Inside your brain, you have over 80 billion neurons – tiny brain cells, all working together to make you the person you are. Neurons talk to each other by sending electrical messages. Each message creates a tiny magnetic field. If enough neurons are talking together, we can listen in on their conversations by measuring the magnetic field around your head.
We call this MEG, which stands for magnetoencephalography (mag-netto-en-keffa-logra-fee).
In our everyday lives, we are surrounded by magnetic fields, coming from computers, mobile phones, and even from the earth itself. Our brain's magnetic fields are tiny in comparison. Listening in on your neurons is like trying to hear the footsteps of an ant – in the middle of a rock concert!
For this reason, MEG machines have to be in a special room with thick metal walls that stop all the other magnetic fields getting in.

License information: CC BY 4.0
MPAA: G
Go to source: https://kids.frontiersin.org/article/10.3389/frym.2014.00010