Electroencephalograms (EEG) and ERPs were recorded using Microtech™ recording cables. ERPs were collected from two monopolar leads (frontal and parietal cortices) referenced to a grounded electrode overlying the cerebellum (i.e., frontal cortex-ground, parietal cortex-ground). EEG signals were recorded on a polygraph, with a band pass of 0.3–35 Hz with a 60-Hz notch filter in. The signals were amplified (75 μV/mm) and the EEG, as well as the calibration signals, were transferred from the Nihon-Kohden polygraph on-line to a Macintosh computer, which also controlled the presentation of the auditory stimuli. ERP trials were digitized at a rate of 256 Hz. Potential artifacts identified by computer software were excluded only after visual analysis of raw EEG. In the first study, B6 and D2 mice were approximately between 10 and 14 weeks of age at the time of the electrophysiological recordings. In the second study, HAP-1, LAP-1 and HS/Ibg mice were initially maintained in a quarantine facility for 7 weeks. They were approximately between 13 and 18 weeks of age at the time of the electrophysiological recording. These studies have been described previously (Ehlers and Somes, 2002, Slawecki et al., 2003).
