Prefrontal lobe functioning and its relationship to working memory in preterm infants

IntroductionAdvances in medical technology continue to improve the survival rate of preterm infants, so that increasing numbers of children who weigh Extensive attempts have been made to identify sensitive predictors of later learning problems in both term and preterm children (5,6). It has been accepted that learning problems have multiple determinants, and it is important to consider the interactions of biological factors (such as medical complications and genetic endowment), environmental factors (such as demographic factors, quality of educational experience, socioeconomic, and psychosocial factors), and developmental factors (such as specific cognitive abilities and general development) (7). Frequently there is an association between perinatal risk and poor social circumstances. Several studies have demonstrated that social factors, particularly low educational level of the parents and socioeconomic status, play an important role in the intellectual outcome of both healthy full-term and preterm infants and those who had perinatal medical complications (8,9). The population of Very Low Birthweight (VLBW, birthweight between 1001-1500 grams) and Extremely Low Birthweight (ELBW, birthweight less than 1000 grams or 750 grams) infants is known to be at increased risk for a broad spectrum of health and developmental problems, and also an increased incidence of psychosocial disadvantages (e.g., poverty, single parenthood, youthful maternal age, and limited parental education), producing a -doubly vulnerable" population, which places their development in even greater jeopardy (10). The assessment of subtle developmental and behavioural delays in infants is complicated, and currently there are few sensitive measures available for the early identification of learning problems in infants. Conventional developmental assessment tools, such as the Bayley Scales of Infant Development, (11) only provide global indicators of development and fail to measure specific skills that may provide sensitive predictions of later learning.The assessment of specific cognitive skills, in particular working memory, rather than a global development score in infancy, has been advocated by a number of investigators (12,13). Working memory is defined as -the ability to maintain an appropriate problem solving set for the attainment of a future goal" (1). Working memory deficits have been linked to a range of developmental problems, including attentional deficit disorder (ADD), learning difficulties, and autism, all of which are more prevalent in children born preterm (14). Studying a group of infants at high-risk for learning difficulties should make it easier to identify factors that are predictive of later learning problems. This may lead to a greater understanding of the etiology of these problems in all children.In Welsh and Pennington's model of working memory, certain information remains at the forefront of cognition, despite distraction, and hence is active for the purpose of guiding appropriate responses. An important characteristic of working memory is that it is prospective, that is, its purpose is to attain a goal. Fuster (15) suggested that this is achieved not only by holding information in mind, but also by guiding goal directed actions. Graham and Harris (16) stated that working memory is also necessary in tasks which require strategy selection, monitoring, and revision of actions. This implies that working memory not only enables information to be held in mind but also to be manipulated. …