Cerebellum

Definition

The cerebellum is a cauliflower-shaped brain structure located just above the brainstem, beneath the occipital lobes at the base of the skull.

Description

The word cerebellum comes from the Latin word for "little brain." The cerebellum has traditionally been recognized as the unit of motor control that regulates muscle tone and coordination of movement. There is an increasing number of reports that support the idea that the cerebellum also contributes to non-motor functions such as cognition (thought processes) and affective state (emotion).

The cerebellum comprises approximately 10% of the brain's volume and contains at least half of the brain's neurons. The cerebellum is made up of two hemispheres (halves) covered by a thin layer of gray matter known as the cortex. Beneath the cortex is a central core of white matter. Embedded in the white matter are several areas of gray matter known as the deep cerebellar nuclei (the fastigial nucleus, the globise-emboliform nucleus, and the dentate nucleus). The cerebellum is connected to the brainstem via three bundles of fibers called peduncles (the superior, middle, and inferior).

Anatomy

The cerebellum is a complex structure. At the basic level, it is divided into three distinct regions: the vermis, the paravermis (also called the intermediate zone), and the cerebellar hemispheres. Fissures, deep folds in the cortex that extend across the cerebellum, further subdivide these regions into 10 lobules, designated lobules I–X. Two of these fissures in particular, the posterolateral fissure and the primary fissure, separate the cerebellum into three lobes that have different functions: the flocculonodular lobe, or the vestibulocerebellum (lobule X); the anterior lobe (lobules I–V); and the posterior lobe (lobules VI–IX).

The cerebellum plays an important role in sending and receiving messages (nerve signals) necessary for the production of muscle movements and coordination. There are both afferent (input) and efferent (output) pathways. The major input pathways (also called tracts) include:

• dorsal spinocerebellar pathway
• ventral spinocerebellar pathway
• corticopontocerebellar pathway
• cerebo-olivocerebellar pathway
• cerebroreticulocerebellar pathway
• cuneocerebellar pathway
• vestibulocerebellar pathway

The major output pathways include the following:

• globose-emboliform-rubral pathway
• fastigial reticular pathway
• dentatothalamic pathway
• fastigial vestibular pathway

There is a network of fibers (cells) within the cerebellum that monitors information to and from the brain and the spinal cord. This network of neural circuits links the input pathways to the output pathways. The Purkinje fibers and the deep nuclei play key roles in this communication process. The Purkinje fibers regulate the deep nuclei, which have axons that send messages out to other parts of the central nervous system.

Function

The flocculonodular lobe helps to maintain equilibrium (balance) and to control eye movements. The anterior lobe parts of the posterior lobe (the vermis and paravermis) form the spinocerebellum, a region that plays a role in control of proximal muscles, posture, and locomotion such as walking. The cerebellar hemispheres (part of the posterior lobe) are collectively known as the cerebrocerebellum (or the pontocerebellum); they receive signals from the cerebral cortex and aid in initiation, coordination, and timing of movements. The cerebrocerebellum is also thought to play a role in cognition and affective state.

The cerebellum has been reported to play a role in psychiatric conditions such as schizophrenia, autism, mood disorders, dementia, and attention deficit hyperactivity disorder (ADHD). Currently, the relationship between the cerebellum and psychiatric illness remains unclear. It is hoped that further research will reveal insights into the cerebellar contribution to these conditions.

Disorders

There are a variety of disorders that involve or affect the cerebellum. The cerebellum can be damaged by factors including:

• toxic insults such as alcohol abuse
• paraneoplastic disorders; conditions in which autoantibodies produced by tumors in other parts of the body attack neurons in the cerebellum
• structural lesions such as strokes, multiple sclerosis, or tumors
• inherited cerebellar degeneration such as in Friedreich ataxia or one of the spinocerebellar ataxias
• congenital anomalies such as cerebellar hypoplasia (underdevelopment or incomplete development of the cerebellum) found in Dandy-Walker syndrome, or displacement of parts of the cerebellum such as in Arnold-Chiari malformation

Typical symptoms of cerebellar disorders include hypotonia (poor muscle tone), movement decomposition (muscular movement that is fragmented rather than smooth), dysmetria (impaired ability to control the distance, power, and speed of an act), gait disturbances (abnormal pattern of walking), abnormal eye movement, and dysarthria (problems with speaking).

BOOKS

Manto, Mario U., and Massimo Pandolfo, eds. The Cerebellum and its Disorders. Cambridge, England: Cambridge University Press, 2001.

De Zeeuw, C. I., P. Strata, and J. Voogd, eds. The Cerebellum: From Structure to Control. St Louis, MO: Elsevier Science, 1997.

PERIODICALS

Daum, I., B. E. Snitz, and H. Ackermann. "Neuropsychological Deficits in Cerebellar Syndromes." International Review of Psychiatry 13 (2001): 268–275.

Desmond, J. E. "Cerebellar Involvement in Cognitive Function: Evidence from Neuroimaging." International Review of Psychiatry 13 (2001): 283–294.

Leroi, I., E. O'Hearn, and R. Margolis. "Psychiatric Syndromes in Cerebellar Degeneration." International Review of Psychiatry 13 (2001): 323–329.

O'Hearn, E., and M. E. Molliver. "Organizational Principles and Microcircuitry of the Cerebellum." International Review of Psychiatry 13 (2001): 232–246.

Rapoport, M. "The Cerebellum in Psychiatric Disorders." >International Review of Psychiatry 13 (2001): 295–301.

Schmahmann, J. D. "The Cerebrocerebellar System: Anatomic Substrates of the Cerebellar Contribution to Cognition and Emotion." International Review of Psychiatry 13 (2001): 247–260.

Shill, H. A., and M. Hallett. "Cerebellar Diseases." International Review of Psychiatry 13 (2001): 261–267.

WEBSITES

"BrainInfo Web Site." Cerebellum Information Page. Neuroscience Division, Regional Primate Research Center, University of Washington, 2000. (May 22, 2004.) <http://braininfo.rprc.washington.edu>.

The Cerebellum Database Site. (May 22, 2004). <http://www.cerebellum.org/8home/>.

The National Institute of Neurological Disorders and Stroke (NINDS). Cerebellar Degeneration Information Page. PO Box 5801 Bethesda, MD, 2003. (May 22, 2004). <http://www.ninds.nih.gov/health_and_medical/disorders/cerebellar_degeneration.htm>.

The National Institute of Neurological Disorders and Stroke (NINDS). Cerebellar Hypoplasia Information Page. PO Box 5801 Bethesda, MD, 2003. (May 22, 2004). <http://www.ninds.nih.gov/health_and_medical/disorders/cerebellar_hypoplasia.htm>.

ORGANIZATIONS

National Institute of Mental Health. 6001 Executive Boulevard, Room 8184, MSC 9663, Bethesda, MD 20892-9663. (301) 443-4513 or (866) 615-6464; TTY: (301) 443-8431; Fax: (301) 443-4279. nimhinfo@nih.gov. <http://www.nimh.nih.gov/>.

National Institute of Neurological Disorders and Stroke (NINDS), NIH Neurological Institute. P.O. Box 5801, Bethesda, MD 20824. (301) 496-5751 or (800) 352-9424; TTY: (301) 468-5981. <http://www.ninds.nih.gov/>.