Optogenetics: The Physics of Mind Control                 

Tom Hartsfield, 01/09/14

Traditionally practiced by pale nerds tuning lasers and mirrors and lenses and crystals in pitch-black underground labs, optics has for decades been the domain of the physicist. But beginning roughly ten years ago, brain researchers began venturing into this dark world. It turns out that optics can supplement – and in some cases replace – the traditional use of electrodes as primary measuring tools for neuroscience.

A traditional neuroscience study begins with the surgical implantation of metal electrodes into the brain of a test animal, often a rabbit or a mouse. These electrodes are targeted to particular types of brain cells, found in particular regions of the brain. The animal is then subjected to a range of external stimuli. Electrical activity of the neurons in contact with the electrode tip is recorded on a computer.

Careful analysis and processing of these raw electrical signals then ascribes them to individual cells firing in particular patterns. These patterns are then correlated to the processes of learning, memory, sensory processing and other brain functions. In this way, electrode-based studies rely on passive observations.

However, optics combined with genetics – a field now known as optogenetics – allows researchers to directly control brain function with extreme precision instead of merely observing it. This has been a major development in neuroscience, wowing many in the field.

Optogenetic studies first introduce a carrier virus to the brain of the animal. A gene that encodes a light-sensitive ion channel protein is loaded into a virus and targeted to particular neurons of interest. (Brains contain many different types of neurons.) A flash of light, provided by a surgically implanted fiber-optic tip, opens the ion channels, causing the neuron to fire.

Thus, brain cells can be quite literally turned on and off. The possibilities of this powerful technique are nearly limitless. Examples include: Restoring eyesight after retinal damage by firing the remaining cells in the vision circuits of the brain; switching on and off a pathway that generates hunger impulses; and training the brain to suppress obsessive-compulsive behavior. There are no current plans to perform optogenetic studies on humans, however.

For this neuro-revolution, biologists should thank physicists who study optics. Lasers have undergone a technological advancement comparable to that of computers over the past 50 years: They are simpler, more reliable and more affordable than ever before. Optical fibers that bend, curve, and snake into tiny spaces such as the inside of a skull have similarly matured. Non-specialists can now assemble and operate commercially available optical systems.

While this is bad news for unemployed physicists, it is exactly the type of practical development that physics should deliver.

Tom Hartsfield is a physics PhD candidate at the University of Texas.

http://www.realclearscience.com/blog/2014/01/optogenetics_the_physics_of_mind_control_108437.html

Male and female brains wired differently, scans reveal       

Maps of neural circuitry show women's brains are suited to social skills and memory, men's perception and co-ordination

Ian Sample, science correspondent, The Guardian, 12/02/13

Scientists have drawn on nearly 1,000 brain scans to confirm what many had surely concluded long ago: that stark differences exist in the wiring of male and female brains.

Maps of neural circuitry showed that on average women's brains were highly connected across the left and right hemispheres, in contrast to men's brains, where the connections were typically stronger between the front and back regions.

Ragini Verma, a researcher at the University of Pennsylvania, said the greatest surprise was how much the findings supported old stereotypes, with men's brains apparently wired more for perception and co-ordinated actions, and women's for social skills and memory, making them better equipped for multitasking.

"If you look at functional studies, the left of the brain is more for logical thinking, the right of the brain is for more intuitive thinking. So if there's a task that involves doing both of those things, it would seem that women are hardwired to do those better," Verma said. "Women are better at intuitive thinking. Women are better at remembering things. When you talk, women are more emotionally involved – they will listen more."

She added: "I was surprised that it matched a lot of the stereotypes that we think we have in our heads. If I wanted to go to a chef or a hairstylist, they are mainly men."

The findings come from one of the largest studies to look at how brains are wired in healthy males and females. The maps give scientists a more complete picture of what counts as normal for each sex at various ages. Armed with the maps, they hope to learn more about whether abnormalities in brain connectivity affect brain disorders such as schizophrenia and depression.

Verma's team used a technique called diffusion tensor imaging to map neural connections in the brains of 428 males and 521 females aged eight to 22. The neural connections are much like a road system over which the brain's traffic travels.

The scans showed greater connectivity between the left and right sides of the brain in women, while the connections in men were mostly confined to individual hemispheres. The only region where men had more connections between the left and right sides of the brain was in the cerebellum, which plays a vital role in motor control. "If you want to learn how to ski, it's the cerebellum that has to be strong," Verma said. Details of the study are published in the journal Proceedings of the National Academy of Sciences.

Male and female brains showed few differences in connectivity up to the age of 13, but became more differentiated in 14- to 17-year-olds.

"It's quite striking how complementary the brains of women and men really are," Ruben Gur, a co-author on the study, said in a statement. "Detailed connectome maps of the brain will not only help us better understand the differences between how men and women think, but it will also give us more insight into the roots of neurological disorders, which are often sex-related."

(請至原網頁參考男性與女性大腦神經網路連接圖)

http://www.theguardian.com/science/2013/dec/02/men-women-brains-wired-differently

The End of Neuro-Nonsense

Is the age of mindless brain research already over?

Daniel Engber, 07/29/13

Brain-bashing, once an idle pastime of the science commentariat, went mainstream in June. At the beginning of the month, Slate contributor Sally Satel and Scott O. Lilienfeld published Brainwashed: The Seductive Appeal of Mindless Neuroscience, a well-informed attack on the extravagances of “neurocentrist” thought. We’re living in dangerous era, they warn in the book’s introduction. “Naïve media, slick neuroentrepreneurs, and even an occasional overzealous neuroscientist exaggerate the capacity of scans to reveal the contents of our minds, exalt brain physiology as inherently the most valuable level of explanation for understanding behavior, and rush to apply underdeveloped, if dazzling, science for commercial and forensic use.” In the United Kingdom, the neuro-gadfly Raymond Tallis -- whose own attack on popular brain science, Aping Mankind, came out in 2011 -- added to the early-summer beat-down, complaining in the Observer that “studies that locate irreducibly social phenomena … in the function or dysfunction of bits of our brains are conceptually misconceived.”

By mid-June, these sharp rebukes made their way into the mind of David Brooks, a long-time dabbler in neural data who proposed not long ago that “brain science helps fill the hole left by the atrophy of theology and philosophy.” Brooks read Brainwashed and became a convert to its cause: “From personal experience, I can tell you that you get captivated by [neuroscience] and sometimes go off to extremes,” he wrote in a recent column with the headline “Beyond the Brain.” Then he gave the following advice: “The next time somebody tells you what a brain scan says, be a little skeptical. The brain is not the mind.”

His final point, that the brain is not the mind -- and therefore maybe not so relevant to daily life -- has provoked a fierce response in recent weeks. The fact that certain studies of the brain have been overhyped or poorly done has little bearing on the value of the field, say scientists whose work has been maligned. Nor does it in any way imply a central flaw in the project to understand the mind by looking at the brain. Satel and Lilienfeld agree: The principles of neuroscience can be applied to every form of subjective experience, they argue in Brainwashed, and even fMRI brain scans -- the brightly colored icons of the neuro-priesthood they so abhor -- have a useful role to play in biomedicine.

But in the ruckus of this back-and-forth, and the backlash to a backlash, I think the neuro-critics missed something important: The “time of mindless neuroscience,” as Satel and Lilienfeld describe it, is already over. In the past few years, the brain has lost its influence; fMRI hucksters are on the run. I don’t mean to say that neuroscientists have given up -- their field of study is as vibrant as it’s ever been, and it still exerts a massive influence on research funding. (President Obama recently announced a $100 million project to map the brain’s connections.) But as a cultural force -- one capable of duping journalists and making money for “slick neuroentrepreneurs” -- the brain is almost cooked.

I’ll even name the year when the public turned its back on neuro-hype: The woo commenced its quick decline in 2008. That was its inflection point, its production peak, the moment when pictures of the brain were tapped for all the easy headlines, strip-mined for credulous investors, and otherwise sucked dry of whatever dopey data they could provide. Five years ago the pop-neuroscience project began to wither.

Such things are hard to measure, of course, but I think there’s circumstantial backup for my claim. In Brainwashed, for example, many of the key examples of mindless neuroscience come from 2008 (or before). Chapter 1, on the fallibility of brain imaging, starts with an article from ’08 by Jeffrey Goldberg, for which he traveled to Los Angeles to find out how his cortex might respond to pictures of Jimmy Carter and Mahmoud Ahmadinejad. It’s a useful study in the practice and promotion of witless pseudoneuroscience, but at the time, Goldberg’s case was not unique: That election season saw a rush of like-minded (and like-mindless) political neuro-coverage. Brain-based marketing firms placed their spurious analyses of presidential candidates and potential voters in the New York Times, the Los Angeles Times, CNN, and many other outlets; the neuropundits were running wild. But a lot has changed since then. Four years later, during the 2012 election, these sorts of stories were nowhere to be seen. At some point in Obama’s first White House term, interest in these political brain scans evaporated.

Chapter 2 of Brainwashed begins with another scene from 2008 -- the publication of the best-selling pop-neuroscience book, Buyology: Truth and Lies About Why We Buy. Satel and Lilienfeld describe its author, Martin Lindstrom, as a leading member of “an upstart generation of Mad Men known as neuromarketers.” But attempts to revolutionize the field of market research through the use of brain-imaging techniques haven’t gained much traction in the past 10 years. Though the marketing giant Nielsen purchased one of the neuromarketing startups in 2011, the industry at large has been (rightfully) suspicious of the concept. In January 2012 the industry-funded Advertising Research Foundation released a careful and quite critical assessment of the field. “What our investigation made very, very clear,” an ARF executive told me, “is that there is a gap between the science and the application and marketing.”

Last year the president of one neuromarketing firm told me that the business concept hadn’t really taken off. “It’s a tough sell,” he said. “I think that people are still reluctant to try it.” Another CEO mentioned that his company had abandoned the term neuromarketing altogether and rebranded its services as consumer neuroscience. Since the publication of Buyology, Lindstrom and his colleagues simply haven’t had much impact.

As for neuro-best-sellers, those too have been on the wane since 2008. I went through the archives of the New York Times best-seller list for hardcover books going back to 2001 and counted up the number of entries that included a mention of the word brain in either the title or the description. Eighty entries met my criteria, including those for Buyology, David Eagleman’s Incognito, Daniel Amen’s Change Your Brain, Change Your Body, and Jill Bolte Taylor’s My Stroke of Insight. The results are shown below.

The neuro-self-help genre may be in winter, too. Jonah Lehrer, the reigning master of that category (and author of the Frontal Cortex blog) published his first two books, Proust Was a Neuroscientist and How We Decide, in 2007 and 2009. In the years since then, he has more or less renounced the brain. “I write here about many scientific studies, but these are not studies of temporary chemistry or cortical folds,” he declared in the proposal for his newest work, on the science of love (which sold to Simon & Schuster in early June in spite of his professional disgrace). “It’s not enough to simply describe the hormones of Romeo, or the fMRI results of Juliet. These scientific results are interesting, but mostly because of what they cannot explain, of all the reality they leave out.”

2008 may also have been the high point for critical neuroscience blogging. The excellent Neuroskeptic wrote his first posts that autumn, in the darkest moments of the neurobabble epidemic. Another sharp-eyed blogger, the Neurocritic, started up in 2006 -- and as of several weeks ago, he’s built a brand-new persona “designed to counter gratuitous anti-neuroscience sentiment.” He calls this one the Neurocomplimenter. Meanwhile, my favorite neuroscience watchdog -- the James S. McDonnell Foundation’s Neuro-Journalism Mill, dedicated to “separating the wheat from the chaff in neurojournalism reporting” -- saw fit to shut its doors in October 2009.

If I’m right that “peak neuro” has already come and gone, then the recent rash of brain science-bashing may be beside the point. Other, trendy modes of explanation have already started to emerge, with a brand-new set of jargon phrases -- epigenetics, anyone? -- that carry out their own dangerous seductions.

http://www.slate.com/articles/health_and_science/science/2013/07/neuroscience_hype_is_brain_science_still_trendy.html

Networks of the Brain

Mark Daley, and Jody C. Culham, Canadian Psychology

Networks of the Brain, by Olaf Sporns. The MIT Press, 2010, 375 pages (ISBN 978-0-262-01469-4, CA $40.00 Hardcover)

The history of psychology and neuroscience is filled with a tension between theories emphasising localization of brain functions versus holistic processing. A third way has been emerging - viewing brain and mind in terms of dynamic, interacting networks. In his recent book Networks of the Brain, Olaf Sporns provides a much-welcomed synthesis of the network perspective. This perspective is not entirely new. First, as indicated by the well-selected quotes from eminent historical figures - Golgi, Cajal, Broca, James, and Hebb included - that Sporns employs to introduce each chapter, network ideas have been considered for some time. Second, the core tools used to analyse networks, primarily graph theory (which dates back to 1 8th century mathematician Leonhard Euler), are well-established. Graph theory has revealed common principles that define "small-world networks" - in which clusters of sparse connections allow short paths between any two nodes - in applications as diverse as social circles, epidemiology and transportation routes. What is new - and exciting - is the application of network analytic approaches to neuroscience: over the past decade, graph theory has been applied to the wiring diagrams or "connectomes" within brains. Specific neuroscience applications span a range of scales: thousands of connections between hundreds of neurons in the simple roundworm, Caenorhabditis elegans; hundreds of connections between dozens of functional areas of the human brain; and potentially even the trillions of connections between billions of neurons in the human brain.

Sporns provides a comprehensive, tour-de-force overview of the cutting edge of the application of network science to neuroscience. This is a book that everyone with an interest in brain function should read. It provides a grand overview of a field that will undoubtedly hold a central position in the future of neuroscience - if it has not already taken that position now. The scope of the book is enormous, yet relatively self-contained. Sporns masterfully reviews and explains core concepts from many neuroscientific, psychological, mathematical, physical, and engineering disciplines in a way which is at once accessible to nonspecialists and, in most cases, does not sacrifice correctness or rigour to achieve that goal. The use of clear, natural language explanations in place of mathematical equations in order to appeal to a broader authence is commendable. Despite the inherent difficulty of such an undertaking, it is exactly the authence members who might be put off by "too many equations" who are most likely to benefit immediately from considering the approaches reviewed by Sporns.

Chapter 1 provides an appetizer of sorts, briefly and clearly outlining a compelling argument for why one might wish to read the rest of the book.

Chapters 2 and 3 provide the necessary background in network theory and neuroscience methods, respectively, to make sense of the rest of the book. The exposition of this material is clear, well written, and given in a wonderfully informal style - as though being guided through a new field over drinks by a very patient and knowledgeable colleague.

Chapters 4-7 outline the application of network theoretic approaches to connections within anatomical circuits in the brain. Sporns is at the top of his game here and writes as one who has masterful knowledge of both the current state of the field and where it is likely to go. Particularly impressive is Sporns' very careful treatment of evolution in Chapter 7; he provides a network-theoretic framework for thinking about structural evolution in the brain by calling on a deep, broad range of supporting literature and making the full argument in terms of modern evolutionary theory.

Chapters 8-11 proceed similarly to the previous four, but this time focused on functional and effective networks in the brain. In Chapter 8, Sporns provides an engaging overview of spontaneous network activity and self-organizing brain dynamics. While neuroscientists and psychologists have emphasised relationships between sensory stimulation and neural and behavioural responses, an emerging literature is revealing continually fluctuating internal states that substantially modulate the stimulus-response relationship. Intriguingly, Sporns provides a compelling argument that these dynamic fluctuations are not necessarily epiphenomenal, but may reflect important principles of development and maintenance of brain networks. Chapter 9 applies network theory to cognition, and most valuably, presents a cogent argument for thinking of brain and mind in terms of hierarchically organized modules and dynamic reconfigurations of networks based on task demands. Chapter 10 reviews the literature on network changes in brain disorders such as brain lesions, Alzheimer's disease, schizophrenia, and autism spectrum disorders. Chapter 1 1 provides a network perspective on brain growth and development, providing further insights regarding self-organisational principles and dynamic reconfigurations of networks over the course of development.

Chapters 12-14 are more self-contained and offer insights into the dynamic systems of networks, network complexity and embodied cognition.

Chapter 13 provides much interesting food for thought, but the overall quality of the exposition does not live up to the high standard set by the rest of the book. Technically, the presentation is less careful and less comprehensive. Sporns outlines what he feels are the "two main categories of complexity measures" (measures which define how difficult it is to build/describe a system and measure of system organisation). Unfortunately, however, he seems to miss the - by now very large - field of computational complexity, which studies the intrinsic difficulty of computational problems and how efficiently they can be solved on particular systems. If one views the brain as a computational system, it seems possible that the theory of computational complexity might have relevant insights. This said, compressing a discussion on the complexity of neural systems into a single chapter is an impossible task and Sporns rightly elected to focus on the big picture.

Chapters 4-8 truly provide the core of the book and Chapters 9-11 provide valuable extensions of the foundational ideas. Sporns directly demonstrates the utility of network-theoretic approaches for both structural and functional networks by example. Through a long chain of carefully selected results, Sporns both exposes the reader to broad variety of network-theoretic tools and demonstrates exactly the types of neuroscientific insights that can be generated with these tools. While it falls a bit short of being a step-by-step "how to" guide (which is certainly not the intent of the book) it provides so many instances of interesting techniques leading to beautiful results that it is hard to imagine any researcher reading these chapters without pen and paper at their side, quickly scribbling down ideas for how these approaches might suit their own interests. The informal writing style and sense of excitement and energy combine with the content to yield something incredibly rare in technical writing: a true page-turner.

Sporns concludes the book with a powerful comparison between connectomics and genomics. Sporns is careful to note that even a precise wiring diagram of the human brain, such as that which may ultimately be provided by the human connectome project, does not equate to understanding the human brain, just as the complete sequence of human genetic material produced by the human genome project does not equate to understanding human biology. Nevertheless, he argues forcefully that connectome and genome mapping facilitate the discovery of systems principles that enrich our understanding. Modern neuroscience is now going through the same type of conceptual, and technical, transition that genetics went through slightly earlier and Sporns' book provides a field guide to what very well may be the future of neuroscience.

Olaf Sporns is a Professor in the Department of Psychological and Brain Sciences at Indiana University in Bloomington, Indiana. He is the recipient of a 201 1-2012 Guggenheim Fellowship and an investigator on the National Institutes of Health Human Connectome Project, which will use neuroimaging approaches to map brain circuits in 1 ,200 healthy adults and provide a freely available database.

[Author Affiliation]

Mark Daley is an Associate Professor in the Departments of Computer Science and Biology at the University of Western Ontario. Trained in mathematics, he has interests in natural computing, high-performance computing, and applications to biological systems. He is currently taking a study leave complete a Master's degree in neuroscience and is working on a project applying graph theory to brain networks measured with neuroimaging.

Jody Culham is an Associate Professor in the Department of Psychology at the University of Western Ontario. She is also a member of the Centre for Brain and Mind and the Graduate Program in Neuroscience at Western. Her lab uses functional MRI, amongst other techniques, to investigate the cognitive neuroscience of human perception and action. DOI: 10.1037/00025503

Publication information: Article title: Networks of the Brain. Contributors: Daley, Mark - Author, Culham, Jody C. - Author.

Journal title: Canadian Psychology. Volume: 52. Issue: 4 Publication date: November 2011. Page number: 321+. © Canadian Psychological Association Aug 1996. Provided by ProQuest LLC. All Rights Reserved.

This material is protected by copyright and, with the exception of fair use, may not be further copied, distributed or transmitted in any form or by any means.

http://www.questia.com/read/1P3-2510852261/networks-of-the-brain

Einstein's Brain Reveals Clues to Genius

Tia Ghose, LiveScience.com, 11/20/12

Einstein's brain had extraordinary folding patterns in several regions, which may help explain his genius, newly uncovered photographs suggest.

The photographs, published Nov. 16 in the journal Brain, reveal that the brilliant physicist had extra folding in his brain's gray matter, the site of conscious thinking. In particular, the frontal lobes, regions tied to abstract thought and planning, had unusually elaborate folding, analysis suggests.

"It's a really sophisticated part of the human brain," said Dean Falk, study co-author and an anthropologist at Florida State University, referring to gray matter. "And [Einstein's] is extraordinary."

Snapshots of a genius

Albert Einstein was the most famous physicist of the 20th century; his groundbreaking theory of general relativity explained how light curves due to the warping of space-time.

When the scientist died in 1955 at age 76, Thomas Harvey, the pathologist who autopsied him, took out Einstein's brain and kept it. Harvey sliced hundreds of thin sections of brain tissue to place on microscope slides and also snapped 14 photos of the brain from several angles.

Harvey presented some of the slides, but kept the photos secret in order to write a book about the physicist's brain.

The pathologist died before finishing his book, however, and the photos remained hidden for decades. But in 2010, after striking up a friendship with one of the new study's co-authors, Harvey's family donated the photos to the National Museum of Health and Medicine in Washington, D.C. Falk's team began analyzing the photos in 2011. [See Photos of Einstein's Brain]

More brainy connections

The team found that, overall, Eintsein's brain had much more complicated folding across the cerebral cortex, which is the gray matter on the surface of the brain responsible for conscious thought. In general, thicker gray matter is tied to higher IQs.

Many scientists believe that more folds can create extra surface area for mental processing, allowing more connections between brain cells, Falk said. With more connections between distant parts of the brain, one would be able to make, in a sense, mental leaps, drawing upon these faraway brain cells to solve some cognitive problem.

The prefrontal cortex, which plays a key role in abstract thought, making predictions and planning, also had an unusually elaborate folding pattern in Einstein's brain.

That may have helped the physicist develop the theory of relativity. "He did thought experiments where he'd imagine himself riding alongside a beam of light, and this is exactly the part of the brain one would expect to be very active" in such thought experiments, Falk told LiveScience.

In addition, Einstein's occipital lobes, which perform visual processing, showed extra folds and creases.

The right and left parietal lobes also looked very asymmetrical, Falk said. It's not clear how those features contributed to Einstein's genius, but that brain region is key for spatial tasks and mathematical reasoning, Falk said.

The jury is still out on whether Einstein's brain was extraordinary from birth or whether years of pondering physics made it special.

Falk believes both played a role.

"It was both nature and nurture," she said. "He was born with a very good brain, and he had the kinds of experiences that allowed him to develop the potential he had."

But most of Einstein's raw ability probably came from a trick of nature rather than a lifetime of hard work, said Sandra Witelson, of the Michael G. De Groot School of Medicine at McMasters University who has done past studies of Einstein's brain. In 1999, her work revealed that Einstein's right parietal lobe had an extra fold, something that was either hardwired into his genes or happened while Einstein was still in the womb.

"It's not just that it's bigger or smaller, it's that the actual pattern is different," Witselson said. "His anatomy is unique compared to every other photograph or drawing of a human brain that has ever been recorded."

Follow LiveScience on Twitter @livescience. We're also on Facebook & Google+.

• 10 Things You Didn't Know About the Brain
• Creative Genius: The World's Greatest Minds
• What's That? Your Physics Questions Answered

Copyright 2012 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

http://news.yahoo.com/einsteins-brain-reveals-clues-genius-210241323.html

Sensory Experience Influences the Shape of Neurons

ScienceDaily (June 14, 2011) — A discovery by researchers at the Institute of Neurosciences of Alicante (UMH-CSIC) Víctor Borrell is a significant advance in understanding the mechanisms involved in the development of the cerebral cortex.

Víctor Borrell has revealed the cellular mechanism that controls the development and differentiation of stellate neurons in layer 4 of the cerebral cortex. The results of this project, obtained in collaboration with Edward M. Callaway of the Salk Institute for Biological Studies in California, show that the development of these neurons occurs in two phases and are largely dependent on neuronal activity. This discovery has been published in the journal The Journal of Neuroscience.

The results of this research show the cellular mechanisms involved in the acquisition of the different morphologies of neurons in the cerebral cortex and demonstrate for the first time the active participation of sensory experience in this process, a critical step for the proper functioning of the brain.

The researcher Víctor Borrell explains that 'for most neurons in the cerebral cortex, the developmental process is relatively simple: to grow and increase in complexity. However, in the case of stellate neurons, the process is different and consists of two completely opposite phases. In a first stage, these neurons increase in size and complexity, becoming similar to the typical morphology of pyramidal neurons. In a second stage, these neurons begin a process of regression, during which they suffer a reduction in the size and complexity of their main dendrite (apical dendrite), and finally reach the typical star shape. This type of development had only been observed in a very particular small population of cortical neurons, but this study shows that the same applies in most layer 4 neurons.'

The cerebral cortex is the most complex structure of the mammalian brain and, without a doubt, the most expanded part of the human brain. The information we receive from the outside world through our senses travels through the nervous system to the cerebral cortex, where this information is processed, integrated and combined with past memories and feelings, leading to our particular perception of the world around us. The cerebral cortex contains a unique repertoire of types of neurons, which are distinguished by their characteristic shape each defined by the extension and arborisation of their dendrites. Most of the excitatory neurons of the cerebral cortex are characterized by a long apical dendrite that predominates over several shorter basal dendrites, giving these neurons a pyramidal appearance. In layer 4, however, the predominant type of neuron has a short apical dendrite similar to the basal dendrites, so these neurons have a very characteristic asterisk or star shape.

Several previous studies have shown that during development of the cerebral cortex pyramidal neurons undergo a remarkable growth and arborisation of all dendrites, which eventually ends up giving the typical pyramidal shape of these neurons in the adult brain. It has also been proposed that the final size and shape of these pyramidal neurons are the result of a combination of intrinsic genetic factors and local environmental influences, including the electrical activity of neurons themselves. In contrast to pyramidal neurons, the mechanisms responsible for leading the development of dendrites towards a star shape, like neurons in layer 4 of the cerebral cortex, and the factors influencing this process were entirely unknown until now.

The importance of senses

Once understood the process by which stellate neurons acquire their final form in two phases, researchers Victor Borrell and Edward Callaway began searching for the factors that regulate this process. They found that sensory activity seems to play a central role. They found that in situations of visual deprivation, where the cerebral cortex does not receive electrical impulses from the retina, neurons in layer 4 only completed successfully the first phase of development: growth and increase of complexity. However, when it was time to start the second phase of development, the retraction of the apical dendrite, most neurons were unable to make that change and remained in a growth phase, maintaining their pyramidal shape. Therefore, sensory perception, and in this case visual perception, plays a fundamental role in the process of brain development because it determines the shape of many of the neurons of the cerebral cortex.

Story Source:

The above story is reprinted from materials provided by Asociación RUVID, via AlphaGalileo.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

1.     Edward M. Callaway and Víctor Borrell. Developmental Sculpting of Dendritic Morphology of Layer 4 Neurons in Visual Cortex: Influence of Retinal Input. The Journal of Neuroscience, 18 May 2011, 31(20): 7456-7470 DOI: 10.1523/%u200BJNEUROSCI.5222-10.2011

http://www.sciencedaily.com/releases/2011/06/110614095645.htm