Executive Functioning in Children Prenatally Exposed to Alcohol
Noland et al, Case Western Reserve University 2003
To be published in
Alcoholism: Clinical & Experimental Research (ACER)
Executive functioning (EF) refers to the management system of the brain's cognitive operations. EF abilities include working memory, planning, and inhibitory control. A new study has found that prenatal alcohol exposure of less than one drink per day is associated with decreased EF at four years of age. Executive functioning (EF) includes a wide range of central control processes of the brain that connect, prioritize, and integrate other functions needed for self-management. Working memory, planning, and inhibitory control are just some of the EF abilities that allow for goal-directed behavior and resistance to competing responses. A study of the effects of prenatal exposure to alcohol, marijuana, and cocaine on EF, published in this month's Alcoholism: Clinical & Experimental Research, has found that prenatal alcohol exposure of less than one drink per day can impair EF in early childhood.
"The results of this study confirm a possible brain-based path through which exposure to a substance does its damage," said Julia S. Noland, senior research associate at Case Western Reserve University and corresponding author for the study. "The subtle changes in attention, planning, and goal orientation that we found to be associated with prenatal substance exposure may not be evident in the daily behavior of most of the children. Yet for a small percentage of lower-functioning individuals, these subtle impairments may make the difference between their being able to cope with the demands of particular employment and learning situations or not. If one multiples that small percentage of affected individuals by the number of births in the U.S. for which the fetus is exposed to these relatively low levels of toxins, you have a public health concern."
"A central problem in understanding the neurobehavioral consequences of prenatal substance abuse is the reality of polyexposure," noted Richard Canfield, senior research associate in the Division of Nutritional Sciences at Cornell University. "That is, mothers who use one substance during pregnancy, such as alcohol, are also likely to use nicotine, marijuana, cocaine, or other drugs of abuse. Of similar importance is the problem of 'confounding,' that is, mothers who use drugs during pregnancy are also likely to have limited access to financial, material, social, and intellectual capital. As a result, identifying developmental impairments as associated with prenatal exposure to a specific drug is a difficult task, and the authors should be commended for attempting to draw these specific linkages."
Four-year-old children (n=316) whose mothers had used various combinations of cocaine, alcohol, and/or marijuana during pregnancy were assigned to overlapping prenatal cocaine-exposed, alcohol-exposed, and/or marijuana-exposed groups. Corresponding control groups included children whose mothers did not use these drugs during pregnancy. Researchers examined the children's responses to three different kinds of EF tasks: tapping inhibition (TI), category fluency, and motor planning. The children were also tested for their verbal, performance, and full-scale IQ. All of the testing took place in a single three- to four-hour session at an off-site, hospital-affiliated lab. In addition, their mothers were asked to self-report current drug/alcohol use, answer questions about psychiatric symptoms, and undergo measures of intellectual functioning. The ability of the children's home environments to provide intellectual stimulation was also assessed.
The children in the alcohol-exposed group had a worse TI performance than the children in the control group. This effect persisted even after controlling for prenatal drug exposure, postnatal environmental factors, and child verbal IQ. "A key finding of this study is the suggestion that consuming less than one alcoholic beverage per day during pregnancy has fairly specific effects on cognitive functioning in the offspring," said Canfield. "Alcohol-exposed children had more difficulty learning and performing a TI task that required them to follow an explicit rule, a rule that conflicted with their natural response tendency. Following rules that may conflict with one's natural desires is fundamental to children's social and academic success in classroom and daycare environments. If, as this study suggests, children exposed prenatally to alcohol find it more difficult to inhibit inappropriate behaviors, this might help explain part of the reason why such children are at greater risk for social and academic problems."
"Adults who have damage to their frontal lobes have difficulty on just the kinds of tasks used in this study," noted Noland. "The brain change associated with alcohol exposure could be in the frontal cortex or another closely related area of the brain that supports the frontal cortex." Canfield added that future research would need to discover whether children who might perform poorly on a TI task have social and academic problems that appear related to deficient inhibitory control.
"We know that FAS is the most common identifiable source of birth deficits and is associated with heavy drinking during pregnancy," said Noland. "However, even drinking at more moderate levels, such as seven drinks per week and/or five drinks per occasion, is associated with long-term changes in attention and memory. And there may be effects at even lower levels. This represent a major heal concern as the CDC estimates that among women who know they are pregnant, two percent continue to drink at a moderate level and five percent continue to have at least two drinks per week. Some additional important public health education messages that still need more attention are the findings that women over the age of 30, women under atypical stress, and those who binge drink, are at particular risk; and that the month prior to pregnancy recognition may be a particularly vulnerable time."
Noland and her colleagues plan to investigate how a woman's experience of stress during pregnancy and consumption of alcohol might interact to affect her offspring. "Given equal amounts of drinking, women living in poverty have children who are diagnosed with FAS at a rate tenfold that of middle-class women," she said. "Stress associated with poverty may be behind these differences."