An international team of scientists have made a paradoxical sounding discovery: the more intelligent a human being is, the less interconnected the nerve cells in his cerebral cortex are. The researchers led by Erhan Genç and Christoph Fraenz from the Ruhr University Bochum in Germany, together with colleagues from Berlin and the US, came to this conclusion after putting subjects through a special form of magnetic resonance imaging (MRI) to gain insights into the microstructural interconnection of the brain.
The scientists studied the brains of 259 men and women using Neurite Orientation Dispersion and Density Imaging. Using this method, they were able to measure the amount of cell processes known as dendrites in the cerebral cortex with which a nerve cell makes contact with other nerve cells. All test participants also completed an intelligence test. Then the researchers put the data in relation to each other and found out that the more intelligent a person is, the fewer dendrites he or she has in the cerebral cortex.
Based on an independent publicly available dataset collected in the Human Connectome project, the team confirmed the result presented in the journal Nature Communications. The relationship between dendrite and intelligence also occurred in this sample, which included around 500 people.
With these new findings, previously conflicting results from research on intelligence can be explained. It was long believed that smarter people tend to have larger brains. “It was assumed that larger brains could contain more nerve cells and thus achieve higher computing power,” says Genç.
However, other studies have shown that smarter people, despite their relatively high number of nerve cells, had less neuronal activity when taking an intelligence test compared to the brains of less intelligent people. “Intelligent brains are characterized by a slim but efficient network of their neurons,” says Genç. “This makes it possible to achieve a high level of thinking with the least possible neural activity.”