To wrap up our stadium analogy: If EEG is like listening to the muffled roar of the crowd from the parking lot because the thick concrete walls (the skull) block the sound, a Neuromagnetic field is like pulling out a highly advanced thermal camera.
Thermal vision doesn't care about the concrete walls. It sees straight through them, giving you a perfectly crisp, undistorted map of exactly where the "heat" (the crowd) is concentrated.
In neuroscience, recording this field is called Magnetoencephalography (MEG). Here is how it works, why it is like a superpower, and the insane engineering required to pull it off.
You don't need any special magnetic tissue in your brain to create a neuromagnetic field. It is a fundamental law of physics: Any time an electrical current moves, it creates a magnetic field around it.
The Right-Hand Rule: Current creates a magnetic field.. Source: petrroudny / Getty Images
When thousands of neurons in a specific fold of your brain fire their electrical signals (synaptic currents) at the same time, they generate a tiny, collective magnetic field that projects outward, right through your skull.
Why bother measuring the magnetic field instead of just measuring the electricity (EEG)?
Because of Volume Conduction. As we discussed with EEG, the skull acts like a terrible resistor. It smears, blurs, and weakens electrical signals.
Bone is completely transparent to magnetic fields.
The magnetic field passes through your brain fluid, skull, and scalp as if they weren't even there. This means MEG gives researchers the "best of both worlds":
If MEG is so perfect, why isn't it used everywhere? Because neuromagnetic fields are unimaginably weak.
To put it in perspective: