MEG brain signal. Computer image of a section through the human head (sagittal section), showing a region in the brain at which electrical stimulation has occurred. The region is demarcated in three dimensions with axes X, Y and Z. These axes are a method of representing direction and intensity of an electrical impulse in the brain in response to a stimulus. The impulse was detected using magnetoencephalography (MEG), a brain scanning technique that measures magnetic fields generated from nerve cell activity in the brain. The image of the head was contructed from 3-D MRI scan data. Photographed at New York University Medical Centre in New York City, USA.