Scientists are unlocking the secrets of your 'little brain'

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original version Of this story appeared in quanta magazine,

In recent decades, neuroscience has seen some amazing advances, and yet an important part of the brain remains a mystery. I'm talking about the cerebellum, which is Latin for “small brain”, which is located like a sphere at the back of the brain. This is no small mistake: the cerebellum contains three-quarters of all the neurons in the brain, arranged in a nearly crystalline arrangement, unlike the tangled masses of neurons found elsewhere.

Encyclopedia articles and textbooks emphasize the fact that the function of the cerebellum is to control body movement. There is no doubt that this is the function of the cerebellum. But scientists now suspect that this long-held view is short-sighted.

Or so I found out while attending the Society for Neuroscience annual meeting in Washington, DC, in November, the largest meeting of neuroscientists in the world. There, a pair of neuroscientists organized a symposium on newly discovered functions of the cerebellum unrelated to motor control. New experimental techniques are showing that in addition to controlling movement, the cerebellum controls complex behavior, social interaction, aggression, working memory, learning, emotion, and much more.

a crack in the dominant intellect

The connection between the cerebellum and movement has been known since the 19th century. Patients suffering from trauma to a brain area that had obvious difficulties with balance and movement were no doubt important for the coordination of movements. Over the decades, neuroscientists have developed a detailed understanding of how the cerebellum's unique neural circuitry controls motor function. The explanation of how the cerebellum worked seemed undeniable.

Then, in 1998, in the journal Brain, neurologists report on widespread emotional and cognitive disabilities in patients with damage to the cerebellum. For example, in 1991, a 22-year-old female college student fell while ice skating; A CT scan revealed a tumor in his cerebellum. After it was surgically removed, she was a completely different person. The gifted college student had lost the ability to write proficiently, perform mental arithmetic, name common objects, or copy a simple diagram. His mood deteriorated. She hid under the blanket and behaved inappropriately, taking off her clothes in the corridors and talking like a child. His social interactions, including recognizing familiar faces, were also impaired.

This and similar cases puzzled writers. These higher-level cognitive and emotional functions are thought to reside in the cerebral cortex and limbic system. “Exactly what that cerebellar role is, and how the cerebellum accomplishes it, has not yet been established,” they concluded.

Despite these clues from clinical studies that the conventional wisdom was on the wrong track, leading authorities still insisted that the function of the cerebellum was to control movement and nothing more. “It's kind of sad, because it's been 20 years since these cases came out,” said DiSinau Fioravante, a neurophysiologist at UC Davis who co-organized the conference symposium.

Other neurologists have observed neuropsychiatric deficits in their patients, said Stephanie Rudolph, a neuroscientist at Albert Einstein College of Medicine, who co-organized the symposium with Fioravante. However, there was no solid physiological evidence of how the cerebellum's unique neural circuitry might control purported psychological and emotional functions, so clinical reports were ignored.