The role of left temporo-parietal and inferior frontal cortex in comprehending syntactically complex sentences: A brain stimulation study.

Anodal transcranial direct current stimulation (a-tDCS) over left temporo-parietal cortex enhances comprehension of complex sentences in uncompromised young speakers. Since a-tDCS over left frontal cortex did not elicit any change, the 'bottleneck' for the understanding of complex sentences seems to be the posterior, temporo-parietal rather than the anterior inferior-frontal 'hub' of language processing. Regarding the attested role of inferior-frontal cortex in syntax processing, we suggest that its function is optimized in competent young speakers, preventing further enhancement by (facilitatory) tDCS. Results shed light on the functional anatomy of syntax processing during sentence comprehension; moreover, they open perspectives for research in the lesioned language network of people with syntactic deficits due to aphasia.