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Abstract:
Phenylketonuria (PKU) is a congenital metabolic disorder
whose early and continuous treatment (ECT-PKU) leaves central
nervous system tyrosine levels slightly depressed,
disproportionately affecting the prefrontal cortex (PFC) dopamine
system, and selectively impairing cognitive functions dependent on
dorsolateral PFC (DLPFC) (working memory and inhibitory control).
ECT-PKU provides an exciting model for investigating the role of
DLPFC in various domains. We gave ECT-PKU children (6-16 years old)
and age-matched controls a task probing lexicon and grammar.
Subjects were asked to produce regular past tenses and plurals,
which are computed by the application of grammatical suffixation
rules, and irregular forms, which must be retrieved from lexical
memory. ECT-PKU children were worse than control children at
producing past tenses and plurals of irregulars, but not regulars.
The impairment at irregulars is consistent with evidence linking
PFC with the search/retrieval of lexical/semantic information. The
ECT-PKU children's deficit is also consistent with inhibitory
control problems, such that retrieval of an irregular fails to
inhibit the regular rule, yielding an increase in
over-regularizations (e.g., digged). Indeed, the majority of their
errors on irregulars were over-regularizations. The apparent
sparing of regulars suggests that grammatical rule processing,
which has previously been linked to frontal regions, may depend on
frontal areas other than DLPFC. NICHD R01-HD35453; Army
DAM-17-93-V-3018; McDonnell-Pew grant
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