Pontine and thalamic influences on fluid rewards: III. Anticipatory contrast for sucrose and corn oil

Abstract

An anticipatory contrast effect (ACE) occurs when, across daily trials, an animal comes to respond less than normally to a first stimulus when it is followed shortly by a second, more preferred solution. Classically, ACE is studied using a low (L) concentration of saccharin or sucrose, followed by access to a higher (H) concentration of sucrose. Subjects in the control condition have two bouts of access to the weaker solution presented on the same schedule. The ACE is measured by the difference in intake of the first bout low solution between subjects in the low-low (L-L) vs. the low-high (L-H) conditions. Here we used this paradigm with sham feeding rats and determined that nutritional feedback was unnecessary for the development of ACE with two concentrations of sucrose or with two concentrations of corn oil. Next we showed that ibotenic acid lesions centered in the orosensory thalamus spared ACEs for both sucrose and corn oil. In contrast, lesions of the pontine parabrachial nuclei (PBN), the second central relay for taste in the rat, disrupted ACEs for both sucrose and corn oil. Although the sensory modalities needed for the oral detection of fats remain controversial, it appears that the PBN is involved in processing the comparison of disparate concentrations of sucrose and oil reward.

Thalamic Contribution to Cortical Processing of Taste and Expectation

“…Interestingly, experiments based on permanent electrolytic lesions of the VPMpc propose its involvement in learning preparatory behaviors based on anticipatory cues (Reilly, 1998; Schroy et al, 2005; but see also Liang et al, 2012). Our results, which rely on temporary inactivation once the animal has learned the task, extend these findings.…”

Relative reward effects on operant behavior: Incentive contrast, induction and variety effects

“…Contrast effects are more consistent when measuring consummatory actions (Dachowski and Brazier, 1991; Daniel et al, 2008), and the majority of recent work on diverse external influences or biological mechanisms has focused on licking rate or food consumption (Flaherty and Rowan, 1986; Liang et al, 2012; Lopez Seal et al, 2013) To complicate matters more, research findings support the idea that instrumental and consummatory contrast can be dissociated from one another and may rely on separate mechanisms (Flaherty and Caprio., 1976). This makes a translation between work on consummatory (e.g., licking rate) and instrumental (e.g., running speeds) contrast difficult and presents an interesting challenge for designing a paradigm that can measure both phases of behavior accurately and repeatedly.…”

“…Internal and external factors combine to influence flexible responding to changes in reward value (Grigson et al, 1994 ;Cromwell et al, 2005; Papini and Pelligrini, 2006; Liang et al, 2012). Incentive contrast paradigms have been utilized extensively to examine factors involved in the dynamic processes of choice, preference and decision-making (Reynolds, 1961; Eisenberger et al, 1975; Blough, 1980; Flaherty, 1996).…”

Bilateral lesions of the thalamic trigeminal orosensory area dissociate natural from drug reward in contrast paradigms.

“…This area was referred to as the trigeminal orosensory area (TOA) of the thalamus by Liang and colleagues (2012a–c). In this set of studies (Liang, Freet, Grigson, & Norgren, 2012a; Liang, Grigson, & Norgren, 2012b; Liang, Norgren, & Grigson, 2012c), rats with lesions centered on the TOA, but also encompassing the majority of the TTA, exhibited increased operant responding for sucrose and corn oil under sham feeding (i.e., open gastric fistula) conditions (Liang, et al, 2012a). This finding is surprising, considering that lesions encompassing only the TTA do not affect operant responding for natural rewards (Reilly & Trifunovic, 1999).…”