Unlocking the mysteries of the little brain

Recently, I adopted an eight-week old dachshund puppy and named him Pablo. For those unfamiliar with dachshunds, they are an incredibly intelligent and lively breed, though quite a stubborn one. Pablo is no exception.

From the get-go, I’ve embarked on a training journey to create a happy and confident life companion and friend. One aspect of Pablo’s training that has greatly intrigued me is helping him to control his impulsivity and the benefits this has brought. 

Sitting behind our brainstem is this small intricate structure largely responsible for controlling impulsivity, as well as balance, coordination, movement and motor skills. This structure is the cerebellum (Latin for “little brain”). Essentially, the cerebellum acts as a Master Yoda of our brain - it trains and fine-tunes our motor skills to make movements adaptive and accurate, just as Yoda trains his padawans to correctly utilise the force.

Traditional anatomical techniques, like anterograde and retrograde tracing, have revealed cerebellar connections to thalamic and cortical structures linked to motor processing. Experimental studies on rhesus monkeys have taught us that motor deficits result upon cerebellar lesions.

It is not surprising, therefore, that for centuries, we once believed the cerebellum was predominantly responsible for motor learning. In fact, this is a prevailing view echoed by many neuroscientists to date, so much so, that one well-renowned textbook cites: 

“The cerebrum… is primarily concerned with sensation and perception, and the cerebellum is primarily a movement control centre” (Bear, Connors and Paradiso 2008)

We now, however, understand that the cerebellum encompasses a much larger and integral role in shaping behaviour. The 1980’s saw a rise in functional human brain imaging experiments which commonly showed cerebellar activation upon simple cognitive tasks, like processing words on a screen. It was later uncovered that the largest cerebellar nucleus, the dentate nucleus, is activated when subjects were asked to solve a puzzle. The cognitive function of the cerebellum, independent to motor control, soon emerged among a wealth of studies.

The start of the 21st century then saw a paradigm shift in our conventional understanding of the cerebellum. In addition to its cognitive role, it was increasingly recognised that the cerebellum also plays a role in affective functions, particularly emotional regulation, and is linked with psychiatric disorders.

Recently, in 2018, a previously unknown region within the cerebellum has been discovered, named the Endorestiform Nucleus. It’s a region whose existence has been speculated about for 3 decades but could only revealed with the advent of innovative imaging technology. 

Researchers believe that the Endorestiform Nucleus is a distinct area from its surrounding region, which is responsible for fine motor control. Interestingly, this nucleus appears to be absent in the rhesus monkey and other studied animals. There’s a possibility this nucleus is one unique to humans, which may then have significant implications for neurodegenerative conditions affecting motor control, like Parkinson’s Disease.  

Although it only occupies approximately 1/10th of the brain’s total volume, the cerebellum is estimated to account for over 80% of the brain’s total neurons. Furthermore, a 2020 study has recently revealed the tight folds of the cerebellum account for almost 80% of the total surface area of the cerebral cortex.

In a nutshell, this is vastly greater than that of primates, suggesting an evolutionary distinction of human abilities. Indeed, it is believed that the cerebellum could be crucially responsible for producing human culture and our complex sociality over other animals.

Evidently, there is no established consensus on what precisely the cerebellum can do.  It is an intricate structure that remains largely undiscovered and, with the use of modern imaging techniques, is still being learned about.

Until the enigma of the cerebellum’s multimodal role can be solved, modern neuroscience textbooks and literature will continue to hold obsolete neuroscientific views.