The Cerebellum May Drive Sex Distinction in Our Social Brain

Purkinje cells in the cerebellum are tied to specific social behavior in males.

Posted Sep 29, 2016

Cerebellum (Latin for "little brain") in red. 
Source: Life Science Databases/Wikimedia Commons

A groundbreaking new study identifies a strong association between impaired social behavior in rats and the disruption of particular types of cells in the cerebellum during a critical period of development. Interestingly, this phenomenon was only observed in males. The paper reporting on the study was published today in the Journal of Neuroscience.

Neuroscientists at the University of Maryland identified a narrow critical period of development for cells in the cerebellum by injecting a compound that triggered inflammation in that part of the brain. This mimicked a natural infection. Then, they observed a chain reaction of increased estrogen production and stunted Purkinje cell growth in the cerebellum that impaired play behavior in male rats over time.

These new findings might help solve a riddle presented last year by researchers at Stanford University who observed distinct sex differences in the core symptoms of autism spectrum disorders (ASD) displayed by girls versus boys. Autism is typically characterized by three core symptoms: social impairments, communication difficulties, and repetitive/restricted behaviors. The number of boys diagnosed with high-functioning autism outnumbers girls by a ratio of four to one.

In a 2015 paper that appeared in the journal Molecular Autism, the Stanford researchers concluded that sex differences in brain morphometry are prominent in the motor system and in areas that comprise the “social brain,” but the researchers only partially homed in on the cerebellum.

"Whatever The Cerebellum Is Doing, It's Doing a Lot of It"

In 1504, Leonardo da Vinci made wax castings of the human brain and noticed a total of four distinct brain hemispheres within the cranial globe. The castings made by da Vinci clearly illustrated that there were two large hemispheres in the cerebrum (Latin for "brain") and two smaller hemispheres neatly tucked underneath this brain mass. Based on these observations, he coined the term cerebellum which is Latin for "little brain." 

Life Science Databases/Wikimedia Common
Cerebrum (Latin for "brain") in red. 
Source: Life Science Databases/Wikimedia Common

Although the cerebellum is only 10 percent of brain volume, it houses well over 50 percent of your brain's total neurons. My father, Richard Bergland (who was a neuroscientist and neurosurgeon) was deeply perplexed by this disproportionate distribution of neurons. He would often say, "We don't know exactly what the cerebellum is doing. But whatever it's doing, it's doing a lot of it."

Historically, both hemispheres of the cerebellum were believed by medical experts to only play a role in ‘non-thinking’ activities such as fine-tuning motor coordination, proprioception, and balance. On the flip side, both hemispheres of the cerebrum were considered to be the exclusive seat of all types of cerebral ‘thinking’ and creativity. However, these outdated concepts of the cerebellum are rapidly changing.

Increasingly, the cerebellum is being noted by thought leaders for its role in social, emotional, and cognitive behaviors. For example, individuals with neurodevelopmental disorders such as autism and schizophrenia display pronounced alterations in the cerebellum. A January 2016 study found a link between post-traumatic stress disorder (PTSD) in combat veterans and Purkinje cells in the cerebellum. 

Additionally, in June 2016, a study by Manish Saggar of Stanford University was published in Cerebral Cortex reporting that increased connectivity between the cerebrum and cerebellum boosts creative capacity.

"Developmental Diaschisis" and Sensitive Periods of Cerebellar Development

For years, Samuel Wang, professor of molecular biology and neuroscience at Princeton University, has been conducting extensive research on the cerebellum’s role in cognition and social thought processes. Sam Wang has a theory that early cerebellum malfunction hinders neural development of the cerebral cortex and disrupts the brain's processing of external and internal information, which may be a possible root of autism.

In 2014, Wang et al. published a paper, “The Cerebellum, Sensitive Periods, and Autism,” in the journal Neuron. Based on a review of existing research, Wang and colleagues concluded that a cerebellar injury at birth makes someone 36 times more likely to score highly on autism screening tests.

Courtesy of Larry Vandervert
These neuron counts of the cerebellum and cerebral cortex are based on studies by Lent, R., et al., 2012.
Source: Courtesy of Larry Vandervert

Cerebellar damage is considered the largest uninherited ASD risk. (Cerebellar is the sister word to cerebral and means "relating to or located in the cerebellum.") Although the cerebellum has been largely overlooked for the role it plays in childhood development, the Princeton University researchers believe that the cerebellum holds many clues for better understanding the onset of autism and the social brain.

Sam Wang’s theory is that atypical cerebellar function or structure during early life leads to something called developmental diaschisis: Malfunction of the cerebellum causes disruptions in how other areas of the brain develop and the brain's overall ability to interpret external stimuli and organize internal processes. In a statement about the research to Princeton University, Wang summed up the ramifications of this theory:

"It is well known that the cerebellum is an information processor. Our neocortex [the largest part of the brain, responsible for much higher processing] does not receive information unfiltered. There are critical steps that have to happen between when external information is detected by our brain and when it reaches the neural cortex.

At some point, you learn that smiling is nice because Mom smiles at you. We have all these associations we make in early life because we don't arrive knowing that a smile is nice. In autism, something in that process goes wrong and one thing could be that sensory information is not processed correctly in the cerebellum."

In Princeton's summary, Mustafa Sahin, a neurologist at Boston's Children Hospital and associate professor of neurology at Harvard Medical School, noted that "the association between cerebellar deficits and autism has been around for a while," and that Wang and his co-authors are expanding what is known about that link.

Santiago Ramón y Cajal/Public Domain
Drawing of Purkinje cell by Santiago Ramón y Cajal circa 1899. 
Source: Santiago Ramón y Cajal/Public Domain

Conclusion: More Research on Purkinje Neurons and the Cerebellum Is Needed

Taken together, this research offers many exciting clues for understanding the role that the cerebellum plays in our social, emotional, and cognitive lives regardless of gender. It also appears that boys’ social brains may be more sensitive to stunted development of Purkinje cells. This research is still in its early phases. Stay tuned for more cutting-edge updates on the cerebellum and Purkinje cells.

If you’d like to read more on this topic, check out my previous Psychology Today blog posts,

© 2016 Christopher Bergland. All rights reserved.

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