Chapter 3. Neurophysiology: The Generation, Transmission, and Integration of Neural Signals

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James Gorman Turning certain brain cells on and off with light — a technique called optogenetics — is one of the most important tools in neuroscience. It allows scientists to test basic ideas about how brains work. But because waves of visible light don’t penetrate living tissue well, the technique requires the insertion of a conduit for the light into the brain— a very thin fiber optic cable. For the first time, researchers say, they have done the same with ultrasound, opening the way to a noninvasive way to probe the functions of neurons. They call the technique sonogenetics. They achieved this in a microscopic worm, a creature so simple that it doesn’t have a brain. But it does have neurons, which have a great deal in common with the neurons in more complex animals that make up the brain and nervous system. If the technique works in more complex animals, it would mean a noninvasive way to do basic research, and perhaps even treat brain circuits. “Previous studies have shown if you use ultrasound, you can manipulate the nervous system,” said Sreekanth H. Chalasani of the Salk Institute in San Diego and senior author of a recent report in Nature Communications that describes the research. But, he said, nobody had shown that, with genetic modifications, specific neurons could be targeted. “It’s going to be a viable technique,” said William Tyler, a neuroscientist at Arizona State University, who said the ability to zero in on one neuron or a group of neurons without having to insert anything into the body was “unparalleled.” © 2015 The New York Times Company

Keyword: Brain imaging
Link ID: 21453 - Posted: 09.28.2015

By Diana Kwon Multiple sclerosis (MS) relapses are known to swing with the seasons. Scientists have attributed these fluctuations to the rise and fall of vitamin D production, which is triggered by exposure to seasonal sunlight. Now a new study suggests that melatonin, a hormone that regulates your internal body clock and sleep cycles, could also play a protective role. MS is a disease of the central nervous system in which an abnormal immune response attacks the myelin sheath, or fatty protective layer, around neurons. The resulting degradation slows signaling between the brain and the rest of the body, potentially leading to a wide variety of symptoms that include weakness, vision problems and cognitive changes. The condition may affect as many as 2.3 million people worldwide. The cause of the disease remains unknown, although researchers have started to identify genetic risks and environmental factors, including smoking, viral infections and vitamin D levels in the bloodstream. The latest environmental influence, observed by Mauricio Farez, a neuroscientist at the Raúl Carrea Institute for Neurological Research, and colleagues could involve peak melatonin levels in the body, which occur during the darker months. The researchers assessed a group of 139 multiple sclerosis patients in Buenos Aires and found a 32 percent reduction in the number of relapses in the fall and winter, when people living in the Southern Hemisphere produce more of the hormone, compared with summer and spring. The results are published on the September 10 Cell. © 2015 Scientific American

Keyword: Multiple Sclerosis; Biological Rhythms
Link ID: 21442 - Posted: 09.24.2015

Helen Shen Neuroscientists have used ultrasound to stimulate individual brain cells in a worm, and hope that the technique — which they call ‘sonogenetics’ — might be adapted to switch on neurons in mice and larger animals. The technique relies on touch-sensitive ‘channel’ proteins, which can be added to particular brain cells through genetic engineering. The channels open when hit by an ultrasonic pulse, which allows ions to flood into a neuron and so causes it to turn on. Ultrasound could be a less-invasive way for researchers to stimulate specific cell types or individual neurons, rather than using implanted electrodes or fibre-optic cables, says neurobiologist Sreekanth Chalasani, at the Salk Institute for Biological Studies in La Jolla, California, who led the study reported today in Nature Communications1. “Our hope is to create a toolbox of different channels that would each respond to different intensities of ultrasound,” he says. "It's a cool new idea, and they show that this could really be feasible," says Jon Pierce-Shimomura, a neuroscientist who studies the nematode Caenorhabditis elegans at the University of Texas at Austin. “This could open a whole new way for manipulating the nervous system non-invasively through genetically encodable tools.” © 2015 Nature Publishing Group,

Keyword: Brain imaging
Link ID: 21417 - Posted: 09.16.2015

By Sarah Schwartz Darkness and light may help prevent multiple sclerosis or fend off its symptoms. People who genetically produce less vitamin D, a compound normally boosted by sun exposure, have a greater risk of multiple sclerosis, researchers find. But the hormone melatonin, which the body produces in response to darkness, may reduce flare-ups for people who have the disease, another team of scientists reports. The studies may help researchers better understand and treat multiple sclerosis, a disease of the nervous system. It causes symptoms including muscle weakness, pain and vision loss in over 2 million people worldwide. Previous studies linked lower vitamin D levels to higher multiple sclerosis risk, but it was unclear whether this relationship was a coincidence. In work appearing August 25 in PLOS Medicine, scientists examined genetic data from thousands of Europeans and found that three genetic changes known to reduce vitamin D levels were associated with increased multiple sclerosis risk. These findings suggest that individuals with a higher risk of developing the disease, such as immediate family members of multiple sclerosis patients, should take steps to ensure they have sufficient levels of vitamin D, says study coauthor Brent Richards, a genetic epidemiologist at McGill University in Montreal. People can raise vitamin D levels to normal by taking an oral supplement. © Society for Science & the Public 2000 - 2015.

Keyword: Multiple Sclerosis; Biological Rhythms
Link ID: 21399 - Posted: 09.11.2015

By Amy Ellis Nutt Magnetic pulses from a device applied to the head appear to "reset" the brains of depressed patients, according to a new study from the United Kingdom. The circuitry in a part of the right prefrontal cortex is known to be too active in depressed patients, causing excessive rumination and self absorption and impaired attention. When the TMS was applied to healthy subjects in this study, the activity in that region slowed. "We found that one session of TMS modifies the connectivity of large-scale brain networks, particularly the right anterior insula, which is a key area in depression," lead scientist Sarina Iwabuchi, told the European College of Neuropsychology at a conference in Amsterdam this week. This was the first time an MRI was used to guide the TMS impulses and, at the same, time measure subtle changes in brain circuit activity. In addition, the researchers used magnetic resonance spectroscopy to analyze subjects' brain chemistry. "We also found that TMS alters concentrations of neurotransmitters. Iwabuchi said, "which are considered important for the development of depression," and which are the targets of most current antidepressant medications. Transcranial Magnetic Stimulation is the use of an electromagnetic coil to deliver small, powerful bursts of energy to targeted areas known to be involved in mood regulation. It is a painless, non-invasive treatment than involves no drugs, no IVs, or any other kind of sedation, and whose chief possible side effect is a headache. (The Food and Drug Administration approved limited use of TMS in 2008 for the treatment of depression.)

Keyword: Depression
Link ID: 21352 - Posted: 08.28.2015

By Michelle Roberts Health editor, BBC News online People genetically prone to low vitamin-D levels are at increased risk of multiple sclerosis, a large study suggests. The findings, based on the DNA profiles of tens of thousands of people of European descent, add weight to the theory that the sunshine vitamin plays a role in MS. Scientists are already testing whether giving people extra vitamin D might prevent or ease MS. Experts say the jury is still out. It is likely that environmental and genetic factors are involved in this disease of the nerves in the brain and spinal cord, they say. And if you think you may not be getting sufficient vitamin D from sunlight or your diet, you should discuss this with your doctor. Taking too much vitamin D can also be dangerous. Research around the world already shows MS is more common in less sunny countries, further from the equator. But it is not clear if this relationship is causal - other factors might be at play. To better understand the association, investigators at McGill University in Canada compared the prevalence of MS in a large group of Europeans with and without a genetic predisposition to low vitamin D. © 2015 BBC.

Keyword: Multiple Sclerosis
Link ID: 21339 - Posted: 08.26.2015

Alison Abbott This is the crackle of neural activity that allows a fruit-fly (Drosophila melanogaster) larva to crawl backwards: a flash in the brain and a surge that undulates through the nervous system from the top of the larva’s tiny body to the bottom. When the larva moves forwards, the surge flows the other way. The video — captured almost at the resolution of single neurons — demonstrates the latest development in a technique to film neural activity throughout an entire organism. The original method was invented by Philipp Keller and Misha Ahrens at the Howard Hughes Medical Institute's Janelia Research Campus in Ashburn, Virginia. The researchers genetically modify neurons so that each cell fluoresces when it fires; they then use innovative microscopy that involves firing sheets of light into the brain to record that activity. In 2013, the researchers produced a video of neural activity across the brain of a (transparent) zebrafish larva1. The fruit-fly larva that is mapped in the latest film, published in Nature Communications on 11 August2, is more complicated. The video shows neural activity not just in the brain, but throughout the entire central nervous system (CNS), including the fruit-fly equivalent of a mammalian spinal cord. And unlike the zebrafish, the fruit fly's nervous system is not completely transparent, which makes it harder to image. The researchers stripped the CNS from the larva’s body to examine it. For up to an hour after removal, the CNS continues to spontaneously fire the coordinated patterns of activity that typically drive crawling (and other behaviours). © 2015 Nature Publishing Group

Keyword: Brain imaging
Link ID: 21291 - Posted: 08.12.2015

Ashley Yeager A mouse scurries across a round table rimmed with Dixie cup–sized holes. Without much hesitation, the rodent heads straight for the hole that drops it into a box lined with cage litter. Any other hole would have led to a quick fall to the floor. But this mouse was more than lucky. It had an advantage — human glial cells were growing in its brain. Glia are thought of as the support staff for the brain’s nerve cells, or neurons, which transmit and receive the brain’s electrical and chemical signals. Named for the Greek term for “glue,” glia have been known for nearly 170 years as the cells that hold the brain’s bits together. Some glial cells help feed neurons. Other glia insulate nerve cell branches with myelin. Still others attack brain invaders responsible for infection or injury. Glial cells perform many of the brain’s most important maintenance jobs. But recent studies suggest they do a lot more. Glia can shape the conversation between neurons, speeding or slowing the electrical signals and strengthening neuron-to-neuron connections. When scientists coaxed human glia to grow in the brains of baby mice, the mice grew up to be supersmart, navigating tabletops full of holes and mastering other tasks much faster than normal mice. This experiment and others suggest that glia may actually orchestrate learning and memory, says neuroscientist R. Douglas Fields. “Glia aren’t doing vibrato. That’s for the neurons,” says Fields, of the National Institute of Child Health and Human Development in Bethesda, Md. “Glia are the conductors.” © Society for Science & the Public 2000 - 2015

Keyword: Learning & Memory; Glia
Link ID: 21289 - Posted: 08.12.2015

Jon Hamilton Lihong Wang creates the sort of medical technology you'd expect to find on the starship Enterprise. Wang, a professor of biomedical engineering at Washington University in St. Louis, has already helped develop instruments that can detect individual cancer cells in the bloodstream and oxygen consumption deep within the body. He has also created a camera that shoots at 100 billion frames a second, fast enough to freeze an object traveling at the speed of light. "It's really about turning some of these ideas that we thought were science fiction into fact," says Richard Conroy, who directs the Division of Applied Science & Technology at the National Institute of Biomedical Imaging and Bioengineering. Wang's ultimate goal is to use a combination of light and sound to solve the mysteries of the human brain. The brain is a "magical black box we still don't understand," he says. Wang describes himself as a toolmaker. And when President Obama unveiled his BRAIN initiative a couple of years ago to accelerate efforts to understand how we think and learn and remember, Wang realized that brain researchers really needed a tool he'd been working on for years. "We want to conquer the brain," Wang says. "But even for a mouse brain, which is only a few millimeters thick, we really don't have a technique that allows us to see throughout the whole brain." Current brain-imaging techniques such as functional MRI or PET scans all have drawbacks. They're slow, or not sharp enough, or they can only see things near the surface. So Wang has been developing another approach, one he believes will be fast enough to monitor brain activity in real time and sharp enough to reveal an individual brain cell. © 2015 NPR

Keyword: Brain imaging
Link ID: 21226 - Posted: 07.27.2015

A study showed that scientists can wirelessly determine the path a mouse walks with a press of a button. Researchers at the Washington University School of Medicine, St. Louis, and University of Illinois, Urbana-Champaign, created a remote controlled, next-generation tissue implant that allows neuroscientists to inject drugs and shine lights on neurons deep inside the brains of mice. The revolutionary device is described online in the journal Cell. Its development was partially funded by the National Institutes of Health. “It unplugs a world of possibilities for scientists to learn how brain circuits work in a more natural setting.” said Michael R. Bruchas, Ph.D., associate professor of anesthesiology and neurobiology at Washington University School of Medicine and a senior author of the study. The Bruchas lab studies circuits that control a variety of disorders including stress, depression, addiction, and pain. Typically, scientists who study these circuits have to choose between injecting drugs through bulky metal tubes and delivering lights through fiber optic cables. Both options require surgery that can damage parts of the brain and introduce experimental conditions that hinder animals’ natural movements. To address these issues, Jae-Woong Jeong, Ph.D., a bioengineer formerly at the University of Illinois at Urbana-Champaign, worked with Jordan G. McCall, Ph.D., a graduate student in the Bruchas lab, to construct a remote controlled, optofluidic implant. The device is made out of soft materials that are a tenth the diameter of a human hair and can simultaneously deliver drugs and lights.

Keyword: Brain imaging
Link ID: 21184 - Posted: 07.18.2015

By Chris Foxx Technology reporter Twitter has responded to an epilepsy charity that said two of its online adverts were "irresponsible". The social media giant had uploaded two short videos on Vine that featured a looping, rapid succession of flashing colours. "Twitter's ads were dangerous to people living with photo-sensitive epilepsy," said Epilepsy Action's deputy chief executive, Simon Wigglesworth. Twitter told the BBC it had removed the videos on Friday morning. Around one in 3,500 people in the UK has photosensitive epilepsy, according to Epilepsy Action. Seizures can be triggered by flashing lights and bold patterns. An episode of Japanese cartoon Pokemon was famously blamed for triggering convulsions in 1997. "Eighty seven people are diagnosed with epilepsy every day and that first seizure can often come out of nowhere," said Mr Wigglesworth. "For a huge corporation like Twitter to take that risk was irresponsible." The Advertising Standards Authority told the BBC that "marketing communications", even those uploaded on a company's own website, should not include "visual effects or techniques that are likely to adversely affect members of the public with photosensitive epilepsy". It said both online and broadcast adverts in the UK had to adhere to rules made by the Committees of Advertising Practice. "We take very seriously ads in online media that might cause harm to people with photosensitive epilepsy," an ASA spokeswoman told the BBC. Twitter's flashing Vine videos were online for 18 hours before the company removed them. © 2015 BBC

Keyword: Epilepsy; Vision
Link ID: 21157 - Posted: 07.11.2015

By Ariel Sabar In televised remarks from the East Room of the White House on April 2, 2013, President Obama unveiled a scientific mission as grand as the Apollo program. The goal wasn’t outer space, but a frontier every bit as bewitching: the human brain. Obama challenged the nation’s “most imaginative and effective researchers” to map in real time the flickerings of all 100 billion nerve cells in the brain of a living person, a voyage deep into the neural cosmos never attempted at so fine a scale. A panoramic view of electric pulses pinballing across the brain could lead to major new understandings of how we think, remember and learn, and how ills from autism to Alzheimer’s rewire our mental circuitry. “We have a chance to improve the lives of not just millions,” the president said, “but billions of people on this planet.” The next month, six miles from the White House, a Harvard professor named Florian Engert grabbed a mic and, in front of the nation’s top neuroscientists, declared Obama’s effort essentially futile. “We have those data now,” said Engert, who, in a room full of professorial blazers and cardigans, was wearing a muscle shirt that afforded ample views of his bulging biceps. “We discovered they’re actually not all that useful.” (“I think whole-brain imaging is just a bunch of bull----,” is how he put it to me later.) To the other researchers, he must have sounded like a traitor. Engert, who is 48, was basically the first person on the planet to observe a brain in the wall-to-wall way Obama envisioned. He and his colleagues had done it with a sci-fi-worthy experiment that recorded every blip of brain activity in a transparent baby zebra­fish, a landmark feat published just a year earlier in the marquee scientific journal Nature. For Engert to suggest that the president’s brain quest was bunk was a bit like John Glenn returning from orbit and telling JFK not to bother with a lunar landing.

Keyword: Brain imaging
Link ID: 21119 - Posted: 07.02.2015

By GARY MARCUS SCIENCE has a poor track record when it comes to comparing our brains to the technology of the day. Descartes thought that the brain was a kind of hydraulic pump, propelling the spirits of the nervous system through the body. Freud compared the brain to a steam engine. The neuroscientist Karl Pribram likened it to a holographic storage device. Many neuroscientists today would add to this list of failed comparisons the idea that the brain is a computer — just another analogy without a lot of substance. Some of them actively deny that there is much useful in the idea; most simply ignore it. Often, when scientists resist the idea of the brain as a computer, they have a particular target in mind, which you might call the serial, stored-program machine. Here, a program (or “app”) is loaded into a computer’s memory, and an algorithm, or recipe, is executed step by step. (Calculate this, then calculate that, then compare what you found in the first step with what you found in the second, etc.) But humans don’t download apps to their brains, the critics note, and the brain’s nerve cells are too slow and variable to be a good match for the transistors and logic gates that we use in modern computers. If the brain is not a serial algorithm-crunching machine, though, what is it? A lot of neuroscientists are inclined to disregard the big picture, focusing instead on understanding narrow, measurable phenomena (like the mechanics of how calcium ions are trafficked through a single neuron), without addressing the larger conceptual question of what it is that the brain does. This approach is misguided. Too many scientists have given up on the computer analogy, and far too little has been offered in its place. In my view, the analogy is due for a rethink. To begin with, all the standard arguments about why the brain might not be a computer are pretty weak. Take the argument that “brains are parallel, but computers are serial.” Critics are right to note that virtually every time a human does anything, many different parts of the brain are engaged; that’s parallel, not serial. © 2015 The New York Times Company

Keyword: Brain imaging
Link ID: 21099 - Posted: 06.27.2015

Elizabeth Gibney A simple injection is now all it takes to wire up a brain. A diverse team of physicists, neuroscientists and chemists has implanted mouse brains with a rolled-up, silky mesh studded with tiny electronic devices, and shown that it unfurls to spy on and stimulate individual neurons. The implant has the potential to unravel the workings of the mammalian brain in unprecedented detail. “I think it’s great, a very creative new approach to the problem of recording from large number of neurons in the brain,” says Rafael Yuste, director of the Neuro­technology Center at Columbia University in New York, who was not involved in the work. If eventually shown to be safe, the soft mesh might even be used in humans to treat conditions such as Parkinson’s disease, says Charles Lieber, a chemist at Harvard University on Cambridge, Massachusetts, who led the team. The work was published in Nature Nanotechnology on 8 June1. Neuroscientists still do not understand how the activities of individual brain cells translate to higher cognitive powers such as perception and emotion. The problem has spurred a hunt for technologies that will allow scientists to study thousands, or ideally millions, of neurons at once, but the use of brain implants is currently limited by several disadvantages. So far, even the best technologies have been composed of relatively rigid electronics that act like sandpaper on delicate neurons. They also struggle to track the same neuron over a long period, because individual cells move when an animal breathes or its heart beats. © 2015 Nature Publishing Group

Keyword: Brain imaging
Link ID: 21034 - Posted: 06.09.2015

by Hal Hodson Electricity is the brain's language, and now we can speak to it without wires or implants. Nanoparticles can be used to stimulate regions of the brain electrically, opening up new ways to treat brain diseases. It may even one day allow the routine exchange of data between computers and the brain. A material discovered in 2004 makes this possible. When "magnetoelectric" nanoparticles (MENs) are stimulated by an external magnetic field, they produce an electric field. If such nanoparticles are placed next to neurons, this electric field should allow them to communicate. To find out, Sakhrat Khizroev of Florida International University in Miami and his team inserted 20 billion of these nanoparticles into the brains of mice. They then switched on a magnetic field, aiming it at the clump of nanoparticles to induce an electric field. An electroencephalogram showed that the region surrounded by nanoparticles lit up, stimulated by this electric field that had been generated. "When MENs are exposed to even an extremely low frequency magnetic field, they generate their own local electric field at the same frequency," says Khizroev. "In turn, the electric field can directly couple to the electric circuitry of the neural network." Khizroev's goal is to build a system that can both image brain activity and precisely target medical treatments at the same time. Since the nanoparticles respond differently to different frequencies of magnetic field, they can be tuned to release drugs. © Copyright Reed Business Information Ltd

Keyword: Brain imaging
Link ID: 21033 - Posted: 06.09.2015

By Esther Hsieh Imagine you are enjoying your golden years, driving to your daily appointment for some painless brain zapping that is helping to stave off memory loss. That's the hope of a new study, in which people who learned associations (such as a random word and an image) after transcranial magnetic stimulation (TMS) were better able to learn more pairings days and weeks later—with no further stimulation needed. TMS uses a magnetic coil placed on the head to increase electrical signaling a few centimeters into the brain. Past studies have found that TMS can boost cognition and memory during stimulation, but this is the first to show that such gains can last even after the TMS regimen is completed. In the new study, which was published in Science, neuroscientists first used brain imaging to identify the associative memory network of 16 young, healthy participants. This network, based around the hippocampus, glues together things such as sights, places, sounds and time to form a memory, explains neuroscientist Joel Voss of Northwestern University, a senior author of the paper. Next, the researchers applied TMS behind the left ear of each participant for 20 minutes for five consecutive days to stimulate this memory network. To see if participants' associative memory improved, one day after the stimulation regimen finished they were tested for their ability to learn random words paired with faces. Subjects who had had TMS performed 33 percent better, compared with those who received placebo treatments, such as sham stimulation. © 2015 Scientific American

Keyword: Learning & Memory; Brain imaging
Link ID: 20977 - Posted: 05.25.2015

Richard Harris American medicine is heading into new terrain, a place where a year's supply of drugs can come with a price tag that exceeds what an average family earns. Pharmacy benefit manager Express Scripts says last year more than half a million Americans racked up prescription drug bills exceeding $50,000. Barbara Haedtke of Portland, Ore., knows this all too well. When she was diagnosed with multiple sclerosis in 2001 at the age of 35, she was prescribed Avonex, at a cost of around $10,000 a year. Her health insurance paid most of that until she and her husband found themselves without jobs during an economic downturn. "We were in the hole, and so $10,000 was a lot of money," she says. "Under the best circumstances it's a lot of money, but then particularly it was really difficult." Barbara Haedtke says she's grateful for a drug-company program that helps cover copays, but doesn't know how long she'll get that benefit. The drug company gave her the medication at no charge until she once again had a job with insurance, and for that, she says, she's really grateful. But the story doesn't end there. Haedtke used Avonex for about a decade and watched with disbelief as the price more than tripled. She's now taking a new drug, Tecfidera, that's priced even higher — $66,000 a year, according to her pharmacy receipt. The drug is supposed to help reduce the number of episodes that characterize multiple sclerosis, a disease in which nerve fibers gradually degenerate, causing muscle weakness, numbness, loss of balance and even paralysis. © 2015 NPR

Keyword: Multiple Sclerosis; Stress
Link ID: 20973 - Posted: 05.25.2015

Nick Davis Mood disorders such as depression are devastating to sufferers, and hugely costly to treat. The most severe form of depression, often called clinical depression or major depressive disorder (MDD), increases the person’s likelihood of suicide and contributes significantly to a person’s disability-adjusted life years (DALYs), a measure of quality of life taking into account periods of incapacity. The healthcare burden of MDD is large in most countries, especially when the person requires a stay in hospital. Putting these factors together, it’s clear we need to develop effective treatments to combat depression. The mechanisms of depressive disorders are not well understood, and it seems likely that there is no single cause. Most modern therapies use drugs that target neurotransmitters – the chemicals that carry signals between neurons. For example, the class of drugs known as SSRIs, or selective serotonin reuptake inhibitors, prevent the neurotransmitter serotonin from being reabsorbed by a neuron; this means that more serotonin is available to wash around between the nerve cells, and is more likely to activate cells in the brain networks that area affected in MDD. But SSRIs and other drugs are not a pharmacological ‘free lunch’. Drug treatments for depression are ineffective for many people, cause side-effects, and may lose their therapeutic effect over time. For these reasons, many researchers are searching for alternative treatments for MDD that overcome these problems, and are more effective or less unpleasant. One potential treatment involves the use of pulses of magnetic energy over the head to target the brain’s mood circuits. This technique, called transcranial magnetic stimulation (TMS), may potentially address some of the problems of pharmaceutical treatments, but we still don’t know exactly how it works, or how effective it will be in treating MDD. © 2015 Guardian News and Media Limited

Keyword: Depression
Link ID: 20946 - Posted: 05.18.2015

Backyard Brains. For 235 years we have been trying to isolate, understand, and analyze the elusive action potential, and here we tell the story that continues today. The progress of understanding Action Potentials can be classed into three main endeavors: 1. Amplification The amplifiers that gave us the first hint of the electrical impulses generated by neurons came from biological tissue itself! Scientists of the 18th and early 19th century used the contractions of muscles as "bioamplifiers" to indirectly measure neural firing. Using friction machines (spark generators), Leyden jars (primitive capacitors), or Voltaic Piles (the first batteries), electrical stimuli could be delivered to motor neurons that were still attached to muscles. The electrical stimulation would cause the nerve to fire action potentials (so people hypothesized), the muscle would then contract, and the force of contraction could be measured with a spring. With increasing electrical stimuli strength (thus more action potentials in the motor neurons), the muscle would contract with increasing force. This technique worked, but led to vigorous debates as to whether the neural tissue was actually generating its own action potentials at all, or whether the muscle contraction was just a direct result of electrical stimulation. By the mid-19th century, galvanometers had been invented, and it was possible to see that nerves were indeed generating their own action potentials. These galvanometers exploited the then new technology of electromagnets. For example, Emil de Bois-Reymond built by hand a type of galvanometer with 24,000 turns around an iron plate. When the nerve fired action potentials, a metal needle suspended by the plate would deflect. These devices worked, but the needle movement was not fast enough to separate the 1 ms individual action potentials, and the machines occupied a lot of time to construct. © 2009-2015 Backyard Brains

Keyword: Miscellaneous
Link ID: 20944 - Posted: 05.18.2015

By GREGORY HICKOK IN 1890, the American psychologist William James famously likened our conscious experience to the flow of a stream. “A ‘river’ or a ‘stream’ are the metaphors by which it is most naturally described,” he wrote. “In talking of it hereafter, let’s call it the stream of thought, consciousness, or subjective life.” While there is no disputing the aptness of this metaphor in capturing our subjective experience of the world, recent research has shown that the “stream” of consciousness is, in fact, an illusion. We actually perceive the world in rhythmic pulses rather than as a continuous flow. Some of the first hints of this new understanding came as early as the 1920s, when physiologists discovered brain waves: rhythmic electrical currents measurable on the surface of the scalp by means of electroencephalography. Subsequent research cataloged a spectrum of such rhythms (alpha waves, delta waves and so on) that correlated with various mental states, such as calm alertness and deep sleep. Researchers also found that the properties of these rhythms varied with perceptual or cognitive events. The phase and amplitude of your brain waves, for example, might change if you saw or heard something, or if you increased your concentration on something, or if you shifted your attention. But those early discoveries themselves did not change scientific thinking about the stream-like nature of conscious perception. Instead, brain waves were largely viewed as a tool for indexing mental experience, much like the waves that a ship generates in the water can be used to index the ship’s size and motion (e.g., the bigger the waves, the bigger the ship). Recently, however, scientists have flipped this thinking on its head. We are exploring the possibility that brain rhythms are not merely a reflection of mental activity but a cause of it, helping shape perception, movement, memory and even consciousness itself. What this means is that the brain samples the world in rhythmic pulses, perhaps even discrete time chunks, much like the individual frames of a movie. From the brain’s perspective, experience is not continuous but quantized. © 2015 The New York Times Company

Keyword: Consciousness; Attention
Link ID: 20914 - Posted: 05.12.2015