최근의 신경과학적인 성과는 뇌는 기능이 지역별 영역별로 나뉘어져서 수행되고 있음을 보이고 있다. 이것이 19세기의 골상학(phrenology)의 부활을 의미하는 것일까? 이 글은 자연의 모습을 근사했을 뿐인 과학적인 메타포를 착각하지 말 것을 회의론적인 입장에서 지적하고 있다.
하지만 이런 것들은 실제로 신경과학자 스스로가 자초한 것이다. 많은 사람들이 도덕 모듈, 신 모듈 등등 뇌에 특정 개념들을 생성하는 기능 모듈이 존재하고 있다고 착각하게 되었다. 최근에도 경제적 판단을 하는 뇌의 부위라는 기사가 동아사이언스에 실렸었다. 글에서도 최근의 예를 들고 있는데 작년 11월 뉴욕타임즈에 마르코 라코보니(Marco Iacoboni)는 "This Is Your Brain on Politics" 이라는 기사에서 정치성향에 따른 뇌 반응의 fMRI 스캔 결과를 공개했다. 그는 뇌의 고차 의식 영역 중에서 불안(anxiety)과 혐오(disgust)를 담당하는 부위들인 편도(amygdala)와 뇌섬엽(insula)이 조합되어 정치적인 기능을 수행한다는 것이었다. "민주당", "공화당", "독립(independent)" 라는 글자를 보여주고 뇌의 반응을 관찰했는데, 사람들은 "공화당"을 보고 이 두 영역을 활성화 했다고 한다. 재미있는 것은 모든 글자에 항상 반응하는 영역이 있는데 보상계로 불리는 복즉 선도체(ventral striatum)와 욕망(desire)와 감정(feeling)이 연결된 부위들이었다. 그래서 "공화당" 은 불안과 협오를 가져오는 단어가 되었는데 이후의 결론들도 혼란스럽기는 마찬가지이다.
과학의 본질은 자체적으로 잘못된 것을 고쳐나가는 자정작업이 늘 일어난다는데 있다. 라코보니의 동료들은 3일 후 곧 성명을 발표한다.
"같은 브레인 이미지 기술을 사용하는 인지 신경과학자로서 우리는 특정 뇌 영역이 활성화된 것만을 보고서 단순하게 연결지어서 그 사람이 불안해 한다거나 어떤 감정을 느끼고 있다는 것을 결정적으로 단정할 수 없다. 뇌의 영역들은 일반적으로 많은 정신적 상태에 관여되기 때문에 단순한 특정 정신 상태와 뇌 영역을 1:1 매핑하는 것은 가능하지 않다."
과학자들 역시 단순성의 아름다움에 경도되는 경향이 있다. 하지만 뇌에 있어서는 특정 영역에 국한된 정신 상태의 이벤트의 매핑은 넌센스다. 이 모든 심리적 개념들은 신경망(Neural Network)의 총체적인 동작에서 수반된다. 새로운 골상학에 현혹되지 말지어다.
● 참고글 : 비싸고 예쁘고 알 수 없는 뇌 by 아이추판다님
하지만 이런 것들은 실제로 신경과학자 스스로가 자초한 것이다. 많은 사람들이 도덕 모듈, 신 모듈 등등 뇌에 특정 개념들을 생성하는 기능 모듈이 존재하고 있다고 착각하게 되었다. 최근에도 경제적 판단을 하는 뇌의 부위라는 기사가 동아사이언스에 실렸었다. 글에서도 최근의 예를 들고 있는데 작년 11월 뉴욕타임즈에 마르코 라코보니(Marco Iacoboni)는 "This Is Your Brain on Politics" 이라는 기사에서 정치성향에 따른 뇌 반응의 fMRI 스캔 결과를 공개했다. 그는 뇌의 고차 의식 영역 중에서 불안(anxiety)과 혐오(disgust)를 담당하는 부위들인 편도(amygdala)와 뇌섬엽(insula)이 조합되어 정치적인 기능을 수행한다는 것이었다. "민주당", "공화당", "독립(independent)" 라는 글자를 보여주고 뇌의 반응을 관찰했는데, 사람들은 "공화당"을 보고 이 두 영역을 활성화 했다고 한다. 재미있는 것은 모든 글자에 항상 반응하는 영역이 있는데 보상계로 불리는 복즉 선도체(ventral striatum)와 욕망(desire)와 감정(feeling)이 연결된 부위들이었다. 그래서 "공화당" 은 불안과 협오를 가져오는 단어가 되었는데 이후의 결론들도 혼란스럽기는 마찬가지이다.
과학의 본질은 자체적으로 잘못된 것을 고쳐나가는 자정작업이 늘 일어난다는데 있다. 라코보니의 동료들은 3일 후 곧 성명을 발표한다.
"같은 브레인 이미지 기술을 사용하는 인지 신경과학자로서 우리는 특정 뇌 영역이 활성화된 것만을 보고서 단순하게 연결지어서 그 사람이 불안해 한다거나 어떤 감정을 느끼고 있다는 것을 결정적으로 단정할 수 없다. 뇌의 영역들은 일반적으로 많은 정신적 상태에 관여되기 때문에 단순한 특정 정신 상태와 뇌 영역을 1:1 매핑하는 것은 가능하지 않다."
과학자들 역시 단순성의 아름다움에 경도되는 경향이 있다. 하지만 뇌에 있어서는 특정 영역에 국한된 정신 상태의 이벤트의 매핑은 넌센스다. 이 모든 심리적 개념들은 신경망(Neural Network)의 총체적인 동작에서 수반된다. 새로운 골상학에 현혹되지 말지어다.
The Brain Is Not Modular: What fMRI Really Tells Us
Metaphors, modules and brain-scan pseudoscience
By Michael Shermer
The atom is like a solar system, with electrons whirling around the nucleus like planets orbiting a star. No, actually, it isn’t. But as a first approximation to help us visualize something that is so invisible, that image works as a metaphor.
Science traffics in metaphors because our brains evolved to grasp intuitively a world far simpler than the counterintuitive world that science has only recently revealed. The functional activity of the brain, for example, is nearly as invisible to us as the atom, and so we employ metaphors. Over the centuries the brain has been compared to a hydraulic machine (18th century), a mechanical calculator (19th century) and an electronic computer (20th century). Today a popular metaphor is that the brain is like a Swiss Army knife, with specialized modules for vision, language, facial recognition, cheating detection, risk taking, spirituality and even God.
Modularity metaphors have been fueled by a new brain-scanning technology called functional magnetic resonance imaging (fMRI). We have all seen scans with highlighted (usually in red) areas where your brain “lights up” when thinking about X (money, sex, God, and so on). This new modularity metaphor is so seductive that I have employed it myself in several books on the evolution of religion (belief modules), morality (moral modules) and economics (money modules). There is a skeptical movement afoot to curtail abuses of the metaphor, however, and it is being driven by neuroscientists themselves. The November 11, 2007, edition of the New York Times, for example, published an opinion piece entitled “This Is Your Brain on Politics,” by neuroscientist Marco Iacoboni of the University of California, Los Angeles, and his colleagues. The writers presented the results of their brain scans on swing voters. “When we showed subjects the words ‘Democrat,’ ‘Republican’ and ‘independent,’ they exhibited high levels of activity in the part of the brain called the amygdala, indicating anxiety,” the authors note. “The two areas in the brain associated with anxiety and disgust—the amygdala and the insula—were especially active when men viewed ‘Republican.’ But all three labels also elicited some activity in the brain area associated with reward, the ventral striatum, as well as other regions related to desire and feeling connected.” So the word “Republican” elicits anxiety and disgust, except for when it triggers feelings of desire and connectedness. The rest of the conclusions are similarly obfuscating.
In a response befitting the self-correcting nature of science, Iacoboni’s U.C.L.A. colleague Russell Poldrack and 16 other neuroscientists from labs around the world published a response three days later in the Times, explaining: “As cognitive neuroscientists who use the same brain imaging technology, we know that it is not possible to definitively determine whether a person is anxious or feeling connected simply by looking at activity in a particular brain region. This is so because brain regions are typically engaged by many mental states, and thus a one-to-one mapping between a brain region and a mental state is not possible.” For example, the amygdala is activated by arousal and positive emotions as well, so the key to interpreting such scans is careful experimental design that allows comparison between brain states.
Additional skepticism arises from knowing that fMRI measures blood-flow change, not neuronal activity, that the colors are artificially added in order to see the blood-flow differences and that those images are not any one person’s brain but are instead a statistical compilation of many subjects’ brains in the experiment. “Some of the claims made by neuroscientists sound like astrology,” Poldrack told me in an interview. “It’s not the science itself that is the problem. It’s taking a little bit of science and going way beyond it.” For example, there is the problem of reversing the causal inference, “where people see some activity in a brain area and then conclude that this part of the brain is where X happens. We can show that if I put you into a state of fear, your amygdala lights up, but that doesn’t mean that every time your amygdala lights up you are experiencing fear. Every brain area lights up under lots of different states. We just don’t have the data to tell us how selectively active an area is.”
University of California, San Diego, philosopher of the mind Patricia S. Churchland told me with unabashed skepticism: “Mental modules are complete nonsense. There are no modules that are encapsulated and just send information into a central processor. There are areas of specialization, yes, and networks maybe, but these are not always dedicated to a particular task.” Instead of mental module metaphors, let us use neural networks.
The brain is not random kludge, of course, so the search for neural networks associated with psychological concepts is a worthy one, as long as we do not succumb to the siren song of phrenology.
Editor's Note: This story was originally printed with the title "A New Phrenology?"
Metaphors, modules and brain-scan pseudoscience
By Michael Shermer
Science traffics in metaphors because our brains evolved to grasp intuitively a world far simpler than the counterintuitive world that science has only recently revealed. The functional activity of the brain, for example, is nearly as invisible to us as the atom, and so we employ metaphors. Over the centuries the brain has been compared to a hydraulic machine (18th century), a mechanical calculator (19th century) and an electronic computer (20th century). Today a popular metaphor is that the brain is like a Swiss Army knife, with specialized modules for vision, language, facial recognition, cheating detection, risk taking, spirituality and even God.
Modularity metaphors have been fueled by a new brain-scanning technology called functional magnetic resonance imaging (fMRI). We have all seen scans with highlighted (usually in red) areas where your brain “lights up” when thinking about X (money, sex, God, and so on). This new modularity metaphor is so seductive that I have employed it myself in several books on the evolution of religion (belief modules), morality (moral modules) and economics (money modules). There is a skeptical movement afoot to curtail abuses of the metaphor, however, and it is being driven by neuroscientists themselves. The November 11, 2007, edition of the New York Times, for example, published an opinion piece entitled “This Is Your Brain on Politics,” by neuroscientist Marco Iacoboni of the University of California, Los Angeles, and his colleagues. The writers presented the results of their brain scans on swing voters. “When we showed subjects the words ‘Democrat,’ ‘Republican’ and ‘independent,’ they exhibited high levels of activity in the part of the brain called the amygdala, indicating anxiety,” the authors note. “The two areas in the brain associated with anxiety and disgust—the amygdala and the insula—were especially active when men viewed ‘Republican.’ But all three labels also elicited some activity in the brain area associated with reward, the ventral striatum, as well as other regions related to desire and feeling connected.” So the word “Republican” elicits anxiety and disgust, except for when it triggers feelings of desire and connectedness. The rest of the conclusions are similarly obfuscating.
In a response befitting the self-correcting nature of science, Iacoboni’s U.C.L.A. colleague Russell Poldrack and 16 other neuroscientists from labs around the world published a response three days later in the Times, explaining: “As cognitive neuroscientists who use the same brain imaging technology, we know that it is not possible to definitively determine whether a person is anxious or feeling connected simply by looking at activity in a particular brain region. This is so because brain regions are typically engaged by many mental states, and thus a one-to-one mapping between a brain region and a mental state is not possible.” For example, the amygdala is activated by arousal and positive emotions as well, so the key to interpreting such scans is careful experimental design that allows comparison between brain states.
Additional skepticism arises from knowing that fMRI measures blood-flow change, not neuronal activity, that the colors are artificially added in order to see the blood-flow differences and that those images are not any one person’s brain but are instead a statistical compilation of many subjects’ brains in the experiment. “Some of the claims made by neuroscientists sound like astrology,” Poldrack told me in an interview. “It’s not the science itself that is the problem. It’s taking a little bit of science and going way beyond it.” For example, there is the problem of reversing the causal inference, “where people see some activity in a brain area and then conclude that this part of the brain is where X happens. We can show that if I put you into a state of fear, your amygdala lights up, but that doesn’t mean that every time your amygdala lights up you are experiencing fear. Every brain area lights up under lots of different states. We just don’t have the data to tell us how selectively active an area is.”
University of California, San Diego, philosopher of the mind Patricia S. Churchland told me with unabashed skepticism: “Mental modules are complete nonsense. There are no modules that are encapsulated and just send information into a central processor. There are areas of specialization, yes, and networks maybe, but these are not always dedicated to a particular task.” Instead of mental module metaphors, let us use neural networks.
The brain is not random kludge, of course, so the search for neural networks associated with psychological concepts is a worthy one, as long as we do not succumb to the siren song of phrenology.
Editor's Note: This story was originally printed with the title "A New Phrenology?"
Further Reading
- At the Edge of Life's Code
- No Directions Required--Software Smartens Mobile Robots
- Visionary Research: Teaching Computers to See Like a Human
- Humans Marrying Robots? A Q&A with David Levy
- Why does my cell phone make screechy noises when I place it near my computer?
- Not Tonight, Dear, I Have to Reboot
- Here and There
- Nothing to Sneeze At
Scientific American Magazine - May 13, 2008
● 참고글 : 비싸고 예쁘고 알 수 없는 뇌 by 아이추판다님
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