Reportage at the Neuroimaging research centre in Pitié Salpêtrière hospital in Paris, France. Magnetoencephalography (MEG) platform. MEG detects variations in the brain's magnetic field during various types of cerebral activity. It studies normal and abnormal brain function. Recording the magnetic field produced by neuronal currents requires ultra sensitive sensors called SQUIDs (Superconducting Quantum Interference Device). The 306 sensors spread over 102 areas allow both near and far magnetic fields to be measured, and the brain's deep structures to be 'seen'. Results of a MEG carried out on a healthy patient receiving visual stimulation. The curves at bottom left show magnetic fields both before and during visual stimulation. The right-hand image combines an MRI scan with the MEG. The active areas of the brain during stimulation can be seen (red line). The top left-hand image shows the brain's magnetic flux.