Rethinking the “little brain”

The surprise player in last week’s post about how meditation can increase your gray matter was the cerebellum. The cerebellum, from the Latin for “little brain”, is a structure that stands apart from the rest of the brain, an orb nestled at the top of the spinal cord. Like the other regions of the “hindbrain”, it plays a vital role in keeping us alive and functioning but, in my experience, is otherwise dismissed as cognitively uninteresting. The cerebellum helps coordinate muscle movements, but the only cognition it gets involved with is learning new motor skills, and even then it doesn’t do too much to distinguish itself. I wouldn’t want mine damaged in any way, but beyond that I didn’t think there was much to know.

And I was completely wrong.

The "little brain" in profile. Photo from Conway Psychology.

The “little brain” in profile. Photo from Conway Psychology.

It turns out that the cerebellum has an entire journal devoted to it, and aptly named The Cerebellum. The journal does feature a number of studies about ataxia and other motor coordination difficulties, often with a level of neurobiological detail about “Purkinje cells” and the role of nitrous oxide that reminds me how my students must feel when I slip hypothalamus and amygdala in a sentence as if they should be as clear as Google. However, it also becomes clear that the cerebellum is seen as a least a support system for a variety of cognitive skills, including:

  • Language, both oral and written. A role in spoken speech and in writing itself is not at all surprising; these are complex motor skills that each developed over a period of years and required a great deal of coordination among either the muscles of the throat and mouth or the muscles of the fingers. The cerebellum doesn’t just stop at motor production, though. It seems to support our ability to make sense of the sounds of speech that we hear, perhaps by translating auditory sounds into meaningful sounds of language; code for certain rules of syntax, and therefore respond when grammar rules are violated; and coordinate eye movements across a page and our inner voice as we read.
  • Verbal working memory, perhaps as an extension of its role in language. Verbal working memory refers to that voice in our head where we repeat something we are trying to remember. The cerebellum may match those speech sounds we hear into the motor plan we would use to make the sounds ourselves, and that plan could then be the foundation of our inner voice. This is again a role as support staff; the prefrontal cortex remains the key player in directing our memory, but the cerebellum could be (part of) what it directs attention to.
  • Pain. Perhaps sensibly given its position on the spinal cord, the cerebellum receives pain signals from the rest of the body. Most importantly, the cerebellum could be a site for dulling pain. Stimulating or administering drugs to the cerebellum will alter how animals respond to pain, and some evidence from brain scans when people are put into pain suggests the cerebellum might help us ignore pain when it’s ongoing.
  • Autism. People diagnosed with autism have a higher rate of cerebellum structural differences than the neurotypical – when people look at the cerebellum in autism, which isn’t often. The one paper I’ve read (and linked to) focuses more on the biological features such as evidence of inflammation and neurotransmitter levels, but does offer some hints at how cerebellum differences could explain some features of autism. The language difficulties that are one of the central diagnostic features make a strong case, and the cerebellum’s role could explain why even those with autism who do produce speech sometimes have odd speech patterns. There are also links to some non-diagnostic criteria, such as a frequent clumsiness with autism that could be explained by difficulty coordinating motor movements. The social features of autism may be the hardest one to explain here, because there doesn’t seem to be too much linking the cerebellum to social interactions – but then, perhaps it’s a combination of changes in the cerebellum and the amygdala that might give us a complete picture of autism.

The heart of these is still that central idea of that the cerebellum coordinates motor activities, with the recognition that coordinating various muscles a) requires having a good sense of what’s going on around you, meaning strong connections with sensation, and b) can be a stepping stone to an awful lot of other cognitive functions.  So it’s not quite the case that the Intro Psychology textbooks are wrong, just that they aren’t giving the cerebellum enough credit for what that seemingly simple job can do. Perhaps the cerebellum will come into its own in the coming years; it’s a brain region to watch.

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