The electric activity of the brain causes very weak electric and magnetic fields. Contrary to electric fields, magnetic fluxes are not distorted by the environment they go through, like skin for instance: it is hence easier to identify the exact place of cerebral activity. But these magnetic fluxes created by the brain are extremely weak, 10 billion times weaker than the earth magnetic field: on the scale of the picotesla. However, it is possible to measure these magnetic fields thanks to MEG (MagnetoEncephaloGraphy).
In order to do that, we put ultrasensitive magnetic sensors on the surface of the patient’s brain, SQUIDs, made of superconducting loops and Josephson junctions.
On this device, the patient’s brain is placed under a helmet containing hundreds of squid sensors that have been cooled in liquid helium to become superconducting. MEG enables to record the electric behaviour of the cerebral activity almost “in live”, every millisecond or so. It works hand in hand with MRI that gives more accurate images of the brain but does not able to see the cerebral activity in real time. MEG is used to study normal and abnormal behaviours of the brain with a time resolution of about a millisecond. It is also non-invasive and harmless for the patient.
MEG can help finding a preoperative diagnosis for epilepsy by locating the active zones of the brain during crises, for instance. MEGs have been installed in Paris at the CENIR and in Rennes.
