gms | German Medical Science

Objective: Repetitive navigated transcranial magnetic stimulation (rTMS) has recently been used as non-invasive technique to study language organization in patients and healthy subjects. However, former mapping protocols revealed deficits of this method, mainly in posterior brain regions. In contrast to previous investigations which especially examined language interruption during an object naming task, this study provides data for three further language tasks compared by two different mapping setups. Hence, this study was designed to compare the effectiveness of different tasks as well as to potentially reveal language sub function, to examine the impact of different mapping frequencies on the error rate and location.

Method: 19 healthy, right-handed subjects (10 female, 9 male) underwent rTMS language mapping of the left hemisphere for two times. Thereby we stimulated 46 previously determined cortical spots, which were distributed over the entire hemisphere. The mapping was performed by four different language tasks: object naming, pseudo-word reading, verb generation, and verb naming. For the first mapping session 5 Hz/10 pulses were applied, the second mapping followed by 7 Hz/10 pulses (0 ms delay). Errors evoked by the stimulation were divided in seven different error categories. The same examiner conducted both investigations; time span between both mappings was 13-15 days.

Results: During both mapping sessions the object naming task evoked the highest error rate (5 Hz 14%, 7 Hz 12%), followed by verb generation (5 Hz 13%, 7 Hz 11%), and verb naming task (5 Hz 11%, 7 Hz 9%). The pseudo-word reading task barely generated errors at all (error rates 5 Hz 4%, 7 Hz 3%). Nevertheless, it showed the highest phonological error rate. With regard to the different applied frequencies our data shows that the mapping frequency affects error occurrences. In all task types (except for pseudo-word reading), when stimulating with 5 Hz, in anterior regions the error rate was significant higher than with 7 Hz stimulations. Furthermore, some error types were more frequent in anterior regions when applying lower frequency, whereas others appear more often in anterior regions applying higher frequency.

Conclusions: In general, the object naming task is the most discriminative test to detect language positive regions in rTMS, at least out of the examined 4 broadly-used tests. However, the other described language tasks can be used for more specific questions.