gms | German Medical Science

Objective: Repetitive navigated transcranial magnetic stimulation (rTMS) in clinical practice is of particular importance for the mapping of cortical language areas. Yet, further studies have tried to detect cortical areas for other neuropsychological functions as well. The aim of this investigation is to localize cortical areas that can be assigned for the function of visuospatial attention by eliciting its referring deficit known as visual neglect.

Method: Ten healthy subjects (5 male, 5 female, all right-handed, mean age 25.8 years) underwent two sessions of rTMS mapping on either side of a two-week stimulation-free period. We applied trials of repetitive pulses at the frequency of 5 Hz (one trial containing 10 pulses) to 52 pre-defined cortical spots on each hemisphere. For the analysis, these spots were transferred into the cortical parcellation system. Visuospatial attention was tested by two different tasks: the greyscale and the landmark task. All subjects performed both tasks, randomly in the first or second session. Setting, screen and picture presentation were used the same as for rTMS language mapping with a picture to trigger interval of 0 ms. The subject's performance was recorded and analysed by video.

Results: With a mean baseline error rate of less than 4% for the landmark task, we found a short display time of 50 ms to be feasible. The greyscale task was designed at a difficulty level of 0 measuring subtle visuospatial tendencies without classifying into right or wrong. Effects by rTMS compared to the performance without stimulation can be shown for both tests. The distribution of the identified cortical areas is provided by cortical maps.

Conclusions: Visual neglect can be elicited non-invasively by rTMS. Its use for pre-surgical mapping has to be shown in upcoming steps.