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The Developmental Cognitive Neuroscience of Language: A New Research Domain
Brain and Language 71, 65–68 (2000) doi:10.1006/brln.1999.2214, available online at http://www.idealibrary.com on
The Developmental Cognitive Neuroscience of Language: A New Research Domain Angela D. Friederici Max Planck Institute of Cognitive Neuroscience, Leipzig, Germany
Over the past decades the field of Cognitive Neuroscience has made enormous progress, also with respect to the language–brain relationship. New imaging techniques have allowed us to identify the neuronal network supporting language functions. Techniques providing a high temporal resolution have started to describe the time course of the neuronal activity related to particular language functions, such as phonological, prosodic, syntactic, and lexical-semantic aspects as well as the possible interplay between these. The picture we are able to draw today is by no means perfect or even complete, but we are beginning to see rough overall shapes as well as details in it. The combination of the new techniques combined with psycholinguistic theorizing will clarify the picture over the decades to come. A new and challenging field of research concerning the study of the language and the brain for the next decade(s) is the area of Developmental Cognitive Neuroscience. Research in adult cognitive neuroscience for different cognitive faculties such as memory, attention, and language, has not even begun in the area of the developmental cognitive neuroscience. This may be due to several reasons. (1) The scientific community in developmental cognitive neuroscience mainly interested in human cognition may not work in close contact with the developmental neuroscience community and often use nonhuman primates as subjects. When considering the area of language the reason why these communities do not come together is all too obvious. (2) Systematic lesion studies in children are rarely possible as the vascular
I thank Doug Saddy for comments on the manuscript. Address correspondence and reprint requests to Angela D. Friederici, Max Planck Institute of Cognitive Neuroscience, P.O. Box 500 355, 04303 Leipzig, Germany. E-mail: [email protected]. 65 0093-934X/00 $35.00
Copyright 2000 by Academic Press All rights of reproduction in any form reserved.
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etiology cases so successfully investigated in adult cognition do not exist with the same systematicity in children. (3) Invasive imaging techniques such as PET cannot be applied normally to children for ethical reasons. There are surely many other challenges to the maturation of the field of developmental cognitive neuroscience. The issue of how brain development and cognitive development in the area of language development co-occur in early development and over a lifetime will be one of the key issues in the coming decades of the third millennium. So far, little is known about this issue, but there are first indications that there is much to learn. Improvements in new brain imaging techniques such as fMRI and high-density EEG and MEG methods and the development of new technologies will allow us to investigate these issues. Three central areas should occupy our attention in the coming years. First, the development of particular cognitive and linguistic functions as well as the interaction between these is not independent of brain development. That is, cognitive functions that appear to be modular in the adult behavior may not be informationally encapsulated in early development. For example, highly interconnected brain systems may be tuned toward less interactivity due to particular input. Syntax may be a candidate that follows such a developmental course (Friederici, 1990). After identifying the particular syntactic structures in a given language, the processing of these may become more and more automatic and thereby independent of, for example, lexical semantic information. Second, the relative contribution of the left and the right hemisphere to language processing may well change over life time. There is some recent evidence that infants heavily rely on prosodic information during early language acquisition (Jusczyk, 1997; Kemler Nelson, Hirsh-Pasek, Jusczyk & Wright Cassidy, 1989; Morgan, 1997). From recent fMRI studies in adults we know that prosodic information is mainly processed in the right hemisphere (Steinhauer, Alter, Meyer, Friederici, & von Cramon, 1999; Meyer, Friederici, & von Cramon, 1999). On the basis of these findings one can speculate that the right hemisphere is of major import once for early language acquisition. For an adequate description of the language–brain relationship during early language development it would be important to know whether this assumption about the early involvement of the right hemisphere holds and, moreover, when and under what conditions the left hemisphere comes into play and finally gets dominant in processing language. There is some recent, although somewhat indirect, evidence that early brain lesions (before the age of 2 years) in the right hemisphere lead to more severe deficits in language acquisition that early brain lesions in the left hemisphere (Bates, Thal, Trauner, Fenson, Aram, Eisele & Nass, 1997). This finding seems to support the view of the primary importance of the right hemisphere in early language development. In an overview of a number of studies investigating
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childhood aphasia it became apparent that children between the age of 5 and 8 years demonstrated a nonfluent, Broca-type of aphasia independent of whether the lesion site was left anterior or left temporal (Friederici, 1994). This finding was taken to suggest that a fluent aphasia can only emerge after the language system has reached a highly automatic status. From adult studies we know that highly automatic syntactic procedures are supported by the Broca’s area and/or the left frontal operculum (for an overview see Friederici, 1999). Thus it may not be surprising that adults with lesions in the left temporal region but intact left inferior frontal region show a fluent aphasia. Children, on the other hand, who have not yet developed highly automatic syntactic procedures (to be established in the inferior frontal regions) do not show a fluent aphasia when the temporal region is lesioned (and the inferior frontal region is intact). These data seem to indicate that there is a shift in the relative contribution of the different language-related brain regions over a lifetime. Third, the relative contribution of different subsystems or their coordination in time may also change in late adulthood. Depending on the mechanics and automaticity of different subsystems supporting language processing major shifts of the relative contribution of these will be observed in late adulthood. A first indication comes from recent event-related brain potential studies in normal adults showing that the brain responses to processes of lexical-semantic integration are slowed down (Gunter, Jackson, & Mulder, 1995). Brain responses evoked by early syntactic processes, i.e., first-pass parsing are age independent whereas those correlated processes of structural reanalysis or repair are slowed down with age (Gunter, Vos, & Friederici, 1999). The impact of these differential slowing processes for language comprehension and the possible compensatory mechanisms are not yet specified. In conclusion, it appears that the issue of the language–brain relationship during early development as well as in late adulthood is a terra incognita. This state of affairs is largely due to technological constraints. Recently, we have seen the first results suggesting a rich area of investigation. New brain imaging techniques such as fMRI and further development of neurophysiological methods such as EEG and MEG will provide us with new tools to persue these issues. We just have to learn to use them appropriately (and whenever necessary to adapt the testing procedures) in order to learn about the language brain relation in its developmental course over lifetime. REFERENCES Bates, E., Thal, D., Trauner, D., Fenson, J., Aram, D., Eisele, J., & Nass, R. 1997. From first words to grammar in children with focal brain injury. Developmental Neuropsychology, 13(3), 275–343. Friederici, A. D. 1990. On the properties of cognitive modules. Psychological Research, 52, 175–180.
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Friederici, A. D. 1994. Funktionale Organisation und Reorganisation der Sprache wa¨hrend der Sprachentwicklung: Eine Hypothese. Neurolinguistik, 8, 41–55. Friederici, A. D. 1999. The neurobiology of language comprehension. In A. D. Friederici (Ed.), Language Comprehension: A biological perspective, 2nd edition (pp. 265–304). Berlin/Heidelberg/New York: Springer. Gunter, Th.C., Jackson, J. L., & Mulder, G. (1995). Language memory and aging: An electrophysiological exploration of the N400 during reading of memory demanding sentences. Psychophysiology, 32, 215–229. Gunter, Th.C., Vos, S. H., & Friederici, A. D. 1999. Memory or aging that’s the question: An electroencephalogical perspective on language. In Kemper, S., & Kliegl, R. (Eds.), Constraints on language: Memory, aging, and grammar (249–282). Norwell, MA: Kluwer Academic. Jusczyk, P. W. 1997. The discovery of spoken language. Cambridge, MA: MIT Press. Kemler Nelson, D. G., Hirsh-Pasek, K., Jusczyk, P. W., & Wright Cassidy, K. 1989. How prosodic cues in motherese might assist language learning. Journal of Child Language, 16, 55–68. Meyer, M., Friederici, A. D., & von Cramon, D. Y. (1998). Processing prosody only: Eventrelated fMRI specifies comprehension mechanisms of delexicalised speech. In A. D. Friederici & D. Y. von Cramon (Eds.), Annual report 1998 (pp. 18–19). Leipzig: Max Planck Institute of Cognitive Neuroscience. Morgan, J. L. 1997. A rhythmic bias in preverbal speech segmentation. Journal of Memory and Language, 35, 666–688. Steinhauer, K., Alter, K., Meyer, M., Friederici, A. D., & von Cramon, D. Y. 1999. Brain activation related to prosodic processing in natural speech: An event-related fMRI study. Journal of Cognitive Neuroscience, Suppl., 54.
The Developmental Cognitive Neuroscience of Language: A New Research Domain Angela D. Friederici Max Planck Institute of Cognitive Neuroscience, Leipzig, Germany
Over the past decades the field of Cognitive Neuroscience has made enormous progress, also with respect to the language–brain relationship. New imaging techniques have allowed us to identify the neuronal network supporting language functions. Techniques providing a high temporal resolution have started to describe the time course of the neuronal activity related to particular language functions, such as phonological, prosodic, syntactic, and lexical-semantic aspects as well as the possible interplay between these. The picture we are able to draw today is by no means perfect or even complete, but we are beginning to see rough overall shapes as well as details in it. The combination of the new techniques combined with psycholinguistic theorizing will clarify the picture over the decades to come. A new and challenging field of research concerning the study of the language and the brain for the next decade(s) is the area of Developmental Cognitive Neuroscience. Research in adult cognitive neuroscience for different cognitive faculties such as memory, attention, and language, has not even begun in the area of the developmental cognitive neuroscience. This may be due to several reasons. (1) The scientific community in developmental cognitive neuroscience mainly interested in human cognition may not work in close contact with the developmental neuroscience community and often use nonhuman primates as subjects. When considering the area of language the reason why these communities do not come together is all too obvious. (2) Systematic lesion studies in children are rarely possible as the vascular
I thank Doug Saddy for comments on the manuscript. Address correspondence and reprint requests to Angela D. Friederici, Max Planck Institute of Cognitive Neuroscience, P.O. Box 500 355, 04303 Leipzig, Germany. E-mail: [email protected]. 65 0093-934X/00 $35.00
Copyright 2000 by Academic Press All rights of reproduction in any form reserved.
66
MILLENNIUM ISSUE
etiology cases so successfully investigated in adult cognition do not exist with the same systematicity in children. (3) Invasive imaging techniques such as PET cannot be applied normally to children for ethical reasons. There are surely many other challenges to the maturation of the field of developmental cognitive neuroscience. The issue of how brain development and cognitive development in the area of language development co-occur in early development and over a lifetime will be one of the key issues in the coming decades of the third millennium. So far, little is known about this issue, but there are first indications that there is much to learn. Improvements in new brain imaging techniques such as fMRI and high-density EEG and MEG methods and the development of new technologies will allow us to investigate these issues. Three central areas should occupy our attention in the coming years. First, the development of particular cognitive and linguistic functions as well as the interaction between these is not independent of brain development. That is, cognitive functions that appear to be modular in the adult behavior may not be informationally encapsulated in early development. For example, highly interconnected brain systems may be tuned toward less interactivity due to particular input. Syntax may be a candidate that follows such a developmental course (Friederici, 1990). After identifying the particular syntactic structures in a given language, the processing of these may become more and more automatic and thereby independent of, for example, lexical semantic information. Second, the relative contribution of the left and the right hemisphere to language processing may well change over life time. There is some recent evidence that infants heavily rely on prosodic information during early language acquisition (Jusczyk, 1997; Kemler Nelson, Hirsh-Pasek, Jusczyk & Wright Cassidy, 1989; Morgan, 1997). From recent fMRI studies in adults we know that prosodic information is mainly processed in the right hemisphere (Steinhauer, Alter, Meyer, Friederici, & von Cramon, 1999; Meyer, Friederici, & von Cramon, 1999). On the basis of these findings one can speculate that the right hemisphere is of major import once for early language acquisition. For an adequate description of the language–brain relationship during early language development it would be important to know whether this assumption about the early involvement of the right hemisphere holds and, moreover, when and under what conditions the left hemisphere comes into play and finally gets dominant in processing language. There is some recent, although somewhat indirect, evidence that early brain lesions (before the age of 2 years) in the right hemisphere lead to more severe deficits in language acquisition that early brain lesions in the left hemisphere (Bates, Thal, Trauner, Fenson, Aram, Eisele & Nass, 1997). This finding seems to support the view of the primary importance of the right hemisphere in early language development. In an overview of a number of studies investigating
MILLENNIUM ISSUE
67
childhood aphasia it became apparent that children between the age of 5 and 8 years demonstrated a nonfluent, Broca-type of aphasia independent of whether the lesion site was left anterior or left temporal (Friederici, 1994). This finding was taken to suggest that a fluent aphasia can only emerge after the language system has reached a highly automatic status. From adult studies we know that highly automatic syntactic procedures are supported by the Broca’s area and/or the left frontal operculum (for an overview see Friederici, 1999). Thus it may not be surprising that adults with lesions in the left temporal region but intact left inferior frontal region show a fluent aphasia. Children, on the other hand, who have not yet developed highly automatic syntactic procedures (to be established in the inferior frontal regions) do not show a fluent aphasia when the temporal region is lesioned (and the inferior frontal region is intact). These data seem to indicate that there is a shift in the relative contribution of the different language-related brain regions over a lifetime. Third, the relative contribution of different subsystems or their coordination in time may also change in late adulthood. Depending on the mechanics and automaticity of different subsystems supporting language processing major shifts of the relative contribution of these will be observed in late adulthood. A first indication comes from recent event-related brain potential studies in normal adults showing that the brain responses to processes of lexical-semantic integration are slowed down (Gunter, Jackson, & Mulder, 1995). Brain responses evoked by early syntactic processes, i.e., first-pass parsing are age independent whereas those correlated processes of structural reanalysis or repair are slowed down with age (Gunter, Vos, & Friederici, 1999). The impact of these differential slowing processes for language comprehension and the possible compensatory mechanisms are not yet specified. In conclusion, it appears that the issue of the language–brain relationship during early development as well as in late adulthood is a terra incognita. This state of affairs is largely due to technological constraints. Recently, we have seen the first results suggesting a rich area of investigation. New brain imaging techniques such as fMRI and further development of neurophysiological methods such as EEG and MEG will provide us with new tools to persue these issues. We just have to learn to use them appropriately (and whenever necessary to adapt the testing procedures) in order to learn about the language brain relation in its developmental course over lifetime. REFERENCES Bates, E., Thal, D., Trauner, D., Fenson, J., Aram, D., Eisele, J., & Nass, R. 1997. From first words to grammar in children with focal brain injury. Developmental Neuropsychology, 13(3), 275–343. Friederici, A. D. 1990. On the properties of cognitive modules. Psychological Research, 52, 175–180.
68
MILLENNIUM ISSUE
Friederici, A. D. 1994. Funktionale Organisation und Reorganisation der Sprache wa¨hrend der Sprachentwicklung: Eine Hypothese. Neurolinguistik, 8, 41–55. Friederici, A. D. 1999. The neurobiology of language comprehension. In A. D. Friederici (Ed.), Language Comprehension: A biological perspective, 2nd edition (pp. 265–304). Berlin/Heidelberg/New York: Springer. Gunter, Th.C., Jackson, J. L., & Mulder, G. (1995). Language memory and aging: An electrophysiological exploration of the N400 during reading of memory demanding sentences. Psychophysiology, 32, 215–229. Gunter, Th.C., Vos, S. H., & Friederici, A. D. 1999. Memory or aging that’s the question: An electroencephalogical perspective on language. In Kemper, S., & Kliegl, R. (Eds.), Constraints on language: Memory, aging, and grammar (249–282). Norwell, MA: Kluwer Academic. Jusczyk, P. W. 1997. The discovery of spoken language. Cambridge, MA: MIT Press. Kemler Nelson, D. G., Hirsh-Pasek, K., Jusczyk, P. W., & Wright Cassidy, K. 1989. How prosodic cues in motherese might assist language learning. Journal of Child Language, 16, 55–68. Meyer, M., Friederici, A. D., & von Cramon, D. Y. (1998). Processing prosody only: Eventrelated fMRI specifies comprehension mechanisms of delexicalised speech. In A. D. Friederici & D. Y. von Cramon (Eds.), Annual report 1998 (pp. 18–19). Leipzig: Max Planck Institute of Cognitive Neuroscience. Morgan, J. L. 1997. A rhythmic bias in preverbal speech segmentation. Journal of Memory and Language, 35, 666–688. Steinhauer, K., Alter, K., Meyer, M., Friederici, A. D., & von Cramon, D. Y. 1999. Brain activation related to prosodic processing in natural speech: An event-related fMRI study. Journal of Cognitive Neuroscience, Suppl., 54.