In full: electroencephalography. A method of measuring the activity in the brain using electrodes that are stuck to the scalp . Usually less than ten to a maximum of twenty electrodes are used. The Sleep Lab and also the Spinoza Center have an electrode cap that has 256 electrodes, a so-called high-density EEG system.
An EEG scan shows accurately to the millisecond when changes in brain activity are taking place, but tells little about which areas of the brain are active. This is more visible with the help of fMRI.