Your brain is made up of billions of neurons all chattering away to each other. MEG allows us to listen in on their conversations by measuring your brain’s magnetic field.
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 (Figure 1).
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 (Figure 2).
The real heroes of MEG are small wire coils called SQUIDs, which pick up your brain’s magnetic field. SQUID stands for super-conducting quantum interference device.
SQUIDS are very sensitive but they only work if the temperature is extremely low – about 270°C below zero! To keep them super-cool, the SQUIDs are covered in liquid helium – the coldest liquid on earth.
Over time, the liquid helium gradually warms up, turns into a gas, and floats away. In our lab, we capture as much of the gas as we can and turn it back into a liquid (Figure 3). Then we put it back into the MEG machine to make sure our SQUIDS stay super-cool!
MEG for Kids
In the MEG machine, hundreds of SQUIDs are arranged outside a helmet. The normal MEG helmet is designed for adults but is way too big for many kids. The SQUIDs end up being a long way from the brain, so they struggle to pick up a good signal.
Getting Inside Your Brain
After the MEG recording has finished, we use a computer to try and figure out what was going on inside your brain.
The computer guesses what might have been happening and works out what all the SQUIDs would have measured if that guess was right. It keeps adjusting its guess until it matches as closely as possible what the SQUIDs really did record.
The computer can then tell us what we would have measured if we had been able to put sensors right inside your brain! (see Figure 5).
What Can MEG Tell Us?
Listening in on your neurons is not easy. But MEG can help us to answer some very interesting questions. How does your brain make sense of the things you see, hear, and touch? How do neurons in different parts of your brain talk to each other? How does this change as you get older?
MEG can also help us understand conditions like epilepsy, which happens when all the neurons start shouting at once. In our lab, we test kids who struggle to speak. We use MEG to see what happens in their brains as they are trying to say a word. We also test kids with autism, who have difficulties interacting with other people. Scientists think this may be because of differences in how their neurons talk to each other.
MEG is a great tool for helping us understand kids’ brains. And it is all thanks to those super-cool SQUIDs.
 ↑ Barnes, G., Hillebrand, A., and Hirata, M. 2010. Magnetoencephalogram. Scholarpedia 5:3172. doi: 10.4249/scholarpedia.3172
 ↑ Tesan, G., Johnson, B. W., Reid, M., Thornton, R., and Crain, S. 2010. Measurement of neuromagnetic brain function in pre-school children with custom sized MEG. J Vis Exp 36:e1693. doi: 10.3791/1693