Eli5 How do EEGs work?


Eli5 How do EEGs work?

In: Biology

They attach electrodes to your scalp. They measure the voltage differences resulting from ionic current within the neurons of your brain

First, what about ECG (electrocardiogram). Electrodes get placed on the skin of the chest and limbs. By looking at the *difference* between electrodes in different spots, we get an idea of how the heart is working. These differences (voltages) get plotted as lines, called *traces*.

And EEG (electroencephalogram) is similar, but the electrodes are on the head. These measure traces between different parts of the head, showing how parts of the brain are behaving. By comparing this to other examples, we can work out what parts of the brain are being used or what’s going wrong.

We can even use it to see if two people are communicating successfully because their brain waves literally sync up (as both are listening to the same speech patterns)!

Your brain generates electricity. When a bunch of neurons in an area fire (activate) in sync, they all generate the electricity at the same time. EEG works by sticking electrodes to your scalp to pick up those electrical signals.

We have a pretty good idea of what different brain areas do, so we put electrodes all over the head in order to measure activity in different areas of the brain. That way you can look at the cluster of electrodes over the frontal lobes, for example, and have a pretty good idea of when the frontal lobes are activated.

The main shortcoming of EEGs is that their ability to detect activity in smaller, more specific areas is pretty bad. As the electricity travels from the brain area to the scalp, it can get pretty warped. So we don’t really use EEG if we want to have an idea of how a very specific brain area is functioning, because it’s too hard to narrow in on that one area specifically. In technical terms, we say EEG has bad Spatial Resolution.

What EEG is VERY good at is what we call Temporal Resolution, or picking up things really quickly and giving you accurate readings of the timing of brain activation. So if you’re undergoing an EEG scan and staring at a blank TV screen and all of a sudden a jumpscare comes on, the EEG will be able to measure EXACTLY when you first noticed this, how long it took your brain to reach peak excitation, and how long it took your brain to go back to normal, down to the millisecond.

The types of electricity that your brain makes are different depending on how alert you are. So EEGs are often used in sleep studies to take a look at how well you stay asleep versus waking up throughout the night for even a minute at a time. They can also be used to measure brain activity in someone who’s in a coma, because dead brains don’t produce any meaningful signals, but alive brains do.

Finally, one of the most popular uses for EEG is in epilepsy. When you have a seizure it basically means the electrical activity in your brain goes haywire, and neurons start firing all at different times. That shows up on an EEG as these crazy, uncoordinated spikes and zigzags, so you can see how many seizures someone has while they are hooked up to the EEG, as well as what kind of seizures they’re having (some only affect part of the brain, some affect the whole brain, and some are “spikier” than others).