An apparatus for classifying a brain tissue area as functional or non-functional by a stimulation of the brain includes a receiver unit for receiving information about a performed stimulation, a recording device for recording images that represent the brain tissue area, a detection unit for detecting a change in perfusion in the brain tissue area, and a classification unit configured to determine with the information whether there is a correlation between the performed stimulation and the detected change in perfusion, and to classify the brain tissue area as functional or as non-functional. The recording device is an endomicroscope for recording endomicroscopic images of the brain tissue area with a spatial resolution better than 20 μm and a frame rate of at least 0.4 frames per second. The detection unit is configured to detect a change in perfusion based on the positions of certain tissue structures in the recorded images.