Yesterday I discussed a study on the possible link between the length and weight of a baby at birth and later intellectual functioning. One of the major strengths of that study was that they examined variations in weight and height in babies born within the normal range in terms of size and gestational age (not premature).  Among premature babies, the research has consistently shown an increased risk for later deficits, including lower intellectual capacity, higher rates of ADHD, learning disabilities, and other conduct problems. Yet the nature, or underlying neurocognitive mechanisms behind these deficits are poorly understood.

Deficits in executive functioning has been examined as a possible source of impairment in premature children. However, executive functioning is a broad term that refers to a number of cognitive processes, such as working memory, cognitive control, planning and organizing, etc, and it is unknown which of these components of executive functioning is particularly affected in preterm children.

The Journal of Abnormal Child Psychology recently published a comprehensive study of executive functioning among children born very preterm (less than 30 weeks gestation). The study included 50 premature children (27 boys, 23 girls) born at a mean gestational age of 28 weeks (range 25 to 30). The study also included 50 comparison children born at a mean gestational age of 37.7 weeks.  All children were about 6 years of age at the time of the study. Both groups completed a comprehensive battery of executive functioning tests (the Go/NoGo test, the Shape School task, the day-night stroop task. a verbal fluency task, Digit span, and the Object Classification Task for children). The children also completed a full IQ test (the WPPSI-R)

The Results:

Before controlling for processing speed and IQ, the premature children had significantly lower performance on tasks examining: accuracy and efficiency of cognitive switching, accuracy and efficiency of inhibitory control, verbal fluency, working memory, and concept categorization.

After controlling for processing speed and IQ separately, most of the previously observed differences remained, indicating that these deficits are not due to speed of processing or overall IQ. The only exception was efficiency in cognitive shifting, which was not different between these kids after controlling for processing speed.

The data suggest that impairments in executive functioning may be one of the underlying mechanism that contribute to the type of challenges that these children experience throughout childhood. However, the authors also raised one very interesting point. It is possible that these results do not reflect a stable pattern of deficits, but instead reflect a developmental lag. That is, these very preterm babies may just be delayed in the development of executive functioning skills and may not show the same patterns of deficits later in life.

The Reference: Aarnoudse-Moens, C., Smidts, D., Oosterlaan, J., Duivenvoorden, H., & Weisglas-Kuperus, N. (2009). Executive Function in Very Preterm Children at Early School Age Journal of Abnormal Child Psychology DOI: 10.1007/s10802-009-9327-z

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