Procedures conducted during conditioning and CS1 testing required animals to be intraorally implanted with cannulae made out of polyethylene tube (Kiefer, 1995; Kiefer et al., 2005). This procedure allowed control over the amount and timing of the intraoral stimulation provided by sucrose infusion (CS1). Surgery took place on P30 for adolescents and P67 for adults. Animals were food deprived for 2 hrs prior to be anesthetized with isoflurane (via vapor 2.5 %, carrier: oxygen, 55 psi). Level of muscle tone and pupil reflexes were assessed to ensure that animals were under the effects of the anesthetic. A small square of fur was shaved at the back of the neck above the scapula and also in the right cheek. Betaiodine and ethanol were rubbed in the skin. An incision was then made in the cheek by means of a thin-walled 14-gauge disposable needle (Harvard Instruments, Columbus, OH). A 10-cm section of PE 10 polyethylene tube (Clay-Adams, Parsippany, NJ) was run through the needle. Following this procedure the needle was removed. Then, a small flange was created in one end of the
