A magnetic sensor such as a SQUID (Superconducting QUantum Interference Device) makes it possible to remotely record brain activity at the scale of a thousand neurons. Magnetoencephalography (MEG) makes use of three hundred sensors of this kind. Unfortunately, they must be cooled at a very low temperature, which precludes putting them in immediate contact with the analyzed area and limits their resolution.

To move further, physicists from IRAMIS have chosen to use giant magnetoresistance (GMR), because it operates at room temperature and because the sensor's geometry can be miniaturized without any loss in sensitivity.

The scientists crafted a sensor on silicon that is biocompatible and segmented in three parts, and placed it below a one-centimeter long "muscle model." They were able to measure the magnetic field associated with the propagation of the action potential when the muscle was stimulated, on the order of 2 nanoteslas (10^-9 T).

From now on the team will be seeking to increase the sensor's sensitivity using magnetic tunnel junctions, while developing a specific "shielding" to reduce interference signals and increase miniaturization to reach the micrometer scale. One of their objectives is to offer a new tool allowing for better understanding of the origin of the signals measured by MEG.