Neuroimaging links brain region to poor spatial navigation in children affected by prenatal alcohol exposure

Fetal alcohol spectrum disorders (FASD) describe the range of effects associated with prenatal alcohol exposure (PAE). The most severe forms of FASD are fetal alcohol syndrome (FAS) and partial fetal alcohol syndrome (PFAS), which have adverse effects on learning and memory and result in observable physical abnormalities, including a distinct pattern of facial dysmorphic features, small head circumference, and growth restriction. Identifying the specific brain regions affected is important to fully understand the impact of PAE. Poor spatial skills are common in children with FASD, and tests of navigation in rodents – and more recently, humans – have linked PAE to impairment in ‘place learning’ (the learning of physical positions or locations of objects). Place learning in rodents and humans depends on the hippocampus, a small seahorse-shaped structure in each side of the brain. The hippocampus is particularly sensitive to PAE and is smaller in people (and rodents) exposed to alcohol in utero than in non-exposed individuals. However, it has not previously been shown whether this alcohol-related hippocampal damage mediates the impact of PAE on spatial navigation. Researchers from Michigan, USA, and Cape Town, South Africa, have published a study in the journal Alcoholism: Clinical and Experimental Research investigating whether hippocampal size accounts, in part, for the link between PAE and place learning.

The researchers analyzed data from fifty 10-year-old children from a community in Cape Town, South Africa, that has among the highest rates of FASD in the world. The children were examined by experts for signs of FAS and PFAS, and information on prenatal drinking was collected from their mothers while they were pregnant. Place-learning skills were evaluated with a computer-based water maze task. This task involved learning the location of a hidden platform in a virtual pool of water, using fixed cues (different objects) on the virtual room walls to help navigate to the platform from different starting positions. A few days later, participants had an MRI brain scan in a child-friendly university neuroimaging center to assess hippocampal size.  

Of the fifty participants, 9 children were diagnosed with FAS or PFAS, 22 had been heavily exposed to alcohol in utero but did not exhibit the physical abnormalities of FAS or PFAS, and 19 had no (or minimal) PAE. The MRI scans showed that children whose mothers drank heavily in pregnancy had a smaller hippocampus (relative to other brain regions) on the right side of the brain than those with no or minimal PAE – regardless of whether they had a diagnosis of FAS or PFAS. Smaller hippocampal size and, as expected, PAE were also associated with poorer place-learning skills in the water maze task. Using statistical modeling, the team was able to show that the relation between PAE and performance on the water maze was due, in part, to reduced hippocampal size. These findings suggest that PAE impairs children’s ability to encode spatial information necessary for place learning, enhancing scientists’ understanding of the far-reaching effects of PAE on the developing brain.

Reduced Hippocampal Volumes Partially Mediate Effects of Prenatal Alcohol Exposure on Spatial Navigation on a Virtual Water Maze Task in Children. N.C. Dodge, K.G.F. Thomas, E.M. Meintjes, C.D. Molteno, J.L. Jacobson, S.W. Jacobson (pages xxx).

ACER-20-4279.R1.

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