U.S. researchers suggested that the cerebellum has a hand in every aspect of higher brain functions, not just movement, but attention, thinking, planning and decision-making.
Having access to more than 10 hours of scans on each of 10 people though the Midnight Scan Club dataset, and using the cortex's networks as a template, the researchers at Washington University School of Medicine in St. Louis could identify the networks in the cerebellum.
Notably, the sensory networks, vision, hearing and touch, are missing, and only 20 percent of the cerebellum is devoted to movement, roughly the same amount as in the cerebral cortex.
The remaining 80 percent is occupied by networks involved in higher-order cognition: the attention network; the default network, which has to do with daydreaming, recalling memories and just idly thinking; and two networks that oversee executive functions such as decision-making and planning.
"The executive function networks are way overrepresented in the cerebellum," said postdoctoral researcher and first author Scott Marek.
The researchers measured the timing of brain activity and found that the cerebellum was consistently the last step in neurologic circuits.
Signals were received through sensory systems and processed in intermediate networks in the cerebral cortex before being sent to the cerebellum. There, the researchers surmise, the signals undergo final quality checks before the output is sent back to the cerebral cortex for implementation.
"If you think of an assembly line, the cerebellum is the person at the end who inspects the car and says, 'This one is good; we'll sell it,' or 'This one has a dent; we have to go back and repair it,'" said senior author Nico Dosenbach, an assistant professor of neurology, of occupational therapy and of pediatrics. "It's where all your thoughts and actions get refined and quality controlled."
People with damage to their cerebellum are known to become uncoordinated, with an unsteady gait, slurred speech and difficulty with fine motor tasks such as eating.
The cerebellum also is quite sensitive to alcohol, which is one of the reasons why people who have had too many drinks stumble around. But the new data may help explain why someone who is inebriated also shows poor judgment.
Just as a person staggers drunkenly because his or her compromised cerebellum is unable to perform the customary quality checks on motor function, alcohol-fueled bad decisions might also reflect a breakdown of quality control over executive functions.
The researchers also performed individualized network analyses on the 10 people in the data set, and found that while brain functions are arranged in roughly the same pattern in everyone's cerebellum, there is enough individual variation to distinguish brain scans performed on any two participants.
The researchers are now investigating whether such individual differences in cerebellar networks correlate with intelligence, behavior, personality traits such as adaptability, or psychiatric conditions.
The findings have been published in Neuron.