Syntax and the brain: Disentangling grammar by selective anomalies

Many paradigms employed so far with functional imaging in language studies do not allow a clear differentiation of the semantic, morphological, and sy ntactic components, as traditionally defined within linguistic theory. In f act, many studies simply consider the brain's response to lists of unrelate d words, rather than to syntactic structures, or do not neutralize the conf ounding effect of the semantic component. In the present PET experiment, we isolated the functional correlates of morphological and syntactic processi ng. The neutralization of the access to the lexical-semantic component was achieved by requiring the detection of anomalies in written sentences consi sting of pseudowords. In both syntactic and morphosyntactic processing, the involvement of a selective deep component of Broca's area and of a right i nferior frontal region was detected. In addition, within this system, the l eft caudate nucleus and insula were activated only during syntactic process ing, indicating their role in syntactic computation. These findings provide original in vivo evidence that these brain structures, whose individual co ntribution has been highlighted by clinical studies, constitute a neural ne twork selectively engaged in morphological and syntactic computation. (C) 2 001 Academic Press.