In 1504, Leonardo da Vinci made wax castings of the human brain and coined the term cerebellum (Latin for "little brain") after he unearthed two small kumquat-shaped hemispheres neatly tucked underneath the relatively mammoth left and right hemispheres of the cerebrum (Latin for "brain"). Cerebellar is the sister word to cerebral and means "relating to or located in the cerebellum."
Since ancient times, the cerebellum—which is only about 10 percent of brain volume but houses approximately 75 percent of the brain's total neurons—has remained mysterious and misunderstood. Only recently, have state-of-the-art advances in technology allowed neuroscientists to begin to solve the many riddles of the cerebellum.
For example, my late father, Richard M. Bergland, was a 20th-century neurosurgeon, neuroscientist, and author of The Fabric of Mind, who speculated that the enigmatic cerebellum might be the seat of implicit muscle memory and learning. Unfortunately, it was impossible for him to prove his cerebellar hypotheses in a laboratory at the time... So, my dad would constantly say "We don't know exactly what the cerebellum is doing. But whatever it's doing, it's doing a lot of it."
One thing we do know is that the left hemisphere of the cerebellum works in conjunction with the right cerebral hemisphere to fine-tune and coordinate voluntary muscle movements on the left side of the body (and vice versa) in a crisscross manner.
Also, people with ataxia or dysmetria usually have cerebellar dysfunctions or lesions in a specific region of the cerebellum—which can result in a disruption of balance, lack of motor coordination, desynchronized eye movements, speech problems, gait abnormalities, etc.
Jeremy D. Schmahmann is a world-renowned professor of neurology at Harvard Medical School and a global thought leader regarding both ataxia and the cerebellum. He's also director of the Massachusetts General Hospital Ataxia Unit, the Laboratory for Neuroanatomy and Cerebellar Neurobiology, and a member of the MGH Cognitive Behavioral Neurology Unit.
Over the years, I've written a wide variety of Psychology Today blog posts about Jeremy Schmahmann's revolutionary "Dysmetria of Thought" hypothesis—which basically posits that (contrary to popular belief) the cerebellum may actually fine-tune our thoughts and emotions much the same way it fine-tunes the timing of our muscle movements. For more on this, check out my PT posts, "The Cerebellum Deeply Influences Our Thoughts and Emotions" and "Harvard Research Shows How the Cerebellum Regulates Thoughts."
In April of 1998, Schmahmann and Janet C. Sherman published a landmark paper, "The Cerebellar Cognitive Affective Syndrome," in the journal Brain. CCAS is also known as "Schmahmann's Syndrome" and refers to a constellation of deficits in the cognitive domains of executive function, spatial cognition, language, and behavior that stem from damage to the cerebellum.
Almost two decades later, on December 1, 2017, Schmahmann and collaborators at Harvard Medical School and the Massachusetts Institute of Technology (MIT) published another groundbreaking CCAS-related study in the journal Brain, "The Cerebellar Cognitive Affective/Schmahmann Syndrome Scale." As the co-authors describe in the abstract, "The aim of this study was to develop an office or bedside cognitive screen to help identify CCAS in cerebellar patients."
Please take a few minutes to watch this December 4, 2017, video by Schmahmann et al. describing the widespread benefits of having a new scale to measure CCAS:
Schmahmann and colleagues were able to validate this new scale in a cohort of 39 cerebellar patients and 55 healthy controls. As the authors describe in the new study abstract:
“We confirm the defining features of CCAS using neuropsychological measures. Deficits in executive function were most pronounced for working memory, mental flexibility, and abstract reasoning. Language deficits included verb for noun generation and phonemic > semantic fluency. Visual spatial function was degraded in performance and interpretation of visual stimuli.
Neuropsychiatric features included impairments in attentional control, emotional control, psychosis spectrum disorders and social skill set. From these results, we derived a 10-item scale providing total raw score, cut-offs for each test, and pass/fail criteria that determined ‘possible’ (one test failed), ‘probable’ (two tests failed), and ‘definite’ CCAS (three tests failed).”
In addition to Jeremy Schmahmann, the other researchers involved in this collaborative effort include: First author Franziska Hoche of the MINDlink foundation (their motto is "Connecting the Cerebellum to Cures"); Xavier Guell of MINDlink and the Gabrieli Lab at MIT; Mark Vangel who is a radiologist at Harvard Medical School and a statistician at MIT; and Janet Sherman who is the Clinical Director of the Psychology Assessment Center and Chief Neuropsychologist at Harvard's Massachusetts General Hospital.
Franziska Hoche, Xavier Guell, Mark G. Vangel, Janet C. Sherman, Jeremy D. Schmahmann. "The Cerebellar Cognitive Affective/Schmahmann Syndrome Scale." Brain (Published: December 1, 2017) DOI: 10.1093/brain/awx317
Schmahmann, Jeremy D. "Disorders of the Cerebellum: Ataxia, Dysmetria of Thought, and the Cerebellar Cognitive Affective Syndrome." The Journal of Neuropsychiatry and Clinical Neurosciences (2004) DOI: 10.1176/jnp.16.3.367
Jeremy D. Schmahmann and Janet C. Sherman. "The Cerebellar Cognitive Affective Syndrome." Brain: A Journal of Neurology (1998) DOI: 10.1093/brain/121.4.561
Schmahmann, Jeremy D. "Dysmetria of Thought: Clinical Consequences of Cerebellar Dysfunction on Cognition and Affect." Trends in Cognitive Sciences (1998) DOI: 10.1016/S1364-6613(98)01218-2