Datensatz

Zusammenfassung

Focal transcranial magnetic stimulation (TMS) is able to elicit phosphenes when applied over the occipital pole. The aim of this study was to test whether the site of the phosphenes in the visual field is linked to the retinotopic map of the visual cortex.
In four subjects we determined the individual retinotopy of the visual field by means of a dynamic mapping technique (eccentricity and polar angle) with functional MRI. Then we used focal TMS to register phosphene sites with different coil positions. These positions were monitored with respect to the head by a custom-made stereotactic measuring device. At each stimulation position, the subject drew the perceived phosphene directly on a touch screen.
Phosphenes were reproducibly elicited not only from positions corresponding to V1 but also from extrastriate areas V2 - V4. The general appearance of the phosphenes did not change with the visual area. In all subjects, displacement of the coil from a cortical position which represents the fovea to a position of more peripheral representation displaced the phosphene from the centre of the visual field towards the periphery. Our data demonstrate that stereotactic TMS can be used to create a detailed map of the visual cortex.