Why Is the Human Cerebellum Making Headline News?

Neanderthal PHLPP1 gene may trigger higher myelination in the human cerebellum.

Posted Dec 14, 2018

 Philipp Gunz (CC BY-NC-ND 4.0)
This image shows that one of the features that distinguishes modern humans (right) from Neanderthals (left) is a globular shape of the braincase.
Source: Philipp Gunz (CC BY-NC-ND 4.0)

Yesterday, the New York Times published an article, “Narrower Skulls, Oblong Brains: How Neanderthal DNA Still Shapes Us,” by Carl Zimmer. This news coverage puts some fascinating new information about the human cerebellum (Latin for "little brain") in the spotlight.

This NYT report is based on a new study, "Neandertal Introgression Sheds Light on Modern Human Endocranial Globularity," by Philipp Gunz and colleagues published December 13 in Current Biology. As Zimmer describes, this research offers an “unprecedented glimpse into the genetic changes influencing the evolution of the human brain.”

CNN, the Independent, Daily Mail.com, and other news outlets around the globe also covered the recent study by Gunz et al. The cerebellum is a trending neuroscience topic. Based on the groundswell of coverage, it looks like the "little brain" is on the verge of becoming a media darling.

Earlier this year, I wrote a Psychology Today post, “The Evolution of Modern Human Brain Shape Linked to Parietal Lobes and Cerebellum,” based on another study (2018) by Gunz and colleagues from the Department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology.

This paper, "The Evolution of Human Brain Shape," reported that modern human skulls became more globular than the elongated rugby-ball shaped Neanderthal skull due to a rapid expansion of the parietal lobes and bulging of the cerebellum. Modern humans have a globular-shaped braincase, with a rounder and expanded posterior cranial fossa in the back of the skull which houses the cerebellum, and bigger parietal bone as seen in the graphic below.

 "Neandertal Introgression Sheds Light on Modern Human Endocranial Globularity" by Gunz et al. (Current Biology, 2018)
Endocranial Shape Differences between Neandertals and Modern Humans
Source: "Neandertal Introgression Sheds Light on Modern Human Endocranial Globularity" by Gunz et al. (Current Biology, 2018)

Notably, the most recent study by Gunz et al. identifies, for the first time, that modern humans who carry two Neanderthal DNA fragments (UBR4 and PHLPP1) have slightly less-rounded heads than Homo sapiens who don’t carry these Neanderthal genes.

The researchers suspect that the neural expression of these two genes in modern humans is linked to neurogenesis (birth of new neurons) in the putamen region of the basal ganglia and more robust myelination in the cerebellum. "Both brain regions receive direct input from the motor cortex and are involved in the preparation, learning, and sensorimotor coordination of movements. The basal ganglia also contribute to diverse cognitive functions, in memory, attention, planning, skill learning, and potentially speech and language evolution," Philipp Gunz said in a statement.

Of all the news reports in the mainstream media I read about the latest Neanderthal UBR4/PHLPP1 research this morning, the passage below from the Times article by Carl Zimmer sums up the findings by Gunz et al. most succinctly:  

These findings suggest that PHLPP1 and UBR4 evolved to work differently in modern human brains. The modern human version of PHLPP1 may have produced extra myelin in the cerebellum. And our version of UBR4 may have made neurons grow faster in the putamen. Why these changes? Simon Fisher, a co-author of the new study at the Max Planck Institute for Psycholinguistics in the Netherlands, speculated that modern humans evolved more sophisticated powers of language. They may have also become better at making tools. “Things like tool use and speech articulation are hugely dependent on motor circuitry,” said Dr. Fisher. Both require the brain to send fast, precise commands to muscles. And it may be no coincidence that the cerebellum and putamen are crucial parts of our motor circuitry — the very regions that helped change the overall shape of the modern human brain.

The online version of this New York Times article includes a breathtaking 13-second video in 3D of a Neanderthal skull and modern human skull rotating side-by-side in negative space.

“We don’t know exactly what the [human] cerebellum is doing. But whatever it’s doing, it’s doing a lot of it.” —Richard M. Bergland, M.D. (20th-century neuroscientist, neurosurgeon, and author of The Fabric of Mind)

For the past decade, I’ve been trying (with minimal success) to pique a general audience’s curiosity about the wondrous and enigmatic cerebellum. Suffice to say, reading a heap of articles published by some of the most influential news outlets this morning—who all mention seemingly wonky details about the cerebellum—put me on cloud nine. I’m sure that if my late father, Richard Bergland (1932-2007) were alive to witness this cutting-edge research being delivered to a massive number of readers, he’d be over the moon, too.

When my father died in 2007, I made a vow to keep my antennae up for any new research that would advance our understanding of “whatever” the mysterious human cerebellum is "doing a lot of" in his honor.

Intriguingly, the human cerebellum is only about 10 percent of whole-brain volume, but contains the majority of the brain’s total neurons. Although specific numbers are debatable, it’s estimated that the human cerebellum houses 101 billion neurons (Andersen et al., 1992 ) whereas the cerebral cortex holds approximately 21–26 billion neurons (Pelvig et al., 2008).

Based on this surprisingly disproportionate distribution of neurons—and the fact that my dad regularly observed cognitive deficits in neurosurgery patients with atypical cerebellar function—he developed an "educated guess" that the human cerebellum was involved with much more than just fine-tuned motor control and coordination. (Cerebellar is the sister word to cerebral and means, "relating to or located in the cerebellum.")

That said, because it has been well established for centuries that the cerebellum plays a central role in fine-tuning muscle movements and coordination, it was a no-brainer to make cerebellar functions the central focus of my first book, The Athlete’s Way (St. Martin’s Press). While writing this manuscript, my father helped me create a cerebrum-cerebellum based model we called “up brain-down brain.” (See, “The Split-Brain: An Ever-Changing Hypothesis” which explored well-known motor functions—along with some hypothetical non-motor functions—of the cerebellum.)

My father passed away four months after the book we collaborated on was published. Since then, I’ve done my best to update dad's hypotheses about the cerebellum based on the latest evidence-based findings. Regardless of how esoteric a new study about the cerebellum might seem to the general reader, as a blogger, I try to report on every significant cerebellar study published in a peer-reviewed journal. My long-term goal is to curate a detailed timeline of how state-of-the-art cerebellum research progressed throughout the early-21st century for posterity.

To stay on top of all the latest research about this topic, I monitor three key words, “cerebellum,” “cerebellar,” and “Purkinje cells,” using Google Alerts. This triad of words relating to the "little brain" came up on a regular basis during conversations with my father about how the whole-brain works. These days, I keep a dialogue about the cerebellum going with leading experts in the field (such as Jeremy Schmahmann) via email correspondence, Twitter, and other social media platforms.

Cerebellum News Is a Trending Topic Across Media Platforms

Normally, I receive a Google Alert message relating to one of the cerebellum-related words mentioned above about once a week. That said, in the past month or so, there have been two times my inbox was flooded with a tsunami of breaking news about the cerebellum being covered by a wide range of media outlets. 

The first time this happened was in late October after NPR reported on a cerebellum study by Scott Marek and colleagues (2018) at Washington University School of Medicine in St. Louis. This research was first announced in a press release with a catchy title, “Mind’s Quality Control Center Found in Long-Ignored Brain Area: Cerebellum Checks and Corrects Thoughts, Movement," and caught on like wildfire in the media. (See, “3 Reasons the 'Little Brain' Might Become the Next Big Thing.”)

The second time cerebellum news set off alarm bells via Google Alerts started yesterday afternoon with the latest study by Philipp Gunz and colleagues. Most likely, in the days ahead multiple other outlets will report on these Neanderthal DNA findings.

Thanks to groundbreaking interdisciplinary research from collaborative teams around the world such as Gunz et al., we are slowly solving the many riddles of the human cerebellum. Hopefully, an increase in media coverage about the "little brain" will translate into funding that keeps all of this pioneering cerebellar research going strong.

References

Philipp Gunz, Amanda K. Tilot, Katharina Wittfeld, Alexander Teumer, Chin Yang Shapland, Theo G.M. van Erp, Michael Dannemann, Benjamin Vernot, Simon Neubauer, Tulio Guadalupe, Guillén Fernández, Han G. Brunner, Wolfgang Enard, James Fallon, Norbert Hosten, Uwe Völker, Antonio Profico, Fabio Di Vincenzo, Giorgio Manzi, Janet Kelso, Beate St. Pourcain, Jean-Jacques Hublin, Barbara Franke, Svante Pääbo, Fabio Macciardi, Hans J. Grabe, Simon E. Fisher. "Neandertal Introgression Sheds Light on Modern Human Endocranial Globularity." Current Biology (First published: December 13, 2018) DOI: 10.1016/j.cub.2018.10.065

Simon Neubauer, Jean-Jacques Hublin, and Philipp Gunz. "The Evolution of Human Brain Shape." Science Advances (First published: January 24, 2018) DOI: 10.1126/sciadv.aao5961

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