In the sixteenth century, writes Gavin Francis:
it was believed that magnets had souls, that swallowing them would give you eloquence, and that their property of “action at a distance” was related to the attraction of love. Now we know that eloquence and love, as they are expressed in the brain, do create magnetic fields: each neuron, as it fires, generates a minuscule magnetic field around the axis of its impulse. Imagine these fields as the ripples on a pond after throwing a stone, then imagine the undulating surface sheen of the water stripped off and wrapped around your head. Haloes of magnetic fields ripple from our brains as we talk, think, experience the world.An introductory note on Magnetoencephalography (MEG) from the York NeuroImaging Centre puts the magnetic fields generated by the brain in context:
The magnitude of magnetic fields outside the head generated by the electrical activity of the brain is of the order of femtotesla (10-15T)...tiny in comparison to the magnetic fields that we are exposed to in everyday life which are of the order of tens of microtesla (10-6). Our hearts generate a field in the order of tens of nanotesla (10-9) and a car moving will generate a magnetic field that is still of the order of femtotesla when the field is recorded one mile away from the car.
Image of electroencephalographs (EEG) by Srivas Chennu/University of Cambridge