A neuronal population code for resemblance between drug and nondrug reward outcomes in the orbitofrontal cortex
The orbitofrontal cortex (OFC) is implicated in choice and decision-making in both human and non-human animals. We previously identified in the rat OFC a mechanism that influences individual drug choices and preferences between a drug and a nondrug (i.e., sweet) outcome that is common across different types of drugs (cocaine and heroin). Importantly, this research also revealed some intriguing drug-specific differences. Notably, the size of non-selective OFC neurons that indiscriminately encode both the drug and the sweet outcomes varies as a function of the drug outcome available (cocaine or heroin). Here we tested the hypothesis that the relative size of the non-selective OFC population somehow represents the degree of resemblance between the drug and nondrug reward outcomes. We recorded OFC neuronal activity in vivo in the same individual rats while they were choosing between two outcomes with varying degrees of resemblance: high (two concentrations of sweet), intermediate (sweet versus heroin) and low (sweet versus cocaine). We found that the percentage of non-selective OFC neurons dramatically increased with the degree of resemblance between choice outcomes, from 26 to 62%. Overall, these findings reveal the existence of a neuronal population code for resemblance between different kinds of choice outcomes in the OFC.
KeywordsChoice Preference Orbitofrontal cortex Outcome resemblance Cocaine Heroin
We thank Christophe Bernard, Eric Wattelet, Audrey Durand and Caroline Vouillac-Mendoza for administrative and technical assistance. We also thank Etienne Gontier from the Bordeaux Imaging Center (BIC) for giving us access to his laboratory facility for brain perfusion.
This work was supported by the French Research Council (CNRS), the Université de Bordeaux, and the Fondation pour la Recherche Médicale (FRM DPA20140629788).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All experiments were carried out in accordance with standard ethical guidelines (European Communities Council Directive 86/609/EEC) and approved by the committee on Animal Health and Care of Institut National de la Santé et de la Recherche (agreement A5012052).
- Jain R, Mukherjee K, Singh R (2004) Influence of sweet tasting solutions on opioid withdrawal. Brain Res Bull 64:319–322. https://doi.org/10.1016/j.brainresbull.2004.08.003 CrossRefPubMedGoogle Scholar
- Koob GF (1992) Neurobiological mechanisms in cocaine and opiate dependence research publications. Assoc Res Nerv Ment Dis 70:79–92Google Scholar
- Vandaele Y, Cantin L, Serre F, Vouillac-Mendoza C, Ahmed SH (2016) Choosing under the influence: a drug-specific mechanism by which the setting controls drug choices in rats. Neuropsychopharmacol Off Publ Am Coll Neuropsychopharmacol 41:646–657. https://doi.org/10.1038/npp.2015.195 CrossRefGoogle Scholar