The purpose of the study was to test the sensitivity of mouse EROs to changes in stimulus probability, frequency and loudness. To accomplish this aim, mice were implanted with stainless steel screws (Small Parts, Miami Lakes, FL; size: 1/16″ in length) in three sites in the calvarium under Halothane anesthesia (1.5-2 liters/min). One screw was placed over more frontal areas (1.5 mm lateral of midline, 1.7 mm anterior to bregma, area M1, primary motor), one over the parietal cortex (2mm lateral to midline,2 mm posterior to bregma, area PPtA, posterior parietal association area). A ground screw was also placed in the thick bony area of the calvarium 5 mm posterior to bregma which obliquely overlies the cerebellum. Each screw was secured to the skull using dental acrylic (Dual Cure Geristore by Den-Mat, Santa Maria, CA). Soldered to each of the three screws was a silver 34 gauge insulated wire (Cooner wire, Chatsworth, CA), to which a pin contact (amphenol) was crimped. The three pins were adhered together with dental cement at an angle perpendicular to the saggital suture and shrink
