Phonotactic violations and case violations activates the left inferior frontal gyrus

The structured sequence processing perspective on language describes common aspects of processing of language, musical and action sequences. For instance, syntactic structure across sequences of word or word categories enables prediction of e.g. the case of words further down the sentence. When presenting violations to sequential regularities in natural or artificial syntax, a common finding is left inferior frontal gyrus (LIFG) activation, indicating the involvement of LIFG in structured sequence processing. However, to our knowledge, only one FMRI-study (Nieuwland, 2011) investigated activity by (Basque) case violations and did not find LIFG activation. In phonology, especially its sub-domain phonotactics, there is structure in phoneme and syllable sequences. So far, one FMRI-study (Vaden, 2011) investigated their brain level substrate using a phonotactic frequency manipulation. High (spill, probe) vs. low (sneak, jolt) phonotactic frequency activated the anterior LIFG. The present FMRI-study (we present results from the first 12 out of 24 planned participants) manipulates syntactic case and phonotactics at the sentences final noun phrase of sentences with high cloze probability. Across participants, the same German sentences appeared in one of three conditions: correct, syntactically incorrect (using a case violation on the sentence final noun phrase) and phonotactically incorrect (using a phonotactically illegal sound cluster in the sentence final word). A pilot study (N=5) indicated that both phonotactic and syntactic violations would activate the LIFG in at least one of three regions of interest (ROIs): the pars opercularis, the pars triangularis and the pars orbitalis. Neither of the two main effects: syntactically incorrect vs. correct and phonotactically incorrect vs. correct generated any significant clusters at FWE correction 0.05 on the whole brain level. In our planned ROI-analysis with a focus on LIFG, the syntactic violations activated pars triangularis while the phonotactic contrast activated pars opercularis and pars triangularis. Our results show that phonotactic violations and syntactic case violations activate LIFG, which is expected from the point of view that LIFG is involved in structured sequence processing in natural language. In our design which controlled for the exact lexical items used, phonotactic violations resulted in activation in the posterior LIFG. In Vaden (2011), phonotactic frequency activated the more anterior parts of LIFG, for high vs low phonotactic frequency. The degree of lexical control, or alternatively our violation (rather than frequency) manipulation, might have caused the differences. In any case, together, these two studies provide a basis for the study of phonotactic representation in LIFG. Since both our phonotactic violations and syntactic case violations activate LIFG at the group level, our paradigm provides a good test bed for investigating neural representation of syntax and phonotactics in LIFG at the single subject level. The single subject approach might increase sensitivity when testing for functional specialization