Individuals differ with regard to their cognitive abilities. For more than a century, scientists have been occupied with the question whether such differences in intelligence are associated with differences in the biological properties of the brain. Evidence from modern neuroscience shows that individuals with bigger brains tend to perform better on intelligence tests compared to individuals with smaller brains. However, research also indicates that the brains of intelligent individuals, despite having a comparably larger number of neurons, exhibit less neuronal activity while working on an intelligence test compared to brains of less intelligent individuals. So far, the cortical microstructure underlying these seemingly contradictive findings remained unknown. Here, a group of researchers from the Biopsychology Department collaborated with scientists from Bochum, Berlin and Albuquerque. They administered a matrix-reasoning test to measure intelligence and utilized a special form of in vivo magnetic resonance imaging to assess the amount of dendritic tissue in the cortex. In doing so, it could be shown for the first time that intelligence is inversely related to the number of dendrites connecting cortical neurons. The respective results could be confirmed by a large independent data set from the Human Connectome Project. According to these findings, intelligent brains are characterized by a slim but efficient circuitry between its cortical neurons, enabling high cognitive performance with neuronal activity remaining as low as possible.

Genç, E., Fraenz, C., Schlüter, C., Friedrich, P., Hossiep, R., Voelkle, M. C., Ling, J. M., Güntürkün, O., Jung, R. E. (2018). Diffusion markers of dendritic density and arborization in gray matter predict differences in intelligence. Nature Communications, 9(1), 1905.