Preserved cortical asymmetry despite thinner cortex in children and adolescents with prenatal alcohol exposure and associated conditions

Abstract

Prenatal alcohol exposure (PAE) is associated with reduced overall brain volume. Although this has been reported consistently across studies, the status of cortical thickness after PAE is more variable. The cortex is asymmetric in typical controls, but it is unclear whether the left and right counter parts of the cortical gray matter are unevenly influenced in postpartum brain development after PAE. Brain MRI was acquired in a newly recruited sample of 157 participants (PAE: N = 78, 5.5-18.9 years, 40 females and controls: N = 79, 5.8-18.5 years, 44 females) across four Canadian sites in the NeuroDevNet project. The PAE group had other confounds such as psychiatric co-morbidity, different living environment, and so on, not present in the control group. In agreement with previous studies, the volumes of all brain structures were reduced in PAE compared to controls, including gray and white matter of cerebrum and cerebellum, and all deep gray matter including the hippocampus, amygdala, thalamus, caudate, putamen, and pallidum. The PAE group showed reductions in global and regional cortical thickness, while the pattern and degree of cortical thickness asymmetry were preserved in PAE participants with the greatest rightward asymmetry in the lateral parietal lobe and the greatest leftward asymmetry in the lateral frontal cortex. This persistent asymmetry reflects that the homologous left and right cortical regions followed typical relative developmental patterns in the PAE group despite being thinner bilaterally than controls. Hum Brain Mapp 39:72-88, 2018. © 2017 Wiley Periodicals, Inc.

Keywords: brain volume; cortical asymmetry; cortical thickness; development; fetal alcohol spectrum disorders (FASD); prenatal alcohol exposure (PAE).

Figure 1

Regional cortical thickness averaged over all 79 controls (a) or all 78 PAE (b). (c,d) PAE yielded regionally thinner cortex bilaterally over widespread areas relative to the controls. Note that cortical thickness was not thicker in any vertex in PAE relative to controls. The mean cortical thickness over all the statistically significant vertices (from (d)) in the left (e) and right (f) hemispheres are shown for all sites combined and the 4 separate sites in controls (Ctr) and PAE (sample size shown in brackets). *P < 0.05; **P < 0.01. [Color figure can be viewed at http://wileyonlinelibrary.com]

Figure 2

Age effect in controls (a) and PAE (b). Cool colors (lighter to darker blues) represent the vertices where cortical thickness decreased linearly with age over 5–18 years. Note that cortical thickness did not increase with age in any vertex. The mean cortical thickness versus age in significant vertices from left and right hemispheres are shown for controls (c,e: indicated by black dots for thickness and black dashed lines for linear regression) and PAE (d,f: red squares for thickness and red solid lines for regression). [Color figure can be viewed at http://wileyonlinelibrary.com]

Figure 3

Asymmetry index (AI) for cortical thickness in controls (a) and PAE (b) is superimposed per vertex on a left hemisphere template for illustration. Cool colors (green, blue, and purple) represent rightward asymmetry (right vertices thicker than their left counterparts), while warm colors (yellow, orange, and red) represent leftward asymmetry. The appearance of the AI maps was similar between PAE and controls where (c) and (d) show one‐sample t tests of AI in controls and PAE, respectively. Mean thickness (e) of left (green triangles) and right (red squares) hemisphere, and their related asymmetry index (f), from a rightward cluster in inferior frontal gyrus in controls are shown against age, in comparison to the rightward cluster in the same region in PAE (g and h). A leftward cluster in parietal gyrus in controls (i and j) is also shown for comparison to a similar located leftward cluster in PAE (k and l). There were no significant linear changes of AI with age in either of these regions (f, h, j, l). [Color figure can be viewed at http://wileyonlinelibrary.com]