Mice were implanted with stainless steel screws (Small Parts, Miami Lakes, FL; size: 000 × 120 × 1/16th) in three sites in the calvarium under halothane anesthesia (1–2% in O2). Screws were placed in the skull overlying the frontal cortex (anterioposterior (AP): + 1.7 mm, mediolateral (ML): ± 1.5 mm; area M1, primary motor) and the parietal cortex (AP: −2.0 mm, ML: ± 2.0 mm; area PPtA, posterior parietal association area) (Franklin and Paxinos, 1997). A third screw, which was grounded during recording, was placed posterior to lambda in the skull overlying the cerebellum. After surgery mice were then returned to their home cages and allowed 3–9 days to recover before the beginning of electrophysiological studies. Further details about the surgical procedures have been described previously (Ehlers and Somes, 2002, Slawecki et al., 2003).
