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A balanced memory network
September 07, 2007Ever wonder how much information we put in our heads" The answer: a lot. For starters, a typical vocabulary is 50,000-250,000 words. And then there are all the little details that stretch back decades - the house we grew up in, the time we spilled orange juice on our test back in third grade, the solution to a quadratic equation (for some of us).
So where do we put it all" If we had hard drives in our heads, the answer would be easy: we would store memories as 0s and 1s. But we don't, we have neurons, connected by synapses, and storing memories in such systems is a lot harder than putting 0s and 1s on a hard drive. Nevertheless, about two decades ago John Hopfield showed that memories could be stored by modifying the strength of synapses in a particular way. Importantly, the number of memories that could be stored using his scheme was proportional to the number of neurons in the network. This solved the storage problem: there are about 50 million neurons in a cubic centimeter of cortex, plenty of room for both a vocabulary and spilled orange juice.
Recently, Roudi and Latham from University College London threw a monkey wrench into this picture. In a study publishing in PLoS Computational Biology on September 7, 2007, they show that for realistic networks of spiking neurons, the number of memories is not proportional to the number of neurons, it's proportional to the number of connections per neurons -- at most about 10,000. Moreover, they provided evidence that the constant of proportionality is small, not more than a few percent, and they eliminated one of theorists' favorite tricks -- reducing the number of neurons involved in any one memory -- for increasing that constant. Thus, if networks use the algorithm proposed by Hopfield, they can store at most about 500 memories, no matter how many neurons they contain.
So we're not exactly back to square one, but we're not much farther than square two: we no longer know how the brain holds so many memories. Roudi and Latham speculate that the answer lies in multiple, weakly coupled networks. However, until that, or some other idea, is shown to be correct, we will have to be content with just remembering, without the added knowledge of how we remember.
Public Library of Science
So we're not exactly back to square one, but we're not much farther than square two: we no longer know how the brain holds so many memories. Roudi and Latham speculate that the answer lies in multiple, weakly coupled networks. However, until that, or some other idea, is shown to be correct, we will have to be content with just remembering, without the added knowledge of how we remember.
Public Library of Science
Neurons Current Events and Neurons News RSSScripps research scientists find new link between insulin and core body temperature
A team led by scientists at The Scripps Research Institute have discovered a direct link between insulin-a hormone long associated with metabolism and metabolic disorders such as diabetes-and core body temperature.
New Down syndrome treatment suggested by Stanford/Packard study in mice
At birth, children with Down syndrome aren't developmentally delayed. But as they age, these kids fall behind. Memory deficits inherent in Down syndrome hinder learning, making it hard for the brain to collect experiences needed for normal cognitive development.
Cognitive dysfunction reversed in mouse model of Down syndrome
A study by neuroscientist William C. Mobley, MD, PhD, chair of the Department of Neurosciences at the University of California, San Diego School of Medicine, and colleagues at Stanford University Medical School has demonstrated a possible new approach to slowing the inevitable progression of cognitive decline found in Down's syndrome.
Pushing the brain to find new pathways
Until recently, scientists believed that, following a stroke, a patient had about six months to regain any lost function. After that, patients would be forced to compensate for the lost function by focusing on their remaining abilities.
Scientists decipher the formation of lasting memories
Researchers at Karolinska Institutet have discovered a mechanism that controls the brain's ability to create lasting memories. In experiments on genetically manipulated mice, they were able to switch on and off the animals' ability to form lasting memories by adding a substance to their drinking water.
Developmental delay could stem from nicotinic receptor deletion
The loss of a gene through deletion of genetic material on chromosome 15 is associated with significant abnormalities in learning and behavior, said a consortium of researchers led by Baylor College of Medicine (www.bcm.edu) in a report that appears online today in the journal Nature Genetics.
New TMS clinic offers noninvasive treatment for major depression
Rush University Medical Center has opened the Transcranial Magnetic Stimulation (TMS) Clinic to offer patients suffering from major depression a safe, effective, non-drug treatment.
Researchers explore new ways to prevent spinal cord damage using a vitamin B3 precursor
Substances naturally produced by the human body may one day help prevent paralysis following a spinal cord injury, according to researchers at Weill Cornell Medical College. A recent $2.5 million grant from the New York State Spinal Cord Injury Research Board will fund their research investigating this possibility.
Estrogen therapy likely must be given soon after menopause to provide stroke protection
For estrogen replacement to provide stroke protection, it likely must be given soon after levels drop because of menopause or surgical removal of the ovaries, scientists report in the Journal of Neuroscience.
Researchers identify drug candidate for treating spinal muscular atrophy
A chemical cousin of the common antibiotic tetracycline might be useful in treating spinal muscular atrophy (SMA), a currently incurable disease that is the leading genetic cause of death in infants.
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The Neuron: Cell and Molecular Biology by Irwin B. Levitan Ph.D. (Author), Leonard K. Kaczmarek Ph.D. (Author) The third edition of The Neuron provides a comprehensive first course in the cell and molecular biology of nerve cells. The first part of the book covers the properties of the many newly discovered ion channels that have emerged through mapping of the genome. These channels shape the way a single neuron generates varied patterns of electrical activity. Next are covered the molecular mechanisms that convert electrical activity into the secretion of neurotransmitter hormones at synaptic junctions between neurons. The second part of the book covers the biochemical pathways that are linked to the action of neurotransmitters and that can alter the cellular properties of neurons or sensory cells that transduce information from the outside world into the electrical code used by neurons. The... |
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Brain Cell (Neuron) Giganticmicrobes By Giant Microbes by Giant Microbes NEW - GIGANTIC Microbes (15-20" plush doll) Plush Educational Toy - The more brain cells you have, the smarter you are. |
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Knowing Neurons Clearance Sale Art Poster Print, 18x24 by AllPosters.com AllPosters.com is the world's #1 seller of posters, prints, photographs, specialty products and framed art. We're dedicated to bringing our customers the best selection of high quality wall décor that is perfect for their home or office. Browse our catalog of over 300,000 items that include entertainment and specialty posters, decorative prints, and art reproductions. Whether you're looking for your favorite movie or music poster, a framed Monet reproduction, or a print of the Eiffel Tower you will find it at AllPosters.com. Visit our Amazon store today at www.amazon.com/allposters to find Special Offers and search by subject category or artist. AllPosters.com provides unmatched service with a 100% satisfaction guarantee. We ship internationally to over 80 countries. Decorate your... |
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