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  • Behavioral studies indicate peak sensitivity to

    2018-11-09

    Behavioral studies indicate peak sensitivity to reward during adolescence (Cauffman et al., 2010), yet neuroimaging results have been inconsistent. Functional magnetic resonance imaging (fMRI) studies have shown developmental peaks in striatal activation when processing rewards (Ernst et al., 2005; Galvan et al., 2006; Geier et al. 2010; Padmanabhan et al. 2011; Van Leijenhorst et al., 2010), as well as developmental troughs (Bjork et al., 2004, 2010; Lamm et al., 2014). Relatively less is known about the development processes underlying loss compared to what is known of these processes for reward (Spear, 2011). In adults, behavioral economics studies indicate that losses are valued two-fold compared to gains (Kahneman and Tversky, 1979; Tversky and Kahneman, 1992) suggesting a psychological difference between rewards and losses. Behaviorally, adolescents and adults tend to exhibit similar levels of loss-aversion, while neuronally adolescents recruit striatal and frontal regions to a greater degree than adults when making decisions involving losses (Barkley-Levenson et al., 2012; Weller et al., 2010). While the circuitry underlying the processing of losses and gains similarly include anterior cingulate, nucleus accumbens (NAcc), and amygdala, it UNC2025 is differentially engaged during these two types of tasks (Levin et al., 2012; Tom et al., 2007). In concert with motivation, inhibitory control, which is a core component of executive function, continues to mature through adolescence (Bunge et al. 2002; Fischer et al., 1997; Luna et al., 2004; Munoz et al., 1998) supported by age-related changes in frontoparietal activation (Bunge et al., 2002; Ordaz et al., 2013). The antisaccade (AS) task probes the integrity of cortico-subcortical inhibitory control (Hallett, 1978) and elicits decreases in dorsolateral PFC activation from childhood to adolescence, when it reaches adult-like levels (Ordaz et al., 2013). The AS task elicits increases in dACC activation from childhood into adulthood, and correlates with performance (Ordaz et al., 2013). These results suggest that inhibitory control is largely available by adolescence but with continued specialization that may undermine cognitive control and influence decision-making. The effect of incentives on cognitive control have shown that incentives enhance activation in task-relevant neural regions (Krawczyk UNC2025 and D’Esposito, 2011; Krawczyk et al., 2007; Locke and Braver, 2008; Yamamoto et al., 2013). In a rewarded AS task, behavioral performance was greater for reward than for non-reward trials, and rewards activated oculomotor circuitry supporting inhibitory control (Geier et al., 2010). Alternatively, others have found that when reward is contingent on suppressing an small immediate reward in favor of a larger delayed reward, regions supporting inhibitory control show relatively decreased activation (O’Connor et al., 2012). The authors suggest that successful inhibitory control over an immediate reward requires attentional disengagement. This would be similar to behavioral studies that have found success in delay of gratification to be facilitated by strategies that involve diverting attention from the immediate reward by engaging in other activities, such as making up unrelated games (Mischel et al., 1989). To examine the developmental effects of potential rewards and losses on cognitive control, we performed an incentivized AS fMRI study using an accelerated longitudinal design. The study sample consisted of individuals ranging from 10- to 20-years of age, with each being sampled two or three times at approximately 15-month intervals. We selected 22 regions typically associated with reward processing and inhibitory control and thought to underlie incentive and cognitive processing, including those that have been found to change through development (e.g. striatum, orbitofrontal cortex, ventromedial prefrontal cortex). Based on past results (Ernst et al., 2005; Galvan et al., 2006; Van Leijenhorst et al., 2010) including our own (Geier et al., 2010; Padmanabhan et al., 2011), we make the following hypotheses. Activation in reward and cognitive control regions will show distinct age related effects across different incentives. During incentive trials, activity in ventral striatum will peak during adolescence while it will not change in neutral trials. Performance will improve with age, and with incentives, especially in younger subjects. As a second aim, we also sought to characterize the shape (linear vs. curvilinear) of developmental trajectories afforded by a longitudinal design.