Phonological picture-word interference in language mapping with transcranial magnetic stimulation: an objective approach for functional parcellation of Broca's region.

Abstract

Functional imaging data suggest different regions for semantic, syntactic, and phonological processing in an anterior-to-posterior direction along the inferior frontal gyrus. Language mapping by use of neuro-navigated transcranial magnetic stimulation (TMS) is frequently applied in clinical research to identify language-related cortical regions. Recently, we proposed a high spatial resolution approach for more detailed language mapping of cortical sub-areas such as Broca's region. Here, we employed a phonological picture-word interference paradigm in healthy subjects to reveal functional specialization in Broca's region for phonological processing. The behavioral phonological priming effect is characterized by accelerated naming responses to target pictures accompanied by phonologically related auditory distractor words. We hypothesized that the inhibitory effects of TMS on language processing would reduce phonological priming only at stimulation sites involved in phonological processing. In active as compared to sham TMS, we found reduced phonological facilitation specifically at sites overlapping with the probabilistic cytoarchitectonic area 44. Our findings complemented functional imaging data by revealing structure-function relationship in Broca's region. The introduction of a reactiontime based interference paradigm into TMS language mapping increases the objectivity of the method and allows to explore functional specificity with high temporal resolution. Findings may help to interpret results in clinical applications.