Probing the involvement of the right hemisphere in language processing with online transcranial magnetic stimulation in healthy volunteers

Abstract

Background: Current models emphasize that language-related functions are predominantly organized in left-lateralized fronto-temporo-parietal cortical networks.

Aims: In this review, we summarize how “online” transcranial magnetic stimulation (TMS) during a language task can be used in healthy individuals to characterize the contribution of the stimulated area to a specific language function with a focus on the functional relevance of the right hemisphere. We first give an introduction to some basic mechanisms of TMS and outline the prerequisites for carrying out TMS studies of language. In particular, we highlight some methodological limitations and pitfalls of the TMS approach. We then review online TMS studies of language processing with a particular focus on the contribution of right hemisphere brain regions to language processing.

Main Contribution: The majority of TMS studies on language have targeted a single left- hemisphere cortical area during a language task to identify the relevance of that area for a specific aspect of language processing. TMS has also been used to characterize the involvement of homologous right hemisphere regions. These studies have provided evidence for a significant role of right hemisphere regions in different aspects of language processing, including word comprehension, reading and paralinguistic features like emotional prosody.

Conclusions: Recently, two areas have been targeted simultaneously with TMS while subjects performed a language task. This multifocal TMS approach has opened up new possibilities to compare the functional involvement of homologous regions in the right and left hemisphere and allows for the characterization of interhemispheric compensation during language processing.

Keywords:

• Compensation
• Lesion
• Lateralization
• Broca
• Wernicke
• Speech

Acknowledgments

GH and HRS were supported by a Grant from the “Bundesministerium fuer Bildung und Forschung” (BMBF; Grant 01GW0663), Germany. HRS was supported by a Grant of Excellence on the Control of Actions “ContAct” from the Lundbeck Foundation (R59 A5399), Denmark.