Cognitive, Behavioral, and Systems NeuroscienceResearch PaperA food predictive cue must be attributed with incentive salience for it to induce c-fos mRNA expression in cortico-striatal-thalamic brain regions
Highlights
▶Individuals respond differently to reward cues. ▶Reward cues can act as predictors and/or incentive stimuli. ▶What brain regions are engaged when a cue has incentive vs. predictive value? ▶The predictive value of a reward cue is not sufficient to engage brain reward systems. ▶Brain reward systems are only engaged when reward cues are incentive stimuli.
Section snippets
Subjects
Male Sprague–Dawley rats (Charles River, Wilmington, MA, USA) weighing 250–300 g upon arrival were used. Rats were housed individually in hanging acrylic cages (8×8×9 cm3) and kept on a 12-h light/dark cycle (lights on at 0800 h) in a temperature- and humidity-controlled colony room. Food and water were available ad libitum for the duration of the study. Procedures were approved by the University Committee on the Use and Care of Animals.
Pavlovian conditioning
Pavlovian training was conducted using an autoshaping
Pavlovian conditioning
Rats were classed as STs or GTs based on their PCA score averaged over the last two days of Pavlovian training (days 6 and 7). Rats with an average approach index of ≥0.3 were designated STs (n=6, average PCA score=+0.6) and those with an index score of ≤−0.3 were designated GTs (n=10, average PCA score=−0.8). Rats with an “intermediate” score were not utilized for this study. Rats in the UN group had a PCA score of ≤0.5 or ≥−0.5 (i.e. did not show a strong preference for either the lever-CS or
Discussion
It is well established that mesocorticolimbic and cortico-striatal-thalamic brain regions that form a so-called “motive circuit” are engaged in response to cues associated with natural rewards (food, sex) and drugs of abuse (Childress et al., 1999, Kalivas and Volkow, 2005, Kelley et al., 2005a), and even to reward cues presented outside of conscious awareness (Childress et al., 2008). Together, these brain regions mediate the integration of learning, emotion, and arousal to produce motivated
Conclusions
In conclusion, it is well known that cues associated with food or drug rewards can exert powerful effects on emotions and behavior and can evoke a motivational state of “craving” or “wanting” (Childress et al., 1999, Robinson and Berridge, 2000; Brody et al., 2002, Berridge and Robinson, 2003). Individuals who attribute reward cues with incentive salience find it more difficult to resist such cues and are thereby more susceptible to disorders of impulse control such as overeating and addiction.
Acknowledgments
We would like to thank James Dell'Orco for technical assistance with the behavioral studies and James Beals, Sharon Burke and Jennifer Fitzpatrick for assistance with the in situ hybridization studies and analysis. We would also like to thank Dr. Fan Meng for assistance with statistics. We thank Kent Berridge, Paul Meyer and Ben Saunders for comments on an earlier version of the manuscript. This research was supported by National Institute of Health grant R37-DA04294 to T.E.R.
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