How electrical activity leaves a magnetic trace
Nerve cells communicate by moving charged particles—mainly ions—across their membranes. When many charges move in the same direction, they form an electrical current. Like any current, that movement produces a magnetic field around it. The field is not stored in the nerves; it exists while the electrical activity is happening.
Why the signal is hard to detect
Currents in the body are small, and their magnetic fields are fainter still. Signals from different cells can also point in different directions, so their fields may partly cancel rather than add together. Meanwhile, ordinary surroundings produce much stronger magnetic interference, from electrical equipment to the Earth itself.
Researchers can still measure some of these faint fields with highly sensitive instruments. Magnetoencephalography, for example, records magnetic signals associated with brain activity. Such measurements offer another way to observe electrical activity: they can complement recordings made with electrodes, which detect voltage differences at the body’s surface.
The practical takeaway is modest but striking: every nerve signal has a magnetic counterpart, even though detecting it requires far more than an ordinary sensor.
