Abstract
Transcranial magnetic stimulation (TMS) has been used to induce speech disturbances and to affect speech performance during different naming tasks. Lately, repetitive navigated TMS (nTMS) has been used for non-invasive mapping of cortical speech-related areas. Different naming tasks may give different information that can be useful for presurgical evaluation. We studied the sensitivity of object and action naming tasks to nTMS and compared the distributions of cortical sites where nTMS produced naming errors. Eight healthy subjects named pictures of objects and actions during repetitive nTMS delivered to semi-random left-hemispheric sites. Subject-validated image stacks were obtained in the baseline naming of all pictures before nTMS. Thereafter, nTMS pulse trains were delivered while the subjects were naming the images of objects or actions. The sessions were video-recorded for offline analysis. Naming during nTMS was compared with the baseline performance. The nTMS-induced naming errors were categorized by error type and location. nTMS produced no-response errors, phonological paraphasias, and semantic paraphasias. In seven out of eight subjects, nTMS produced more errors during object than action naming. Both intrasubject and intersubject analysis showed that object naming was significantly more sensitive to nTMS. When the number of errors was compared according to a given area, nTMS to postcentral gyrus induced more errors during object than action naming. Object naming is apparently more easily disrupted by TMS than action naming. Different stimulus types can be useful for locating different aspects of speech functions. This provides new possibilities in both basic and clinical research of cortical speech representations.
Highlights
Transcranial magnetic stimulation (TMS) is a noninvasive technique where a strong and brief magnetic pulse is delivered to the brain and induces electrical currents
Naming errors were induced when Navigated TMS (nTMS) was delivered to angular gyrus, inferior frontal gyrus (IFG), middle frontal gyrus (MFG), postcentral gyrus (PoG), precentral gyrus (PrG), superior temporal gyrus (STG), middle temporal gyrus (MTG), and supramarginal gyrus (SMG) (Table 1 and Figure 2)
In the object naming task, 25% of the sites associated with naming errors were located in the PoG, 23% in the STG, 19% in the IFG, 12% in the PrG, 9% in the SMG, 8% in the MTG, 3% in the MFG, and 2% in the angular gyrus (anG) (Table 1 and Figure 2)
Summary
Transcranial magnetic stimulation (TMS) is a noninvasive technique where a strong and brief magnetic pulse is delivered to the brain and induces electrical currents. We studied the sensitivity of object and action naming tasks to nTMS and compared the distributions of cortical sites where nTMS produced naming errors. Two studies have used object naming and nTMS to compare language mapping on patients with brain tumors and healthy subjects, suggesting tumor-induced plasticity of speech representation areas (Krieg et al, 2013; Rösler et al, 2013).
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