«Subjective language aptitude is linked to neural activity in Broca’s area, but not to objective performance during a semantic priming task»

Language, including speech and thought, is often affected in mental illnesses. In psychosis, the dimension of language symptoms shows a great variability between patients. A dimensional approach allows to study language as continuum from health to psychosis. Therefore, in the current study, we investigated the heterogeneity of a healthy population during a language task, additionally to a subjective rating of one’s language aptitude. The aim was to analyze the spectrum of inter-individual differences and its association with language-related brain networks, specifically Broca’s area. The observed heterogeneity in the healthy group would enable an extrapolation to clinical end of the spectrum. To this end, 102 healthy adult subjects performed a lexical priming task while measuring brain activity with fMRI. Subjects had to indicate whether a visually presented target word would form the generic term of a previously shown a prime word, in terms of its category (e.g. Apple – Fruit) or its relation (e.g. Apple – Pear). To see the difference in language aptitude, we asked the participants to rate on 7-point Likert scale, how they thought their language abilities are. According to the rating they were then grouped into high, mid or low language aptitude groups. Although reaction time (RT) and accuracy showed no significant differences between all three groups, we found differences in brain activation in BA45 among the language aptitude groups. We looked at activation in the Broca areas (BA45, BA44) during preparation (waiting for the target after the indication of task type) and processing (target word processing) phases. We found differences between the groups in BA45 during the preparation and processing phases. The Post hoc analysis revealed that the high group showed significantly greater activation in BA45 compared to the low group, while there was no significant difference between the groups in BA 44. Furthermore, the RT was correlated with activation of BA 45 in the high language aptitude group during the preparation phase, indicating that increased activation in BA45 reflects faster responses in the high language aptitude group. Moreover, for the other two groups correlations with RT were found in BA44. These results show that, according to subjective evaluation of their own language aptitude, one differently utilizes the language-related brain areas during the language task. These insights into the dimension of language is facilitating upcoming research, that compares these healthy population profiles to the profiles of a population with psychosis.