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Cereb Cortex. 2016 Jun;26(6):2590-2601. doi: 10.1093/cercor/bhv092. Epub 2015 May 7.

Dissociating Parieto-Frontal Networks for Phonological and Semantic Word Decisions: A Condition-and-Perturb TMS Study.

Author information

1
Language and Aphasia Laboratory, Department of Neurology, University of Leipzig, D-04103 Leipzig, Germany.
2
Max Planck Institute for Human Cognitive and Brain Sciences, D-04103 Leipzig, Germany.
3
Department of Psychology, Christian-Albrechts-University, D-24118 Kiel, Germany.
4
Danish Research Centre for Magnetic Resonance, Copenhagen University Hospital Hvidovre, 2650 Hvidovre, Denmark.
5
Human Cortical Physiology and Motor Control Laboratory, Department of Neurology, University of Leipzig, D-04103 Leipzig, Germany.

Abstract

Left posterior inferior frontal gyrus (pIFG) and supramarginal gyrus (SMG) are key regions for phonological decisions, whereas angular gyrus (ANG) and anterior IFG (aIFG) are associated with semantics. However, it is less clear whether the functional contribution of one area changes in the presence of a dysfunctional area within the network. Using repetitive transcranial magnetic stimulation (rTMS), we first tested whether perturbing one area would disrupt behavior. Second, we applied a condition-and-perturb approach, combining parietal offline rTMS with frontal online rTMS to investigate how the functional contribution of a frontal region changes in the presence of a dysfunctional parietal region. We found that rTMS over SMG or pIFG delayed phonological decisions, but this was not enhanced by combining supramarginal rTMS with pIFG rTMS. In contrast, semantic decisions were only impaired when angular rTMS was combined with aIFG rTMS. We infer that offline rTMS caused a dysfunction of ANG which increased the functional relevance of aIFG for semantic decisions and sensitized this network to the disruptive effects of aIFG rTMS. The results provide causal evidence that ANG and aIFG contribute to semantics and that the functional significance of one area within this network depends on the functional integrity of the other.

KEYWORDS:

inferior frontal gyrus; language; parietal cortex; transcranial magnetic stimulation; virtual lesion

PMID:
25953770
DOI:
10.1093/cercor/bhv092
[Indexed for MEDLINE]

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