All subjects will undergo QEEG recording in a manner similar to that employed clinically, using procedures that have been approved in other protocols by the UCLA Medical IRB and that are consistent with standard clinical EEG procedures promulgated by ABRET (American Board of Registered Electroencephalographic Technologists). Recording electrodes are applied to the scalp using an electrode cap (ElectroCap, Inc., Eaton OH); electrodes are arrayed to record electrical activity from all major brain regions using a standard extension of the International 10-20 system (figure 1). Recording electrodes are connected to an isolation amplifier that is part of the digital EEG system (NuAmp System, NeuroScan, Inc., El Paso, TX). Data are recorded in real-time on computer disk. During recording, subjects will be resting in a quiet room with subdued lighting, in the eyes-closed, maximally alert state; the EEG technologists will alert the subjects whenever drowsiness is evident on the computer monitor. Data will be displayed in real-time on a computer monitor during recording, with adjustable filtering and amplification to facilitate identification of EEG patterns as well as artifact. Data will be collected using a bandpass filter of 0.3 to 70 Hz, and will be digitized at a rate of 250 samples/channel/second. Data will be recorded with a Pz referential montage, and the NeuroScan software then will reformat the data into bipolar montages as needed for the cordance calculations. Three EOG leads will be used (RIO-A2, ROC-A2, and LOC-A1) so that lateral, horizontal, or oblique eye movement artifact may be detected easily. Data for quantitative analysis will be selected from the data recorded according to standard procedures: each EEG will be reviewed by a technician and the first 20-32 seconds of artifact-free data will be selected to be processed to obtain absolute and relative power in four frequency bands (0.5-4 Hz, 4-8 Hz, 8-12 Hz, and 12-20 Hz) after the selections are confirmed by a second technician; both technicians will be blinded to clinical status while making or reviewing the selections.