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Cerebellum

2007 Schools Wikipedia Selection. Related subjects: General Biology

   Figure 1a: A human brain, with the cerebellum in purple.
   Enlarge
   Figure 1a: A human brain, with the cerebellum in purple.

   The cerebellum (Latin: "little brain") is a region of the brain that
   plays an important role in the integration of sensory perception and
   motor output. Many neural pathways link the cerebellum with the motor
   cortex—which sends information to the muscles causing them to move—and
   the spinocerebellar tract—which provides feedback on the position of
   the body in space ( proprioception). The cerebellum integrates these
   pathways, using the constant feedback on body position to fine-tune
   motor movements.

   Because of this 'updating' function of the cerebellum, lesions within
   it are not so debilitating as to cause paralysis, but rather present as
   feedback deficits resulting in disorders in fine movement, equilibrium,
   posture, and motor learning. Initial observations by physiologists
   during the 18th century indicated that patients with cerebellar damage
   show problems with motor coordination and movement. Research into
   cerebellar function during the early to mid 19th century was done via
   lesion and ablation studies in animals. Research physiologists noted
   that such lesions led to animals with strange movements, awkward gait,
   and muscular weakness. These observations and studies led to the
   conclusion that the cerebellum was a motor control structure. However,
   modern research shows that the cerebellum has a broader role in a
   number of key cognitive functions, including attention and the
   processing of language, music, and other sensory temporal stimuli.
   Figure 1b: MRI image showing a mid-sagittal view of the human brain,
   with the cerebellum in purple.
   Enlarge
   Figure 1b: MRI image showing a mid-sagittal view of the human brain,
   with the cerebellum in purple.

General features

   The cerebellum is located in the inferior posterior portion of the head
   (the hindbrain), directly dorsal to the pons, and inferior to the
   occipital lobe (Figs. 1 and 3). Because of its large number of tiny
   granule cells, the cerebellum contains nearly 50% of all neurons in the
   brain, although it constitutes only 10% of total brain volume. The
   cerebellum receives nearly 200 million input fibers; in contrast, the
   optic nerve is composed of a mere one million fibers.

   The cerebellum is divided into two large hemispheres, much like the
   cerebrum, and contains ten smaller lobules. The cytoarchitecture
   (cellular organization) of the cerebellum is highly uniform, with
   connections organized into a rough, three-dimensional array of
   perpendicular circuit elements. This organizational uniformity makes
   the nerve circuitry relatively easy to study. To envision this
   "perpendicular array", one might imagine a tree-lined street with wires
   running straight through the branches of one tree to the next.

Development and evolution

   Figure 2: Drawing of the cells in the chicken cerebellum by S. Ramón y
   Cajal.
   Enlarge
   Figure 2: Drawing of the cells in the chicken cerebellum by S. Ramón y
   Cajal.

   During the early stages of embryonic development, the brain starts to
   form in three distinct segments: the prosencephalon, mesencephalon, and
   rhombencephalon. The rhombencephalon is the most caudal (toward the
   tail) segment of the embryonic brain; it is from this segment that the
   cerebellum develops. Along the embryonic rhombencephalic segment
   develop eight swellings, called rhombomeres. The cerebellum arises from
   two rhombomeres located in the alar plate of the neural tube, a
   structure that eventually forms the brain and spinal cord. The specific
   rhombomeres from which the cerebellum forms are rhombomere 1 (Rh.1)
   caudally (near the tail) and the "isthmus" rostrally (near the front).

   The neural tube is organized so that the alar plate typically gives
   rise to structures involved in sensory functions; the basal (ventral,
   or lower) plate gives rise to motor functioning structures. Given its
   alar plate origins, the cerebellum would be expected to be devoted
   primarily to sensory functions. Despite its embryological origin, one
   of the many ironies of the cerebellum is that it functions primarily to
   modulate motor function.

   Two primary regions are thought to give rise to the neurons that make
   up the cerebellum. The first region is the ventricular zone in the roof
   of the fourth ventricle. This area produces Purkinje cells and deep
   cerebellar nuclear neurons. These cells are the primary output neurons
   of the cerebellar cortex and cerebellum. The second germinal zone
   (cellular birthplace) is known as the external granular layer. This
   layer of cells—found on the exterior the cerebellum—produces the
   granule neurons. Once born, the granule neurons migrate from this
   exterior layer to form an inner layer known as the internal granule
   layer. The external granular layer ceases to exist in the mature
   cerebellum, leaving only granule cells in the internal granule layer.
   The cerebellar white matter may be a third germinal zone in the
   cerebellum; however, its function as a germinal zone is controversial.

   The cerebellum is of archipalliar phylogenetic origin. The pallium is a
   term for gray matter that forms the cortex. The archipallium is the one
   of the most evolutionarily primitive brain regions. The circuits in the
   cerebellar cortex look similar across all classes of vertebrates,
   including fish, reptiles, birds, and mammals (e.g., Fig. 2). This has
   been taken as evidence that the cerebellum performs functions important
   to all vertebrate species.

Anatomy

   The cerebellum contains similar gray and white matter divisions as the
   cerebrum. Embedded within the white matter—which is known as the arbor
   vitae ( Tree of Life) in the cerebellum due to its branched, treelike
   appearance—are four deep cerebellar nuclei. Three gross phylogenetic
   segments are largely grouped by general function. The three cortical
   layers contain various cellular types that often create various
   feedback and feedforward loops. Oxygenated blood is supplied by three
   arterial branches off the basilar and vertebral arteries.

Divisions

   Figure 3: Cerebellum and surrounding regions; sagittal view of one
   hemisphere. A: Midbrain. B: Pons. C: Medulla. D: Spinal cord. E: Fourth
   ventricle. F: Arbor vitae. G: Tonsil. H: Anterior lobe. I: Posterior
   lobe.
   Enlarge
   Figure 3: Cerebellum and surrounding regions; sagittal view of one
   hemisphere. A: Midbrain. B: Pons. C: Medulla. D: Spinal cord. E: Fourth
   ventricle. F: Arbor vitae. G: Tonsil. H: Anterior lobe. I: Posterior
   lobe.

   There are three phylogenetic divisions within the cerebellum: the
   flocculonodular, anterior, and posterior lobes (Fig. 3). These
   divisions are also called the archicerebellum, paleocerebellum, and
   neocerebellum, respectively, terms that more clearly reflect the method
   of dividing the lobes by their evolutionary age. The archicerebellum
   represents the oldest evolutionary cerebellar structure, and the
   neocerebellum represents the most recently evolved region. These
   divisions are divided from the front to the back of the cerebellum;
   starting with the flocculonodular lobe in the front, and ending with
   the posterior lobe in the back. The anterior and posterior lobes are
   separated by the primary fissure. The posterior and flocculonodular
   lobes are separated by the posterolateral fissure (Fig. 4).

   The cerebellum can also be divided by function rather than evolutionary
   age. This results in three functional divisions that run perpendicular
   to the previously mentioned phylogenetic divisions. Rather than running
   from front to back, like the phylogenetic divisions, the functional
   regions align from the midline outwards toward the sides of the body.
   The midline division is called the medial zone, also known as the
   cerebellar vermis (“worm”) because of its long, slender shape; the
   vermis is further subdivided into smaller regions called lobules. The
   region just lateral (away from the centre) of the vermis is called the
   intermediate zone; the most lateral, outer region is the lateral zone
   (Fig. 4).

   Much of what is understood about the functions of the cerebellum stems
   from careful documentation of the effects of focal lesions in human
   patients who have suffered from injury or disease or through animal
   lesion research.

Cerebellar structure and function from a phylogenetic perspective

Archicerebellum

   The archicerebellum is associated with the flocculonodular lobe and is
   mainly involved in balance ( vestibular system) and eye movement
   functions. It receives input from the inferior and medial vestibular
   nuclei and sends fibers back to the vestibular nuclei, creating a
   feedback loop that allows for the constant maintenance of balance.

Paleocerebellum

   The paleocerebellum controls proprioception related to muscle tone
   (constant, partial muscle contraction that is important for the
   maintenance of posture). The paleocerebellum receives its inputs from
   the dorsal and ventral spinocerebellar tracts, which carry information
   about the position and forces acting on the legs. The paleocerebellum
   then sends axonal projections to the deep cerebellar nuclei.

Neocerebellum

   The neocerebellum receives input from the pontocerebellar tract and
   projects to the deep cerebellar nuclei. The pontocerebellar tract
   originates at the pontine nuclei, which receive their input from the
   cerebral motor cortex. Thus, the neocerebellum is associated with motor
   control, in particular, the coordination of fine finger movements such
   as those required by typing.

The functional organization of the cerebellum

   Figure 4: Schematic representation of the major anatomical subdivisions
   of the cerebellum. Superior view of an "unrolled" cerebellum, placing
   the vermis in one plane.
   Enlarge
   Figure 4: Schematic representation of the major anatomical subdivisions
   of the cerebellum. Superior view of an "unrolled" cerebellum, placing
   the vermis in one plane.

Vermis

   The vermis receives its inputs mainly from the spinocerebellar tracts
   from the trunk of the body. These tracts carry to the vermis
   information on the position and balance of the torso. The vermis sends
   projections to the fastigial nucleus of the cerebellum, which then
   sends output to the vestibular nuclei. The vestibular nuclei are
   structures important for the maintenance of balance.

Intermediate zone

   The intermediate zone (or paravermis) receives input from the
   corticopontocerebellar fibers that originate from the motor cortex.
   These fibers carry a duplicate of the information that was sent from
   the motor cortex to the spine in order to effect a movement. The
   intermediate zone also receives sensory feedback from the muscles.
   These two streams of information are integrated by this region,
   allowing for the feedback comparison of what the muscles are supposed
   to be doing with what they are actually doing.

Lateral zone

   The lateral zone receives input from the parietal cortex via
   pontocerebellar mossy fibers regarding the location of the body in the
   world. The large numbers of feedback circuits allow for the integration
   of this body position information with indications of muscle position,
   strength, and speed.

Deep nuclei

   The four deep cerebellar nuclei are in the centre of the cerebellum,
   embedded in the white matter. These nuclei receive inhibitory (
   GABAergic) inputs from Purkinje cells in the cerebellar cortex and
   excitatory ( glutamatergic) inputs from mossy fibre pathways. Most
   output fibers of the cerebellum originate from these nuclei. One
   exception is that fibers from the flocculonodular lobe synapse directly
   on vestibular nuclei without first passing through the deep cerebellar
   nuclei. The vestibular nuclei in the brainstem are analogous structures
   to the deep nuclei, since they receive both mossy fibre and Purkinje
   cell inputs.

   From lateral to medial, the four deep cerebellar nuclei are the
   dentate, emboliform, globose, and fastigial. An easy mnemonic device to
   remember these names and positions relative to their position from the
   midline is the phrase "Don't Eat Greasy Food", where each letter
   indicates the lateral to medial location in the cerebellar white
   matter. Some animals do not have distinct emboliform and globose
   nuclei, instead having a single, fused nucleus interpositus (interposed
   nucleus). In animals with distinct emboliform and globose nuclei, the
   term interposed nucleus is often used to refer collectively to these
   two nuclei.

   In general, each pair of deep nuclei is associated with a corresponding
   region of cerebellar surface anatomy. The dentate nuclei are deep
   within the lateral hemispheres, the interposed nuclei are located in
   the paravermal (intermediate) zone, and the fastigial nuclei are in the
   vermis. These structural relationships are generally maintained in the
   neuronal connections between the nuclei and associated cerebellar
   cortex, with the dentate nucleus receiving most of its connections from
   the lateral hemispheres, the interposed nuclei receiving inputs mostly
   from the paravermis, and the fastigial nucleus receiving primarily
   afferents from the vermis.

Cortical layers

   Figure 5: Microcircuitry of the cerebellum. Excitatory synapses are
   denoted by (+) and inhibitory synapses by (-). MF: Mossy fiber. DCN:
   Deep cerebellar nuclei. IO: Inferior olive. CF: Climbing fiber. GC:
   Granule cell. PF: Parallel fiber. PC: Purkinje cell. GgC: Golgi cell.
   SC: Stellate cell. BC: Basket cell.
   Enlarge
   Figure 5: Microcircuitry of the cerebellum. Excitatory synapses are
   denoted by (+) and inhibitory synapses by (-). MF: Mossy fibre. DCN:
   Deep cerebellar nuclei. IO: Inferior olive. CF: Climbing fibre. GC:
   Granule cell. PF: Parallel fibre. PC: Purkinje cell. GgC: Golgi cell.
   SC: Stellate cell. BC: Basket cell.
   Figure 6: Confocal micrograph from mouse cerebellum expressing
   green-fluorescent protein in Purkinje cells.
   Enlarge
   Figure 6: Confocal micrograph from mouse cerebellum expressing
   green-fluorescent protein in Purkinje cells.

   There are three layers to the cerebellar cortex; from outer to inner
   layer, these are the molecular, Purkinje, and granular layers. The
   function of the cerebellar cortex is essentially to modulate
   information flowing through the deep nuclei. The microcircuitry of the
   cerebellum is schematized in Figure 5. Mossy and climbing fibers carry
   sensorimotor information into the deep nuclei, which in turn pass it on
   to various premotor areas, thus regulating the gain and timing of motor
   actions. Mossy and climbing fibers also feed this information into the
   cerebellar cortex, which performs various computations, resulting in
   the regulation of Purkinje cell firing. Purkinje neurons feed back into
   the deep nuclei via a potent inhibitory synapse. This synapse regulates
   the extent to which mossy and climbing fibers activate the deep nuclei,
   and thus control the ultimate effect of the cerebellum on motor
   function. The synaptic strength of almost every synapse in the
   cerebellar cortex has been shown to undergo synaptic plasticity. This
   allows the circuitry of the cerebellar cortex to continuously adjust
   and fine-tune the output of the cerebellum, forming the basis of some
   types of motor learning and coordination. Each layer in the cerebellar
   cortex contains the various cell types that comprise this circuitry.

Granular layer

   The innermost layer contains the cell bodies of two types of cells: the
   numerous and tiny granule cells, and the larger Golgi cells. Mossy
   fibers enter the granular layer from their main point of origin, the
   pontine nuclei. These fibers form excitatory synapses with the granule
   cells and the cells of the deep cerebellar nuclei. The granule cells
   send their T-shaped axons—known as parallel fibers—up into the
   superficial molecular layer, where they form hundreds of thousands of
   synapses with Purkinje cell dendrites. The human cerebellum contains on
   the order of 60 to 80 billion granule cells, making this single cell
   type by far the most numerous neuron in the brain (roughly 70% of all
   neurons in the brain and spinal cord, combined). Golgi cells provide
   inhibitory feedback to granule cells, forming a synapse with them and
   projecting an axon into the molecular layer.

Purkinje layer

   The middle layer contains only one type of cell body—that of the large
   Purkinje cell. Purkinje cells are the primary integrative neurons of
   the cerebellar cortex and provide its sole output. Purkinje cell
   dendrites are large arbors with hundreds of spiny branches reaching up
   into the molecular layer (Fig. 6). These dendritic arbors are
   flat—nearly all of them lie in planes—with neighboring Purkinje arbors
   in parallel planes. Each parallel fibre from the granule cells runs
   orthogonally through these arbors, like a wire passing through many
   layers. Purkinje neurons are GABAergic—meaning they have inhibitory
   synapses—with the neurons of the deep cerebellar and vestibular nuclei
   in the brainstem. Each Purkinje cell receives excitatory input from
   100,000 to 200,000 parallel fibers. Parallel fibers are said to be
   responsible for the simple (all or nothing, amplitude invariant)
   spiking of the Purkinje cell.

   Purkinje cells also receive input from the inferior olivary nucleus via
   climbing fibers. A good mnemonic for this interaction is the phrase
   "climb the olive tree", given that climbing fibers originate from the
   inferior olive. Each Purkinje cell receives input from a single
   climbing fibre in the form of a powerful excitatory signal. These
   action potentials are of a rare class in that the excitatory
   postsynaptic response from climbing fibers are amplitude variant. These
   responses are known as complex spikes.

Molecular layer

   This outermost layer of the cerebellar cortex contains two types of
   inhibitory interneurons: the stellate and basket cells. It also
   contains the dendritic arbors of Purkinje neurons and parallel fibre
   tracts from the granule cells. Both stellate and basket cells form
   GABAergic synapses onto Purkinje cell dendrites.

Peduncles

   Similarly, the cerebellum follows the trend of "threes", with three
   major input and output peduncles (fibre bundles). These are the
   superior (brachium conjunctivum), middle (brachium pontis), and
   inferior (restiform body) cerebellar peduncles. There are three sources
   of input to the cerebellum, in two categories consisting of mossy and
   climbing fibers, respectively. Mossy fibers can originate from the
   pontine nuclei, which are clusters of neurons located in the pons that
   carry information from the contralateral cerebral cortex. They may also
   arise within the spinocerebellar tract whose origin is located in the
   ipsilateral spinal cord. Most of the output from the cerebellum
   initially synapses onto the deep cerebellar nuclei before exiting via
   the three peduncles. The most notable exception is the direct
   inhibition of the vestibular nuclei by Purkinje cells.

Superior cerebellar peduncle

   While there are some afferent fibers from the anterior spinocerebellar
   tract that are conveyed to the anterior cerebellar lobe via this
   peduncle, most of the fibers are efferents. Thus, the superior
   cerebellar peduncle is the major output pathway of the cerebellum. .
   Most of the efferent fibers originate within the dentate nucleus which
   in turn project to various midbrain structures including the red
   nucleus, the ventral lateral/ventral anterior nucleus of the thalamus,
   and the medulla. The dentatorubrothalamocortical (dentate nucleus > red
   nucleus > thalamus > premotor cortex) and cerebellothalamocortical
   (cerebellum > thalamus > premotor cortex) pathways are two major
   pathways that pass through this peduncle and are important in motor
   planning.

Middle cerebellar peduncle

   This is composed entirely of afferent fibers originating within the
   pontine nuclei as part of the massive corticopontocerebellar (cerebral
   cortex > pons > cerbellum) tract. These fibers descend from the sensory
   and motor areas of the cerebral neocortex and make the middle
   cerebellar peduncle the largest of the three cerebellar peduncles.

Inferior cerebellar peduncle

   This carries many types of input and output fibers that are mainly
   concerned with integrating proprioceptive sensory input with motor
   vestibular functions such as balance and posture maintenance.
   Proprioceptive information from the body is carried to the cerebellum
   via the dorsal spinocerebellar tract. This tract passes through the
   inferior cerebellar peduncle and synapses within the paleocerebellum.
   Vestibular information projects onto the archicerebellum. This peduncle
   also carries information directly from the Purkinje cells to the
   vestibular nuclei in the dorsal brainstem located at the junction
   between the pons and medulla.

Blood supply

   Figure 7: The three major arteries of the cerebellum: the SCA, AICA,
   and PICA.
   Enlarge
   Figure 7: The three major arteries of the cerebellum: the SCA, AICA,
   and PICA.

   Three arteries supply blood to the cerebellum (Fig. 7): the superior
   cerebellar artery (SCA), anterior inferior cerebellar artery (AICA),
   and posterior inferior cerebellar artery (PICA).

Superior cerebellar artery

   The SCA branches off the lateral portion of the basilar artery, just
   inferior to its bifurcation into the posterior cerebral artery. Here it
   wraps posteriorly around the pons (to which it also supplies blood)
   before reaching the cerebellum. The SCA supplies blood to most of the
   cerebellar cortex, the cerebellar nuclei, and the middle and superior
   cerebellar peduncles.

Anterior inferior cerebellar artery

   The AICA branches off the lateral portion of the basilar artery, just
   superior to the junction of the vertebral arteries. From its origin, it
   branches along the inferior portion of the pons at the cerebellopontine
   angle before reaching the cerebellum. This artery supplies blood to the
   anterior portion of the inferior cerebellum, and to the facial (CN VII)
   and vestibulocochlear nerves (CN VIII).

   Obstruction of the AICA can cause paresis, paralysis, and loss of
   sensation in the face; it can also cause hearing impairment.

Posterior inferior cerebellar artery

   The PICA branches off the lateral portion of the vertebral arteries
   just inferior to their junction with the basilar artery. Before
   reaching the inferior surface of the cerebellum, the PICA sends
   branches into the medulla, supplying blood to several cranial nerve
   nuclei. In the cerebellum, the PICA supplies blood to the posterior
   inferior portion of the cerebellum, the inferior cerebellar peduncle,
   the nucleus ambiguus, the vagus motor nucleus, the spinal trigeminal
   nucleus, the solitary nucleus, and the vestibulocochlear nuclei.

Dysfunction

   Patients with cerebellar dysfunction experience problems in walking,
   balance, and accurate hand and arm movement. Recent brain imaging
   studies using functional magnetic resonance imaging (fMRI) show that
   the cerebellum is important for language processing and selective
   attention. Neuropsychiatric disorders such as dyslexia, schizophrenia
   and autism appear to be associated with a deficiency in the cerebellum,
   which may also play a role in the development of certain ataxias,
   including a form of cerebral palsy. Spinocerebellar ataxia patients
   suffer cerebellar degeneration. It is believed that opsoclonus
   myoclonus syndrome is caused by an autoimmune attack on the cerebellum
   among other brain regions.

Lesions of the cerebellum

   Patients with cerebellar lesions (injuries) typically exhibit deficits
   during movement execution. For example, they show "intention tremors"—a
   tremor occurring during movement rather than at rest, as seen in
   Parkinson's disease. Patients may also show dysmetria, i.e., an
   overestimation or underestimation of force, resulting in overshoot or
   undershoot when reaching for a target. Another common sign of
   cerebellar damage is an inability to perform rapid alternating
   movements.

   The anterior and medial aspects of the cerebellum represent information
   ipsilaterally; thus, damage to this region on one side affects the
   movement on the same side of the body. The posterior and lateral
   aspects of the cerebellum represent information bilaterally; damage to
   this region has been shown to impair sensory–motor adaptation, while
   leaving motor control unaffected. In certain instances, a patient
   experiences a focal lesion. Such localized lesions cause a wide variety
   of symptoms related to their location in the cerebellum. A striking
   example is archicerebellar lesions, which cause motor symptoms not
   unlike those seen during intoxication: uncoordinated movements,
   swaying, unstable walking, and a wide gait. To avoid suspicion by the
   police of public drunkenness, American patients who suffer
   archicerebellar lesions carry identification cards written by their
   physicians, indicating their medical condition.

   A lesion to the paleocerebellum causes severe disturbance in muscle
   tone and bodily posture, resulting in weakness to the side of the body
   opposite the lesion. A neocerebellar lesion is associated with deficits
   in skilled voluntary movement, such as playing the piano. A lesion to
   the intermediate zone causes problems with fine-tuning and corrective
   movements. Patients with this type of lesion who hold their fingers in
   front of them have great difficulty in moving those fingers together.
   Patients with a lesion to the lateral zone have difficulty in
   controlling fine muscle movements and exhibit symptoms similar to those
   of patients with an intermediate zone lesion.

   Alcohol abuse is also a common cause of cerebellar lesions. Alcohol
   abuse can lead to thiamine deficiency, which in the cerebellum will
   cause degeneration of the anterior lobe. This degeneration leads to a
   wide, staggering gait but does not affect arm movement or speech.

Ischemia and thrombosis

   An obstruction of the posterior inferior cerebellar artery (known as
   'PICA syndrome') can cause a wide range of characteristic effects. An
   obstruction of the artery causes cell death as the cells are deprived
   of oxygen and nutrients provided by the blood. PICA syndrome manifests
   as a loss of sensation in the contralateral limbs due to damage of the
   inferior cerebellar peduncle as well as dizziness and nausea due to
   loss of blood to the nucleus ambiguus and vestibulocochlear nuclei.

Theories about cerebellar function

   Three main theories address the function of the cerebellum. One claims
   that the cerebellum functions as a regulator of the "timing of
   movements". This has emerged from studies of patients whose timed
   movements are disrupted. The second theory claims that the cerebellum
   operates as a learning machine, encoding information as does a
   computer. This was first proposed by Marr and Albus in the early 1970s.
   The third, "Tensor Network Theory" provides a mathematical model of
   transformation of sensory (covariant) space-time coordinates into motor
   (contravariant) coordinates by cerebellar neuronal networks.

   Like many controversies in the physical sciences, there is evidence
   supporting the above hypotheses. Studies of motor learning in the
   vestibulo-ocular reflex and eyeblink conditioning demonstrate that the
   timing and amplitude of learned movements are encoded by the
   cerebellum. Many synaptic plasticity mechanisms have been found
   throughout the cerebellum. The Marr-Albus model mostly attributes motor
   learning to a single plasticity mechanism: the long-term depression of
   parallel fibre synapses. The Tensor Network Theory of sensorimotor
   transformations by the cerebellum has also been experimentally
   supported.

   With the advent of more sophisticated neuroimaging techniques such as
   positron emission tomography (PET), and fMRI, numerous diverse
   functions are now at least partially attributed to the cerebellum. What
   was once thought to be primarily a motor/sensory integration region is
   now proving to be involved in many diverse cognitive functions.
   Paradoxically, despite the importance of this region and the
   heterogeneous role it plays in motor and sensory functions, people who
   have lost their entire cerebellum through disease, injury, or surgery
   can live reasonably normal lives.

Cerebellar modeling

   As mentioned in the preceding section, there have been many attempts to
   model the cerebellar function. The insights provided by the models have
   also led to extrapolations in the domains of artificial intelligence
   methodologies, especially neural networks. Some of the notable
   achievements have been Cerebellatron , Cerebellar Model Associative
   Memory or CMAC networks, and Spikeforce for robotic movement control,
   and "Tensor Network Theory".

Additional images

   Lobes

        Diencephalon

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