|A Sporty Blue EEG Cap|
Of course, everyone starts with the wikipedia page. It's an OK page. It's too long to be a good introduction. I do find its discussion of the history of EEG to be interesting (it's 90 years old!) and I like the discussion of the different EEG frequency bands. Sadly, it's not too helpful on how to actually do an EEG.
There's no good, simple description of how to do a very basic, hacker-style EEG. I'm going to have to fix that. Until that time, we're stuck with others' descriptions.
Here's a decent link that talks about a number of aspects of EEG, but I like the pictures of the electrodes, of the electrode placement, and of typical EEG artifacts...especially of eye motion.
The BCI2000 folks also have a lot of good information. Here's a basic on electrodes, placement, and typical signal artifacts.
Typical EEG Signals:
The links above talked about about some typical signals, especially of "artifacts", which are the undesirable signals that get picked up by the EEG system. These artifacts are usually not associated with brain activity, which is why they are considered bad.
Actual brain signals in EEG are often discussed and analyzed based on their frequency content. These are the so-called "Alpha waves", "Beta waves", "Theta waves", and such. The Wikipedia page above discusses these different frequency band. So does the link below:
Another way of discussing EEG signals is by the shape of the waves, not just their frequency content. This is the "morphology" of the waves. These are the "Sleep Spindles" and "K Complexes". Some of the morphologic features in EEG signals:
Finally, here's a more formal (and detailed!) discussion of some normal types of signals that you might see in an EEG. It spends a lot of time discussing alpha waves.