Specific and nonspecific effects of transcranial magnetic stimulation on picture–word verification

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Abstract
Repetitive transcranial magnetic stimulation (rTMS) can temporarily impair or improve performance, including language processing. It remains unclear, however, (i) which scalp sites are most appropriate to achieve the desired effects and (ii) which experimental setups produce facilitation or inhibition of language functions. We assessed the effects of TMS at different stimulation sites on picture-word verification in healthy volunteers. Twenty healthy volunteers with left language lateralization, as determined by functional transcranial Dopplersonography, performed picture-word verification prior to and after rTMS (1 Hz for 600 s at 110% of subjects' resting motor thresholds). Stimulation sites were the classical language areas (Broca's and Wernicke's), their homolog brain regions of the right hemisphere, and the occipital cortex. Additionally, sham stimulation over Broca's area was applied in a subsample of 11 subjects. As a control task, 10 volunteers performed a colour-tone matching task under the same experimental conditions. There was a general nonspecific arousal effect for both verum and sham TMS for both the picture-word verification and for the control task. However, superimposed there were opposite effects on picture-word verification for stimulation of Wernicke's area and Broca's area, namely a relative inhibition in the case of Wernicke's area and a relative facilitation in the case of Broca's area. These results demonstrate that low frequency rTMS has both general arousing effects and domain-specific effects.