically, they followed the growth of new “dendritic spines,” structures that form the connections (synapses) between nerve cells.

“For the first time we are able to observe the spatial distribution of new synapses related to the encoding of memory,” said Yi Zuo, assistant professor of molecular, cell and developmental biology at UC Santa Cruz and corresponding author of the paper.

In a previous study, Zuo and others documented the rapid growth of new dendritic spines on pyramidal neurons in the motor cortex during the learning process. These spines form synapses where the pyramidal neurons receive input from other brain regions involved in motor memories and muscle movements. In the new study, first author Min Fu, a postdoctoral researcher in Zuo’s lab, analyzed the spatial distribution of the newly formed synapses.

Initial results of the spatial analysis showed that one third of the newly formed synapses were located next to another new synapse. These clustered synapses tended to form over the course of a few days during the learning period, when the mouse was repeatedly performing the new behavior. Compared to non-clustered counterparts, the clustered synapses were more likely to persist through the learning sessions and after training stopped.

In addition, the researchers found that after formation of the second spine in a cluster, the first spine grew larger. The size of the spine head correlates with the strength of the synapse. “We found that formation of a second connection is correlated with a strengthening of the first connection, which suggests that they are likely to be involved in the same circuitry,” Zuo said. “The clustering of synapses may serve to magnify the strength of the connections.”

Another part of the study also supported the idea that the clustered synapses are involved in neural circuits specific to the task being learned. The researchers studied mice trained first in one task and then in a different task. Instead of grabbing a seed, the mice had to learn how to handle a piece of capellini pasta. Both tasks induced the formation of clustered spines, but spines formed during the learning of different tasks did not cluster together.

The researchers also looked at mice that were challenged with new motor tasks every day, but did not repeat the same task over and over like the ones trained in seed-grabbing or capellini-handling. These mice also grew lots of new dendritic spines, but few of the new spines were clustered.

“Repetitive activation of the same cortical circuit is really important in learning a new task,” Zuo said. “But what is the optimal frequency of repetition? Ultimately, by studying the relationship between synapse formation and learning, we want to find out the best way to induce new memories.”

The study used mice that had been genetically altered to make a fluorescent protein within certain neurons in the motor cortex. The researchers used a special microscopy technique (two-photon microscopy) to obtain images of those neurons near the surface of the brain. The noninvasive imaging technique enabled them to view changes in individual brain cells of the mice before, during, and after learning a new behavior.  

Source: Medical News Today

February 14th, 2012

Humans move between ‘patches’ in their memory using the same strategy as bees flitting between flowers for pollen or birds searching among bushes for berries.

Researchers at the University of Warwick and Indiana University have identified parallels between animals looking for food in the wild and humans searching for items within their memory – suggesting that people with the best ‘memory foraging’ strategies are better at recalling items.

Scientists asked people to name as many animals as they could in three minutes and then compared the results with a classic model of optimal foraging in the real world, the marginal value theorem, which predicts how long animals will stay in one patch before jumping to another.

Dr Thomas Hills, associate professor in the psychology department at the University of Warwick, said: “A bird’s food tends to be clumped together in a specific patch – for example on a bush laden with berries.

“But when the berries on a bush are depleted to the point where the bird’s energy is best focused on another more fruitful bush, it will move on.

“This kind of behaviour is predicted by the marginal value theorem, for a wide variety of animals.

“Because of the way human attention has evolved, we wondered if humans might use the same strategies to forage in memory. It turns out, they do.

“When faced with a memory task, we focus on specific clusters of information and jump between them like a bird between bushes. For example, when hunting for animals in memory, most people start with a patch of household pets—like dog, cat and hamster.

“But then as this patch becomes depleted, they look elsewhere. They might then alight on another semantically distinct ‘patch’, for example predatory animals such as lion, tiger and jaguar.”

The study shows that people who either stay too long or not long enough in one ‘patch’ did not recall as many animals as those who better judged the best time to switch between patches.

In other words, people who most closely adhered to the marginal value theorem produced more items.

The study Optimal Foraging in Semantic Memory, published in Psychological Review, asked 141 undergraduates (46 men and 95 women) at Indiana University to name as many animals as they could in three minutes.

They then analysed the responses using a categorisation scheme and also a semantic space model, called BEAGLE, which identifies clusters in the memory landscape based on the way words are related to one another in natural language.

Source: Neuroscience News 

Article Date: 05 Feb 2012 - 0:00 PST

Drinking decaffeinated coffee may improve brain energy metabolism associated with diabetes type 2, according to a study published in Nutritional Neuroscience and carried out by researchers at Mount Sinai School of Medicine. Brain energy metabolism is a dysfunction with a known risk factor for dementia and other neurodegenerative disorders like Alzheimer’s disease.

Giulio Maria Pasinetti, MD, PhD, and team decided to investigate whether dietary supplementation with a standard decaffeinated coffee prior to diabetes onset could improve insulin resistance and glucose utilization in mice with diet-induced type 2 diabetes.

The mice were given the supplement for five months, after which the researchers assessed the animals’ brain’s genetic response. They discovered that the brain could metabolize glucose more effectively and that it was used for cellular energy in the brain. People with type 2 diabetes have reduced glucose utilization in the brain, which often leads to neurocognitive problems.

Dr. Pasinetti stated:

"Impaired energy metabolism in the brain is known to be tightly correlated with cognitive decline during aging and in subjects at high risk for developing neurodegenerative disorders. This is the first evidence showing the potential benefits of decaffeinated coffee preparations for both preventing and treating cognitive decline caused by type 2 diabetes, aging, and/or neurodegenerative disorders."

Drinking coffee is not recommended for everyone, because of its association with cardiovascular health risks, including elevated blood cholesterol and blood pressure, both of which result in a higher risk of developing heart disease, stroke, and premature death. However, these negative effects have mainly been caused because of the high caffeine content of coffee - the study findings prove that some components in decaffeinated coffee have beneficial health factors for mice.

Dr. Pasinetti wants to investigate whether decaffeinated coffee as a dietary supplement in humans can act as a preventive measure.

He concludes:

"In light of recent evidence suggesting that cognitive impairment associated with Alzheimer’s disease and other age-related neurodegenerative disorders may be traced back to neuropathological conditions initiated several decades before disease onset, developing preventive treatments for such disorders is critical."

Petra Rattue 

Source: Medical News Today

Article Date: 02 Feb 2012 - 1:00 PST

Holding information within one’s memory for a short while is a seemingly simple and everyday task. We use our short-term memory when remembering a new telephone number if there is nothing to write at hand, or to find the beautiful dress inside the store that we were just admiring in the shopping window. Yet, despite the apparent simplicity of these actions, short-term memory is a complex cognitive act that entails the participation of multiple brain regions. However, whether and how different brain regions cooperate during memory has remained elusive. A group of researchers from the Max Planck Institute for Biological Cybernetics in Tubingen, Germany have now come closer to answering this question. They discovered that oscillations between different brain regions are crucial in visually remembering things over a short period of time.

It has long been known that brain regions in the frontal part of the brain are involved in short-term memory, while processing of visual information occurs primarily at the back of the brain. However, to successfully remember visual information over a short period of time, these distant regions need to coordinate and integrate information.

To better understand how this occurs, scientists from the Max Planck Institute of Biological Cybernetics in the department of Nikos Logothetis recorded electrical activity both in a visual area and in the frontal part of the brain in monkeys. The scientists showed the animals identical or different images within short intervals while recording their brain activity. The animals then had to indicate whether the second image was the same as the first one.

The scientists observed that, in each of the two brain regions, brain activity showed strong oscillations in a certain set of frequencies called the theta-band. Importantly, these oscillations did not occur independently of each other, but synchronized their activity temporarily: “It is as if you have two revolving doors in each of the two areas. During working memory, they get in sync, thereby allowing information to pass through them much more efficiently than if they were out of sync,” explains Stefanie Liebe, the first author of the study, conducted in the team of Gregor Rainer in cooperation with Gregor Hörzer from the Technical University Graz. The more synchronized the activity was, the better could the animals remember the initial image. Thus, the authors were able to establish a direct relationship between what they observed in the brain and the performance of the animal.

The study highlights how synchronized brain oscillations are important for the communication and interaction of different brain regions. Almost all multi-faceted cognitive acts, such as visual recognition, arise from a complex interplay of specialized and distributed neural networks. How relationships between such distributed sites are established and how they contribute to represent and communicate information about external and internal events in order to attain a coherent percept or memory is still poorly understood.

Source: Medical News Today