Spilled Coffee and Toppling Babies

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The human brain astounds me! Its architecture is incredibly intricate, and each area plays a vital role in how we function. Known as the “little brain”, the cerebellum is the bump on the back-underside of the brain. And while researchers are still uncovering the complexity of the cerebellum’s design, function, and roles, it is understood that it helps in:

  • Visuospatial abilities
  • Balance
  • Emotional processing
  • Verbal functioning
  • Executive functioning
  • Coordination of bodily movements
  • Motor learning

To narrow the scope of this article, let’s focus primarily on the role of the cerebellum in coordination and motor learning. 

Coordination

Modification

It’s easy to imagine the cerebellum acting like a telephone exchange from the 1800s, receiving and sending information between many parts of the brain and body via nerve pathways. But unlike early phone technology, our body’s telephone switchboard operator, the cerebellum, has the power to change the messages it receives and sends for the benefit of the body’s coordination and movement. Here’s how it happens.

After the cerebellum receives messages from the brain and body, it compares the brain’s planned movement with the body’s actual movement, and then it quickly modifies the comprehensive movement plan so that the body’s movement occurs as the brain intended. Perhaps it would be more accurate to state that the brain and body copy the cerebellum on messages they send to each other so that the cerebellum can modify the messages as needed. Either way, you can see how vital the cerebellum is to facilitate the body’s coordination and movement.

Prediction

And there’s more. Not only does the cerebellum help to adjust the brain’s motor commands in real-time, but it also helps to predict which muscle actions are needed to produce an even more coordinated movement than the one originally planned. Neuroscientists call this phenomenon “feed-forward sensorimotor control.” This phenomenon is important because, by the time our brain receives sensory input from our eyes, ears, or limbs, the information is already out of date. Thus, for us to make the most punctual, silky smooth, and precise movements possible, the cerebellum predicts what needs to occur in the head, eyes, trunk, arms, and legs, communicating those requirements appropriately.

Motor Learning

While the cerebellum’s ability to make “on the fly” adjustments is both helpful and important, much about movement requires a pre-planned blueprint. This blueprint is created through motor learning.

Motor learning is a broad term referring to the ability to create and sustain effective movement patterns, and it occurs via a complex symphony of neural connections in many areas of the brain. The cerebellum is thought to be a key player in motor learning because it refines movements based on errors from previous attempts. It is also thought to serve a role in the cognitive processes of learning.

Any time we imperfectly perform a movement, the cerebellum makes a better prediction for the next movement. It happens over and over and over again, every time we imperfectly perform a movement. It makes this better prediction by identifying errors in the past movement and adjusting to prevent those errors in subsequent trials.

Here’s a real-life example:

I typically bowl with a 10-pound ball. When I first transition to a 15-pound bowling ball, I will likely throw gutter balls and be off balance for the first several frames. However, after some motor learning occurs, I may manage to get a spare in the 5th frame of the game. The subsequent improvement in movement displayed as I continue to bowl with the heavier ball is a result of the ongoing predictions by the cerebellum.

Spilled Coffee

Let’s pretend someone wants a sip of coffee. A short, fictional dialogue between the cortex, the cerebellum, and the body can describe how the cerebellum aids in coordination and motor learning. As you read the conversation, remember the roles of our actors. The Cortex is our pre-motor and motor cerebral cortex. The Body consists of our motor and sensory nerve pathways. And the star of our show is the Cerebellum, aka Little Brain.

Cortex: “Body, you pick up that mug. I’ll go ahead and let Cerebellum know my plan.”

Cerebellum: “Great idea, Cortex! That’s a pretty good plan, but I’m going to change it just a bit so that we don’t make a mess. Last time we reached for the coffee, we almost knocked the mug over.”

Cerebellum immediately sends the revised plan to the body via multiple nerve pathways. The body picks up the mug in a coordinated fashion.

Body: “Guys, the mug is quite a bit lighter than you expected.”

Cerebellum: “Body, don’t activate as many muscle fibers to raise it up then.”

Cortex: “Body, look inside the mug. Why is it so light?”

Body: “There is no brown liquid inside the mug.”

Cortex: “THE COFFEE IS GONE!

This hypothetical dialogue is an incredibly oversimplified depiction of what occurs in your brain for every movement that you make. There are many other players in this scenario, such as the basal ganglia, limbic system, visual cortex, somatosensory cortex, spinal cord tracts, vestibular-ocular system, pontine nuclei, thalamus, etc. Nonetheless, this scenario demonstrates that the cerebellum aids in augmenting your brain’s plans to produce smooth, efficient movements.

Toppling Babies

The above examples involve the cerebellum of an adult. Let’s now look at a baby’s cerebellum and see it in a less mature state.

Right now, as I write this article, my six-month-old sits on the floor in front of me. I call his name. He flashes me a toothless grin as he raises his arms in excitement. But the momentum of his arms causes his entire body to topple backward.

His cerebellum and other brain centers are still learning how the movement of his arms impacts his balance. His brain, body, and cerebellum are still working on their communication. He has not developed sufficient motor strategies to maintain a sitting balance or to smoothly pick up a toy. Thankfully, the human brain is an amazing creation, and it has the capacity for constant change and learning. After many trials and errors over the next few months, he will be able to sit, stand, and bring a Cheerio to his mouth, and maybe even say “mama.”

This begs the question, what happens when the cerebellum is not intact in an adult? Undoubtedly, one of the consequences of a malfunctioning cerebellum are termed cerebellar ataxia

Cerebellar Ataxia

With cerebellar ataxia, the cerebellum cannot create a predictive template of movement as outlined above. The cortex’s plan is not accurately modified, and so the body is forced to adjust as it goes without the valuable assistance of the little brain. Jerky, inaccurate movements ensue, which can result in imbalance, dysarthria (difficulty forming and pronouncing words), irregular eye movements, and general difficulty with activities of daily living. Can cerebellar ataxia be treated? Yes, and in my next article, I will describe strategies and challenges when treating cerebellar ataxia as a physical therapist.

References

  • Hull C. Prediction signals in the cerebellum: beyond supervised motor learning. Elife. 2020 Mar 30;9:e54073. doi: 10.7554/eLife.54073.
  • Motor Learning. Krakauer JW, Hadjiosif AM, Xu J, Wong AL, Haith AM.  Comprehensive Physiology. 2019 April; Vol 9.
  • Academy of Neurological Physical Therapy: 4D Deep Dive into Degenerative Diseases Podcast. Cerebellar Ataxia: Neurophysiology, Assessment, and Treatment with Amy Bastian (2019).

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1 Response
  1. Gary M

    Extremely well done article! It explains, in simple terms, what Ataxia does to the Brain functions. My son has Ataxia and I can only imagine what hardships it puts upon him. He does share with me but that is not the same as having to live with this disease.

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