Table 1. Experimental Design for Experiments 1, 2, and 3.

Blocking procedure
Exp	Pretreatment/drug	Stage one	Stage two	Test
1	Sucrose, saccharin, or water	A+	AB+ CD+	B D
2	Sucrose or water/quinpirole or saline	A+	AB+ CD+	B D
3	Ghrelin or saline	A+	AB+ CD+	B D

Pretreatment indicates the diet or neuronal manipulation taken place before the behavioral procedure. That is, rats received sucrose or ghrelin treatment before commencing the blocking procedures and so any effect on learning is due to a long-term change in learning produced by a history of sucrose or ghrelin exposure. The drug column indicates the drug animals received during stage-two blocking where CSA fails to block CSB (marked in bold). During stage-one conditioning, rats were initially trained with visual stimulus (A) paired with reinforcement. In stage two, rats were presented with two audio-visual compounds, one comprising the previously trained stimulus (AB) and another novel compound (CD). At test, animals were presented with stimuli B and D alone under extinction. All stimuli were counterbalanced within modality where stimulus A and C are visual stimuli (either flashing panel lights or a house light) and stimuli B and D are auditory stimuli (either clicker or a white noise).+ indicates delivery of a 40-mg grain pellet.