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.

 

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