Localization of the syntactic mismatch negativity in the temporal cortex: an MEG study

Recent auditory oddball studies using syntactic stimuli report a syntactic effect on the mismatch negativity (sMMN) around 100-200 ms. For morphosyntactic violations, this sMMN effect has been localized in the left superior temporal cortex. Independently, a recent visual sentence processing study introduced a "sensory hypothesis" which postulates that sensory cortices are sensitive to syntactic violations when these are overtly marked by closed-class morphemes, and thus contribute to early syntax-related effects in EEG and MEG. The present study aimed to test the sensory hypothesis in the auditory modality by localizing the neuronal sources of the sMMN to phrase structure violations. Using whole head magnetoencephalography, two-word utterances which were syntactically correct, uncommon or incorrect due to a word category violation were presented in an auditory oddball paradigm. In the sMMN time window (100-180 ms), incorrect phrases elicited strongest activation in the left Sylvian fissure (including the primary auditory cortex) and in the left superior temporal sulcus. Prior to this, a very early grammaticality effect (40-80 ms), focused in the left Sylvian fissure, was found. An additional grammaticality effect in a later time window (280-380 ms) was localized in the anterior part of the superior temporal gyrus, the planum polare. Processing of an uncommon phrase did not differ from processing a correct phrase in any of the time windows, indicating the genuinely syntactic nature of the sMMN effect. Our results are in line with previous studies localizing the sMMN to morphosyntactic violations and are furthermore compatible with the sensory hypothesis of closed-class morphology based syntactic processes.