Abstract
BackgroundAlthough language mapping by repetitive navigated transcranial magnetic stimulation (rTMS) gains importance in neuropsychological research and clinical utility, neuroscientists still use different mapping protocols including different stimulation frequencies. To refine the existing language protocol, we tested two different repetition rates of 5 Hz/10 pulses and 7 Hz/10 pulses with a 0 ms delay in 19 healthy subjects. We furthermore investigated differences between both frequencies in case of performance of four different language tasks: object naming, pseudoword reading, verb generation, and action naming.ResultsEven the small variance in frequencies revealed statistically significant differences concerning the number and type of language errors. Stimulation with 5 Hz evoked a higher number of all occurred language errors in all language tasks (error rate object naming 14% (5 Hz) vs. 12% (7 Hz); pseudoword reading 4% (5 Hz) vs. 3% (7 Hz); verb generation 13% (5 Hz) vs. 11% (7 Hz); action naming 11% (5 Hz) vs. 9% (7 Hz)), whereas 7 Hz evoked specifically more total speech arrests.ConclusionThese findings suggest that the stimulation frequency has to be adapted to the aim of the rTMS language investigation.
Highlights
Language mapping by repetitive navigated transcranial magnetic stimulation gains importance in neuropsychological research and clinical utility, neuroscientists still use different mapping protocols including different stimulation frequencies
Thereby, several protocols have been tested by using different stimulus parameters, which has probably contributed to the high inter-study variability in occurrence of language errors
Language errors induced by different frequencies Sum of all errors When taking into account all error categories, during all four language tasks our data showed higher error rates at a repetition rate of 5 Hz than at 7 Hz repetition rate (Figure 2a; Table 3)
Summary
Language mapping by repetitive navigated transcranial magnetic stimulation (rTMS) gains importance in neuropsychological research and clinical utility, neuroscientists still use different mapping protocols including different stimulation frequencies. In 1991, Pascual-Leone et al performed the first repetitive transcranial magnetic stimulation (TMS) language study in order to find a noninvasive method to determine the language-dominant hemisphere [1]. Thereby, several protocols have been tested by using different stimulus parameters, which has probably contributed to the high inter-study variability in occurrence of language errors. Initial TMS language studies used high frequencies up to 32 Hz and trains of up to 10 s (e.g., [1,2,4]), which resulted in discomfort. Because higher frequencies led to more discomfort due to increased muscle stimulation, Epstein et al suggested 4-8 Hz to be the best ratio of efficacy to pain
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