Overdominant Effect of aCHRNA4Polymorphism on Cingulo-Opercular Network Activity and Cognitive Control
Authors: Sadaghiani Sepideh , Ng Bernard , Altmann Andre , Poline Jean-Baptiste , Banaschewski Tobias , Bokde Arun L.W. , Bromberg Uli , Büchel Christian , Burke Quinlan Erin , Conrod Patricia , Desrivières Sylvane , Flor Herta , Frouin Vincent , Garavan Hugh , Gowland Penny , Gallinat Jürgen , Heinz Andreas , Ittermann Bernd , Martinot Jean-Luc , Paillère Martinot Marie-Laure , Lemaitre Hervé , Nees Frauke , Papadopoulos Orfanos Dimitri , Paus Tomáš , Poustka Luise , Millenet Sabina , Fröhner Juliane H. , Smolka Michael N. , Walter Henrik , Whelan Robert , Schumann Gunter , Napolioni Valerio , Greicius Michael 
Published: September 2017

The nicotinic system plays an important role in cognitive control and is implicated in several neuropsychiatric conditions. However, the contributions of genetic variability in this system to individuals' cognitive control abilities are poorly understood and the brain processes that mediate such genetic contributions remain largely unidentified. In this first large-scale neuroimaging genetics study of the human nicotinic receptor system (two cohorts, males and females, fMRI totalN= 1586, behavioral totalN= 3650), we investigated a common polymorphism of the high-affinity nicotinic receptor α4β2 (rs1044396 on theCHRNA4gene) previously implicated in behavioral and nicotine-related studies (albeit with inconsistent major/minor allele impacts). Based on our prior neuroimaging findings, we expected this polymorphism to affect neural activity in the cingulo-opercular (CO) network involved in core cognitive control processes including maintenance of alertness. Consistent across the cohorts, all cortical areas of the CO network showed higher activity in heterozygotes compared with both types of homozygotes during cognitive engagement. This inverted U-shaped relation reflects an overdominant effect; that is, allelic interaction (cumulative evidencep= 1.33 * 10−5). Furthermore, heterozygotes performed more accurately in behavioral tasks that primarily depend on sustained alertness. No effects were observed for haplotypes of the surroundingCHRNA4region, supporting a true overdominant effect at rs1044396. As a possible mechanism, we observed that this polymorphism is an expression quantitative trait locus modulatingCHRNA4expression levels. This is the first report of overdominance in the nicotinic system. These findings connectCHRNA4genotype, CO network activation, and sustained alertness, providing insights into how genetics shapes individuals' cognitive control abilities.

SIGNIFICANCE STATEMENTThe nicotinic acetylcholine system plays a central role in neuromodulatory regulation of cognitive control processes and is dysregulated in several neuropsychiatric disorders. Despite this functional importance, no large-scale neuroimaging genetics studies have targeted the contributions of genetic variability in this system to human brain activity. Here, we show the impact of a common polymorphism of the high-affinity nicotinic receptor α4β2 that is consistent across brain activity and behavior in two large human cohorts. We report a hitherto unknown overdominant effect (allelic interaction) at this locus, where the heterozygotes show higher activity in the cingulo-opercular network underlying alertness maintenance and higher behavioral alertness performance than both homozygous groups. This gene–brain–behavior relationship informs about the biological basis of interindividual differences in cognitive control.