All animals were anesthetized using urethane (1.2–1.5 g/kg of 65–80% solution, intraperitoneal injections). Urethane anesthesia allows for spontaneous theta oscillations in the HC through stimulation of the pontine reticular formation (Kramis et al. 1975; Vertes 1981; Vertes and Kocsis 1997). The animals’ head were fastened in a stereotaxic frame, and small burred wholes were made to allow for electrode placement. Two pairs of twisted stainless steel wires with 1mm distal separation were implanted in HC (3.7 mm posterior to bregma, 2.2 mm lateral to midline, and 4.8 mm below the brain surface), and nRE (2.5 mm posterior to bregma, on the midline, and 6.5 mm below the brain surface). Two single electrode wires were implanted in the right and left PFC (3.2 mm anterior to bregma, 0.5 mm lateral to midline, and 4.8 mm below the brain surface). A pair of stimulating stainless steel electrodes was implanted in the reticular nucleus pontis oralis (RPO) (8 mm posterior to bregma, 1.5 mm lateral to midline, and 8 mm below the brain surface). Skull screws overlying the nasal bone and cerebellum served
