August 15, 2005
Prenatal Alcohol Exposure Can Lead to Lasting Changes in Cognitive Processing
- Prenatal alcohol exposure is often linked to slower cognitive reaction times and poorer attention.
- A new study investigates cognitive function and speed as tasks become more complex.- Findings indicate that alcohol-exposed children can perform as well as other children on simple tasks, but as tasks become more demanding and challenging, processing speed slows down significantly.
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 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 FAS 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 FAS," 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. 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. We used the Sternberg paradigm because it indicates how fast an individual generates the correct response to a number of problems, providing an overall measure of speed; and it examines the rate at which response times increase as problem difficulty increases, providing a processing efficiency measure."
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. 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."
"The conclusion drawn here is that the reaction-time deficits associated with prenatal alcohol exposure are seen more in demanding/challenging cognitive tasks that involve the integration of working memory," said Croxford. "The real-world implications of this are that children exposed prenatally to alcohol may be able to perform simple tasks, but may struggle with tasks that are more challenging and require complex cognition and the use of working memory. This is likely to mean that these children may be more and more challenged the older they get by the demands placed on them within the school system and within their day-to-day social interactions."
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.
"In this study, we accounted for more than 20 of these potentially confounding influences in the analyses," said Burden. "The effect of alcohol exposure in utero persisted above and beyond any other influences present."
What this means, said Croxford, is that alcohol itself causes specific, identifiable and permanent deficits in brain development and physiology. "This reinforces the current public health message that women should not drink alcohol during pregnancy," she said.
Burden said that he and his colleagues will continue to examine the long-term effects of prenatal alcohol exposure on the same children. "In addition to neuropsychological and behavioral measures, we will also be using electrophysiological techniques such as event-related potentials and neuroimaging (fMRI) to more directly connect cognitive performance with brain function," he said.
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