UBC Theses and Dissertations
Dissociable involvement of the nucleus accumbens subregions in effort-based decision making Ghods-Sharifi, Sarvin
Animals routinely engage in cost-benefit analysis, choosing between different courses of actions with potentially greater response costs that may lead to greater rewards. Previous research has shown that the preference to exert more physical effort to obtain a larger magnitude of reward is mediated by a complex neural circuit including the anterior cingulate, basolateral amygdala, and mesoaccumbens dopamine system. Past studies investigating the neural basis of effort-based decision making have utilized a T-maze task whereby rats have had to choose between climbing a barrier in one arm to obtain a high reward (HR), or retrieve a low reward (LR) from an arm with no barrier. Destruction of dopamine terminals in the nucleus accumbens (NAc) has been shown to reduce the preference to work harder to obtain a larger reward. Yet, the role of the different subregions of the NAc on this form of decision making is not very clear. The present study investigated the contributions of the NAc core and shell in effort-based decision making using an automated procedure conducted in an operant chamber. The task consisted of 4 discrete blocks of 10 trials. A response on one lever delivered an LR immediately (2 reward pellets), whereas responding on the other lever delivered an HR (4 pellets) after a fixed ratio of presses, which increased with each block (2, 5, 10, or 20). Inactivation of the NAc core, but not shell, via infusion of GABAA/B agonists muscimol/baclofen (75 ng each) reduced the preference for animals to exert greater effort to obtain the HR. In order to control for the greater delay from initiation of response to delivery of reward in the HR compared to LR condition, we conducted a subsequent experiment that equalized the delay. Inactivation of the core, but not shell reduced the preference for the HR. Therefore the NAc core, but not the shell, is part of a neural circuit that mediates effort-based decision making. Additionally the contributions by the NAc core to this form of decision making are distinct from those involving delay-based decisions.
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