Functional MR imaging exposes differential brain responses to syntax and prosody during auditory sentence comprehension

Abstract

In two experiments using event-related functional magnetic resonance imaging we studied healthy adults who listened to sentences that either focused on lexical, syntactic, or prosodic information. In the first experiment two sentence conditions were employed: normal speech which contained function and content words, and pseudo speech which contained function and pseudo words. Sentence processing generally activated the superior temporal region (STR) bilaterally. Relative to normal sentences hearing pseudo sentences corresponded to stronger brain responses in the anterior STR (planum polare) and in the fronto-opercular region bilaterally. A second experiment was designed to test whether right hemisphere activation can be explained by processing prosodic aspects of speech, i.e. sentence intonation. In addition to normal and pseudo speech the second study examined degraded speech that neither contained morphosyntactic nor lexical information but only prosodic information, i.e. intonation, amplitude, duration, and spectral tilt. Statistical analyses based on regions of interest found differential activation patterns for frontal and temporal areas in the brain. Relative to sentences, degraded speech produced generally stronger activation in frontal regions. Furthermore, the data pointed to a particular involvement of right fronto-lateral regions in processing sentence melody. For the STR an inverse pattern was found: relative to degraded speech sentence conditions produced stronger activation in anterior, mid, and posterior parts of the left supratemporal plane, particular in the planum polare and planum temporale. In sum, the results show that the left planum polare and the left planum temporale mediate syntactic and semantic processing, whereas right fronto-lateral areas seem to be more sensitive to prosodic cues available in spoken language.