title: Role of gustatory thalamus in anticipation and comparison of rewards over time in rats.
abstract: Rats reduce intake of a palatable saccharin solution when it is followed by access to a preferred sucrose solution. This phenomenon, referred to as an anticipatory contrast effect (ACE), is thought to occur because the value of the saccharin conditioned stimulus pales in comparison to the highly rewarding sucrose unconditioned stimulus expected in the near future. Although relatively little is known about the underlying neural substrates, lesions of the gustatory thalamus fully disrupt the phenomenon (Reilly S, Bornovalova M, and Trifunovic R. Behav Neurosci 118: 365-376, 2004; Reilly S and Pritchard TC. Behav Neurosci 110: 746-759, 1996). The present set of experiments revisited this issue to determine the nature of this deficit. Rats with bilateral ibotenic acid lesions of the gustatory thalamus were given 3-min access to 0.15% saccharin and, after a 0-s or 5-min interval, were given 3-min access to either the same saccharin solution or a highly preferred 1.0 M sucrose solution. In experiment 1, ACE testing began with the 5-min interstimulus interval (ISI) and then switched to the 0-s ISI. For experiment 2, the order of ISI testing was reversed. The results show that axon-sparing, neurotoxic lesions of the gustatory thalamus prevent ACEs with a 0-s ISI and lead to a reversal (i.e., a reinforcement effect) with a 5-min ISI. Together, the results suggest that the lesion leads to a specific reward comparison deficit, whereby the rats fail to compare the value of an available reward with the memory of a preferred reward that is anticipated in the near future.
authors.affiliation: Department of Neural and Behavioral Sciences, Pennsylvania State University. College of Medicine, Hershey, Pennsylvania 17033, USA.
authors.forename: Pearl Lee
authors.initials: PL
authors.lastname: Schroy
authors.forename: Robert A
authors.initials: RA
authors.lastname: Wheeler
authors.forename: Collin
authors.initials: C
authors.lastname: Davidson
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Scalera
authors.forename: Robert C
authors.initials: RC
authors.lastname: Twining
authors.forename: Patricia S
authors.initials: PS
authors.lastname: Grigson
mesh_terms: D000818:Animals; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D005508:Food Deprivation / Q000502:physiology; D006185:Habituation, Psychophysiologic; D007051:Ibotenic Acid / Q000494:pharmacology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012054:Reinforcement, Psychology; D012201:Reward; D012439:Saccharin / Q000494:pharmacology; D013549:Sweetening Agents / Q000494:pharmacology; D013649:Taste / Q000502:physiology*; D013788:Thalamus / Q000033:anatomy & histology / Q000502:physiology*; D013997:Time Factors; D020651:Ventral Thalamic Nuclei / Q000033:anatomy & histology / Q000502:physiology
chemical_list: D018690:Excitatory Amino Acid Agonists; D013549:Sweetening Agents; D007051:Ibotenic Acid; D012439:Saccharin