What is an EEG?

Ok, so people often get confused over what exactly an EEG is. Time to look at some EEG fish....

In our fish tank we have loads of fish swimming around randomly. There are also 3 cameras looking at different parts. The first sees only one fish (how sad), the next sees 3 fish swimming to the left and the next sees loads of fish swimming to the right. If we add in a bonus camera then we could probably figure out which way the fish were swimming at a certain depth.

Replace cameras with electrodes and fish with action potentials and you've got an EEG. Remember the crazy squigly line trace you get from an electrode is the result of groups of neurons (fish) firing (swimming).