Differential effects on effort discounting induced by inactivations of the nucleus accumbens core or shell.

Abstract

The authors investigated the contribution of the nucleus accumbens (NAc) core and shell to effort-based decision making using a discounting procedure. Selection of 1 lever delivered a smaller, 2-pellet reward immediately, whereas the other lever delivered a 4-pellet reward after a fixed ratio of presses (2, 5, 10, or 20) that increased over 4 blocks of 10 discrete choice trials. Subsequent testing employed an equivalent delays procedure, whereby the relative delay to reward delivery after selection of either option was equalized. In well-trained rats, inactivation of the core, but not the shell, via infusion of GABA A/B agonists muscimol/baclofen reduced preference for the high-effort option under standard conditions and also when rats were tested using an equivalent delays procedure. However, inactivation of the core did not alter preference for 4-pellet versus 2-pellet rewards when the relative costs of each option were the same (1 press). Thus, the NAc core, but not the shell, appears to be part of a neural circuit that biases choice toward larger rewards associated with a greater effort cost. Furthermore, the contributions by the NAc core to this form of decision making can be dissociated from its role in delay discounting.

Motivational states influence effort-based decision making in rats: The role of dopamine in the nucleus accumbens

“…These findings suggest that in a cost-benefit task such as the one used in our study, the AcbS could be one important subregion that, via DA-ergic mechanisms, mediates the effects of a downshift in motivation on effort allocation. Contrasting with this view, a recent study suggested that the AcbC rather than the AcbS is part of the neural circuit mediating effort-based decision making (Ghods-Sharifi & Floresco, 2010). However, to allow for an adaption to motivational states, the AcbS could impact in an indirect manner on the neural circuit mediating effort-based decision making-for instance, by feedforward propagation of information from the AcbS to the AcbC via striatonigrostriatal pathways (Haber, Fudge, & McFarland, 2000).…”

“…On the basis of these findings, changes in accumbens DA efflux have been suggested to mediate effects of motivational states on effort-based decision making (Phillips, Walton, & Jhou, 2007); however, empirical evidence in support of this account is lacking. Recent studies have further indicated that the core subregion of the nucleus accumbens (AcbC; Hauber & Sommer, 2009;Salamone, Correa, Farrar, & Mingote, 2007), but not the shell subregion (AcbS; Ghods-Sharifi & Floresco, 2010), plays a key role in effort-based decision making. Moreover, accumbens DA depletions encompassing AcbC and AcbS rendered rats cost-aversive (Cousins, Atherton, Turner, & Salamone, 1996;Salamone, Cousins, & Bucher, 1994).…”

Toll-Like Receptor 4 Deficiency Causes Reduced Exploratory Behavior in Mice Under Approach-Avoidance Conflict

“…Although GABAergic interneurons make up about 2% of all neurons in the NAc [41], GABA receptor agonists have been widely used to inactivate the NAc [42,43]. Infusion of one tenth of the regular doses of GABA receptor agonists into the NAcSh was effective in rescuing the novelty-seeking behavior of TLR4 -/-mice under motivational conflict.…”

Contributions of the nucleus accumbens and its subregions to different aspects of risk-based decision making

“…Many of these studies have focused on the contribution of this nucleus to effortor delay-related judgments. Thus, lesion or inactivation of the NAc core reduces the preference to work harder or wait longer for larger rewards (Cardinal, Pennicott, Sugathapala, Robbins, & Everitt, 2001;Ghods-Sharifi & Floresco 2010;Hauber & Sommer, 2009;Pothuizen, Jongen-Rêlo, Feldon, & Yee, 2005). These forms of decision making are also altered by manipulations of the basolateral amygdala (Ghods-Sharifi, Winstanley, Theobald, Cardinal, & Robbins, 2004) or different regions of the prefrontal cortex (Mobini et al, 2002;Rudebeck, Walton, Smyth, Bannerman, & Rushworth, 2006;Winstanley et al, 2004), regions that have also been implicated in decision-making processes in humans.…”

“…Accordingly, lesions of the NAc core or shell have been reported to produce dissociable effects on a variety of behaviors, including instrumental action, latent inhibition, set shifting, and cue-induced reinstatement of food-seeking behavior (Corbit, Muir, & Balleine, 2001;Floresco, GhodsSharifi, Vexelman, & Magyar, 2006;Floresco, McLaughlin, & Haluk, 2008;Weiner, 2003). Studies of cost/benefit decision making using subregion-selective manipulations of the NAc have also identified dissociations between the core and the shell, with the core appearing to play a more critical role than the shell in mediating both delay-and effort-based decision making (Cardinal et al, 2001;Ghods-Sharifi & Floresco, 2010;Hauber & Sommer, 2009;Pothuizen et al, 2005). With respect to risk-based decision making, Cardinal and Howes (2005) lesioned the more lateral portions of the NAc core, but these lesions also included considerable damage to the more medial portions of the shell.…”