Choice between reinforcer delays versus choice between reinforcer magnitudes: Differential Fos expression in the orbital prefrontal cortex and nucleus accumbens core

Abstract

Lesions of the orbital prefrontal cortex (OPFC) and the nucleus accumbens core (AcbC) can disrupt performance in inter-temporal choice tasks, possibly by increasing the organism's sensitivity to delay and/or magnitude of reinforcement. This experiment examined whether exposure to an inter-temporal choice would induce neuronal activation in these areas, as indicated by enhanced expression of the Fos protein. Twelve rats were trained to press levers A and B under an adjusting-delay schedule in which a response on A delivered 50 μl of a sucrose reinforcer after 2 or 18 s, whereas a response on B delivered the same reinforcer after a delay that was adjusted in accordance with the rat's choices. Another 12 rats were trained under a similar schedule in which a response on A delivered an immediate reinforcer of size 20 or 180 μl, whereas a response on B delivered an immediate reinforcer whose size was adjusted in accordance with the rat's choices. A third group received training under a schedule that did not entail variation of reinforcer size or delay, or choice between reinforcers, and a control group underwent food restriction without behavioural training. Exposure to the adjusting-delay schedule was associated with enhanced Fos expression in both the OPFC and AcbC, whereas exposure to the adjusting-magnitude schedule was associated with enhanced Fos expression in the OPFC but not the AcbC, compared to the control group. The results are consistent with previous findings that implicated the AcbC and OPFC in delay discounting, and the OPFC in sensitivity to reinforcer size.

Mechanisms of Individual Differences in Impulsive and Risky Choice in Rats

“…The mPFC has been implicated in the representation of reward incentive value (Peters & Büchel, 2010;Peters & Büchel, 2011), the encoding of the magnitude of future rewards (Daw, O'Doherty, Dayan, Seymour, & Dolan, 2005), the determination of positive reinforcement values (Frank & Claus, 2006), the processing of immediate rewards (McClure, Laibson, Loewenstein, & Cohen, 2004), and the determination of cost and/or benefit information (Basten, Heekeren, & Fiebach, 2010;Cohen, McClure, & Yu, 2007). The orbitofrontal cortex (OFC) contributes to both impulsive and risky choice (da Costa Araújo et al, 2010;Mobini et al, 2002) and is a candidate for encoding the action value of a choice (Hare, O'Doherty, Camerer, Schultz, & Rangel, 2008;Kable & Glimcher, 2009;Kringlebach & Rolls, 2004;Peters & Büchel, 2010;Peters & Büchel, 2011;Schoenbaum, Roesch, Stalnaker, & Takahashi, 2009). While these structures form only a portion of the reward valuation system, they are likely to play a central role in the determination of domain-general valuation of rewards that guides impulsive and risky choice behavior and should drive the correlations.…”

“…The orbitofrontal cortex (OFC) contributes to both impulsive and risky choice (da Costa Araújo et al, 2010;Mobini et al, 2002) and is a candidate for encoding the action value of a choice (Hare, O'Doherty, Camerer, Schultz, & Rangel, 2008;Kable & Glimcher, 2009;Kringlebach & Rolls, 2004;Peters & Büchel, 2010;Peters & Büchel, 2011;Schoenbaum, Roesch, Stalnaker, & Takahashi, 2009). While these structures form only a portion of the reward valuation system, they are likely to play a central role in the determination of domain-general valuation of rewards that guides impulsive and risky choice behavior and should drive the correlations.…”

“…The BLA is involved in processing sensory aspects of rewards (Blundell, Hall, & Killcross, 2001), so this structure should be considered as a potential candidate for producing individual differences in reward magnitude sensitivity that would be relevant in both tasks. The orbitofrontal cortex (OFC) is also involved in encoding reward magnitude (da Costa Araújo et al, 2010), so this is another potential candidate structure for reward magnitude processing that could affect performance on both impulsive and risky choice tasks. …”

Nucleus accumbens and delay discounting in rats: evidence from a new quantitative protocol for analysing inter-temporal choice

“…The principal dependent variable, the adjusting delay to the larger reinforcer (d B ), is seen to oscillate during an extended period of training, the amplitude of oscillation gradually declining as d B approaches a quasi-stable value, which is usually taken to represent the indifference delay, d B(50) (Mazur 1987(Mazur , 1988. da Costa Araújo et al (2009Araújo et al ( , 2010 suggested that the pattern of oscillation of d B , analysed using Fourier transform, may provide information about the effects of neurobiological interventions on the organism's adaptation to changing delays to reinforcement. Evidence obtained to date indicates that the power spectrum of oscillations is sensitive to the ratio of reinforcer sizes (q B /q A ; da Costa Araújo et al 2009Araújo et al , 2010Valencia-Torres et al 2011).…”

“…da Costa Araújo et al (2009Araújo et al ( , 2010 suggested that the pattern of oscillation of d B , analysed using Fourier transform, may provide information about the effects of neurobiological interventions on the organism's adaptation to changing delays to reinforcement. Evidence obtained to date indicates that the power spectrum of oscillations is sensitive to the ratio of reinforcer sizes (q B /q A ; da Costa Araújo et al 2009Araújo et al , 2010Valencia-Torres et al 2011). However, it seems not to be affected by lesions of the AcbC (da Costa Araújo et al 2009Araújo et al , 2010.…”