Phonological decisions require both the left and right supramarginal gyri

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 107; no. 38; pp. 16494 - 16499
• Main Authors: Hartwigsen, Gesa, Baumgaertner, Annette, Price, Cathy J., Koehnke, Maria, Ulmer, Stephan, Siebner, Hartwig R.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 21.09.2010; National Acad Sciences
• Subjects: Adult; Anatomy; Articulation disorders; Auditory Perception; Auditory stimulation; Brain; Brain Mapping; Cerebral hemispheres; Decision Making; Female; Functional Laterality - physiology; Humans; image analysis; Information processing; Language; Lateral stability; Lesions; Magnetic Resonance Imaging; Male; NMR; Nuclear magnetic resonance; Parietal Lobe - physiology; Patients; Phonetics; Reaction Time - physiology; Semantics; Social Sciences; Transcranial Magnetic Stimulation; Visual stimulation; Young Adult
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1008121107

Recent functional imaging studies demonstrated that both the left and right supramarginal gyri (SMG) are activated when healthy right-handed subjects make phonological word decisions. However, lesion studies typically report difficulties with phonological processing after left rather than right hemisphere damage. Here, we used a unique dual-site transcranial magnetic stimulation (TMS) approach to test whether the SMG in the right hemisphere contributes to modality-independent (i.e., auditory and visual) phonological decisions. To test task-specificity, we compared the effect of real or sham TMS during phonological, semantic, and perceptual decisions. To test laterality and anatomical specificity, we compared the effect of TMS over the left, right, or bilateral SMG and angular gyri. The accuracy and reaction times of phonological decisions were selectively disrupted relative to semantic and perceptual decisions when real TMS was applied over the left, right, or bilateral SMG. These effects were not observed for TMS over the angular gyri. A follow-up experiment indicated that the threshold-intensity for inducing a disruptive effect on phonological decisions was identical for unilateral TMS over the right or left SMG. Taken together, these findings provide converging evidence that the right SMG contributes to accurate and efficient phonological decisions in the healthy brain, with no evidence that the left and right SMG can compensate for one another during TMS. Our findings motivate detailed studies of phonological processing in patients with acute or long-term damage of the right SMG.