Review
Neuropsychological outcomes of children born very preterm

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Summary

Considerable research has investigated the consequences of being born very preterm (VP; <32 weeks of gestation), especially in relation to cognitive functioning. While numerous cognitive and neuropsychological outcome studies have been published, it is important to consider methodological issues when reviewing this research, as the generalizability of the studies varies greatly. This article describes the nature of cognitive difficulties confronting VP children, both in terms of the frequency and severity of deficits. The breadth of cognitive difficulties reported in this population implies a generalized cognitive impairment; however, the presence of selective or primary cognitive deficits is discussed. It is concluded that whereas mortality and neonatal morbidity rates have decreased significantly in VP infants in recent decades, these children continue to be at significant risk for cognitive impairments and need to be closely monitored throughout childhood.

Introduction

This review article describes the nature of the cognitive impairments exhibited by very preterm (VP) children. As well as examining general outcomes such as IQ and academic achievement, functioning in specific cognitive domains are reviewed, including processing speed, attention, visual–spatial abilities, language, memory and learning, and executive function.

Section snippets

Methodological considerations

The quality of VP outcomes studies varies greatly and study design requires careful consideration when reviewing the cognitive outcome literature. Before the 1990s, the inclusion criteria for outcome studies tended to be based on birth weight [e.g. very low birth weight (VLBW), <1500 g; extremely low birth weight (ELBW), <1000 g] rather than on gestational age due to the lack of certainty of obstetric estimation. Whereas birth weight and gestational age are related, they are not interchangeable

General cognitive ability

The foundation of neuropsychological assessments is an assessment of general cognitive ability (IQ). Numerous IQ measures are reported in the literature, and in recent times there has been a movement towards abbreviated measures, which allows additional time to evaluate specific cognitive domains. However, caution is needed when interpreting IQ scores from abbreviated measures as they are based on fewer tasks and assess fewer abilities. Even more caution is needed when abbreviated scales are

Processing speed

Processing speed refers to the time required to interpret and respond to incoming stimuli or information, and is assessed by measures of reaction time and decision time. Processing speed is an ‘elementary’ cognitive process [13], as it is critical to the functioning of other cognitive domains. Processing speed develops rapidly in childhood [14], and its developmental trajectory mimics that of working memory and fluid intelligence, leading to speculation that increasing efficiency in information

Attention

Attention is another core cognitive ability, critical for the acquisition of new skills and knowledge [20]. Attention is a multifaceted construct [21], [22], consisting of the capacity to selectively focus (i.e. focus on relevant stimuli and ignore distracting stimuli), sustain (i.e. maintain alert state for extended period), encode (i.e. hold information in temporary store), shift (i.e. fluently transfer focus from one activity to another), and divide attention (i.e. focus on multiple

Visual and perceptual skills

Visual sensory, perceptual and motor skills are important for academic functioning, social interactions and other everyday activities [26]. Thought to be related to retinopathy of prematurity or periventricular white matter injury, an elevated rate of visual problems is often reported in preterm children, including impaired visual acuity and contrast sensitivity, and strabismus [27], [28], [29]. Visual perceptual difficulties have also been reported in VP children [28]. In a recent study of

Memory and learning

Memory is a complex system which is fundamental for everyday functioning. New information enters immediate memory, and, while in this temporary storage system, can be processed or manipulated – a capacity referred to as working memory. Information in temporary storage can be transferred to long-term memory. Implicit (procedural) and explicit (declarative) memory are two forms of long-term memory, with the majority of outcome studies focusing on explicit memory ability. Explicit memory can be

Language

Language and communications skills are critical for interpersonal relationships and social interactions, and are highly correlated with academic achievement [46]. Whereas language is commonly divided into expressive and receptive skills, a comprehensive evaluation assesses semantics (meaning of words and sentences), grammar (sentence structure), phonological awareness (speech sounds), discourse (understanding passages of text or conversation) and pragmatics (use of language in social contexts)

Executive function

Executive functioning refers to a set of inter-related cognitive skills needed for purposeful, goal-directed behavior [49]. Numerous skills have been linked to executive functioning, including (a) anticipation and deployment of attention, (b) impulse control and self-regulation, (c) initiation of activity, (d) working memory, (e) mental flexibility and utilization of feedback, (f) planning ability and organization, (g) selection of efficient problem-solving strategies, and (h) monitoring of

Educational outcomes

Research consistently demonstrates that VP children perform poorer on standardized measures of academic attainment *[2], [52], [53], [54]. For example, a large geographic cohort of EP/ELBW 8-year-olds performed 0.5–0.6 SD below matched term controls on tests of reading, spelling and mathematics [2]. The level of academic underachievement increases with decreasing gestational age ∗[35], [55], and at 11 years of age the EPICure cohort (<26 weeks of gestational age) performed below term classmates

Selective versus generalized cognitive impairment

The VP population is vulnerable to impairments in all cognitive domains, which would imply a generalized cognitive impairment *[2], [54]; however, the presence of selective or primary impairments is still possible. For example, working memory, attention and processing speed are core cognitive skills, and deficits in these domains may at least partly explain difficulties in higher-order learning, language and executive function domains.

Determining the profile of cognitive vulnerabilities in VP

Summary

The breadth of cognitive difficulties highlighted in this review paints a relatively grim picture for families and health professionals of VP children. However, in reality, the majority of VP children have relatively mild impairments or no problems at all and go on to live very productive lives [62]. Whereas numerous risk and resilience factors have been associated with long-term impairments in VP survivors, it is clear that outcome is ultimately related to an interplay of genetic, medical,

Conflict of interest statement

None declared.

Funding sources

This work was supported by the Australian National Health and Medical Research Council (Senior Research Fellowship ID 628371 to PA), and the Victorian Government Operational Infrastructure Support Program.

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