Present address: The M.I.N.D. Institute, University of California, Davis, 2805 50th Street, Room 1411, Sacramento, CA 95817, USA.
The effects of selective amygdala, orbital frontal cortex or hippocampal formation lesions on reward assessment in nonhuman primates
Article first published online: 6 JUN 2007
European Journal of Neuroscience
Volume 25, Issue 9, pages 2885–2904, May 2007
How to Cite
Machado, C. J. and Bachevalier, J. (2007), The effects of selective amygdala, orbital frontal cortex or hippocampal formation lesions on reward assessment in nonhuman primates. European Journal of Neuroscience, 25: 2885–2904. doi: 10.1111/j.1460-9568.2007.05525.x
- Issue published online: 6 JUN 2007
- Article first published online: 6 JUN 2007
- Received 31 October 2006, revised 7 March 2007, accepted 9 March 2007
- ibotenic acid;
- Macaca mulatta;
- reinforcer devaluation;
We examined the effects of bilateral amygdaloid, hippocampal or orbital frontal cortex lesions on reward assessment in rhesus monkeys (Macaca mulatta). In Experiment 1, basic preferences for foods and inedible nonfoods were measured pre- and postsurgery. None of the lesions produced changes in animals' preferences for palatable foods or raw meat relative to presurgery, although amygdaloid or hippocampal lesions yielded increased preference for inedible nonfoods postsurgery. When the reinforcement value of each animal's highest-preferred food was decreased by selective satiation, only animals with neurotoxic orbital frontal cortex lesions continued to select the sated food. Experiment 2 measured the impact of each lesion on learning 60 concurrent discrimination problems and, then, on flexibly avoiding objects associated with sated foods in favour of objects associated with nonsated foods. None of the lesions affected concurrent discrimination learning, but animals with neurotoxic amygdala or aspiration orbital frontal lesions could not refrain from displacing items covering devalued foods. Only animals with orbital lesions also selected the devalued food beneath the object. The results indicate a functional dissociation for the amygdala and orbital frontal cortex in reward assessment, depending on the type of the reinforcer available (objects vs. food). Finally, this is the first study indicating that the hippocampal formation is involved in the assessment of familiar nonfoods, but not in judging the current value of unconditioned and conditioned reinforcers.