For ERO recordings, all animals were in electrically shielded light, sound and temperature controlled recording chambers where the animals are unrestrained but are spatially restricted. EEG signals were recorded on a polygraph. The bandpass for recordings was set at 0.3 - 35 Hz with a 60 Hz notch filter in. The signals were amplified (75 microvolts/mm) and the EEG, as well as calibration signals, were transferred from the Nihon-Kohden polygraph on-line to a Macintosh computer which also controlled the presentation of the auditory stimuli. Free field auditory stimuli were presented through a small speaker centered approximately 18 cm above the mouse’s head. Five minutes of resting, awake EEG was additionally collected from each mouse.
