Down syndrome (DS) is the most common genetic form of intellectual disability. DS results in a characteristic proﬁle of cognitive and neurological dysfunction. The predominant theory of the pattern of neural deﬁcits in this syndrome suggests that DS aﬀects ‘late-developing’ neural systems, including the function of the prefrontal cortex and hippocampus. In order to evaluate the validity of this theory, in this review, I highlight data addressing the neurological and cognitive phenotype in DS across development. In particular, I address the evidence suggesting that DS may impact late-developing neural systems and end with the conclusion that some cognitive diﬃculties in DS must result from poor communication between late-developing regions. Analogous to recent theories of cognitive processing in autism, cognitive deﬁcits in DS may be substantially impacted by less eﬃcient interregional communication. Finally, I discuss some ways in which understanding the impact of altered neurodevelopment in DS has the potential to inform our understanding of species-typical trajectories of cognitive development. WIREs Cogn Sci 2013, 4:307–317. doi: 10.1002/wcs.1221
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