The Mysterious Cerebellum

Much, Much More than Coordination

The cerebellum hosts 80% of all our neurons. That is an astounding figure. It would suggest that four-fifths of our brain processing sits in this small part of the brain - often called the small brain - at the back of our head. Not only that, but considering that 80% of our neurons sit in this region, it is all the more surprising that this part of the brain does not get more publicity.

Generally, the cerebellum has been considered a centre of coordination and balance, but the cerebellum's role in much of cognition is generally ignored. Let us review this fascinating structure of the brain.

The cerebellum sits at the back of the head and has a surprisingly strong, and often underestimated, influence on all our cognitive processes - and incidentally houses 80% of all of our neurons. This figure of housing 80% of our neurons is a sobering and stunning figure, and somewhat surprisingly hasn’t caused as much head scratching as we would expect in the neurosciences. Let’s put this into context – this is equivalent say, to 80% of the population of Britain living in a notable but unspectacular city in the UK, say Bristol. This would cause many researchers to wonder why Bristol with so many inhabitants weren’t a more important city – then again can we imagine that a city housing 80% of the population wouldn’t be a country’s most important city?

Now this discrepancy has been known for a long time and recently supported by the innovative research of Suzana Herculano-Houzel who finally gave us solid answers to how many neurons and glial cells (supporting cells in the brain) we actually have. So, this has just been one of those curious facts about the brain that falls into the “fascinating information” category with nothing further to add. But this size has led others, such as Richard M. Bergland, to surmise that “…whatever the cerebellum does, it does a lot of it.”

This mystery thickens when we consider recent research mapping the surface area of the cerebellum. Looking at a picture of the cerebellum we can see that it is significantly smaller than the cerebrum, our outer cortex. However, we can also see that it is more wrinkled. It is indeed much more tightly folded. In 2020 researchers managed to calculate the surface area of the cerebellum and have shown that it reaches an amazing 80% of the size of the cerebrum. So much for small brain. It seems like we have a big brain complemented by another big brain. So, the cerebellum has the majority of neurons and almost equivalent surface area to our much-lauded cerebrum.

Why?