The Underestimated Cerebellum Gains New Respect From Brain Scientists

Oct 25, 2018
Originally published on October 26, 2018 4:28 pm

An ancient part of the brain long ignored by the scientific world appears to play a critical role in everything from language and emotions to daily planning.

It's the cerebellum, which is found in fish and lizards as well as people.

But in the human brain, this structure is wired to areas involved in higher-order thinking, a team led by researchers from Washington University in St. Louis reports Thursday in the journal Neuron.

"We think that the cerebellum is acting as the brain's ultimate quality control unit," says Scott Marek, a postdoctoral research scholar and the study's first author.

The finding adds to the growing evidence that the cerebellum "isn't only involved in sensory-motor function, it's involved in everything we do," says Dr. Jeremy Schmahmann, a neurology professor at Harvard and director of the ataxia unit at Massachusetts General Hospital.

Schmahmann, who wasn't involved in the new study, has been arguing for decades that the cerebellum plays a key role in many aspects of human behavior, as well as mental disorders such as schizophrenia.

But only a handful of scientists have explored functions of the cerebellum beyond motor control.

"It's been woefully understudied," says Dr. Nico Dosenbach, a professor of neurology at Washington University whose lab conducted the study.

Even now, many scientists think of the cerebellum as the part of the brain that lets you pass a roadside sobriety test. It helps you do things like walk in a straight line or stand on one leg or track a moving object — if you're not drunk.

But the Washington University team thought there was a lot more going on in this part of the brain. So they used a special type of MRI to study the brain wiring of 10 people.

This allowed the team to quantify the various connections between the cerebellum and other brain areas. And what they found was that just 20 percent of the cerebellum was dedicated to areas involved in physical motion, while 80 percent was dedicated to areas involved in functions such as abstract thinking, planning, emotion, memory and language.

"We already thought that the cerebellum was cooler than most people thought," Dosenbach says. "But these results were way more exciting and clear than I could have ever dreamt."

The cerebellum doesn't directly carry out tasks like thinking, just as it doesn't directly control movement, Marek says. Instead, he says, it appears to monitor the brain areas that are doing the work and make them perform better.

In essence, this structure appears to act as a kind of editor, constantly reviewing and improving a person's thoughts and decisions, Dosenbach says. If that's true, he says, it's no surprise that alcohol affects more than our physical movements.

"We have an explanation for all the bad ideas people have when they're drunk," he says. "They're lacking cerebellar editing of your thoughts."

The new study suggests how the cerebellum has evolved over hundreds of millions of years, Schmahmann says.

"What's happened over time is that the cerebellum has expanded enormously," he says. And this extra capacity has allowed it to take on functions beyond motion.

But the way the cerebellum works hasn't changed, Schmahmann says. It makes a process smoother and faster and more accurate. "What we now understand is that what cerebellum does to motor control, it does to cognition and emotion as well."

And the cerebellum does all this automatically, allowing our conscious mind to focus on more important things, Schmahmann says.

But when the cerebellum isn't doing its job, Schmahmann says, the result may be a brain disorder.

"There is increasing evidence from a variety of fields now that psychiatric diseases from autism spectrum, schizophrenia, depression, obsessive compulsive disorder, all have a link to cerebellum," he says.

So Schmahmann and a few other researchers have begun trying to treat patients with some of these problems by improving the function of this ancient structure in the brain.

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MARY LOUISE KELLY, HOST:

The cerebellum is a part of the brain that is best known for helping us keep our balance. Turns out this ancient part of the brain may have been underestimated. A new study suggests it also helps us manage everything from emotions to social interactions to planning. NPR's Jon Hamilton has more.

JON HAMILTON, BYLINE: The cerebellum doesn't get much respect. Scientists often dismiss it as that part of the brain that lets you pass a roadside sobriety test. It helps you do things like walk in a straight line or stand on one leg if you're sober. But researchers at Washington University in St. Louis thought there was more to the cerebellum, so they used a special type of MRI to study the brain wiring of 10 people. And Dr. Nico Dosenbach says they found some surprising connections.

NICO DOSENBACH: About 20 percent of the cerebellum is dedicated to motion but that 80 percent is dedicated to higher-order cognitive functions.

HAMILTON: What kind of cognitive functions? Scott Marek, a postdoc in Dosenbach's lab, offers some examples.

SCOTT MAREK: Abstract thinking, forward planning, even holding something in memory, producing the words that you're saying - it's important for all of those day-to-day functions that you really take for granted and that seem effortless.

HAMILTON: Marek says the cerebellum doesn't carry out these tasks directly just as it doesn't directly control movement. Instead, he says, it appears to monitor the brain areas that are doing the work and make them perform better.

MAREK: So we think that the cerebellum is acting as the brain's ultimate quality control unit.

HAMILTON: That's still speculation, but Dosenbach says the finding published in the journal Neuron adds to the evidence that this ancient part of the brain plays a critical role in modern life.

DOSENBACH: We already thought that the cerebellum is cooler than most people thought, but these results were way more exciting and clear than I could have ever dreamt.

HAMILTON: Dosenbach says most researchers haven't paid much attention to the cerebellum perhaps because its most obvious function involves something pretty mundane - physical movement.

DOSENBACH: But really it's much more about editing your thoughts and your internal life. It's just much harder to notice that. And I think that's why scientists and neurologists have been missing it for a long time.

HAMILTON: And Dosenbach says the new study offers a good reason why alcohol affects a lot more than a person's balance when it impairs the cerebellum.

DOSENBACH: We have an explanation for all the bad ideas people have when they're drunk. They're lacking cerebellar editing of your thoughts.

HAMILTON: One scientist who's not surprised by the new study's results is Jeremy Schmahmann, a professor at Harvard Medical School. He's been arguing for decades that the cerebellum is involved in both human behavior and disorders like schizophrenia. Schmahmann says the cerebellum has changed dramatically since it appeared in fish and lizards hundreds of millions of years ago.

JEREMY SCHMAHMANN: What's happened over time is that the cerebellum has expanded enormously. And the parts of cerebellum that are talking to the parts of the brain upstairs that are involved in cognition means that cerebellum is involved in those processes as well.

HAMILTON: Schmahmann says the cerebellum is performing more or less the same function it always has. But instead of just making a physical movement smoother and more accurate, it's smoothing out our emotional responses or improving our ability to make good decisions and focus on a task.

SCHMAHMANN: What we now understand is that what cerebellum does to motor control it does to cognition and emotion as well.

HAMILTON: Schmahmann says the cerebellum does all this automatically, so we're unaware of its contribution. But when it stops working, he says, the result may be a brain disorder.

SCHMAHMANN: There is increasing evidence from a variety of fields now that psychiatric diseases from autism spectrum, schizophrenia, depression, obsessive compulsive disorder all have a link to cerebellum.

HAMILTON: And Schmahmann says he and other researchers are already trying to fix some of these problems using treatments that make the cerebellum itself work better. Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.