MEG
MEG Channels Layout And Classification
MEG channels are of three types (see illustration here):
- Magnetometers, measuring the net magnetic field perpendicular to the head surface close to the sensor;
- Planar gradiometers measuring the magnetic field gradient along the longitude;
- Planar gradiometers measuring the magnetic field gradient along the latitude.
The three types of sensors are named 'mag', 'grad1' and 'grad2', respectively, in the Fieldtrip analysis pipeline. Labels corresponding to the three types of sensors can be found in the file /neurospin/meg/meg_tmp/tools_tmp/pipeline/SensorClassification.mat.
Here's the MEG channels layout.
For a detailed description, read the hardware manual, paragraphs 1.4 and 1.5.