Chapter 8. General Principles of Sensory Processing, Touch, and Pain
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Laura Sanders Pain can sear memories into the brain, a new study finds. A full year after viewing a picture of a random, neutral object, people could remember it better if they had been feeling painful heat when they first saw it. “The results are fun, they are interesting and they are provocative,” says neuroscientist A. Vania Apkarian of Northwestern University in Chicago. The findings “speak to the idea that pain really engages memory.” Neuroscientists G. Elliott Wimmer and Christian Büchel of University Medical Center Hamburg-Eppendorf in Germany reported the results in a paper online at BioRxiv.org first posted December 24 and revised January 6. The findings are under review at a journal, and Wimmer declined to comment on the study until it is accepted for publication. Wimmer and Büchel recruited 31 brave souls who agreed to feel pain delivered by a heat-delivering thermode on their left forearms. Each person’s pain sensitivity was used to calibrate the amount of heat they received in the experiment, which was either not painful (a 2 on an 8-point scale) or the highest a person could endure multiple times (a full 8). While undergoing a functional MRI scan, participants looked at a series of pictures of unremarkable household objects, such as a camera, sometimes feeling pain and sometimes not. Right after seeing the images, the people took a pop quiz in which they answered whether an object was familiar. Pain didn’t influence memory right away. Right after their ordeal, participants remembered about three-quarters of the previously seen objects, regardless of whether pain was present, the researchers found. © Society for Science & the Public 2000 - 2015.
Pete Etchells Autonomous Sensory Meridian Response, or ASMR, is a curious phenomenon. Those who experience it often characterise it as a tingling sensation in the back of the head or neck, or another part of the body, in response to some sort of sensory stimulus. That stimulus could be anything, but over the past few years, a subculture has developed around YouTube videos, and their growing popularity was the focus of a video posted on the Guardian this last week. It’s well worth a watch, but I couldn’t help but feel it would have been a bit more interesting if there had been some scientific background in it. The trouble is, there isn’t actually much research on ASMR out there. To date, only one research paper has been published on the phenomenon. In March last year, Emma Barratt, a graduate student at Swansea University, and Dr Nick Davis, then a lecturer at the same institution, published the results of a survey of some 500 ASMR enthusiasts. “ASMR is interesting to me as a psychologist because it’s a bit ‘weird’” says Davis, now at Manchester Metropolitan University. “The sensations people describe are quite hard to describe, and that’s odd because people are usually quite good at describing bodily sensation. So we wanted to know if everybody’s ASMR experience is the same, and of people tend to be triggered by the same sorts of things.” The study asked a range of questions about where, when and why people watch ASMR videos, whether there was any consistency in ASMR-triggering content, as well as whether individuals felt it had any effect on their mood. There was a remarkable consistency across participants in terms of triggering content – whispering worked for the majority of people, followed by videos involving some sort of personal attention, crisp sounds, and slow movements. For the most part, participants reported that they watched ASMR videos for relaxation purposes, or to help them sleep or deal with stress. © 2016 Guardian News and Media Limited
Keyword: Pain & Touch
Link ID: 21767 - Posted: 01.09.2016
By Emily Underwood As long as she can remember, 53-year-old Rosa Sundquist has tallied the number of days per month when her head explodes with pain. The migraines started in childhood and have gotten worse as she’s grown older. Since 2008, they have incapacitated her at least 15 days per month, year-round. Head-splitting pain isn’t the worst of Sundquist’s symptoms. Nausea, vomiting, and an intense sensitivity to light, sound, and smell make it impossible for her to work—she used to be an office manager—or often even to leave her light-proofed home in Dumfries, Virginia. On the rare occasions when she does go out to dinner or a movie with her husband and two college-aged children, she wears sunglasses and noise-canceling headphones. A short trip to the grocery store can turn into a full-blown attack “on a dime,” she says. Every 10 weeks, Sundquist gets 32 bee sting–like injections of the nerve-numbing botulism toxin into her face and neck. She also visits a neurologist in Philadelphia, Pennsylvania, who gives her a continuous intravenous infusion of the anesthetic lidocaine over 7 days. The lidocaine makes Sundquist hallucinate, but it can reduce her attacks, she says—she recently counted 20 migraine days per month instead of 30. Sundquist can also sometimes ward off an attack with triptans, the only drugs specifically designed to interrupt migraines after they start. Millions of others similarly dread the onset of a migraine, although many are not afflicted as severely as Sundquist. Worldwide, migraines strike roughly 12% of people at least once per year, with women roughly three times as likely as men to have an attack. © 2016 American Association for the Advancement of Science.
By Stephani Sutherland A technique called optogenetics has transformed neuroscience during the past 10 years by allowing researchers to turn specific neurons on and off in experimental animals. By flipping these neural switches, it has provided clues about which brain pathways are involved in diseases like depression and obsessive-compulsive disorder. “Optogenetics is not just a flash in the pan,” says neuroscientist Robert Gereau of Washington University in Saint Louis. “It allows us to do experiments that were not doable before. This is a true game changer like few other techniques in science.” Since the first papers were published on optogenetics in the mid-aughts some researchers have mused about one day using optogenetics in patients, imagining the possibility of an off-switch for depression, for instance. The technique, however, would require that a patient submit to a set of highly invasive medical procedures: genetic engineering of neurons to insert molecular switches to activate or switch off cells, along with threading of an optical fiber into the brain to flip those switches. Spurred on by a set of technical advances, optogenetics pioneer Karl Deisseroth, together with other Stanford University researchers, has formed a company to pursue optogenetics trials in patients within the next several years—one of several start-ups that are now contemplating clinical trials of the technique. Circuit Therapeutics, founded in 2010, is moving forward with specific plans to treat neurological diseases. (It also partners with pharmaceutical companies to help them use optogenetics in animal research to develop novel drug targets for human diseases.) © 2016 Scientific America
Keyword: Pain & Touch
Link ID: 21758 - Posted: 01.07.2016
A woman born incapable of feeling pain has been hurt for the first time – thanks to a drug normally prescribed for opioid overdoses. She was burned with a laser, and quite liked the experience. The breakthrough may lead to powerful new ways to treat painful conditions such as arthritis. Only a handful people around the world are born unable to feel pain. These individuals can often suffer a range of injuries when they are young. Babies with the condition tend to chew their fingers, toes and lips until they bleed, and toddlers can suffer an increased range of knocks, tumbles and encounters with sharp or hot objects. The disorder is caused by a rare genetic mutation that results in a lack of ion channels that transport sodium across sensory nerves. Without these channels, known as Nav1.7 channels, nerve cells are unable to communicate pain. Researchers quickly sought to make compounds that blocked Nav1.7 channels, thinking they might be able to block pain in people without the disorder. “It looked like a fantastic drug target,” says John Wood at University College London. “Pharma companies went bananas and made lots of drugs.” But while a few compounds saw some success, none brought about the total pain loss seen in people who lack the channel naturally. © Copyright Reed Business Information Ltd.
By David Noonan The 63-year-old chief executive couldn't do his job. He had been crippled by migraine headaches throughout his adult life and was in the middle of a new string of attacks. “I have but a little moment in the morning in which I can either read, write or think,” he wrote to a friend. After that, he had to shut himself up in a dark room until night. So President Thomas Jefferson, in the early spring of 1807, during his second term in office, was incapacitated every afternoon by the most common neurological disability in the world. The co-author of the Declaration of Independence never vanquished what he called his “periodical head-ach,” although his attacks appear to have lessened after 1808. Two centuries later 36 million American migraine sufferers grapple with the pain the president felt. Like Jefferson, who often treated himself with a concoction brewed from tree bark that contained quinine, they try different therapies, ranging from heart drugs to yoga to herbal remedies. Their quest goes on because modern medicine, repeatedly baffled in attempts to find the cause of migraine, has struggled to provide reliable relief. Now a new chapter in the long and often curious history of migraine is being written. Neurologists believe they have identified a hypersensitive nerve system that triggers the pain and are in the final stages of testing medicines that soothe its overly active cells. These are the first ever drugs specifically designed to prevent the crippling headaches before they start, and they could be approved by the U.S. Food and Drug Administration next year. If they deliver on the promise they have shown in studies conducted so far, which have involved around 1,300 patients, millions of headaches may never happen. © 2015 Scientific American
Keyword: Pain & Touch
Link ID: 21662 - Posted: 11.28.2015
By Nala Rogers If you travel with a group of friends, you might delegate navigation to the person with the best sense of direction. But among homing pigeons, the leader is whoever flies the fastest—even if that pigeon has to pick up navigation skills on the job, according to a new study. To find out how the skills of individual pigeons influence flock direction, researchers tested four flocks on journeys from three different locations, each about 5 kilometers from their home loft near Oxford, U.K. At each site, the researchers tracked the pigeons during solo flights before releasing them together for several group journeys. The fastest birds surged to the front during group flights and determined when the flock turned, despite the fact that these leaders were often poor navigators during their initial solo expeditions. But on a final set of solo flights—made after the group journeys—these same leaders chose straighter routes than followers, the researchers report today in Current Biology. Apparently, being responsible for group decisions helped pigeons learn the route, say scientists, raising questions about the two-way interplay between skills and leadership. © 2015 American Association for the Advancement of Science
Ian Sample Science editor Tiny biological compasses made from clumps of protein may help scores of animals, and potentially even humans, to find their way around, researchers say. Scientists discovered the minuscule magnetic field sensors in fruit flies, but found that the same protein structures appeared in retinal cells in pigeons’ eyes. They can also form in butterfly, rat, whale and human cells. The rod-like compasses align themselves with Earth’s geomagnetic field lines, leading researchers to propose that when they move, they act on neighbouring cell structures that feed information into the nervous system to create a broader direction-sensing system. Professor Can Xie, who led the work at Peking University, said the compass might serve as a “universal mechanism for animal magnetoreception,” referring to the ability of a range of animals from butterflies and lobsters to bats and birds, to navigate with help from Earth’s magnetic field. Whether the compasses have any bearing on human navigation is unknown, but the Peking team is investigating the possibility. “Human sense of direction is complicated,” said Xie. “However, I believe that magnetic sense plays a key role in explaining why some people have a good sense of direction.” The idea that animals could sense Earth’s magnetic field was once widely dismissed, but the ability is now well established, at least among some species. The greatest mystery that remains is how the sensing is done. © 2015 Guardian News and Media Limited
Keyword: Animal Migration
Link ID: 21638 - Posted: 11.17.2015
By Virginia Morell Plunge a live crab into a pot of boiling water, and it’s likely to try to scramble out. Is the crab’s behavior simply a reflex, or is it a sign of pain? Many scientists doubt that any invertebrate (or fish) feels pain because they lack the areas in the brain associated with human pain. Others argue this is an unfair comparison, noting that despite the major differences between vertebrate and invertebrate brains, their functions (such as seeing) are much the same. To get around this problem, researchers in 2014 argued that an animal could be classified as experiencing pain if, among other things, it changes its behavior in a way that indicates it’s trying to prevent further injury, such as through increased wariness, and if it shows a physiological change, such as elevated stress hormones. To find out whether crabs meet these criteria, scientists collected 40 European shore crabs (Carcinus maenas), shown in the photo above, in Northern Ireland. They placed the animals into individual tanks, and gave half 200-millisecond electrical shocks every 10 seconds for 2 minutes in their right and left legs. The other 20 crabs served as controls. Sixteen of the shocked crabs began walking in their tanks, and four tried to climb out. None of the control crabs attempted to clamber up the walls, but 14 walked, whereas six didn’t move at all. There was, however, one big physiological difference between the 16 shocked, walking crabs and the 14 control walkers, the scientists report in today’s issue of Biology Letters: Those that received electrical jolts had almost three times the amount of lactic acid in their haemolymph, a fluid that’s analogous to the blood of vertebrates—a clear sign of stress. Thus, crabs pass the bar scientists set for showing that an animal feels pain. © 2015 American Association for the Advancement of Science.
By Arlene Karidis Several years ago, Peggy Chenoweth began having excruciating cramping in her ankle. It felt severely sprained and as if her toe were twisting to the point where it was being ripped off her foot. “The pain is right here,” she told an orthopedic surgeon, “in my ankle and foot.” But the 41-year-old Gainesville, Va., resident no longer had that ankle and foot. Her leg had been amputated below the knee after a large piece of computer equipment fell off a cart, crushed her foot and caused nerve damage. Further, she insisted that since the amputation, she could feel her missing toes move. Chenoweth’s surgeon knew exactly what was going on: phantom pain. Lynn Webster, an anesthesiologist and past president of the American Academy of Pain Medicine, explains the phenomenon: “With ‘phantom pain,’ nerves that transmitted information from the brain to the now-missing body part continue to send impulses, which relay the message of pain.” It feels as if the removed part is still there and hurting, but pain is actually in the brain. The sensation ranges from annoying itching to red-hot burning. Physicians wrote about phantom pain as early as the 1860s, but U.S. research on this condition has increased recently, spurred by the surge of amputees returning from warfare in Iraq and Afghanistan and by increasing rates of diabetes. (Since 2003, nearly 1,650 service members have lost limbs, according to the Congressional Research Service. In 2010, about 73,000 amputations were performed on diabetics in the United States, according to the Centers for Disease Control and Prevention.)
Keyword: Pain & Touch
Link ID: 21620 - Posted: 11.10.2015
By Jason G. Goldman When a monkey has the sniffles or a headache, it doesn't have the luxury of popping a few painkillers from the medicine cabinet. So how does it deal with the common colds and coughs of the wildlife world? University of Georgia ecologist Ria R. Ghai and her colleagues observed a troop of more than 100 red colobus monkeys in Uganda's Kibale National Park for four years to figure out whether the rain forest provides a Tylenol equivalent. Monkeys infected with a whipworm parasite were found to spend more time resting and less time moving, grooming and having sex. The infected monkeys also ate twice as much tree bark as their healthy counterparts even though they kept the same feeding schedules. The findings were published in September in the journal Proceedings of the Royal Society B. The fibrous snack could help literally sweep the intestinal intruder out of the simians' gastrointestinal tracts, but Ghai suspects a more convincing reason. Seven of the nine species of trees and shrubs preferred by sick monkeys have known pharmacological properties, such as antisepsis and analgesia. Thus, the monkeys could have been self-medicating, although she cannot rule out other possibilities. The sick individuals were, however, using the very same plants that local people use to treat illnesses, including infection by whipworm parasites. And that “just doesn't seem like a coincidence,” Ghai says. © 2015 Scientific American,
by Laura Sanders Babies’ minds are mysterious. Thoughts might be totally different in a brain that lacks words, and sensations might feel alien in a body so new. Are babies’ perceptions like ours, or are they completely different? Even if babies could talk, words would surely fail to convey what it’s like to experience, oh, every single thing for the first time. A recent paper offers a sliver of insight into young babies’ inner lives. The study, published October 19 in Current Biology, finds an example in which 4-month-old babies are happily oblivious to the external world. The research focuses on a perceptual trick that suckers adults and 6-month-old babies alike. When the hands are crossed, people often mistake which hand feels a touch. Let’s say your left hand (now crossed over to the right side of your body) gets a tickle. Your eyes would see a hand on the right side of your body get touched — a place usually claimed by your right hand, but now occupied by your left. Those mismatches between sight, touch and expectation can thwart you from quickly and correctly saying which hand was touched. Here’s the twist: 4-month-old babies don’t fall for this trick, Andrew Bremner of Goldsmiths, University of London and his colleagues found. In the experiment, a researcher would hold infants’ legs in either a crossed position or straight, while one of two remote-controlled buzzers taped to their feet tickled one foot. The researchers then watched which foot or leg wiggled as a result. If the buzzed foot moved, that meant that the baby got it right. © Society for Science & the Public 2000 - 2015.
David Cyranoski A Chinese neuroscientist has been sacked after reporting he had used magnetic fields to control neurons and muscle cells in nematode worms (pictured), using a protein that senses magnetism. Tsinghua University in Beijing has sacked a neuroscientist embroiled in a dispute over work on a long-sought protein that can sense magnetic fields. The university has not given a specific reason for its dismissal, however, and the scientist involved, Zhang Sheng-jia, says that he will contest their action. In September, Zhang reported in the journal Science Bulletin1 that he could manipulate neurons in worms by applying a magnetic field — a process that uses a magnetic-sensing protein. But a biophysicist at neighbouring Peking University, Xie Can, who claims to have discovered the protein’s magnetic-sensing capacity and to have a paper detailing his research under review, complained that Zhang should not have published his paper before Xie’s own work appeared. Xie said that by publishing, Zhang violated an agreement that the pair had reached — although the two scientists tell different versions about the terms of their agreement, and have different explanations of how Zhang came to be working with the protein. © 2015 Nature Publishing Group
Keyword: Animal Migration
Link ID: 21608 - Posted: 11.06.2015
By SINDYA N. BHANOO Some kinds of itching can be caused by the lightest of touches, a barely felt graze that rustles tiny hairs on the skin’s surface. This type of itch is created via a dedicated neural pathway, a new study suggests. The finding, which appears in the journal Science, could help researchers better understand chronic itchiness in conditions like eczema, diabetic neuropathy, multiple sclerosis and some cancers. The study also may help researchers determine why certain patients do not respond well to antihistamine drugs. “In the future, we may have some way to manipulate neuron activity to inhibit itching,” said Quifu Ma, a neurobiologist at Harvard University and one of the study’s authors. In the study, Dr. Ma and his colleagues inhibited neurons that express a neuropeptide known as Y or NPY in mice. When these neurons were suppressed and the mice were poked with a tiny filament, they fell into scratching fits. Normally, mice would not even respond to this sort of stimuli. “We start to see skin lesions — they don’t stop scratching,” Dr. Ma said. “It’s pretty traumatic.” The neurons only seem related to itches prompted by light touching, known as mechanically induced itches. Chemical itches, like those caused by a mosquito bite or an allergic reaction, are not transmitted by the same neurons. © 2015 The New York Times Company
Keyword: Pain & Touch
Link ID: 21593 - Posted: 11.03.2015
By Hanae Armitage Fake fingerprints might sound like just another ploy to fool the feds. But the world’s first artificial prints—reported today—have even cooler applications. The electronic material, which mimics the swirling designs imprinted on every finger, can sense pressure, temperature, and even sound. Though the technology has yet to be tested outside the lab, researchers say it could be key to adding sensation to artificial limbs or even enhancing the senses we already have. “It’s an interesting piece of work,” says John Rogers, materials scientist at the University of Illinois, Urbana-Champaign, who was not involved in the study. “It really adds to the toolbox of sensor types that can be integrated with the skin.” Electronic skins, known as e-skins, have been in development for years. There are several technologies used to mimic the sensations of real human skin, including sensors that can monitor health factors like pulse or temperature. But previous e-skins have been able to “feel” only two sensations: temperature and pressure. And there are additional challenges when it comes to replicating fingertips, especially when it comes to mimicking their ability to sense even miniscule changes in texture, says Hyunhyub Ko, a chemical engineer at Ulsan National Institute of Science and Technology in South Korea. So in the new study, Ko and colleagues started with a thin, flexible material with ridges and grooves much like natural fingerprints. This allowed them to create what they call a “microstructured ferroelectric skin” The e-skin’s perception of pressure, texture, and temperature all come from a highly sensitive structure called an interlocked microdome array—the tiny domes sandwiched in the bottom two layers of the e-skin, also shown in the figure below. © 2015 American Association for the Advancement of Science
Laura Sanders A fly tickling your arm hair can spark a maddening itch. Now, scientists have spotted nerve cells in mice that curb this light twiddling sensation. If humans possess similar itch-busters, the results, published in the Oct. 30 Science, could lead to treatments for the millions of people who suffer from intractable, chronic itch. For many of these people, there are currently no good options. “This is a major problem,” says clinician Gil Yosipovitch of Temple University School of Medicine in Philadelphia and director of the Temple Itch Center. The new study shows that mice handle an itch caused by a fluttery touch differently than other kinds of itch. This distinction “seems to have clinical applications that clearly open our field,” Yosipovitch says. In recent years, scientists have made progress teasing apart the pathways that carry itchy signals from skin to spinal cord to brain (SN: 11/22/2008, p. 16). But those itch signals often originate from chemicals, such as those delivered by mosquitoes. All that’s needed to spark a different sort of itch, called mechanical itch, is a light touch on the skin. The existence of this kind of itch is no surprise, Yosipovitch says. Mechanical itch may help explain why clothes or even dry, scaly skin can be itchy. The new finding came from itchy mice engineered to lack a type of nerve cell in their spinal cords. Without prompting, these mice scratched so often that they developed sore bald patches on their skin. © Society for Science & the Public 2000 - 2015
Keyword: Pain & Touch
Link ID: 21587 - Posted: 10.31.2015
Adam Cole Watch a scary movie and your skin crawls. Goose bumps have become so associated with fear that the word is synonymous with thrills and chills. But what on earth does scary have do to with chicken-skin bumps? For a long time, it wasn't well understood. Physiologically, it's fairly simple. Adrenaline stimulates tiny muscles to pull on the roots of our hairs, making them stand out from our skin. That distorts the skin, causing bumps to form. Call it horripilation, and you'll be right — bristling from cold or fear. Charles Darwin once investigated goose bumps by scaring zoo animals with a stuffed snake. He argued for the now accepted theory that goose bumps are a vestige of humanity's ancient past. Our ancestors were hairy. Goose bumps would have fluffed up their hair. When they were scared, that would have made them look bigger — and more intimidating to attackers. When they were cold, that would have trapped an insulating layer of air to keep them warm. We modern humans still get goose bumps when we're scared or cold, even though we've lost the advantage of looking scarier or staying warmer ourselves. And researchers have found that listening to classical music (or Phil Collins), seeing pictures of children or drinking a sour drink can also inspire goose bumps. There's clearly a link with emotion and reward, too. © 2015 npr
by Helen Thompson Five, six, seven, eight! All together now, let's spread those jazz hands and get moving, because synchronized dancing improves our tolerance of pain and helps us bond as humans, researchers suggest October 28 in Biology Letters. A team of psychologists at the University of Oxford taught high school students varied dance routines — each requiring different levels of exertion and synchronized movement — and then tested their pain tolerance with the sharp squeeze of a blood pressure cuff. Statistically, routines with more coordinated choreography and full body movement produced higher pain thresholds and sunny attitudes toward others in the group. Coordinated dancing with a group and exerting more energy may independently promote the release of pain-blocking endorphins as well as increase social bonding, the team writes. |© Society for Science & the Public 2000 - 2015
Keyword: Pain & Touch
Link ID: 21575 - Posted: 10.28.2015
Mr Tickle can’t bamboozle a baby. Unlike grown-ups, young infants don’t let the positioning of their bodies confuse their sense of touch. If adults who can see are touched on each hand in quick succession while their hands are crossed, they can find it hard to name which hand was touched first. Adults who have been blind from birth don’t have this difficulty, but people who become blind later in life have the same trouble as those who can still see. “That suggests that early on in life, something to do with visual experience is crucial in setting up a typical way of perceiving touch,” says Andrew Bremner at Goldsmiths, University of London. To investigate how this develops in infancy, Bremner and his colleagues compared how babies reacted to having one foot tickled. With their legs crossed over, babies aged 6 months moved the foot being tickled half of the time. But 4-month-olds did better, moving the tickled foot 70 per cent of the time – as often as they did with their legs uncrossed. The team concludes that at 4 months, babies haven’t yet learned to relate what they touch to the physical space that their body occupies. For many adults, the concept might be difficult to envision. “It’s like imagining that you feel a touch on your body, but not really knowing how that’s related to what you’re looking at,” says Bremner. “It’s almost like you have multiple sensory worlds: a visual world, an auditory world and a tactile world, which are separate and not combined in space.” © Copyright Reed Business Information Ltd.
By Robert F. Service Prosthetic limbs may work wonders for restoring lost function in some amputees, but one thing they can’t do is restore an accurate sense of touch. Now, researchers report that one day in the not too distant future, those artificial arms and legs may have a sense of touch closely resembling the real thing. Using a two-ply of flexible, thin plastic, scientists have created novel electronic sensors that send signals to the brain tissue of mice that closely mimic the nerve messages of touch sensors in human skin. Multiple research teams have long worked on restoring touch to people with prosthetic limbs. 2 years ago, for example, a group at Case Western Reserve University in Cleveland, Ohio, reported giving people with prosthetic hands a sense of touch by wiring pressure sensors on the hands to peripheral nerves in their arms. Yet although these advances have restored a rudimentary sense of touch, the sensors and signals are very different from those sent by mechanoreceptors, natural touch sensors in the skin. For starters, natural mechanoreceptors put out what amounts to a digital signal. When they sense pressure, they fire a stream of nerve impulses; the more pressure, the higher the frequency of pulses. But previous tactile sensors have been analogue devices, where more pressure produces a stronger electrical signal, rather than a more frequent stream of pulses. The electrical signals must then be sent to another processing chip that converts the strength of the signals to a digital stream of pulses that is only then sent on to peripheral nerves or brain tissue. © 2015 American Association for the Advancement of Science.