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shallowdeep -> RE: Just Curious... (9/18/2011 3:46:55 AM)
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Perhaps elaborating just a bit more:
When neurons in your brain fire, channels open and electrically charged ions get moved around; this movement of charge produces changes in electric potential in the surrounding space. Outside the skull, the changes are very small, but electrodes placed on the scalp can still pick them up. EEGs do exactly that. By measuring the voltages on the electrodes over time, you can get a sense of the underlying brain activity that is producing the fluctuations in voltage. The voltages tend to go up and down with consistent rhythms, or frequencis, hence the term brain waves. An EEG typically uses a number of electrodes placed in a specific pattern to map out brain activity. By analyzing the data, it may be possible to find problems.
I've attached a picture showing what some actual EEG data looks like. The top left part shows electrode placement and the top right is a plot of the voltage for each of the various channels over time. That sort of plot can be difficult to interpret, so it's common for the data to be analyzed in the frequency domain instead. A spectrogram, like the one shown in the bottom, can make it easier to see things. For instance, the area in the gray box represents the brain activity during an epileptic seizure, and is noticeably different from the surrounding, normal, brain activity.
As Endivius pointed out, an EEG is a painless, non-invasive procedure. To make sure that there's good contact with the scalp (essential to pick up the small electrical signals) a conductive paste is often used when applying the electrodes. The paste can sometimes get a little messy with hair, but that's been the worst of it for me. The video here explains a bit about the application of an EEG electrode, although the styles can vary a bit. I've never had a clinical EEG, but I've gotten to play with them in labs and, if anything, it's kind of fun to see your brain's activity – so the test isn't something I'd be too worried about.
Good luck with your EEG!
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