The prefrontal cortex has been implicated in the mediation of executive processes that facilitate learning and memory. The authors hypothesized that children with prefrontal dysfunction related to phenylketonuria (PKU) would experience deficits in learning and memory because of impaired strategy use. They evaluated 23 children with PKU and 23 controls by using the California Verbal Learning Test-Children's Version (CVLT-C). General executive abilities were tested using the Stroop Color and Word Test, the Wisconsin Card Sorting Test, and phonemic and category fluency. Children with PKU, especially older children, showed poorer learning across trials and less use of semantic clustering on the CVLT-C but intact retention of previously encoded information. With the exception of phonemic fluency, deficits were not observed in general executive control. Results are discussed within the context of abnormalities in the prefrontal cortex and white matter of the brain.

The prefrontal cortex of the brain has been shown to play a crucial role in working memory, and age-related changes in prefrontal function may contribute to the improvements in working memory that are observed during childhood. We examined the developmental trajectory of working memory in school-age children with early-treated phenylketonuria (PKU), a metabolic disorder that results in prefrontal dysfunction. Using a recognition procedure, we evaluated working memory for letters, abstract objects, and spatial locations in 20 children with PKU and 20 typically developing control children. Children in both groups ranged from 6 to 17 years of age. Our findings revealed poorer performance across all three types of materials for children with PKU. In addition, there was a significant difference in the developmental trajectory of working memory for children with PKU as compared with controls. Specifically, deficits were not apparent in younger children with PKU. Instead, deficits were observed only in older children, suggesting the presence of a developmental deficit rather than a developmental delay in the working memory of children with PKU. (JINS, 2002,8, 1–11.)

This study examined whether children with early-treated phenylketonuria (ETPKU) exhibited a disruption in communication between the hemispheres as a function of computational complexity (Banich & Belger, 1990; Belger & Banich, 1992, 1998) when compared to neurologically uncompromised children who were matched in age and IQ. This investigation was motivated by findings that phenylketonuria affects myelination of neurons, including those that make up the corpus callosum, the main neural conduit for interhemispheric interaction. Children performed 2 tasks: a less complex physical-identity task and a more complex name-identity task. For both tasks, we compared performance on across-hemisphere trials, which require interhemispheric interaction, and on within-hemisphere trials, in which no hemispheric interaction is required. On the more complex name-identity task, children with ETPKU exhibited less of a benefit from across-hemisphere processing than did neurologically intact children. These results suggest that the interhemispheric interaction required to complete computationally complex tasks is compromised in children with ETPKU. Such an insufficiency may explain some of the attentional deficits observed in this group of children.

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