NOVELTY - The method involves illuminating a field (11) of brain (13) of a patient for acquiring an image sequence of the field. The field is illuminated after stimulating the patient for acquiring another image sequence. The image sequences are evaluated by determining analysis image values based on amplitudes or frequencies of temporal changes of image values of pixels in both the image sequences. An output image is determined from the analysis image values, and topography data representing topography of the field is acquired, where the output image is displayed based on the topography data.