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Conversations with Dorothea Metzen: Gauging the links between genetics and intelligence.

A recent study explored the link between genes and behavior. Researchers, led by Dorothea Metzen from Ruhr University Bochum and Dr. Erhan Genç, formerly of the same institution and now at the Leibniz Research Centre, examined the relationship between genes, brain characteristics, and intelligence.

Their groundbreaking study, published in Human Brain Mapping on 4 April 2023, involved multiple institutions across Europe and combined gene analyses, MRI scans, and intelligence tests on 557 participants aged 18-75. By analyzing saliva samples, they gauged gene variations linked to high intelligence. Furthermore, brain scans revealed cerebral cortex details and network efficiency, culminating in an intelligence test.

While numerous associations between genetic variations and brain characteristics were found, only specific regions showed a link between genes, brain structure, and intelligence test outcomes. Notably, brain surface size and structural connectivity efficiency were pivotal. Genç suggests that their methodology, examining the genes-brain-behavior triad, could be adapted for broader studies on different traits.

Dorothea Metzen set aside some time to discuss the study with SCINQ.

Dorothea Metzen (Copyrights © RUB, Marquard)

Could you explain how the summary score was calculated for each participant to indicate their genetic predisposition for high intelligence?

Intelligence is understood to be highly polygenic, implying that it is influenced by possibly hundreds or thousands of genes. Many of these genetic variations have already been identified. Polygenic scores serve as a summary of these genetic variations. For each participant, we examined the presence of specific variations associated with intelligence. Ultimately, this results in a summary score that reflects the participant’s genetic predisposition for intelligence, based on the known genetic variations.

How was the efficiency of the structural and functional networks in the brain determined, and how do these findings correlate with intelligence?

To determine efficiency, we employed graph theory, a branch of mathematics. In this context, a network consists of nodes, representing brain areas, and the connections between these nodes. Efficiency gauges how effectively different brain regions connect with each other and the energy efficiency with which signals are transferred between them. An individual with high network efficiency would require fewer connections to transmit a signal from one brain region to another.

The term “structural network” pertains to the fiber tracts that facilitate the physical transfer of signals between brain regions. In contrast, “functional efficiency” addresses the synchronized activity of different brain areas. Prior research has indicated a correlation between superior structural efficiency and higher intelligence. This association is particularly evident in regions crucial for intelligence, such as the prefrontal and parietal cortex. However, the correlation between functional efficiency and intelligence remains less defined, consistent with our study, which did not find a significant association between the two.

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The study observed limited connections between genetic variations, brain characteristics, and intelligence test performance in certain brain regions. Could you elaborate on these specific regions and their significance?

Previous research has underscored that intelligence doesn’t stem from a singular brain area. Instead, our cognitive capabilities arise from a broad network of brain regions. Predominantly, these regions are found in the prefrontal, occipital, parietal, and temporal cortexes. Some of the regions our study highlighted—such as the inferior frontal sulcus, intraparietal areas, lateral occipital cortex, and premotor areas—are constituents of this established intelligence network. It’s understood that primary sensory information originating from occipital areas is processed further in the parietal and frontal regions, where problem-solving mechanisms take shape.

Interestingly, we also pinpointed regions not typically associated with the conventional intelligence network, like the opercular cortex and the motor cortex. One potential explanation for this could stem from our unique methodological approach centered on connectivity. While much of preceding research has been grounded in examining structural attributes like volume or activity, studies focusing on connectivity are relatively nascent and haven’t been seamlessly incorporated into the prevailing understanding of the intelligence network.

Could you provide more details about the key brain characteristics highlighted in your research: the size of the brain’s surface area and the efficiency of its structural connectivity? How do these attributes relate to intelligence?

One of the most consistent findings in intelligence research is the association between a larger brain volume and surface area with higher intelligence scores. This correlation is particularly pronounced in areas that form the intelligence network. A likely reason for this is that a larger surface area correlates with an increased number of neurons, leading to greater computational power. In simple terms, it operates on a “more-is-more” basis.

The notion of efficiency, however, is a tad more intricate. While one could assume that having numerous fibers linking every brain region to one another would be indicative of higher intelligence, it’s not as straightforward. Multiple connections demand significant energy. This is where the importance of efficiency arises. An optimally efficient network not only establishes necessary connections but also eliminates redundant ones between brain regions. Such an efficient brain ensures rapid and energy-conserving communication across different areas.

Given the findings of our study, how might our method—examining the interplay between genes, brain characteristics, and behavioral traits—be utilized in other research domains?

The interconnected framework of genes, brain attributes, and behavioral patterns can be instrumental when integrated into diverse research areas, promising rich insights. Take, for instance, many mental disorders like depression: they are known to have partial genetic underpinnings and are intrinsically linked with specific brain structures and functionalities. By employing our mediation approach, researchers could discern which brain features linked to a disorder emerge from genetic factors. Consequently, it would offer clarity on which brain attributes are environmentally influenced—traits that are malleable and can be potentially reshaped through therapeutic interventions. This line of inquiry could significantly enhance treatment strategies. Broadly, our triad-centric methodology could be adapted to study any intricate human trait with genetic roots that also corresponds with brain structure and activity.

The study focuses on the intricate relationships between genes, brain attributes, and intelligence. From your perspective, what could be the potential ramifications or applications of such findings in domains like education or mental health

Intelligence plays a pivotal role in determining various life outcomes, from educational achievements and career progression to overall health indicators such as susceptibility to cardiovascular diseases and even lifespan. Hence, deciphering the genetic foundations of intelligence becomes imperative in comprehending these correlations. There are multifaceted explanations for the link between intelligence and, say, longevity. It’s plausible that specific genetic variations contributing to heightened intelligence also promote better health outcomes. Conversely, genetic factors leading to lower intelligence might be associated with adverse health consequences. Another perspective suggests that higher intelligence may enable individuals to better comprehend and act upon health-related information, thereby fostering healthier lifestyles.

By unraveling how genetic variations shape our brain and intelligence, we inch closer to grasping the genetic interplay between intelligence and health. Such insights are indispensable for pinpointing environmental variables that, once modified, can enhance overall health and well-being.


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