High-resolution language mapping of Broca’s region with transcranial magnetic stimulation
Broca’s region, corresponding roughly to cytoarchitectonic areas 44 and 45 in the inferior frontal cortex, holds a multifunctional role in language processing, as shown, e.g., by functional imaging data. Neuro-navigated transcranial magnetic stimulation (TMS) enables complementary non-invasive mapping of cortical functions with high spatial resolution. Here, we report on detailed TMS language mapping of Broca’s region in 12 healthy participants. The test protocol with an object naming task was adapted for high-resolution and semi-quantitative mapping of TMS-induced effects on speech and language performance. Hierarchical cluster analysis of normalized ratings of error frequency and severity revealed a clear focus of TMS impact at dorso-posterior target sites, close to the inferior frontal junction. Adjacent clusters of moderate and slightly affected stimulation sites yielded a posterosuperior-to-anteroinferior gradient of TMS susceptibility. Our findings indicate that the part of Broca’s region most susceptible to TMS-induced language inhibition in object naming is located in the dorsal area 44.
KeywordsCytoarchitectonic mapping Transcranial magnetic stimulation Language mapping Broca’s region Hierarchical cluster analysis
We would like to thank Julia Amunts for valuable help in stimulus selection, material preparation, and data analysis assistance as well as Johanna Blume-Schnitzler for support with data acquisition and analysis. For excellent technical advice and support, we thank Uli Heuter of the Audio-Visual-Media-Centre of the Faculty of Medicine, RWTH Aachen University. For their endurance through the process of exporting the stimulation markers, we thank Johanna Blume-Schnitzler and Jonas Ort. Hong Chen and Simon Koppers programmed valuable MATLAB scripts, and Ryssa Moffat (Ottawa, Canada) proofread the manuscript. Finally, we send cordial thanks to our volunteers for their participation.
Compliance with ethical standards
This research project was supported by a grant from the START Programme [25/14] of the Faculty of Medicine, RWTH Aachen University. The funding source had no involvement in study design, in collection, analysis and interpretation of data, in writing of the report, and in the decision to submit the article for publication.
Our experimental standards and all procedures performed in this study involving human participants were in accordance with the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards and were approved by the local ethics committee [EK 054/13]. Prior to investigation, we obtained written informed consent from all of our volunteers. This article does not contain any studies with animals performed by any of the authors.
Conflict of interest
The authors declare that they have no personal financial or institutional interest in any of the materials or devices described in this paper.
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