Neural responses to Finnish inflected forms during overt and covert production: The role of stem frequency and stem allomorphy

Despite extensive behavioral research on complex word recognition, the neural mechanisms involved in the production of inflections in agglutinative languages, such as Finnish, are still poorly understood. Finnish inflected nouns typically involve morphophonological alternations of the stem (i.e. consonant gradation; CG), which is less common in other languages. Behavioral research on recognition of inflected nouns containing consonant gradation has shown that the number of stem allomorphs results in faster recognition times. To our knowledge, no functional magnetic resonance imaging (fMRI) studies have explicitly investigated consonant gradation in word production. In this study, participants performed covert and overt production tasks during event-related fMRI. Our stimuli comprised real word stems of high and medium frequency as well as pseudoword stems. The stems either included consonant gradation or were non-gradating. Our findings showed that the production of inflected forms containing high frequency stems or CG stems (irrespective of frequency and lexicality) yield enhanced activation of the left inferior frontal and middle frontal gyri (LIFG and MFG, respectively). This suggests that CG stems, that is, stems with more than one allomorph, facilitate lexical lookup, and that the activation of multiple stem allomorphs is reflected in increased recruitment of frontal brain regions.