The present study used a

The present study used a novel, child-friendly, and fNIRS compatible Stroop task for preschool children. As such, our finding that the Pet Store Stroop Task elicited left DLPFC activation, in children as young as three years, makes several contributions to the cognitive development literature. While previous work has explored children’s neuro-electrical activity during a cognitive flexibility task (see Wolfe and Bell, 2004, 2007), it is only recently, through non-fMRI techniques, that researchers have localized anatomical neural substrates of preschool cognitive flexibility. This small body of literature has largely focused on neural activation during the Dimensional Change Card Sort task (DCCS; Zelazo, 2006), a task with distinct differences from the Pet Store Stroop Task. For example, most 3 year olds fail the DCCS (are unable to shift from sorting stimuli along one dimension to sorting along a second dimension) while most 5 year olds pass (Zelazo, 2006). In the present study, while Stroop performance improved with age, 3 year olds were still able to understand and successfully complete the Pet Store Stroop Task (3 year olds were 51% accurate on Stroop trials and 62% accurate on Non-Stroop trials, with a 25% chance rate). In addition, two fNIRS studies by Moriguchi and Hiraki (2009, 2011) using the DCCS in 3–5 year-old children found significant pre-post switch 5z increases only among children capable of passing the DCCS, not in the significant number of 3 year-olds who failed. In contrast, in the Pet Store Stroop Task, 3 year-olds showed significant DLPFC activation between Stroop and Non-Stroop conditions. This finding suggests that the neural substrates of cognitive flexibility might develop more continuously rather than in the stage-like (Piaget, 1971) format that has been previously measured by existing tasks. The DCCS and Pet Store Stroop Task thus represent complementary strategies for investigating early cognitive flexibility. The high difficulty level of the DCCS may be ideal for detecting age effects, whereas the low difficulty and repetitive trials of the Pet Store Stroop Task may be uniquely suited for detecting cognitive flexibility-related neural variability when behavioral abilities related to executive functions are in the early stages of emergence. Some have suggested that certain emerging executive functions are strongly integrated with managing emotion while others are more removed from emotion (Zelazo and Carlson, 2012). This contention is largely based on studies showing that executive functions presumed to involve managing emotion, such as inhibitory control, and executive functions presumed to be distinct from emotion, such as cognitive flexibility, load onto separate factors (Kim et al., 2013; Willoughby et al., 2011). The Pet Store Stroop Task used in the present study had no reward associated with performance and was designed to be consistent with other, non-emotional, “cool”, measures of cognitive flexibility (Zelazo et al., 2005). Without the neural activation data collected in the present study, the non-association between irritability and Stroop performance might suggest that individual differences in children’s response to frustration are unrelated to developing cognitive flexibility. Instead, we found evidence that in order to perform at the level of their peers, preschoolers with relatively higher but non-impairing levels of irritability showed greater DLPFC activation during our cognitive flexibility task. Given the importance of cognitive flexibility in the development of competent social and academic functioning (Blair and Razza, 2007; Clark et al., 2002), the field has seen an increase in interventions designed to directly strengthen cognitive flexibility in preschool children (e.g. Bodrova and Leong, 2007). The integration of irritability and cognitive flexibility in early childhood suggests that individual differences in irritability might predict preschool children’s response to training programs designed to boost executive functions. Alternatively, early childhood interventions that target both emotion regulation and cognitive flexibility may be more efficacious.