The Cerebellum Is the Body's Little Brain

Named for the Latin term for "little brain," and hanging off the back of the main brain, the adorable sounding anatomical feature packs a major punch for its diminutive size. "The brain weighs about 3 pounds (1.36 kilograms) and the cerebellum makes up about 10 percent of that," says Janice Wiesman, M.D., clinical associate professor in the department of neurology at the NYU School of Medicine, in an email interview. "It's made up of three lobes, the vermis in the center ('vermis' means 'worms' in Latin and it is a long, thin, structure that looks like a worm), and a cerebellar hemisphere on each side of that."

"It weighs about 5 ounces (147 milliliters)," adds Pediatric Neurophysiology Fellow at Nationwide Children's Hospital, Daniel Freedman, D.O., in an email. "It's the coordination center of the brain and receives a large amount of sensory input from the spinal cord and brain regarding the body's movements and position. It uses this information to maintain smooth coordinated movements."

We'll get to how the cerebellum translates all that input into action in a second, but let's go deeper on the brain structure's super distinctive appearance. "It has a beautiful branched appearance which is very unique," says Parneet Grewal, a fellow at RUSH University Medical Center, in an email interview. "It has a complex circuitry and is divided into midline vermis (named for its worm-like appearance) and two cerebellar hemispheres on either side of the vermis."

"The vermis is most associated with coordinating movement of the trunk and legs and the cerebellar hemispheres work to coordinate the movement of the arms, hands and fingers," Weisman says. "The cerebellum coordinates voluntary movements like posture, balance, coordination, and speech, resulting in smooth muscle movements."

"When cut in half, the branching pattern of the cerebellar white matter required to connect all the 'folia' (Latin for leaves) can be seen," Freedman says. "This resembles a head of cauliflower or broccoli and is referred to as the 'arbor vitae' (Latin for 'tree of life')."

Appearances aside, the cerebellum plays a major role in a variety of everyday functions. "The function most doctors think about is smooth, coordinated control of movement," Wiesman says. "The cerebellum gets sensory input from the joints in the limbs and the trunk and also from the motor areas of the brain – the parts that plan and direct movement. The cerebellum matches those two inputs to make sure that the limb or trunk is doing what the motor cortex in the brain wants it to. This is how you can walk a straight line or close your eyes and touch your nose without missing! It coordinates the movement of your eyes so that you can smoothly track an object. It also coordinates the muscles of swallowing and speech so you don't choke on your food and so you can say 'Peter Piper picked a peck of pickled peppers.'"

But according to research published in October of 2018 in the journal Neuron, all these important functions are just part of the picture — the cerebellum is apparently capable of a whole lot more. "Recently, scientists have found that this most well-known function may be only one of many functions of the cerebellum and only involve 20 percent of it," Wiesman says. "Other functions include modulation of emotion, memory, language and abstract thinking. Like with movement, the cerebellum monitors these functions to make sure they are being done the right way — it's been referred to as the 'editor' of the brain."

With all this responsibility, you can't help but wonder what might happen if the cerebellum were to suffer any kind of damage.

"The primary symptom of a damaged cerebellum is 'ataxia' or uncoordinated movement," Freedman says. "Permanent damage to the cerebellum can come from stroke, tumors, infection, or alcohol use. Ataxia can also be temporary as seen in alcohol intoxication. When police officers conduct a roadside sobriety test, they are checking cerebellar function by having you touch finger to nose or walk a straight line."

"Symptoms and signs of cerebellar disease include difficulty coordinating movements, such as walking, moving the arms, and coordinating the muscles of swallowing and speech into a smooth pattern," Wiesman says. "People can have trouble with balance, moving the arms and hands in the way they want, swallowing and coordinating the voice when they speak and the speech can sound slurred. Cerebellar damage can cause a tremor of the limbs, trunk, or voice."

Because the cerebellum also regulates smooth movements of the eyes, people with cerebellar damage may also experience double vision or abnormal eye movements. And because the cerebellum is apparently a player in cognitive and emotional function, researchers believe damage could contribute to mental illnesses like schizophrenia.

"Trouble with speech, eye movements and onset of a tremor can also be seen in cerebellar disorders," Grewal says. "These symptoms are often accompanied by intense nausea, vomiting and vertigo, with lesions that can lead to herniation sometimes presenting with depressed consciousness."

So how can such a tiny structure incur so much damage? "The cerebellum can be damaged a number of ways," Wiesman says. "In a person with high blood pressure, a blood vessel can burst and cause a hemorrhagic stroke. A clot in the heart or large arteries can break off and cause an ischemic stroke. Accidents can cause physical trauma to the cerebellum. Degenerative brain diseases affect the cerebellum. Some are inherited like the spino-cerebellar ataxias or Friedreich's ataxia, some occur sporadically like multiple systems atrophy, some are caused by infectious proteins called prions and that are known to be the cause of mad-cow disease in cows and humans or Creutzfeldt-Jacob disease in humans. Some toxins, like alcohol and some medications can cause atrophy of parts of the cerebellum. Rarely as a side effect of cancer, antibodies are made to cells in the cerebellum and damage those cells."

While all this sophisticated circuitry certainly may seem exclusively reserved for human brains, the cerebellum predates us by a longshot. "The cerebellum is an evolutionarily old structure, hundreds of millions of years old, found in fish and reptiles as well as mammals," Weisman says. "After all, fish have to swim straight!"

"The cerebellum is present in other species also and is not unique to humans," Grewal says. "It performs important functions in all species. Circuits of cerebellum are similar in vertebrates with variation in size and shape. The largest cerebellar size is present in elephants."

Weisman adds some food for thought: "Since the cerebellar vermis and hemispheres coordinate different parts of the body, as you look up the evolutionary scale, as animals begin to use their hands in a way different from their legs, their cerebellar hemispheres get larger – but which came first – the structure or the action?"