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Пуденко Сергей
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Пуденко Сергей
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03.07.2006 14:50:22
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Рубрики
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Прочее; В стране и мире;
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чудовищные открытия -нейроны реагируют только на Куста - WANTED!!(*)
обнауржил и разрываю на ходу любопытную цепочку
просьба поучаствовать желающих. Нужен достпу к архиву Scientific American Mind;
Это видимо клон Сайентифик Америкен в сети
Пример
http://www.sciamdigital.com/browse.cfm?sequencenameCHAR=item2&methodnameCHAR=resource_getitembrowse&interfacenameCHAR=browse.cfm&ISSUEID_CHAR=B258443D-2B35-221B-60099B43A82CACE2&ARTICLEID_CHAR=B263A032-2B35-221B-600E74077760AB2F&sc=I100322
April 2005
Scientific American Mind
а вот собственно чужовищное открытие
http://ded-maxim.livejournal.com/196186.html
Пишет Дед Максим (ded_maxim)
@ 2006-03-03 11:39:00
Настроение: working
Музыка: Cat Power: THE GREATEST
нейрон реагирует на изображения Дженнифер Анистон
А вот, оказывается, у одного мужика нашли в мозгу нейрон, который реагирует на изображения Дженнифер Анистон!
Invariant visual representation by single-neurons in the human brain (PDF)
R. Quian Quiroga, L. Reddy, G. Kreiman, C. Koch and I. Fried
Nature, 435: 1102-1107; 2005
Меня вообще интересует, каким образом можно делать какие-либо выводы на основании измерений spike trains относительно небольшого числа нейронов? Тот факт, что на определенные стимулы реагирует небольшая инвариантная группа нейронов в гиппокампе, не означает, что в то же самое время нигде больше в мозгу нет когерентной активности, ассоциирующейся с какими-то другими статистическими параметрами данной группы стимулов, и что полное внутреннее представление данного объекта не кодируется этой совместной активностью. Can you say "sparse overcomplete representations" or even "convergence zones" (Antonio Damasio)?
Вот, кстати, хорошая статья на тему количественного описания координированной активности нейронных структур:
K.L. Klinkner, C.R. Shalizi and M. Camperi, "Measuring Shared Information and Coordinated Activity in Neuronal Networks", in Advances in Neural Information Processing Systems 18, Yair Weiss, Bernhard Scholkopf and John C. Platt (eds.), MIT Press, 2006
http://arxiv.org/abs/q-bio.NC/0506009
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kotovski
2006-03-03 06:22 pm UTC (ссылка)
спасибо за статьи, буду читать, первую для смеха, а вторая мне может пригодиться.
на самом деле я тебе в любом мозгу (ну почти в любом) найду дохрена нейрононов, реагирующих хоть на дженнифер анистон, хоть на ксюшеньку собчак -- это как раз то, чем мы занимаемся, изучаем face perception. есть такая жырная область, называется fusiform face area, реагирует на вид человеческих лиц.
твой вопрос очень хороший. он как бы очевидный, но на самом деле в науке сейчас творится полный бардак, появились новые способы измерения активности мозга, но методологии еще до сих пор не обкатаны, поэтому до сих пор появляются исследования типа "мы показали субъекту фотографию чорта в ступе, у него среагировала область мозга Икс, из чего мы делаем вывод, что область мозга Икс ответственна за восприятие чертей в ступах". я долго могу на эту тему говорить... но ты поднял проблему, которая на самом деле остро стоит.
"sparse overcomplete representations" -- тоже сейчас горячая тема, разрабатывается модель для early visual cortex, над этим работают в том числе bruno olshausen и david field.
еще была классическая статья j. haxby et al "the distributed human neural system for face perception" по поводу того, что мол информация в visual system кодифицируется не столько одной областью, сколько совместным реагированием многих областей, объединенных в network.
ты читал дамазио? респект :) я не читал пока.
(Ответить) (Ветвь дискуссии)
kotovski
2006-03-03 06:58 pm UTC (ссылка)
vse, chto ya napisal, otnositsya k fMRI, a ne k single-unit recordings :)
(Ответить) (Уровень выше) (Ветвь дискуссии)
ded_maxim
2006-03-03 11:27 pm UTC (ссылка)
Почитай вторую статью, там есть полезные штуки, которые могут пригодиться для обработки данных fMRI тоже -- берутся экспериментальные данные, и по ним восстанавливается "скрытый" процесс, управляющий этими данными. Этот процесс -- марковский, с переходной матрицей, зависящей от времени, и является достаточной статистикой для прогнозирования наблюдаемого процесса.
(Ответить) (Уровень выше)
wildant
2006-03-03 07:25 pm UTC (ссылка)
в scientific american mind про это читал
(Ответить)
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Features
February 2006 issue
One Person, One Neuron?
Nerve cells devoted to recognizing Halle Berry or Bill Clinton? Absurd. That's what most neuroscientists thought--until recently
By Katja Gaschler
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Two neurons (yellow-green and red blobs) in the amygdala, a brain region involved in emotions.
Think of the hundreds of people you can remember ever having met. Add those individuals--such as celebrities, politicians and other famous figures--whose faces you know well only from movies, TV and photographs. Is it possible that each of those individuals, along with thousands of other objects you can easily recognize from earlier encounters, could be captured in your memory by its own personal brain cell?
Perhaps. A recent study published in the journal Nature by scientists at the California Institute of Technology and the University of California, Los Angeles, suggests that our brains use far fewer cells to interpret any given image than previously believed. For instance, researchers discovered a "Bill Clinton cell" that responds almost exclusively to the former president. Another neuron fires only when the actor Halle Berry comes into view.
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The neuron responded to three different pictures of Clinton but not of other American presidents.
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Exactly how the brain recognizes images has been a matter of debate. Two wildly divergent theories exist. In one, millions of neurons work together to create a cohesive picture. In the extreme version of the other, the brain contains a separate neuron for each individual object and person. In 1967 Polish neurophysiologist Jerzy Konorski described his theory of "gnostic neurons"--derived from gnosis, Greek for "recognition." According to this theory, the activity of one or several nerve cells determines whether someone thinks of his boss, wife or grandmother. Jerome Lettvin, then a neuroscientist at the Massachusetts Institute of Technology, thus dubbed the neurons "grandmother cells," and the name stuck.
Many researchers immediately criticized the theory: Wouldn't such one-to-one congruence take up too much space? Opinions were still much the same two decades later. "It's very hard to take the grandmother cell theory seriously," commented neurobiologist and Nobel Prize laureate David H. Hubel in the 1980s.
Back then, it was not even clear how to go about exploring the entire problem of the neuronal foundations of consciousness. Using electrodes, neurophysiologists at the time had managed to trace the activity of individual neurons in the brains of monkeys and cats. But animal subjects cannot discuss their thoughts with us, making experiments on consciousness and perception more than a little difficult. Analogous tests on human beings had not yet been undertaken because of the obvious risks of inserting electrodes into the brain.
Surprise Volunteers
In recent years, however, a set of human volunteers unexpectedly emerged: patients suffering from forms of epilepsy that cannot be treated with medication. In the early 1990s a number of patients were slated to undergo brain surgery to remove the zone in their brain responsible for the onsets of their seizures. Sometimes techniques such as electroencephalography and magnetic resonance imaging cannot locate the zone precisely enough. In such cases, neurosurgeons may implant as many as 10 thin electrodes in the brain. These fine sensors monitor neuronal activity day and night on a continuous basis until the seizure-onset zone can be localized with sufficient precision and can then be removed by the neurosurgeon.
Researchers realized that this procedure offered a unique opportunity to study the activities of individual cells. This fact led neurosurgeon Itzhak Fried of U.C.L.A., one of the principal investigators in the current research, to design a study as early as 1992 and then invite otherwise untreatable epileptics to participate in this basic neural research. The grandmother cell study, carried out with bioengineer Rodrigo Quian Quiroga of the University of Leicester in England as chief experimentalist, was rather simple. Test subjects lay in bed watching while photographs flashed on a computer screen at one-second intervals. At the same time, Quian Quiroga monitored the electrical signals coming from the "attached" neurons.
One Person, One Neuron?
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One of the first gnostic neurons discovered using this method was the Bill Clinton cell, located deep inside one female patient's amygdala--the almond-shaped region of the brain involved in emotions. The neuron responded to three different pictures of Clinton: a drawing, a painting and a group portrait with other politicians. When the patient looked at photographs of other American presidents, from George Washington to George H. W. Bush, the cell remained silent.
Shortly thereafter, Fried's team found similar selective nerve cells in other patients in the medial temporal lobe that responded to the Beatles, the TV cartoon Simpsons family and one neuron that was galvanized into action only at the sight of Jennifer Aniston. In another test subject, one nerve cell in the right hippocampus fired as soon as Halle Berry appeared on the screen--even when she was in a Catwoman costume and her face was masked. Apparently, the cell responded to the idea of her as a person, not just to a view of her face: the caption "Halle Berry" was enough to get the neuron going.
Quian Quiroga and his co-workers were fascinated. They theorized that the specialized nerve cells were crucial to the process of recognition. Their locations were in the hippocampus, entorhinal cortex, parahippocampal gyrus and amygdala--all structures in the medial temporal lobe known to be involved in long-term memory. But how are we to conceive of a single neuron capable of representing something as complex as the identity of Bill Clinton?
From the point of view of information theory, this question is not hard to answer, according to computational neuroscientist Christof Koch of Caltech, who was also involved in the study and has been working with Fried's team since 1998. In his book The Quest for Consciousness (Roberts & Company Publishers, 2004), Koch illustrates this premise with an analogy. When we turn on the TV, the screen presents us with an explicit--that is, immediate--pattern of multicolored pixels distributed over the monitor. Yet implicitly concealed within this pattern is specific information, such as data about Bill Clinton's face.
Let us assume that a robot is tasked with determining whether the ex-president's image is currently on the screen. Its electronic brain has to expend enormous computational resources to extract the concealed information from the array of pixels. The computation involves many iterations, with some level of screening for Clinton-like information going on at each one, and each iteration involves a more and more sophisticated Clinton search through a smaller and smaller set of screened data. Whereas the initial mass of data shrinks with each computational step, the "logical depth of processing" increases steadily. In the end, a minute quantity of information--one bit--remains, indicating explicitly whether Clinton is present or not: 1 (Bill) or 0 (no Bill).
According to a theory of consciousness developed by Koch and his late colleague and friend, the Nobel Prize-winning Francis Crick, our brain proceeds in similar fashion. From its initial impression on the retina to actual consciousness, Clinton's face generates a firestorm of neuronal activity. But whereas many groups of neurons are involved at the lower processing levels, such activity is limited to fewer and fewer nerve cells in subsequent steps.
"I'm not claiming that a single cell represents the total neuronal correlate of Bill Clinton," Koch emphasizes. "The firing of a single neuron would be much too weak a signal." Nevertheless, he considers it probable that the concerted activity of a small group of neurons would be strong enough to catapult Clinton into consciousness. Because these cells encode only the abstract idea of Clinton, the tilt of the head in relation to the picture or whether Clinton is wearing a ski cap has no effect whatsoever on the behavior of the cells. And if we were to destroy all these cells? Then the perception of "Look, there's Bill Clinton" would turn to "Look, there's a guy who looks familiar, but I can't quite place him."
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