This study tested prefrontal and hippocampal functions in a sample of 28 school-aged (M = 14.7 years, SD = 2.7) individuals with Down syndrome (DS) compared with 28 (M = 4.9 years, SD = .75) typically developing children individually matched on mental age (MA). Both neuropsychological domains were tested with multiple behavioral measures. Benchmark measures of verbal and spatial function demonstrated that this DS sample was similar to others in the literature. The main finding was a significant Group x Domain interaction effect indicating differential hippocampal dysfunction in the group with DS. However, there was a moderate partial correlation (r = .54, controlling for chronological age) between hippocampal and prefrontal composite scores in the DS group, and both composites contributed unique variance to the prediction of MA and adaptive behavior in that group. In sum, these results indicate a particular weakness in hippocampal functions in DS in the context of overall cognitive dysfunction. It is interesting that these results are similar to what has been found in a mouse model of DS. Such a model will make it easier to understand the neurobiological mechanisms that lead to the development of hippocampal dysfunction in DS.
Everyone perseverates at one time or another, repeating previous behaviors when they are no longer appropriate. Such perseveration often occurs in situations with working memory demands, and the ability to overcome perseveration has been linked to brain regions critical for working memory. Many theories thus explain perseveration in terms of working memory deficits. However, perseveration also occurs in situations without apparent working memory demands, in which the visible environment specifies appropriate behavior. Such findings appear to challenge working memory accounts of perseveration. To evaluate this challenge, a neural network model of a working memory account of perseveration was tested on tasks with visible solutions. With advances in the mechanisms that support working memory, networks became increasingly able to attend to relevant information in the environment. These developments led to improvements in performance on tasks with visible solutions, paralleling the developmental progression observed in infants. The simulations demonstrate how mechanisms of working memory can subserve perseveration and success on tasks with and without obvious memory demands. In both types of tasks, controlled processing occurs through the activation of task-relevant representations, which provide top-down biasing of other processing pathways. More generally, the simulations demonstrate how common mechanisms can support working memory and attention.
The developmental modeling approach to investigating developmental disorders appears highly promising. In this commentary, we question the untapped potential of this approach for supporting insights into particular developmental disorders, developmental processes across the life span, and the viability of traditional theories of developmental disorders.
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