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Identification of Functional Connectivity among Cortical Language
Areas with Trallscranial Magnetic Stimulatioll
tt*;PJfJ'E~*Ec*~*~~~*B~%Jt1~;PJfJ'E~4lij]fj[~It is a central issue in cognitive neuroscience whether language ability is specialized in thehuman brain. We found that transcranial magnetic stimulation (TMS) to the left inferior
frontal gyrus (Broca's area) results in selective priming effects on syntactic decisions, but noton semantic decisions. This effect is observed at a specific timing and location, as the stimu­
lation to the left middle frontal gyrus has no significant effect. These results provide thedirect evidence of the involvement of Broca's area in syntactic processing. To further visual­ize cortical activations during TMS, single-pulse TMS was applied to the left primary motorarea, and cortical responses at the stimulation site were measured simultaneously with event­related optical topography (OT). When TMS was applied at 110% motor threshold (MT) ,we observed significant oxyhemoglobin increases that were both time-locked and correlatedwith the hen10dynamic basis function. Moreover, when TMS was applied at 90% MT, signifi­
cant oxyhemoglobin increases were detected even though there were no motor-evoked poten­
tials. These results confirmed that OT can directly measure cortical responses to subthresholdsingle-pulse TMS.
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Sakai, K. L., Noguchi, Y., Takeuchi,
T. & Watanabe, E. (2002), Selective
priming of syntactic processing by event-related transcranial magnetic stimula·(2)tion of Broca's area. Neuron 35, 1177­
1182.
Noguchi, Y., Watanabe, E. & Sakai, K.
L. (2003). An event-related optical
topography study of cortical activationinduced by single-pulse transcranial
magnetic stimulation. N eurolmage 19,156-162.

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