![\"John](\"https:\/\/www.salk.edu\/wp-content\/uploads\/2013\/01\/reynoldssharpee625.jpg\")
\nFrom left: John Reynolds, Anirvan Nandy and Tatyana Sharpee<\/p>\n
Bild: Mit freundlicher Genehmigung des Salk Institute for Biological Studies<\/p>\n<\/div>\n
Their deep and detailed research\u2014involving recordings from hundreds of neurons\u2014may also have future clinical and practical implications, says the study’s senior co-authors, Salk neuroscientists Tatyana Sharpee<\/a> und John Reynolds<\/a>.<\/p>\n “Understanding how the brain creates a visual image can help humans whose brains are malfunctioning in various different ways\u2014such as people who have lost the ability to see,” says Sharpee, an associate professor in the Labor f\u00fcr computergest\u00fctzte Neurobiologie<\/a>. “One way of solving that problem is to figure out how the brain\u2014not the eye, but the cortex\u2014processes information about the world. If you have that code then you can directly stimulate neurons in the cortex and allow people to see.”<\/p>\n Reynolds, a professor in the Labor f\u00fcr Systemneurobiologie<\/a>, says an indirect benefit of understanding the way the brain works is the possibility of building computer systems that can act like humans.<\/p>\n “The reason that machines are limited in their capacity to recognize things in the world around us is that we don’t really understand how the brain does it as well as it does,” he says.<\/p>\n The scientists emphasize that these are long-term goals that they are striving to reach, a step at a time.<\/p>\n In these studies, Salk neurobiologists sought to figure out how a part of the visual cortex known as area V4 is able to distinguish between different visual stimuli even as the stimuli move around in space. V4 is responsible for an intermediate step in neural processing of images.<\/p>\n “Neurons in the visual system are sensitive to regions of space\u2014they are like little windows into the world,” says Reynolds. “In the earliest stages of processing, these windows\u2014known as receptive fields\u2014are small. They only have access to information within a restricted region of space. Each of these neurons sends brain signals that encode the contents of a little region of space\u2014they respond to tiny, simple elements of an object such as edge oriented in space, or a little patch of color.”<\/p>\n Neurons in V4 have a larger receptive field that can also compute more complex shapes such as contours. They accomplish this by integrating inputs from earlier visual areas in the cortex\u2014that is, areas nearer the retina. These earlier-stage areas have small receptive fields, and send information to higher level processing regions that allow us to see complex images, such as faces.<\/p>\n Both new studies investigated the issue of translation invariance\u2014the ability of a neuron to recognize the same stimulus within its receptive field no matter where it is in space, where it happens to fall within the receptive field.<\/p>\n Die Neuron<\/em> paper looked at translation invariance by analyzing the response of 93 individual neurons in V4 to images of lines and shapes like curves, while the PNAS<\/em> study looked at responses of V4 neurons to natural scenes full of complex contours.<\/p>\n Dogma in the field is that V4 neurons all exhibit translation invariance.<\/p>\n “The accepted understanding is that individuals neurons are tuned to recognize the same stimulus no matter where it was in their receptive field,” says Sharpee.<\/p>\n For example, a neuron might respond to a bit of the curve in the number 5 in a CAPTCHA image, no matter how the 5 is situated within its receptive field. Researchers believed that neuronal translation invariance\u2014the ability to recognize any stimulus, no matter where it is in space\u2014increases as an image moves up through the visual processing hierarchy.<\/p>\n “But what both studies show is that there is more to the story,” she says. “There is a trade off between the complexity of the stimulus and the degree to which the cell can recognize it as it moves from place to place.”<\/p>\n The Salk researchers found that neurons that respond to more complicated shapes\u2014like the curve in 5 or in a rock\u2014demonstrated decreased translation invariance. “They need that complicated curve to be in a more restricted range for them to detect it and understand its meaning,” Reynolds says. “Cells that prefer that complex shape don’t yet have the capacity to recognize that shape everywhere.”<\/p>\n On the other hand, neurons in V4 tuned to recognize simpler shapes, like a straight line in the number 5, have increased translation invariance. “They don’t care where the stimuli they are tuned to is, as long as it is within their receptive field,” Sharpee says.<\/p>\n “Previous studies of object recognition have assumed that neuronal responses at later stages in visual processing remain the same regardless of basic visual transformations to the object’s image. Our study highlights where this assumption breaks down, and suggests simple mechanisms that could give rise to object selectivity,” says Jude Mitchell, a Salk research scientist who was the senior author on the Neuron<\/em> paper.<\/p>\n “It is important that results from the two studies are quite compatible with one another, that what we find studying just lines and curves in one first experiment matches what we see when the brain experiences the real world,” says Sharpee, who is well known for developing a computational method to extract neural responses from natural images.<\/p>\n “What this tells us is that there is a deeper mystery here to be solved,” Reynolds says. “We have not figured out how translation invariance is achieved. What we have done is unpacked part of the machinery for achieving integration of parts into wholes.”<\/p>\n Minjoon Kouh, a former postdoctoral fellow at Salk, participated in the PNAS<\/em> study. Salk postdoctoral researcher Anirvan Nandy and senior staff scientist Jude Mitchell, of the\u00a0Salk Systems Neurobiology Laboratory, were co-authors of the Neuron<\/em> paper.<\/p>\n Both studies were funded by grants from the Nationale Gesundheitsinstitute<\/a> (R01EY019493), the McKnight Scholarship and the Ray Thomas Edwards<\/a> und W. M. Keck Foundations<\/a>. In addition, the PNAS<\/em> study received a grant from the Searle Funds. The Neuron<\/em> study was additionally funded by grants from the Alfred P. Sloan Foundation<\/a>, the National Institutes of Health (EY0113802), the Gatsby Charitable Foundation<\/a> und die Swartz Foundation<\/a>, and a Pioneer Fund postdoctoral fellowship.<\/p>\n Die Leistungen der Fakult\u00e4t wurden mit zahlreichen Auszeichnungen gew\u00fcrdigt, darunter Nobelpreise und Mitgliedschaften in der National Academy of Sciences. Das 1960 vom Polio-Impfstoff-Pionier Dr. Jonas Salk gegr\u00fcndete Institut ist eine unabh\u00e4ngige gemeinn\u00fctzige Organisation und ein architektonisches Wahrzeichen.<\/p>","protected":false},"featured_media":0,"template":"","faculty":[107,66],"disease-research":[124],"class_list":["post-2435","disclosure","type-disclosure","status-publish","hentry","faculty-john-reynolds","faculty-tatyana-sharpee","disease-research-neuroscience-and-neurological-disorders"],"acf":[],"yoast_head":"\nIntegrating parts into wholes<\/h2>\n
A deeper mystery to be solved<\/h2>\n
\n\u00dcber das Salk Institute for Biological Studies:<\/strong>
\nDas Salk Institute for Biological Studies ist eine der weltweit f\u00fchrenden Institutionen f\u00fcr Grundlagenforschung, an der international renommierte Fakult\u00e4tsmitglieder grundlegende Fragen der Biowissenschaften in einem einzigartigen, kollaborativen und kreativen Umfeld untersuchen. Mit dem Fokus auf Entdeckungen und die Ausbildung zuk\u00fcnftiger Forschergenerationen leisten Salk-Wissenschaftler bahnbrechende Beitr\u00e4ge zu unserem Verst\u00e4ndnis von Krebs, Alterung, Alzheimer, Diabetes und Infektionskrankheiten durch die Untersuchung von Neurowissenschaften, Genetik, Zell- und Pflanzenbiologie sowie verwandten Disziplinen.<\/p>\n