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Fetal Alcohol Exposure Slows Cognitive Processing

Cognitive Effects Can Be Long-Lasting

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Updated August 15, 2005

Decades of research have left little doubt that prenatal alcohol exposure has adverse effects on intellectual and neurobehavioral development. A recent study of the effects of moderate to heavy prenatal alcohol exposure on cognitive function confirms earlier findings of slower processing speed and efficiency, particularly when cognitive tasks involve working memory. Results are published in the August 2005 issue of Alcoholism: Clinical & Experimental Research.

"Prenatal alcohol exposure is often associated with slower reaction times and poorer attention in infancy, and some of these deficits may be at the core of poorer academic performance and behavior problems often seen later in childhood," said Matthew J. Burden, postdoctoral research fellow at Wayne State University School of Medicine and corresponding author for the study.

"In cases of fetal alcohol syndrome (FAS) … lower IQ scores are common, often reaching the level of mental retardation. This is because alcohol consumed by the mother has a direct impact on the brain of the fetus. However, full fetal alcohol syndrome is not required to see this impact; it is just less obvious to detect across the array of exposures found in fetal alcohol spectrum disorders (FASD), which include effects of prenatal alcohol at lower drinking levels."

Julie Croxford, graduate research assistant at Wayne State University, says there is a need for researchers to look at the damage caused by prenatal alcohol exposure at lower-than-heavy levels of drinking. "In the past, much focus was placed on studying the full-blown fetal alcohol syndrome," she said. "More recent research has considered those individuals damaged by lower levels of exposure. This is an important focus."

For this study, researchers assessed 337 African-American children (197 males, 140 females) at 7.5 years of age; selected from the Detroit Prenatal Alcohol Longitudinal Cohort, the children were known to have been prenatally exposed to moderate-to-heavy levels of alcohol. Their mothers were originally recruited between September 1986 and April 1989 during their first prenatal visit to a maternity hospital clinic.

Distinct Aspects of Cognition

The children were assessed on processing speed and efficiency in four domains of cognitive function – short-term memory scanning, mental rotation, number comparison, and arrow-discrimination processing – using a Sternberg paradigm, which examines speed of completion as problems become increasingly more difficult.

"We chose these four domains because they allow us to study distinct aspects of cognition within the same cognitive framework," said Burden. "This helps to distinguish potentially specific deficits from those that are more global in nature; that way we get a better understanding of how prenatal alcohol exposure affects cognitive functioning many years later in childhood."

Speed Slowed Significantly

Although the alcohol-exposed children were able to perform as well as the other children when tasks were simple – such as naming colors within a timed period – when pressed to respond quickly while having to think about the response, their processing speed slowed down significantly.

"This suggests that processing speed deficits are more likely to occur within the context of some cognitive demand," said Burden. "We also found that prenatal alcohol exposure was associated with poorer efficiency on number processing, a finding consistent with past research showing more specific adverse effects in the arithmetic domain. Arithmetic performance may be relatively more compromised with prenatal alcohol exposure than other types of intellectual performance, such as verbal abilities.

Effects Speed and Working Memory

"We also looked at how processing speed related to other aspects of cognition, working memory in particular. Prenatal alcohol exposure had some impact on both speed and working memory, but the effect on working memory was partly accounted for by the deficits in speed – in other words, slower performance contributes in part to poorer working memory."

Both Burden and Croxford noted that this study also examined the impact of "confounding" factors such as home environment, socioeconomic status, and current maternal drinking levels, which researchers believe may contribute to the poor outcomes seen in children exposed to prenatal alcohol.

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