Stimulation frequency determines the distribution of language positive cortical regions during navigated transcranial magnetic brain stimulation

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.

Results on the spatial resolution of repetitive transcranial magnetic stimulation for cortical language mapping during object naming in healthy subjects

“…Mappings were successfully performed in 19 healthy, right-handed volunteers, which were already analyzed for different purposes in previous investigations [11, 12]. Table 2 gives an overview of subject-related characteristics and mapping parameters.…”

“…However, these regions showed error rates to a higher extent when it comes to other error categories, which were incorporated into analysis of the same dataset in other publications focusing on different purposes [11, 12]. Hence, considerable error rates were achieved during mapping of the opIFG and trIFG, but belonging to other types than no responses.…”

“…All mapping sessions were originally performed in 19 healthy, right-handed (as indicated by the Edinburgh Handedness Inventory = EHI) subjects in 2013 to investigate different research questions of rTMS-based language mapping [11, 12]. The enrolled volunteers were German native speakers without general transcranial magnetic stimulation (TMS) exclusion criteria (e.g., metal implants).…”

“…The task consisted of a total amount of 100 colored photographs, similar to the objects of the Snodgrass and Vanderwart picture set (1980) [11–13]. The photographs portrayed familiar living as well as non-living objects (e.g., banana, chair, snake), and had to be named in German as quickly and precisely as possible.…”

“…Overall, 46 left-hemispheric cortical spots, which were manually tagged on the 3-D MRI scan of the volunteer prior to mapping, were stimulated three times each in a row without any particular order (Fig. 1), as reported previously [11, 12]. Thus, mapping was carried out over predefined spots.

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