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Localizing cognitive operations
Brain Research Bulletin, Vol. 50, Nos. 5/6, p. 413, 1999 Copyright © 1999 Elsevier Science Inc. Printed in the USA. All rights reserved 0361-9230/99/$–see front matter
PII S0361-9230(99)00170-7
Localizing cognitive operations Michael I. Posner* Sackler Institute, Weill Medical College, New York, NY, USA [Received 26 April 1999; Accepted 26 April 1999] ations by finding the time course of activation of anatomical areas through recording from scalp electrodes [1]. It is hard to imagine as one reads journals devoted to cognitive neuroscience or mapping the human brain that there could ever have been doubts that there was a specific anatomy related to the performance of mental computations. The distributed nature of the activations in any realistic cognitive task helps explain why Lashley and others could have thought that the brain operated as a whole. Any task is represented by a network of brain areas. The more tissue that is removed the more this network is likely to be affected and the poorer overall performance. However, where we have been able to dissect tasks into plausible component operations, it is these operations not the task themselves that are localized. As new generations of brain imagers are attracted to efforts to map human brain function it will be important to keep in mind the difficulties of localization and importance of careful task analysis for demonstrating it.
Every psychologist who entered the field in the mid-20th century studied the history of efforts to localize higher level mental activity in the brain. We were taught that Karl Lashley [2] had discovered in his work with rats learning mazes that the effect of a brain lesion depended on how much tissue was removed and not on what part of the cortex was taken out. Studies of human patients with frontal lesions were also interpreted as showing that the brain operated as a whole with respect to cognition. The somewhat vague principles of mass action and equipotentiality were used to explain failures to find any precise localization. We were also cautioned about efforts to analyze cognitive processes into elements because the whole was more than the sum of the parts, or to use the subtractive method because tasks were completely altered when any part was changed. I participated in three events which satisfied me that the facts were quite different. The first was showing that unilateral lesions of the parietal lobe, thalamus, or colliculus interfered with attention to visual events on the side of space opposite the lesion, but in very different and quite precise ways that could be described in terms of component operations that together shifted attention between locations [5]. The second was a study employing positron emission tomography to find brain areas active in processing words. Specific areas related to chunking letters into an orthographic unit, sounding things out and determining meaning were revealed quite directly by subtracting less complex tasks (e.g., repeating a word) from more complex ones (generating a use for the word) to eliminate component operations [3]. Moreover, the brain areas were generally related to lesion data. These two events were enough to convince me that mental operations studied in cognition were localized in specific brain tissue [4]. A third step was to support the relation between brain areas and mental oper-
REFERENCES 1. Abdullaev, Y.; Posner, M. I. Event related potential imaging of semantic encoding during single word processing. Neuroimage 7:1–13; 1998. 2. Lashley, K. S. Mass action in cerebral function. Science 73:245–254; 1931. 3. Petersen, S. E.; Fox, P. T.; Posner, M. I.; Mintun, M.; Raichle, M. E. Positron emission tomographic studies of the cortical anatomy of single word processing. Nature 331:585–589; 1987. 4. Posner, M. I.; Petersen, S. E.; Fox, P. T.; Raichle, M. E. Localization of cognitive functions in the human brain. Science 240:1627–1631; 1988. 5. Posner, M. I.; Presti, D. Selective attention and cognitive control. Trends Neurosci. 10:12–17; 1987.
* Address for correspondence: Prof. Michael I. Posner, Dept. of Psychiatry, Box 171, Sackler Institute, Weill Medical College of Cornell University, 1300 York Ave., New York, NY 10021, USA. E-mail: [email protected]
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PII S0361-9230(99)00170-7
Localizing cognitive operations Michael I. Posner* Sackler Institute, Weill Medical College, New York, NY, USA [Received 26 April 1999; Accepted 26 April 1999] ations by finding the time course of activation of anatomical areas through recording from scalp electrodes [1]. It is hard to imagine as one reads journals devoted to cognitive neuroscience or mapping the human brain that there could ever have been doubts that there was a specific anatomy related to the performance of mental computations. The distributed nature of the activations in any realistic cognitive task helps explain why Lashley and others could have thought that the brain operated as a whole. Any task is represented by a network of brain areas. The more tissue that is removed the more this network is likely to be affected and the poorer overall performance. However, where we have been able to dissect tasks into plausible component operations, it is these operations not the task themselves that are localized. As new generations of brain imagers are attracted to efforts to map human brain function it will be important to keep in mind the difficulties of localization and importance of careful task analysis for demonstrating it.
Every psychologist who entered the field in the mid-20th century studied the history of efforts to localize higher level mental activity in the brain. We were taught that Karl Lashley [2] had discovered in his work with rats learning mazes that the effect of a brain lesion depended on how much tissue was removed and not on what part of the cortex was taken out. Studies of human patients with frontal lesions were also interpreted as showing that the brain operated as a whole with respect to cognition. The somewhat vague principles of mass action and equipotentiality were used to explain failures to find any precise localization. We were also cautioned about efforts to analyze cognitive processes into elements because the whole was more than the sum of the parts, or to use the subtractive method because tasks were completely altered when any part was changed. I participated in three events which satisfied me that the facts were quite different. The first was showing that unilateral lesions of the parietal lobe, thalamus, or colliculus interfered with attention to visual events on the side of space opposite the lesion, but in very different and quite precise ways that could be described in terms of component operations that together shifted attention between locations [5]. The second was a study employing positron emission tomography to find brain areas active in processing words. Specific areas related to chunking letters into an orthographic unit, sounding things out and determining meaning were revealed quite directly by subtracting less complex tasks (e.g., repeating a word) from more complex ones (generating a use for the word) to eliminate component operations [3]. Moreover, the brain areas were generally related to lesion data. These two events were enough to convince me that mental operations studied in cognition were localized in specific brain tissue [4]. A third step was to support the relation between brain areas and mental oper-
REFERENCES 1. Abdullaev, Y.; Posner, M. I. Event related potential imaging of semantic encoding during single word processing. Neuroimage 7:1–13; 1998. 2. Lashley, K. S. Mass action in cerebral function. Science 73:245–254; 1931. 3. Petersen, S. E.; Fox, P. T.; Posner, M. I.; Mintun, M.; Raichle, M. E. Positron emission tomographic studies of the cortical anatomy of single word processing. Nature 331:585–589; 1987. 4. Posner, M. I.; Petersen, S. E.; Fox, P. T.; Raichle, M. E. Localization of cognitive functions in the human brain. Science 240:1627–1631; 1988. 5. Posner, M. I.; Presti, D. Selective attention and cognitive control. Trends Neurosci. 10:12–17; 1987.
* Address for correspondence: Prof. Michael I. Posner, Dept. of Psychiatry, Box 171, Sackler Institute, Weill Medical College of Cornell University, 1300 York Ave., New York, NY 10021, USA. E-mail: [email protected]
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