gms | German Medical Science

Objective: Repetitive navigated transcranial magnetic stimulation (rTMS) is able to elicit language errors by stimulation of language eloquent brain regions. However, the current protocols need to undergo further improvement in order to improve specificity and predictive values. Thus, this study investigates the impact of rTMS coil position and stimulation parameters on language mapping.

Method: Five purely right-handed healthy subjects underwent rTMS language mapping of Broca’s area and Wernicke’s area. After resting motor threshold (RMT) determination 3 different parameters were examined: angulation, frequency, and intensity. For angulation, the anterior-posterior (ap) coil orientation was used as reference position. Stimulation within both areas was performed as follows:

1.

Angulation: variation in steps of 45° (beginning with ap coil orientation), 10 stimulations per position (8 positions = 80 stimulations).

2.

Frequency: stimulation with 5, 7, 10, and 20 Hz in ap and optimal orientation (as found in 1), 10 stimulations per position and frequency (4 frequencies x 2 positions x 10 = 80 stimulations).

3.

Intensity (% RMT): stimulation with 100%, 80% and 120% RMT in ap and optimal orientation, 10 stimulations per position and intensity (3 intensities x 2 positions x 10 = 60 stimulations).

Results: Ap orientation was defined as the optimal position in no case, and a higher frequency as well as a higher intensity lead to an increased number of language errors at Broca’s and Wernicke’s area:

1.

Angulation: Angulation of 90° to ap coil orientation lead to the highest amount of language errors within Broca’s area in 3 cases. With regard to Wernicke’s area, an inhomogeneous distribution of coil angulations was observed.

2.

Frequency: 20 Hz was defined as the optimal frequency in 2 cases at Broca’s area and in 3 cases at Wernicke’s area.

3.

Intensity: During stimulation of Broca’s as well as Wernicke’s area, an intensity of 120% RMT was defined as optimal in 3 cases, whereas 100% RMT lead to the most language disturbances in 2 cases.

Conclusions: Angulation, frequency, stimulation intensity have a significant impact on language impairment during rTMS language mapping. Variation of only one parameter already causes clearer impairment of language performance. Therefore, individually adapted stimulation parameters have to be determined prior to language mapping in order to improve mapping results for the individual patient.