 Magnetoencephalogram MEG scans will be performed on some participants. The precise and undistorted signals available with MEG will be used to enhance the interpretation of alertness and sleep-related characteristics of the EEG signals, which can vary quite dramatically across subjects. In addition, the MEG signals will provide preliminary spatial localization of the sleep-dependent changes more precisely than is possible with EEG. MRI scanner noise will be simulated using tape recordings to allow comparison with the MRIEEG data. MEG scans will last 45 minutes to 2 hours. At all times during any of the brain scans the participant will be able to communicate the MRI scientist or MEGEEG technician and can ask to be removed from the device at any time. 