br Conclusions br Acknowledgements The authors would like

Conclusions
Acknowledgements The authors would like to thank Danielle Dellarco, Alexa Hubbard, Natasha Mehta, Gloria Pedersen, and Theresa Teslovich Woo for their help in recruiting and testing participants. We thank the Tenovin-6 who participated in this study. This work was supported by the National Institutes of Health (R01 NICHD 0691780, F31 NIMH 94056).
Introduction The preschool years (ages 3–5) represent a period of acute acceleration in the development of executive functions, and the neural systems that underlie them (Carlson, 2005; Garon et al., 2008). The preschool period is also a time when children rapidly develop emotion regulation skills important for adapting to everyday challenges (Garner and Power, 1996), making this a period in which one of these neurodevelopmental processes may be particularly sensitive to the development of the other and highly influenced by the environment. The mastering of associated cognitive and emotional skills are hypothesized to interact, as the child reaches the more advanced stages of development, and to forecast social and academic outcomes at school age (Loeber and Hay, 1997; Tramontana et al., 1988). There have, however, been few studies testing how cognition and emotion are integrated in the preschool years, particularly at the neural level (Crone, 2009). The integration of cognitive flexibility and emotion regulation in early childhood has been hypothesized as bi-directional (Zelazo and Cunningham, 2007). Researchers have postulated that emerging cognitive flexibility, defined as the ability to mentally switch between two or more demands (Scott, 1962), forms the basis of early emotion regulation strategies (Kopp, 1989; Zelazo and Cunningham, 2007). Relevant research has supported this hypothesis. For example, 5–6 year olds were able to flexibly change their thoughts and goals to reduce the intensity of negative affect (Davis et al., 2010). Relatedly, children who used a cognitive flexibility-based strategy, such as shifting their gaze or distracting themselves, delayed gratification longer than peers (Cole et al., 2011; Mischel and Mischel, 1983). Conversely, individual differences in emotion regulation may impact how executive functions like cognitive flexibility develop. It has been postulated that young children’s ability to successfully implement executive functions invariably involves managing accompanying emotion (Metcalfe and Mischel, 1999). Consider a 4 year-old who has been promised ice cream after dinner, but is given a cookie when his parents realize they are out of ice cream. To respond adaptively to this situation, the child would need to have both the flexibility to shift expectations and attention towards the pleasant but unanticipated treat, but also the emotion regulation abilities to modulate negative affect brought on by the unexpected outcome. The potentially concordant development of these skills suggests that cognitive flexibility and emotion regulation may share common neural substrates and mutually affect maturational change. Cognitive flexibility is associated with activation of the dorsolateral prefrontal cortex (DLPFC) in adults (Bunge and Crone, 2009), and these findings appear to extend to earlier developmental stages. Wood et al. (2009), using a numerical Stroop task, found that children ages 8–12 years, like adults, showed bilateral DLPFC activation when trying to sort numbers by numerical value instead of incongruent size. Morton et al. (2009) examined cognitive flexibility in children ages 11–13 years and adults who completed a modified version of the Dimensional Change Card Sort task (DCCS; Zelazo, 2006). Results showed increased DLPFC activation associated with switching dimensions in both children and adults. More recent advancements in functional Near Infrared Spectroscopy (fNIRS), a neuroimaging tool capable of measuring hemoglobin changes in the outer cortex non-invasively, has allowed researchers to measure neural activation in early childhood (Aslin and Mehler, 2005). Using fNIRS, Moriguchi and Hiraki (2009, 2011) recorded lateral PFC hemoglobin levels in preschool children and adults who completed a modified DCCS task. Results indicated that both preschool children and adults showed DLPFC activation while shifting mental sets. In addition, as children aged from 3 to 4 years, activation in this region increased as their performance improved.