Prenatal alcohol exposure affects visual processing

February 14, 2002

Problems with attention are so frequently reported in association with Fetal Alcohol Syndrome (FAS) that some researchers believe they may comprise a "core feature" of FAS. Attention, however, is a complex phenomenon. What is usually associated with the impulsivity and behavioral inattention found in studies of FAS subjects can in fact be referred to as "sustained attention" - the effort, resource or capacity to maintain a focused alertness in perceiving a signal. A study in the February issue of Alcoholism: Clinical & Experimental Research examines the ability of adolescents, with and without prenatal exposure to alcohol, to maintain visual and auditory sustained attention.

"We wanted to know if there are specific effects of FAS," said Claire D. Coles, professor of psychiatry and behavioral sciences at the Emory University School of Medicine and lead author of the study. "Are these effects different than those of kids who are mentally retarded or just have a low IQ? Also, how can we identify functional deficits and behaviors? How are those linked to specific areas in the brain?"

Study participants were 265 low-income and predominantly African American adolescents with an average age of 15 years. The adolescents were divided into four groups: 53 controls who were not prenatally exposed to alcohol; 46 alcohol-exposed adolescents who showed physical effects of this exposure (dysmorphic); 82 alcohol-exposed adolescents who did not show physical effects of their exposure; and 84 adolescents who belonged to local special-education programs.

"I believe that those people who are dysmorphic are more affected than those who are not," said Coles. "I think dysmorphia is an external sign of internal neurological damage. We know that facial features are forming pretty much at the same time as the brain ... so we would assume that those people who were dysmorphic would be more likely to be neurologically damaged as well. We included the special education group because we thought that maybe there was something specific about this group - perhaps the effect of being in 'special education,' or of being disabled, etc. - that was going to affect outcome. This has not been done before."

Sustained attention was measured by a computerized task. A stimulus was presented, either to the ear or the eye, that was identical in all ways except for the medium (visual or auditory). For example, the letter "X" would flash on the computer screen (for 85 milliseconds) in a random manner. The adolescent was instructed to press the space bar only when they saw the letter "A" precede the "X." Their task was to remain vigilant for the "A," which would alert them to respond to the "X." The auditory task was identically presented through earphones.

Most of the adolescents processed visual information more effectively than auditory information. In contrast, the dysmorphic adolescents performed as effectively when presented with auditory stimuli, but were less efficient in processing visual information. These results suggest there may be specific patterns to the impact of prenatal alcohol exposure on cognitive performance than can be identified during adolescence. In particular, visual modality processing seemed to be more affected than auditory modality processing among dysmorphic adolescents.

"For the average person, maybe the visual task is more efficient that the auditory task," Coles speculated. "Certainly for most of this population of kids, the visual worked better for them than the auditory. Yet the dysmorphic children showed the opposite pattern; they're different from the others. They may have a specific deficit in visual processing. That is, the part of their brain that involves visual processing appears to be the part that's effected by the alcohol."

"Clearly the key findings of this study are the differential effects on visual and auditory attention," concurred Sarah Mattson, assistant professor in the Department of Psychology, and Associate Director of the Center for Behavioral Teratology at San Diego State University. "This suggests that attention is not uniformly affected in this population, that areas of strength and weakness may be found. Knowing this may aid in the development of remediative programs. Future research in this area should be aimed at addressing the inconsistencies with previous research, further characterizing both the strengths and weaknesses identified in this study as well as any patterns that may exist and, finally, linking these strengths and weaknesses to brain areas that may be affected by prenatal alcohol exposure."

"These findings certainly help us understand why it's important not to drink during pregnancy," said Coles. "These are long-term outcomes, even after 15 years. Furthermore, we have found in other tests that there are some very specific effects on particular academic function. People with FAS are relatively good on language-related academic tests, reading and spelling, but specifically bad on math-related tasks. When you consider that drinking for the average person is a choice, a source of pleasure, but not a necessity, I really don't see any purpose in risking it during pregnancy. It seems to me that the sensible thing to do during pregnancy is not to drink."
Co-authors of the Alcoholism: Clinical & Experimental Research paper included: Kathleen A. Platzman and Mary Ellen Lynch of the Department of Psychiatry and Behavior Sciences at Emory University School of Medicine; and David Freides of the Department of Psychology at Emory University. The study was funded by the National Institute on Alcohol Abuse and Alcoholism.

Alcoholism: Clinical & Experimental Research

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