Humans have at least two functional networks in their cerebral cortex that aren't found in rhesus monkeys, and which appear to be unique.
Our ancestors split from those of rhesus monkeys about 25 million years ago. Since then, brain areas have been added, have disappeared or have changed in function.
"We did 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," says neurophysiologist Wim Vanduffel of KU Leuven and Harvard Medical School.
"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 resting state networks in humans and monkeys are surprisingly similar, but we found two networks unique to humans and one unique network in the monkey."
The study used functional Magnetic Resonance Imaging scans to visualise brain activity by detecting changes in blood flow. The oxygen content and the amount of blood in a given brain area vary according to a particular task, thus allowing activity to be tracked.
When watching a movie, the cortex processes an enormous amount of visual and auditory information - and the human-specific resting state networks react to this stimulation in a totally different way than any part of the monkey brain. This means, says Vanduffel, that they also have a different function from 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," he says.
"Our unique 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."