Chapter 7. Vision: From Eye to Brain

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By Stephen L. Macknik When Susana Martinez-Conde and I talk to audiences about NeuroMagic—our research initiative to study the brain with magic (and vice-versa), people often ask us how we bring both fields together. They want to know in what ways magic tricks can inform neuroscience, and what a day in the life of a neuromagic scientist looks like. How do we run a neuromagic experiment, from collecting the data to using the results to gain knowledge about the mind's inner secrets? Our new study, led by Anthony Barnhart (aka Magic Tony) and just published in the Journal of Eye Movement Research, illustrates some of the ways in which we investigate magic in the lab. You can download the paper for free, but as it is written for academics, I'll give you the gist here. The experiment addresses how various neural circuits interact in your brain while you watch a magic performance. There's the visual system—critical for perception—there's the oculomotor system—critical for targeting and moving the eyes—and there's the attentional system—critical for filtering out irrelevant information and allowing you to literally and figuratively focus both the visual and oculomotor systems at the right place and at the right time. Without all three of these systems working together, you would be unable to conduct most visual tasks. Advertisement Magic is one of the inroads available to dissect the function of many perceptual and cognitive systems, and especially so in situations that are fairly similar to those we encounter in real life. This concept—ecological validity—is important to testing whether neuroscience theories will hold up outside of the lab, and one of the reasons why magic tricks are attractive for studying everyday perception and cognition. © 2019 Scientific American

Keyword: Vision; Attention
Link ID: 26412 - Posted: 07.13.2019

Partial sight has been restored to six blind people via an implant that transmits video images directly to the brain. Some vision was made possible – with the participants’ eyes bypassed – by a video camera attached to glasses which sent footage to electrodes implanted in the visual cortex of the brain. University College London lecturer and Optegra Eye Hospital surgeon Alex Shortt said it was a significant development by specialists from Baylor Medical College in Texas and the University of California Los Angeles. “Previously all attempts to create a bionic eye focused on implanting into the eye itself. It required you to have a working eye, a working optic nerve,” Shortt told the Daily Mail. “By bypassing the eye completely you open the potential up to many, many more people. “This is a complete paradigm shift for treating people with complete blindness. It is a real message of hope.” How eye-gaze technology brought creativity back into an artist's life The technology has not been proven on those born blind. The US team behind the study asked participants, each of whom has been completely blind for years, to look at a blacked-out computer screen and identify a white square appearing randomly at different locations on the monitor. The majority of the time, they can find the square. © 2019 Guardian News & Media Limited

Keyword: Vision; Robotics
Link ID: 26411 - Posted: 07.13.2019

By Chris Woolston When Sylvia Groth steps through the doors of the Vanderbilt Eye Institute in Nashville, she knows she has a tough day ahead. Before she goes home, she’ll likely have at least one hard talk with a person whose sight has been ravaged by glaucoma. “When I make a diagnosis of advanced glaucoma, I do it with a heavy heart,” the ophthalmologist says. “It’s such an empty feeling to not be able to do anything.” An incurable eye disease that kills vital nerve cells at the back of the retina, glaucoma is a leading cause of irreversible blindness in the world. More than 70 million people have it, and 3 million of them already are blind. Nothing can be done to restore vision once it’s lost, and even the best treatments can’t always slow disease progression. But researchers foresee a time when they can offer therapies to protect nerve cells in the eye and perhaps even restore lost sight. “We’re making advances with every different type of treatment,” ophthalmologist Leonard Levin of McGill University in Montreal says. Researchers have long understood the basics of the most common form of glaucoma, called open-angle glaucoma. The eye is nourished by a clear fluid called the aqueous humor that keeps the eyeball inflated, plump and healthy. But just like a tire, the eye can become overinflated. If the aqueous humor can’t drain properly, pressure inside the eye grows too high and can crush cells within the optic nerve — the sensory cable that carries images from the retina to the optical centers of the brain. Pressure probably hurts nerve cells in other ways too, ophthalmologist Harry Quigley of Johns Hopkins University says. © 1996-2019 The Washington Post

Keyword: Vision
Link ID: 26376 - Posted: 07.02.2019

Millions of people in the UK are putting their sight at risk by continuing to smoke, warn specialists. Despite the clear connection, only one in five people recognise that smoking can lead to blindness, a poll for the Association of Optometrists (AOP) finds. Smokers are twice as likely to lose their sight compared with non-smokers, says the RNIB. That is because tobacco smoke can cause and worsen a number of eye conditions. How smoking can harm your eyes Cigarette smoke contains toxic chemicals that can irritate and harm the eyes. For example, heavy metals, such as lead and copper, can collect in the lens - the transparent bit that sits behind the pupil and brings rays of light into focus - and lead to cataracts, where the lens becomes cloudy. Smoking can make diabetes-related sight problems worse by damaging blood vessels at the back of the eye (the retina). Smokers are around three times more likely to get age-related macular degeneration - a condition affecting a person's central vision, meaning that they lose their ability to see fine details. And they are 16 times more likely than non-smokers to develop sudden loss of vision caused by optic neuropathy, where the blood supply to the eye becomes blocked. In the poll of 2,006 adults, 18% correctly said that smoking increased the risk of blindness or sight loss, while three-quarters (76%) knew smoking was linked to cancer. © 2019 BBC

Keyword: Drug Abuse; Vision
Link ID: 26375 - Posted: 07.02.2019

Laura Sanders Some nerve cells in the brain are multitaskers, responding to both color and shape, a survey of over 4,000 neurons in the visual systems of macaque monkeys finds. The finding, described in the June 28 Science, counters earlier ideas that vision cells nestled in the back of the brain each handle information about only one aspect of sight: an object’s color or its orientation, an element of shape. Some scientists had thought that those aspects were then put together by other brain cells in later stages of visual processing to form a more complete picture of the world. In the new experiment, four macaques looked at a series of sights made of moving lines on a screen. Each time, the lines were one of 12 possible colors and moved at particular angles, creating an effect similar to a spinning candy cane in two dimensions. Using genetic tricks that made nerve cells glow when active, the researchers watched for action among the monkeys’ cells in an area of the brain that handles vision. Called V1, this stretch at the back of the brain is one of the first areas to interpret sight signals. Most of the cells that had a favorite color, indicated by their activity, also had a favorite orientation of lines, the researchers found. “Thus, textbook models of primate V1 must be updated,” the team writes. PUTTING IT TOGETHER This video captures nerve cells in a monkey’s visual system firing off signals. Some of these cells respond both to a favorite color and favorite shape. The discovery counters previous ideas that information about color is processed separately from information about shape in the brain. |© Society for Science & the Public 2000 - 2019.

Keyword: Vision
Link ID: 26374 - Posted: 07.02.2019

Even if you know that looking at a phone, tablet or computer screen at night is bad for your sleep, it’s hard to stop. That’s one reason there has been a growing interest in glasses or apps that can block the blue parts of the light spectrum that experts say are especially bad for sleep. This light doesn’t necessarily appear blue; it’s part of any bright white light, says Charles Czeisler, chief of the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital in Boston. “Our light exposure between when the sun sets and the sun rises is probably the primary driver of sleep deficiency in our society,” Czeisler says. While that includes artificial light of all kinds, light from electronic devices that emit blue light — such as the LED displays in smartphones, tablets, and modern computer and TV screens — is particularly troublesome for sleep, he says. A number of studies indicate that using blue-blocking glasses and apps like f.lux or Apple’s Night Shift mode may improve sleep in certain cases, but they won’t cure insomnia on their own. Experts say much more research is needed on how well they work, who can benefit the most and how to best use them. Still, they may help, though thinking about light exposure throughout the day may be even more useful. “It just depends on how many problems a person is having with their sleep,” says Lisa Ostrin, an assistant professor at the University of Houston College of Optometry who has conducted research into ways that blocking blue light affects sleep. To understand how glasses or apps affect sleep, it helps to understand light’s role in the first place. © 1996-2019 The Washington Post

Keyword: Sleep; Vision
Link ID: 26353 - Posted: 06.25.2019

By Tim Vernimmen The image above, “A Sunday Afternoon on the Island of La Grande Jatte,” was painted in 1884 by French artist Georges Seurat. The black lines crisscrossing it are not the work of a toddler wreaking havoc with a permanent marker, but that of neuroscientist Robert Wurtz of the National Eye Institute in the US. Ten years ago, he asked a colleague to look at the painting while wearing a contact lens–like contraption that recorded the colleague’s eye movements. These were then translated into the graffiti you see here. Art lovers may cringe, yet it is likely that Seurat would have been intrigued by this augmentation of his work. The movement Seurat kick-started with this painting — Neo-Impressionism — drew inspiration from the scientific study of how our vision works. Particularly influential was the pioneering research of Hermann von Helmholtz, a German physician, physicist and philosopher and author of a seminal 1867 book, Handbook of Physiological Optics, on the way we perceive depth, color and motion. One of the questions that occupied Helmholtz, and quite possibly Seurat, is why we don’t perceive the constant eye movements we make when we are scanning our surroundings (or a painted representation of them). Consider that the lines above were drawn in just three minutes. If we saw all those movements as we made them, our view of the world would be a blur of constant motion. As Wurtz and his Italian colleagues Paola Binda and Maria Concetta Morrone explain in two articles in the Annual Review of Vision Science, there’s a lot we know about why that doesn’t happen — and more yet to learn.

Keyword: Vision
Link ID: 26341 - Posted: 06.20.2019

By Madison Dapcevich An optical illusion designed by researchers to test how contrast deceives the brain appears to show a diamond moving across the screen, twitching up and down and left to right, without ever physically changing location. Dubbed the “Perceptual Diamond”, the illusion “produces motion continuously and unambiguously” to trick the viewer into thinking it is moving around the screen, yet it remains steady and slightly illuminated. Rather, its motion is mimicked by changing the contrast between the edges of strips around the diamond’s edges and the background. Shifts in contrasts around the edges, like in this illusion, can create the perception of motion. The Perpetual Diamond illusion provides no clues as to its orientation or direction until it is animated, generating movement through contrast signals alone, wrote the authors in i-Perception. "We often take the perception of motion for granted because we assume that motion corresponds to objects shifting location in the real world," explained study author Arthur Shapiro, from the American University in Washington DC, in an email to IFLScience. "However, the brain has many processes that can lead to the perception of motion, and there are many types of images that can stimulate these processes." Depending on the combination of illuminated edges, the diamond will appear to move in different directions. For example, if the two top edges blink between black and white and the two bottom edges do the opposite, the diamond appears to continuously move upward.

Keyword: Vision
Link ID: 26337 - Posted: 06.19.2019

Strobe lighting at music festivals can increase the risk of epileptic seizures, researchers have warned. The Dutch team said even people who have not been diagnosed with epilepsy might be affected. Their study was prompted by the case of a 20-year-old, with no history of epilepsy, who suddenly collapsed and had a fit at a festival. The Epilepsy Society said festivals should limit lighting to the recommended levels. Epilepsy is a condition that affects the brain. There are many types, and it can start at any age. Around 3% of people with epilepsy are photosensitive, which means their seizures are triggered by flashing or flickering lights, or patterns. The Health and Safety Executive recommends strobe lighting should be kept to a maximum of four hertz (four flashes per second) in clubs and at public events. 'Life-affirming' The researchers studied electronic dance music festivals because they often use strobe lighting. They looked at data on people who needed medical care among the 400,000 visitors to 28 day and night-time dance music festivals across the Netherlands in 2015. The figures included 241,000 people who were exposed to strobe lights at night-time festivals. Thirty people at night-time events with strobe lighting had a seizure, compared with nine attending daytime events. The team, led by Newel Salet of the VU Medical Centre in Amsterdam, writing in BMJ Open, said other factors could increase the risk of seizures. But they added: "Regardless of whether stroboscopic lights are solely responsible or whether sleep deprivation and/or substance abuse also play a role, the appropriate interpretation is that large [electronic dance music] festivals, especially during the night-time, probably cause at least a number of people per event to suffer epileptic seizures." They advise anyone with photosensitive epilepsy to either avoid such events or to take precautionary measures, such as getting enough sleep and not taking drugs, not standing close to the stage, and leaving quickly if they experience any "aura" effects. © 2019 BBC

Keyword: Epilepsy; Vision
Link ID: 26323 - Posted: 06.12.2019

Children can keep full visual perception — the ability to process and understand visual information — after brain surgery for severe epilepsy, according to a study funded by the National Eye Institute (NEI), part of the National Institutes of Health. While brain surgery can halt seizures, it carries significant risks, including an impairment in visual perception. However, a new report by Carnegie Mellon University, Pittsburgh, researchers from a study of children who had undergone epilepsy surgery suggests that the lasting effects on visual perception can be minimal, even among children who lost tissue in the brain’s visual centers. Normal visual function requires not just information sent from the eye (sight), but also processing in the brain that allows us to understand and act on that information (perception). Signals from the eye are first processed in the early visual cortex, a region at the back of the brain that is necessary for sight. They then travel through other parts of the cerebral cortex, enabling recognition of patterns, faces, objects, scenes, and written words. In adults, even if their sight is still present, injury or removal of even a small area of the brain’s vision processing centers can lead to dramatic, permanent loss of perception, making them unable to recognize faces, locations, or to read, for example. But in children, who are still developing, this part of the brain appears able to rewire itself, a process known as plasticity. “Although there are studies of the memory and language function of children who have parts of the brain removed surgically for the treatment of epilepsy, there have been rather few studies that examine the impact of the surgery on the visual system of the brain and the resulting perceptual behavior,” said Marlene Behrmann, Ph.D., senior author of the study. “We aimed to close this gap.”

Keyword: Development of the Brain; Vision
Link ID: 26303 - Posted: 06.05.2019

Nicole Karlis There is no way Leonardo da Vinci could have predicted that the Mona Lisa would remain one of the most widely-debated works of art in modern day — thanks in no small part to her intriguing expression. Indeed, as one of the most famous paintings in the world, Mona Lisa's facial expression continues to beguile both commoners and academics. A 2017 study published in the journal Scientific Reports (part of the network of Nature's journals) proclaimed that Mona Lisa’s smile did indeed depict genuine happiness, according to the study's subjects who compared it with subtly manipulated facial expressions. Now, a new study published in the neuroscience journal Cortex says that her smile is non-genuine. In other words, she's faking it. The three neuroscience and cognition researchers who penned the article fixated on the asymmetry of Mona Lisa’s smile. Some historical theories suggest the facial asymmetry is due to the loss of the subject's anterior teeth, while others have speculated it could have been related to Bell’s Palsy. The Cortex article's authors note that as the upper part of her face does not appear to be active, it is possible to interpret her smile as “non-genuine.” This would relate to theories of emotion neuropsychology, which is the characterization of the behavioral modifications that follow a neurological condition. © 2018 Salon Media Group, Inc

Keyword: Emotions; Vision
Link ID: 26300 - Posted: 06.05.2019

By Susana Martinez-Conde and Stephen L. Macknik The man and the woman sat down, facing each other in the dimly illuminated room. This was the first time the two young people had met, though they were about to become intensely familiar with each other—in an unusual sort of way. The researcher informed them that the purpose of the study was to understand “the perception of the face of another person.” The two participants were to gaze at each other’s eyes for 10 minutes straight, while maintaining a neutral facial expression, and pay attention to their partner’s face. After giving these instructions, the researcher stepped back and sat on one side of the room, away from the participants’ lines of sight. The two volunteers settled in their seats and locked eyes—feeling a little awkward at first, but suppressing uncomfortable smiles to comply with the scientist’s directions. Ten minutes had seemed like a long stretch to look deeply into the eyes of a stranger, but time started to lose its meaning after a while. Sometimes, the young couple felt as if they were looking at things from outside their own bodies. Other times, it seemed as if each moment contained a lifetime. Throughout their close encounter, each member of the duo experienced their partner’s face as everchanging. Human features became animal traits, transmogrifying into grotesqueries. There were eyeless faces, and faces with too many eyes. The semblances of dead relatives materialized. Monstrosities abounded. The bizarre perceptual phenomena that the pair witnessed were manifestations of the “strange face illusion,” first described by the psychologist Giovanni Caputo of the University of Urbino, Italy. Urbino’s original study, published in 2010, reported a new type of illusion, experienced by people looking at themselves in the mirror in low light conditions. © 2019 Scientific American

Keyword: Attention; Vision
Link ID: 26230 - Posted: 05.14.2019

By Elizabeth Pennisi When the ancestors of cave fish and certain crickets moved into pitchblack caverns, their eyes virtually disappeared over generations. But fish that ply the sea at depths greater than sunlight can penetrate have developed super-vision, highly attuned to the faint glow and twinkle given off by other creatures. They owe this power, evolutionary biologists have learned, to an extraordinary increase in the number of genes for rod opsins, retinal proteins that detect dim light. Those extra genes have diversified to produce proteins capable of capturing every possible photon at multiple wavelengths—which could mean that despite the darkness, the fish roaming the deep ocean actually see in color. The finding "really shakes up the dogma of deep-sea vision," says Megan Porter, an evolutionary biologist studying vision at the University of Hawaii in Honolulu who was not involved in the work. Researchers had observed that the deeper a fish lives, the simpler its visual system is, a trend they assumed would continue to the bottom. "That [the deepest dwellers] have all these opsins means there's a lot more complexity in the interplay between light and evolution in the deep sea than we realized," Porter says. At a depth of 1000 meters, the last glimmer of sunlight is gone. But over the past 15 years, researchers have realized that the depths are pervaded by a faint bioluminescence from flashing shrimp, octopus, bacteria, and even fish. Most vertebrate eyes could barely detect this subtle shimmer. To learn how fish can see it, a team led by evolutionary biologist Walter Salzburger from the University of Basel in Switzerland studied deep-sea fishes' opsin proteins. Variation in the opsins' amino acid sequences changes the wavelength of light detected, so multiple opsins make color vision possible. One opsin, RH1, works well in low light. Found in the eye's rod cells, it enables humans to see in the dark—but only in black and white. © 2019 American Association for the Advancement of Science

Keyword: Vision
Link ID: 26224 - Posted: 05.10.2019

Maria Temming New artwork created by artificial intelligence does weird things to the primate brain. When shown to macaques, AI-generated images purposefully caused nerve cells in the monkeys’ brains to fire more than pictures of real-world objects. The AI could also design patterns that activated specific neurons while suppressing others, researchers report in the May 3 Science. This unprecedented control over neural activity using images may lead to new kinds of neuroscience experiments or treatments for mental disorders. The AI’s ability to play the primate brain like a fiddle also offers insight into how closely AIs can emulate brain function. The AI responsible for the new mind-bending images is an artificial neural network — a computer model composed of virtual neurons — modeled after the ventral stream. This is a neural pathway in the brain involved in vision (SN Online: 8/12/09). The AI learned to “see” by studying a library of about 1.3 million labeled images. Researchers then instructed the AI to design pictures that would affect specific ventral stream neurons in the brain. Viewing any image triggers some kind of neural activity in a brain. But neuroscientist Kohitij Kar of MIT and colleagues wanted to see whether the AI’s deliberately designed images could induce specific neural responses of the team’s choosing. The researchers showed these images to three macaques fitted with neuron-monitoring microelectrodes. |© Society for Science & the Public 2000 - 2019.

Keyword: Vision
Link ID: 26206 - Posted: 05.03.2019

Ruth Williams Showing monkeys a series of computer-generated images and simultaneously recording the animals’ brain cell activities enables deep machine learning systems to generate new images that ramp up the cells’ excitation, according to two papers published today (May 2) in Cell and Science. “It’s exciting because it’s bridging the fields of deep learning and neuroscience . . . to try and understand what is represented in different parts of the brain,” says neuroscientist Andreas Tolias of Baylor College of Medicine who was not involved with either of the studies, but has carried out similar experiments in mice. “I think these methods and their further development could provide a more systematic way for us to open the black box of the brain,” he says. It’s a goal of sensory neuroscience to understand exactly which stimuli activate which brain cells. In the primate visual system, certain neurons in the visual cortex and inferior temporal cortex (two key vision areas) are known to respond preferentially to certain stimuli—such as colors, specific directions of motion, curves, and even faces. But, says neuroscientist Carlos Ponce of Washington University School of Medicine in St. Louis, who co-authored the Cell paper, “the problem is, we’ve never quite known whether, in our selection of pictures, we have the secret true image that the cell really is encoding.” Maybe, he suggests, a cell isn’t responding to a face, but to an arrangement of features and shapes found in a face that may also be found in other images. And with countless available images, “it’s impossible to test all of them,” he says. In short, it has been impossible to determine the exact visual stimulus that would maximally activate a given neuron. © 1986–2019 The Scientist.

Keyword: Vision
Link ID: 26205 - Posted: 05.03.2019

By Susana Martinez-Conde Human night vision is not as precise as day vision. That’s why getting up barefoot in the middle of the night comes with a much higher risk of stepping on painful Lego pieces than walking along the same path during the day. I have three kids of ages twelve and under, so I know. But the specific ways in which our night vision is worse than our day vision are surprisingly counterintuitive to most of us. I remember learning in college that night-vision is achromatic (meaning that we only see in grayscale at night) and not really believing it. It took some careful night-time observation to conclude that my professor was right: objects that were colorful during the day had no hue at night. Most shocking of all was the realization that, though I had always suffered from night-time color blindness (as all of us do), I had never been aware of my deficiency. A recent study by Alejandro Gloriani and Alexander Schütz, from the University of Marburg, Germany, published earlier this month in Current Biology, shows that our night vision self-delusion is even more pervasive than previously thought. Advertisement To appreciate Gloriani and Schütz’s discovery, the first thing to understand is that day and night vision rely on the activity of different types of photoreceptors (these are the retinal cells that convert light energy into electrical signals, which your brain can then process). ‘Cones’ are active during the day (or when you turn the lights on at night). ‘Rods’ are active during the night (or at very dim light levels). © 2019 Scientific American

Keyword: Vision
Link ID: 26181 - Posted: 04.29.2019

National Institutes of Health scientists studying the progression of inherited and infectious eye diseases that can cause blindness have found that microglia, a type of nervous system cell suspected to cause retinal damage, surprisingly had no damaging role during prion disease in mice. In contrast, the study findings indicated that microglia might delay disease progression. The discovery could apply to studies of inherited photoreceptor degeneration diseases in people, known as retinitis pigmentosa. In retinitis pigmentosa cases, scientists find an influx of microglia near the photoreceptors, which led to the belief that microglia contribute to retina damage. These inherited diseases appear to damage the retina similarly to prion diseases. Prion diseases are slow degenerative diseases of the central nervous system that occur in people and various other mammals. No vaccines or treatments are available, and the diseases are almost always fatal. Prion diseases primarily involve the brain but also can affect the retina and other tissues. Expanding on work published in 2018, scientists at NIH’s National Institute of Allergy and Infectious Diseases (NIAID) used an experimental drug to eliminate microglia in prion-infected mice. They studied prion disease progression in the retina to see if they could discover additional details that might be obscured in the more complex structure of the brain. When the scientists examined their prion-infected study mice, they found that photoreceptor damage still occurred – even somewhat faster – despite the absence of microglia. They also observed early signs of new prion disease in the photoreceptor cells, which may provide clues as to how prions damage photoreceptors. Their work appears in Acta Neuropathologica Communications.

Keyword: Vision; Prions
Link ID: 26088 - Posted: 03.28.2019

David Cyranoski A Japanese committee has provisionally approved the use of reprogrammed stem cells to treat diseased or damaged corneas. Researchers are now waiting for final approval from the health ministry to test the treatment in people with corneal blindness, which affects millions of people around the world. The cornea, a transparent layer that covers and protects the eye, contains stem cells that repair it when damaged. But these can be destroyed by disease or by trauma from chemicals or burns, which can result in patients losing their vision. Currently, cornea transplants from donors who have died are used to treat damaged or diseased corneas, but good-quality tissue is scarce. A team led by ophthalmologist Kohji Nishida at Osaka University plans to treat damaged corneas using sheets of tissue made from induced pluripotent stem cells. These are created by reprogramming cells from a donor into an embryonic-like state that can then transform into other tissue, such as corneal cells. Nishida’s team plans to lay 0.05-millimetre-thick sheets of corneal cells across patients’ eyes. Animal studies have shown1 that this can save or restore vision. The health ministry is expected to decide soon. If Nishida and his team receive approval, they will treat four people, whom they will then monitor for a year to check the safety and efficacy of the treatment. The first treatment is planned to take place before the end of July. Other Japanese researchers have carried out clinical studies using induced pluripotent stem cells to treat spinal cord injury, Parkinson's disease and another eye disease. © 2019 Springer Nature Publishing AG

Keyword: Vision; Stem Cells
Link ID: 26045 - Posted: 03.18.2019

Liam Drew A mouse scurries down a hallway, past walls lined with shifting monochrome stripes and checks. But the hallway isn’t real. It’s part of a simulation that the mouse is driving as it runs on a foam wheel, mounted inside a domed projection screen. While the mouse explores its virtual world, neuroscientist Aman Saleem watches its brain cells at work. Light striking the mouse’s retinas triggers electrical pulses that travel to neurons in its primary visual cortex, where Saleem has implanted electrodes. Textbooks say that these neurons each respond to a specific stimulus, such as a horizontal or vertical line, so that identical patterns of inputs should induce an identical response. But that’s not what happens. When the mouse encounters a repeat of an earlier scene, its neurons fire in a different pattern. “Five years ago, if you’d told me that, I’d have been like, ‘No, that’s not true. That’s not possible’,” says Saleem, in whose laboratory at University College London we are standing. His results, published last September1, show that cells in the hippocampus that track where the mouse has run along the hallway are somehow changing how cells in the visual cortex fire. In other words, the mouse’s neural representation of two identical scenes differs, depending on where it perceives itself to be. It’s no surprise that an animal’s experiences change how it sees the world: all brains learn from experience and combine multiple streams of information to construct perceptions of reality. But researchers once thought that at least some areas in the brain — those that are the first to process inputs from the sense organs — create relatively faithful representations of the outside world. According to this model, these representations then travel to ‘association’ areas, where they combine with memories and expectations to produce perceptions.

Keyword: Learning & Memory; Vision
Link ID: 26039 - Posted: 03.15.2019

Matthew Warren Cue the super-mouse. Scientists have engineered mice that can see infrared light normally invisible to mammals — including humans. To do so, they injected into the rodents’ eyes nanoparticles that convert infrared light into visible wavelengths1. Humans and mice, like other mammals, cannot see infrared light, which has wavelengths slightly longer than red light — between 700 nanometres and 1 millimetre. But Tian Xue, a neuroscientist at the University of Science and Technology of China in Hefei, and his colleagues developed nanoparticles that convert infrared wavelengths into visible light. The nanoparticles absorb photons at wavelengths of around 980 nanometres and emit them at shorter wavelengths, around 535 nanometres, corresponding to green light. Xue’s team attached the nanoparticles to proteins that bind to photoreceptors — the cells in the eye that convert light into electrical impulses — and then injected them into mice. The researchers showed that the nanoparticles successfully attached to the photoreceptors, which in turn responded to infrared light by producing electrical signals and activating the visual-processing areas of the brain. The team conducted experiments to show that the mice did actually detect and respond to infrared light.

Keyword: Vision
Link ID: 25999 - Posted: 03.01.2019