, 2011). Roesch et al. (2009) reported that nucleus accumbens neurons integrate information about the value of an expected reward with features of the motor output (i.e., response speed or choice) that occur during decision making. DA release may set a threshold for worthwhile cost expenditures, and under some signaling pathway circumstances may provide an opportunistic drive for exploitation of resources (Fields et al., 2007; Gan et al., 2010; Beeler et al., 2012). This suggestion is consistent with the proposed involvement of accumbens

DA in the behavioral economics of instrumental behavior, particularly in terms of cost/benefit decision making (Salamone et al., 2007, 2009). As stated above, organisms typically are separated from primary motivational stimuli or goals by obstacles Olaparib ic50 or constraints. Another way of saying this is that the process of engaging in motivated behavior requires that organisms overcome the “psychological distance” between themselves and motivationally relevant

stimuli. The concept of psychological distance is an old idea in psychology (e.g., Lewin, 1935; Shepard, 1957; Liberman and Forster, 2008) and has taken on many different theoretical connotations in different areas of psychology (e.g., experimental, social, personality, etc.). In the present context, it is simply used as a general reference to the idea that objects or events are often not directly present or experienced, and therefore organisms are separated along multiple dimensions

ID-8 (e.g., physical distance, time, probability, instrumental requirements) from these objects or events. In various ways, mesolimbic DA serves as a bridge that enables animals to traverse the psychological distance that separates them from goal objects or events. Multiple investigators have phrased this in diverse ways or emphasized different aspects of the process (Everitt and Robbins, 2005; Kelley et al., 2005; Salamone et al., 2005, 2007, 2009; Phillips et al., 2007; Nicola, 2010; Lex and Hauber, 2010; Panksepp, 2011; Beeler et al., 2012; see Figure 2), but many of the functions in which accumbens DA has been implicated, including behavioral activation, exertion of effort during instrumental behavior, Pavlovian to instrumental transfer, responsiveness to conditioned stimuli, event prediction, flexible approach behavior, seeking, and energy expenditure and regulation, are all important for facilitating the ability of animals to overcome obstacles and, in a sense, transcend psychological distance. Overall, nucleus accumbens DA is important for performing active instrumental responses that are elicited or maintained by conditioned stimuli (Salamone, 1992), for maintaining effort in instrumental responding over time in the absence of primary reinforcement (Salamone et al.