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How genes, brain characteristics and intelligence are connected

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Published on Tuesday, 04 April 2023

Genes influence different structures and the function of the brain. These in turn explain differences in behaviour. Analysing all three aspects at once is a challenge – and has been achieved for the first time.

Intelligence is partly heritable. There are studies that show that certain genetic variations are linked to better performance in intelligence tests. Other studies show that a variety of brain characteristics, such as network efficiency, are related to intelligence. Researchers from the Ruhr University Bochum and the University of Luxembourg now analysed simultaneously gene analyses, magnetic resonance imaging and intelligence tests to demonstrate which brain characteristics form the link between genes and behaviour.

The study, published in the journal “Human Brain Mapping”, was designed by Robert Kumsta, professor in Biopsychology at the Faculty of Humanities, Education and Social Sciences of the University of Luxembourg, together with Dorothea Metzen at Ruhr University Bochum and Dr. Erhan Genç at the Leibniz Research Centre for Working Environment and Human Factors.

Genes, brain, behaviour – a unique data set

The team included 557 persons aged between 18 and 75 years in the study. Using saliva samples, they analysed which individuals possessed how many gene variations associated with high intelligence. “There are thousands of genes that contribute to intelligence,” explains Dorothea Metzen. “We calculated a summary score for each person that reflects the genetic predisposition for high intelligence.”

In addition, all participants took part in brain scans, which the researchers used to determine not only the thickness and surface area of the cerebral cortex, but also how efficiently the structural and functional networks in the brain are organised. All participants also completed an intelligence test. “The broadness and detailed recording of various data in this study is, as far as I am aware, unprecedented,” emphasises Erhan Genç. “For the first time, we looked at the triad of genes, different brain characteristics and behavioural traits as a whole.”

Interplay of genes, brain characteristics and intelligence in a few brain regions

When the team only looked at the connection between genetic variations and brain characteristics – that is, disregarding intelligence test results – they found numerous associations in many regions distributed across the entire brain. Significantly fewer associations were apparent when the researchers investigated which brain characteristics were associated with intelligence test performance.

When they considered all three parameters at once – genes, brain characteristics and intelligence test performance – an association was only found in few brain areas in the frontal, parietal and visual cortex. This means that there are only specific areas in the brain where gene variations influence brain characteristics, and these characteristics simultaneously affect intelligence. The decisive brain characteristics were the size of the brain surface and the efficiency of structural connectivity. The researchers found very few such connections between genes, brain and behaviour when they examined the thickness of the cerebral cortex and the efficiency of functional connectivity.

Method also transferable to other areas

The researchers hope this method can be applied to larger cohorts, or to other areas, such the impact of age. “We will continue investigating the contribution of genetic variability to different traits, especially in the context of stress research,” states Robert Kumsta. ” Here, we focus on the interplay between genes and stress exposure to understand how different types of stress contribute to mental health problems.”

Scientists at the Humboldt-Universität Berlin, the Central Institute of Mental Health in Mannheim, the Medical School Hamburg were also involved in the study.

Erhan Genç, Dorothea Metzen, Christoph Fraenz, Caroline Schlüter, Manuel C. Voelkle, Larissa Arning, Fabian Streit, Huu Phuc Nguyen, Onur Güntürkün, Sebastian Ocklenburg, Robert Kumsta: Structural architecture and brain network efficiency links polygenic scores to intelligence, in: Human Brain Mapping, 2023, DOI: 10.1002/hbm.26286

This article was first published on the website of the Ruhr Universität Bochum.

© Photo: Ruhr Universität Bochum