Phonological Short Term Memory Impairment in Children with Down syndrome

Abstract

own syndrome (DS) is a complex genetic disorder caused by the presence of three copies of the whole or part of the chromosome 21 in humans. The resulting gene-dosage imbalance is responsible for a variety of phenotypes affecting various organs and notably leads to intellectual disability (ID) in the whole DS population. Some characteristics of the syndrome are near universal, including a characteristic facial appearance, learning disability, muscle hypotonia, motor dysfunction, and Alzheimer’s disease neuropathology after 35 years of age. However, there are large individual differences in the DS phenotype and severity of associated symptoms. Besides the mild to severe ID, language is often reported to be a domain of particular difficulties. Children and adolescents with DS reach developmental language milestones only with a considerable delay, often lagging even behind expectations based on their nonverbal mental development. Phonological short term memory (PSTM) is another domain where individuals with DS are significantly impaired in comparison to control participants matched in nonverbal mental age. PSTM is a component of working memory. Most prominent in research on developmental language disorders is Baddeley’s model of working memory. The model consists of two modality-specific short-term storage systems where restricted amounts of information can be maintained for only a short period of time: the visuo-spatial sketchpad concerned with visual and spatial information and the phonological loop responsible for the temporary storage of phonological representations. The phonological loop has two components; a storage component (the phonological store) and an articulatory subvocal rehearsal process. Speech-based information has automatic access to the phonological store, but suffers from forgetting from this passive store over time. However, forgetting can be countered by active subvocal rehearsal of this information which is thought to refresh items within the store.