Progressive ratio performance in rats with gustatory thalamus lesions.

Abstract

To determine whether damage of the gustatory thalamus (the parvicellular region of the ventroposteromedial nucleus) disrupts the perceived value of reinforcing stimuli, the performance of rats with bilateral, electrophysiologically guided, electrolytic lesions of the area was examined in Experiment 1 with a progressive-ratio schedule of reinforcement. Lesioned rats showed normal concentration-dependent changes in break point (an index of the amount of effort a subject will expend to obtain reinforcement) and in consummatory responding (licking) for the sucrose reward. In the reward comparison procedure of Experiment 2, however, the same lesioned rats failed to show morphine-induced suppression of alanine consumption. The results provide no support for the view that the thalamic taste area is involved in the perception of the absolute reinforcing value of gustatory stimuli.

Role of gustatory thalamus in anticipation and comparison of rewards over time in rats

“…In support of this, rats with lesions of the gustatory thalamus not only fail to demonstrate an ACE but also a successive negative contrast effect that occurs when intact rats are unexpectedly shifted from a greater to a lesser reward (40,42,43). In this case, intake of the lesser 0.15% saccharin reward is reduced in the lesioned rats when downshifted from a 1.0 M sucrose solution, but only to the level of the unshifted saccharin controls (42).…”

“…In support of this, rats with lesions of the gustatory thalamus not only fail to demonstrate an ACE but also a successive negative contrast effect that occurs when intact rats are unexpectedly shifted from a greater to a lesser reward (40,42,43). In this case, intake of the lesser 0.15% saccharin reward is reduced in the lesioned rats when downshifted from a 1.0 M sucrose solution, but only to the level of the unshifted saccharin controls (42). Oddly, although fully impaired in these two contrast paradigms, rats with similar lesions of the gustatory thalamus exhibit perfect simultaneous contrast effects when given the opportunity to compare the same saccharin and the sucrose solutions closely in time in the same daily session (41).…”

“…4,42). The first stage, which typically occurs on the first postshift day, involves detection, rejection, and a search for the missing reward.…”

The role of conditioning history and reinforcer strength in the reinforcement enhancing effects of nicotine in rats

“…Experiment 1 established that the method of increasing step-sizes under the PR schedule (Richardson and Roberts 1996) established breaking-points (i.e., the point at which the motivation to obtain the reinforcer is outweighed by the response requirement) which were systematically related to the reinforcing efficacy of sucrose (Reilly 1999;Reilly and Trifunovic 1999;Sclafani and Ackroff 2003). Experiment 1 also demonstrated that nicotine could increase the motivation to obtain the sucrose reinforcer.…”

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

“…In other tasks, CS intensity appears to affect learning by PBNx rats. Specifically, PBNx rats were able to learn a conditioned flavor preference (CFP) as well as controls when the CS contained a higher concentration of Kool-Aid [26] but not when the concentration was reduced to 0.05% [24, 27–33]. The failure to show an ACE for the corn oil pairs may be due to the failure to appropriately identify the reward disparity between the CS and the US.…”