During anything we do - perceiving, speaking, moving, or sleeping - electrical signals are transmitted by brain cells. The transmission of low-level electrical signals allows 10 trillions of neurons in our brain to communicate and exchange information. By means of electroencephalograpy (EEG) it is possible to measure changes in these electrical signals on the surface of the head, and to represent these graphically. To do so, we use an elastic cap that fits in the size of the head similar to a bathing cap. Electrodes are fixed at the cap to measure the change of the electrical signals - similar to measuring body temperature. Thus, we can see what regions of the brain are more active than others in a certain situation. EEG is a popular measurment method that is used in a lot of research centres all over the world.