Cerebellum, mind, and mood

The cerebellum is an evolutionarily old part of the brain. It is a multilayered structure that lies beneath and behind the larger paired areas of the brain called the cerebral hemispheres. The word, cerebellum, was thought to have first been used in 1501 by the German anatomist, Magnus Hundt, and derives from the Latin for, “little brain.” It has been considered little both in size and in contribution to the mind.

It was long believed that the cerebellum acted merely to organize and coordinate movement. The most obvious effect of damage to the cerebellum is loss of balance and coordination. A person with such damage has trouble walking or simply standing still. They reach past objects they are trying to grasp. Another hallmark of cerebellar damage, called dysdiadochokinesia, is the inability to perform rapidly alternating muscle movements.  That might include rapidly tapping the index fingers and thumbs together or alternatingly slapping their palms and back sides of their hands on their thighs. Cerebellar lesions may also produce ataxic speech in which words come slowly, with syllables oddly separated and not distinguished by the usual varying emphasis in tone. Language is one of the highest faculties of the human mind. However, it was thought that ataxic speech from cerebellar damage was merely due to difficulty in coordinating the movements of the mouth, tongue, throat, and diaphragm necessary to articulate words. It was not suspected that such damage could cause difficulties in organizing the thinking behind the words.

It was the neurologist, Dr. Jeremy D. Schmahmann, that first formally considered the effects of cerebellar injury on cognitive function and mood. He identified a constellation of deficits in executive and emotional processing that can appear after cerebellar injury. He called this Cerebellar Cognitive Affective Syndrome, though it is sometimes referred to as Schmahmann Syndrome. In a 1998 paper, Schmahmann noted that injury to the cerebellum could produce symptoms that included impaired planning and abstract thinking; inability to shift focus; poor verbal fluency; and difficulties with  visual-spatial organization; as well as personality changes, with blunting or disinhibition of emotions, and inappropriate behavior.

Interestingly, there are great similarities between the cognitive and emotional symptoms of Schmahmann Syndrome and those seen in Attention Deficit Hyperactivity Disorder, or ADHD. I once saw a patient that had suffered cerebellar damage after a stroke. They initially came to see me due to depression that arose after the stroke. Indeed, any severe, debilitating illness can cause depression. However, even after the depression had begun to lift, the patient remained unable to return to work as an executive in a large corporation. The patient was no longer able to make important decisions, organize the day, or retain focus.  There had been various case reports of the successful use of methylphenidate, the medication used to treat ADHD, to treat the symptoms of Schmahmann Syndrome. The patient, who had never suffered ADHD, agreed to a trial of the medication and noted substantial improvement in focus and organization as we adjusted the dose. Although full function was never regained, improvement was enough to return to work for several months until arrangements could be made for early retirement.

Along with injuries to the cerebellum, congenital deficits in cerebellar function can also contribute to psychiatric illness. Imaging studies have shown cerebellar abnormalities in psychiatric disorders including schizophrenia, bipolar disorder, major depressive disorder, and ADHD. In schizophrenia, the cerebellum is often reduced in size, and the flow of activity between the cerebellum and the higher centers in the cerebral cortex is reduced. In Bipolar Disorder, there is often slight atrophy of cerebellar structures and reduced blood flow. Studies also suggest some cerebellar atrophy in patients with unipolar depression that correlates with severity and lack of response to antidepressants. Children with ADHD often exhibit  “soft neurological signs” such as subtle ataxia, poor coordination, dysdiadochokinesia, and intention tremor that are suggestive of cerebellar dysfunction. MRIs have shown overall reductions in the size and activity of the cerebellum in ADHD compared to typically developing controls.

If deficits in cerebellar function due to injury, disease, or genetic predisposition can cause psychiatric symptoms, might such symptoms be improved by exercising the cerebellum and enhancing its function? Studies suggest so. It is known that exercise helps many forms of psychiatric illness. However, while aerobic exercise can improve symptoms of ADHD, practicing martial arts that require cerebellar control of balance, timing, and sequencing of movements, is more helpful. Learning to play the drums, which  similarly exercises the  cerebellum, has also been found to improve symptoms of ADHD and other childhood cognitive disorders. Interestingly, stimulation of the cerebellum causes release of dopamine in the prefrontal cortex, an effect mimicked by ADHD medications. Evidence shows that exercising the cerebellum enhances the function of the entire brain and mind.  Perhaps, the “little brain” should play a larger role in psychiatric evaluation and treatment.