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Chapter 5
accompanied by reward-based changes in flexible cognitive control, where older participants
no longer exhibit an effect of reward motivation on task switching performance.
Reward-induced changes in the speed-accuracy tradeoff have not been widely studied, and
never in the context of a cognitive task. However, at least one study suggests that potential
rewards can induce more cautious (i.e. more accurate and slow) behavior (Bijleveld et al.,
2010). We replicate this effect in the cognitively less demanding repeat trials by showing that
young participants exhibit reward-induced cautious behavior in the repeat condition. We
extend this finding by showing that reward induced less accurate and faster responding on
the more demanding switch trials in younger participants. These results suggest that reward
can modulate cautious behavior differentially in distinct cognitive conditions.
Reward motivation, cognitive control and the interaction between reward and cognitive
control implicate, among other mechanisms, dopamine in the striatum (Roberts et al., 1994;
Ikemoto and Panksepp, 1999; Aarts et al., 2010; Aarts et al., 2011). Furthermore, changes in
speed-accuracy tradeoff strategies have been associated with changes in connectivity between
the cortex and the striatum (Bogacz et al., 2010). More specifically, stronger corticostriatal
connections have been found to promote faster (and premature) responses. The current
study does not address the neural mechanisms of age-related effects on rewarded task
switching directly. However, several independent studies have revealed age-related changes
in dopamine signaling (Volkow et al., 1996b; Bäckman et al., 2000) Erixon-Lindroth et al.,
2005), starting in early adulthood (Backman and Farde, 2005). Also, age-related decreases in
corticostriatal connectivity, accompanied by slower (and more accurate) responses have been
reported (Forstmann et al., 2011). Accordingly, here, we put forward the hypothesis that the
observed change in speed-accuracy strategy during the integration of reward and cognitive
performance reflects reduced dopamine signaling in the striatum, and a subsequent reduction
in the adaptation of corticostriatal responses to the task conditions. The increased effect of
reward in younger versus older participants is also in line with a number of previous findings
in adolescents. First, neuroimaging work has revealed increases in reward sensitivity and
ventral striatal responses in adolescents (Somerville and Casey, 2010). In addition, previous
work has reported reward-related improvements in impulse control in adolescents (Kohls et
al., 2009; Geier et al., 2010). In older participants, however, if anything a decrease in reward
sensitivity is reported (Schott et al., 2007; Rademacher et al., 2014). We extend these findings
by showing that young (i.e. < 26 years old) subjects can show reward-related adaptations of
flexible cognitive control during task switching, whereas older participants (i.e. > 25 years
old) cannot.
One limitation of the current study is the fact that we pooled data from several studies. As
a result, there are a number of factors of no interest that differ as a function of age, such as
effects of maximum available reward. However, we accounted for this by replicating the effects
in a subgroup of participants who received exactly the same amount of reward and number of
trials. Nevertheless, it is clear that the reported results require replication in future, preferably
longitudinal, work using a single study set-up. Also, it should be noted that a large number of