Unilateral electrode implantation procedures were carried out after stereotaxic injection, and electrodes were implanted in the same hemisphere that was targeted by injection. Hemispheres were counterbalanced across groups, and the methods for implantation have been described in detail previously (11, 12, 24, 25, 40, 41). Rats were chronically implanted with a drivable bundle of 10, 25-µm diameter FeNiCr wires (Stablohm 675, California Fine Wire, Grover Beach, CA) into either the left or right hemisphere of the DMS using the following coordinates relative to bregma (AP: −0.4 mm; ML: ±2.4 mm; DV: −3.5 mm). Coordinates were chosen based on our previous results investigating the role of the DMS using the STOP-change task (12). Immediately prior to implantation, wires were freshly cut with surgical scissors to extend ∼1 mm beyond the cannula and were electroplated with platinum (H2Cl6Pt) to an impedance of ∼300 kOhms. Cephalexin (15 mg/kg per os) was administered twice daily for 7 d following surgery to prevent infection.
