Humans have at least two functional networks in their cerebral cortex not found in rhesus monkeys. Researchers who made the finding believe new brain networks were likely added in the course of evolution from our primate ancestor to human.
The findings, based on an analysis of functional brain scans, were published after a study by neurophysiologists at the Dutch-speaking KU Leuven university in Flanders and the US Harvard Medical School, in collaboration with a team of Italian and other American researchers.
Human ancestors evolutionarily split from those of rhesus monkeys about 25 million years ago, and since then brain areas have been added, have disappeared or have changed in function. The researchers say this raises the question of whether evolution has resulted in humans having unique brain structures.
Scientists have entertained this idea before but conclusive evidence was lacking. By combining different research methods, they now have a first piece of evidence that could prove humans do have unique cortical brain networks.
The researchers performed functional brain scans in humans and rhesus monkeys at rest and while watching a movie to compare both the place and the function of cortical brain networks.
Even at rest, the brain is very active: different brain areas that are active simultaneously during rest form so-called 'resting state’ networks. For the most part, these networks in humans and monkeys are surprisingly similar but two networks were found to be unique to humans and there was one unique network in the monkey.
When watching a movie, the cortex processes an enormous amount of visual and auditory information. The human-specific resting state networks react to this stimulation in a totally different way than any part of the monkey brain. This means they also have a different function than any of the resting state networks found in the monkey.
In other words, brain structures that are unique in humans are anatomically absent in the monkey and there no other brain structures in the monkey that have an analogous function. The unique human brain areas are primarily located high at the back and at the front of the cortex and are probably related to specific human cognitive abilities, such as human-specific intelligence.
The study used functional Magnetic Resonance Imaging scans to visualise brain activity; such scans map functional activity in the brain by detecting changes in blood flow and, because the oxygen content and amount of blood in a given brain area varies according to a particular task, brain activity can be tracked.
A report of the study, “Evolutionarily Novel Functional Networks in the Human Brain?”, was published in The Journal of Neuroscience.
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