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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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