Proefschrift_Holstein

Reward modulation of cognitive function: aging

Introduction The world around us is changing constantly, imposing on us an overwhelming amount of information, choices and temptations. The ability to adapt behavior flexibly to these constant changes is a hallmark of human cognition and requires flexible cognitive control. This is a complex, multifactorial construct, but generally refers to the ability to inhibit impulses, set, maintain and update goals and pursue them without being distracted. Failures in the ability to exert flexible cognitive control can have vast consequences, leaving our economies a wreck and our traffic deadly. Aging is one of today’s grand societal challenges. The current proportion of people aged 60 and older is 23% in developed countries and still increasing (United_Nations, 2012). As people age, their ability to look after themselves decreases and most people will eventually require assistance or permanent care. Many of the day-to-day tasks that are required to live independently have a cognitive component. It is well established that older participants are impaired in several aspects of cognition, including memory, speed of processing, task switching (Salthouse, 1996; West, 1996; Kray et al., 2002; Park et al., 2002), and interference- and inhibitory control (i.e. stopping automatic tendencies or motor impulsivity) (Rush et al., 2006; van de Laar et al., 2011). At least some aspects of age-related cognitive decline may begin already early in adulthood (i.e. from 20 years onwards) (Salthouse, 2009) Task switching, which is considered an important aspect of flexible cognitive control (Monsell et al., 2003), encompasses the ability to quickly update current task demands and to adapt behavior accordingly. It is this cognitive ability that is the focus of the current paper, given accumulating evidence that it is particularly sensitive to aging (Van Asselen and Ridderinkhof, 2000; Kray et al., 2002), (but see Wasylyshyn et al., 2011). However, in addition to cognitive deficits, aging is also accompanied by reward and motivational anomalies. For example, studies have shown age-related deficits in reward-related processing and reward learning (Marschner et al., 2005; Mell et al., 2005; Schott et al., 2007; Chowdhury et al., 2013), (but see Samanez-Larkin et al., 2007). Although often studied as separate entities, reward and cognition interact closely: Adaptive behavior becomes more important when higher rewards are at stake. Indeed, several studies have shown that reward motivation can improve cognitive performance (e.g. Locke and Braver, 2008; Aarts et al., 2010; Pessoa and Engelmann, 2010; van Holstein et al., 2011; Braver et al., 2014). In fact, reward-related deficits have been argued to underlie at least some of the cognitive processing deficits observed in psychiatric disorders, such as attention deficit hyperactivity disorder (ADHD) and schizophrenia (Velligan et al., 2006; Aarts et al., 2015). This might also be true for cognitive deficits in aging. In the current study, we used a task-switching paradigm in which we manipulated the amount of reward participants could earn on each trial to test the hypothesis that aging across the life span is accompanied by reduced impact of reward motivation on flexible cognitive control. Given the hypothesis that age-related decreases in cognitive functioning may start early in

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