Slide Slam K9
Compositional meaning influences the BOLD response in language critical cortex via interaction between LIFG and LMTG
Daniel Sharoh1, Kirsten Weber2, Lenno Ruijters1, David Norris1, Peter Hagoort1,2; 1Donders Institute for Brain, Cognition and Behaviour, 2Max Planck Institute for Psycholinguistics
Left inferior frontal gyrus(LIFG)has been proposed to exhibit hub-like properties in various network contexts, often in the context of brain networks observed during language experiments(Hagoort,2014).Specifically,it has been claimed that LIFG facilitates the construction of combinatorial representations derived from linguistic input and known world-information via bi-directional interactions with other brain regions(Hagoort,2017). If so,then traces of this functionality should be observable in terms of LIFG related, brain-network BOLD activity, both via a top-down route which might target regions that respond more acutely to individual words,and via its own response to bottom-up signaling from these same regions.The combinatorial procedures underlying these dynamics are assumed to give rise to sentence-level meaning, which can’t be explained in terms of the lexical meanings of individual words.METHODS:To investigate this,we designed a priming experiment.Participants were asked to read well-formed sentences and scrambled versions of these sentences,in which the word order did not form a proper sentence.Sentences and their scrambled versions were followed by a target-word.Target-words related to the preceding text in one of four distinct manners.Targets could be(1)primed by the compositional meaning of a sentence,(2)primed by repetition of a single word that was embedded in a sentence,(3)primed by repetition of a single word embedded in a scramble,or(4)not primed at all by the preceding scramble.Repetition primes were expected to facilitate lexical access,but they were not expected to influence top-down information available to the core language network via signaling from LIFG. By including a manipulation whereby a repetition-prime was also embedded in a scramble,it was possible to dissociate repetition priming from compositional/repetition-priming effects.We were thus able to observe three modes of priming(1.compositional only,2.compositional with repetition,and 3.repetition only).This allowed us to test the prediction that LIFG generally facilitates unification in the linguistic domain with broadly contoured compositional information,beyond more specific phonological,semantic or syntactic combinatorial processes. A 3T fMRI experiment(n=19)was performed in which participants read prime/target pairs via word-by-word presentation while in the scanner.No experimentally relevant task was performed during the experiment.RESULTS:Group-level results showed a BOLD contrast in LIFG during the reading of a compositional-target compared with a sentence/repetition-target. This suggests that compositional information drove LIFG activity differently in the absence of repetition priming.Additional contrasts probing the response differences between primes and targets were also analyzed, and support the interpretation that sentence/compositional-targets are processed using the same network as used when reading the priming sentences.A subsequent gPPI connectivity analysis was performed using individualized LIFG ROIs based on the group contrast described above.The group level connectivity profile associated with this contrast revealed an interaction with left middle temporal gyrus.CONCLUSION:Together, the results provide evidence that sentence/repetition priming facilitated lexical access in LMTG by providing an additional means of priming beyond the compositional route.This resulted in reduced BOLD throughout language critical cortex,mediated by an interaction with LIFG. In contrast, sentence/compositional priming resulted in increased BOLD in similar brain regions,most prominently in LIFG. Interpreted in light of the gPPI result,we argue that dynamic connectivity of LIFG with LMTG during word reading contributes to establishing compositional representations,referring to sentence-level meaning beyond the lexical meanings of individual words.