Cognitive control and parsing: reexamining the role of Broca's area in sentence comprehension.

A century of investigation into the role of the human frontal lobes in complex cognition, including language processing, has revealed several interesting but apparently contradictory findings. In particular, the results of numerous studies suggest that left inferior frontal gyrus (LIFG), which includes Broca's area, plays a direct role in sentence-level syntactic processing. In contrast, other brain-imaging and neuropsychological data indicate that LIFG is crucial for cognitive control--specifically, for overriding highly regularized, automatic processes, even when a task involves syntactically undemanding material (e.g., single words, a list of letters). We provide a unifying account of these findings, which emphasizes the importance of general cognitive control mechanisms for the syntactic processing of sentences. On the basis of a review of the neurocognitive and sentence-processing literatures, we defend the following three hypotheses: (1) LIFG is part of a network of frontal lobe subsystems that are generally responsible for the detection and resolution of incompatible stimulus representations; (2) the role of LIFG in sentence comprehension is to implement reanalysis in the face of misinterpretation; and (3) individual differences in cognitive control abilities in nonsyntactic tasks predict correlated variation in sentence-processing abilities pertaining to the recovery from misinterpretation.