Functional Neuroimaging of Sentence Comprehension.

Abstract:
We hypothesize that grammatically-defined processing demands contribute to sentence comprehension. We monitored cerebral activity with fMRI in seven healthy, right-handed native English speakers while they determined the agent of the action. Each sentence contained an antecedent noun phrase (NP) and a center-embedded clause with a "gap" where the NP is interpreted. Half the sentences contained a seven-word span between NP and gap ("long"); half contained a three-word span ("short"). For each of these two settings, half of the clauses were subject-relative (SR), preserving canonical word order; half were object-relative (OR), violating canonicity. Subjects saw eight 40-sec blocks of each sentence type presented visually word-by-word for 500 and 750 msec/word. SR-short and OR-short sentences activated left posterior-superior temporal cortex. SR-long sentences additionally recruited the right hemisphere homologue. OR-long sentences also activated left inferior frontal, left caudate, and left hippocampal regions. These data suggest that sentence comprehension is sustained by left posterior-superior temporal and inferior frontal regions. Syntactic constraints provided by antecedent-gap linkages in non-canonical sentences attempt to block the construction of a canonical representation. The mismatch between the input and what the cognitive system constructs, in the setting of lengthy antecedent-gap linkages, may require a recovery operation subserved by left inferior frontal cortex.