The headsets contain a sensor that detects various mental states, and a chip converts the signals from analog format to digital so they can travel wirelessly to a computer.
As a test, I downloaded files from HDtracks.com, an online retailer specializing in hi-res audio, plugged a device known as a digital-to-analog converter (DAC) into my computer and listened over earphones.
You can record from any stereo source with a stereo in-line jack and won't have to get any specialized software to put recordings back on your computer--all you need is an analog or digital source at bit rates up to 160 kbps.