Cerebellum - the 'little brain' controlling thought and senses - not so little after all, research suggests

Neuroscientists have for decades thought that much of how humans experience movement, vision and thinking is operated by a very small portion of our brains, called the cerebellum.

That notion is being challenged by research results released last month by U.S., U.K. and Holland-based researchers who suggest the cerebellum, Latin for "little brain," may not be so little after all.

"The cerebellum has long been recognized as a partner of the cerebral cortex, and both have expanded greatly in human evolution. The thin cerebellar cortex is even more tightly folded than the cerebral cortex," the research article published July 28 in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) says. 

Researchers scanned a human cerebellum specimen at ultra-high magnetic fields and found they could "computationally reconstruct" that portion of the specimen's surface down to its smallest folds. Doing so revealed that the cerebellar cortex in the representative specimen contained almost 80% of the cortex's surface area.

A comparison with the same area of another primate's brain yielded significant differences, according to the research results. 

"By performing the same procedure on a monkey brain, we found that the surface area of the human cerebellum has expanded even more than that of the human cerebral cortex, suggesting a role in characteristically human behaviors, such as toolmaking and language," the article says.

Martin I. "Marty" Serena, with University College London and Birkbeck University of London, in addition to professor and director of San Diego State University's MRI Imaging Facility Department, is the lead contact author on the research article.

Other authors include Jörn Diedrichsen with the Institute of Cognitive Neuroscience at the University College London and the departments for computer science and statistics at the University of Western Ontario; Mohamed Tachrount with the Institute of Neurology at the University College London and the Department of Clinical Neurosciences at the University of Oxford; Guilherme Testa-Silva with the department of chemistry and chemical biology and Harvard University; Helen d’Arceuil with the Center for Biomedical Imaging at Massachusetts General Hospital in Charlestown, Massachusetts; and Chris De Zeeuw with the Department of Neuroscience at the Netherlands Institute for Neuroscience in Amsterdam.

The human cerebellum, which guides a person's coordination and movement, is located beneath the cerebrum at the back of the skull. Together with the brain stem, the cerebellum is generally considered the most primitive part of the human brain. 

All communication through the cerebellum passes through the brain stem's pons, to which the cerebellum is attached. That connection allows humans to experience the senses, along with movement, emotion, pain and even thought and comprehension.

The article counters what neuroscientists had long known about the human cerebellum: that it accounts for only about 10% of brain mass, yet also houses more than half of the brain's neurons.

Researchers used specific software to reconstruct, unfold and flatten entire cerebellar cortex, the article says.

"Our estimate of the total cerebellar surface area was larger than any previous estimate, at 78% of the surface area of the entire human neocortex," the article says.