Sensory-motor integration and synaptic plasticity in the cerebelar ...

EISSN 1676-5133
doi:10.3900/fpj.2.2.91.e
Sensory-motor integration and synaptic
plasticity in the cerebelar cortex
Original Article
Marlo Cunha
Setor de Neuroimagem Funcional, Instituto de Psiquiatria (IPUB) – UFRJ
marlo.marques@bol.com.br
Victor Hugo Bastos
Programa de Pós-Graduação Stricto Sensu em Ciência da Motricidade Humana da
UCB - RJ
victorhvbastos@bol.com.br
Avenilda Silva
Programa de Pós-Graduação Stricto Sensu em Ciência da Motricidade Humana da
UCB - RJ
cacalegarape@ig.com.br
Vernon Furtado
Programa de Pós-Graduação Stricto Sensu em Ciência da Motricidade Humana da
UCB - RJ
fabianaalmeida@uol.com.br
Heloisa Veiga
Setor de Neuroimagem Funcional, Instituto de Psiquiatria (IPUB) – UFRJ
heloisaveiga@hotmail.com
Roberto Piedade
Setor de Neuroimagem Funcional, Instituto de Psiquiatria (IPUB) – UFRJ
rpiedade@ig.com.br
Alair Pedro Ribeiro
Programa de Pós-Graduação Stricto Sensu em Ciência da Motricidade Humana da
UCB - RJ
Departamento de Biociências – Escola de Educação Física e Desportos (EEFD) - UFRJ
Setor de Neuro imagem Funcional
CUNHA, M.; BASTOS, V.H.; SILVA, A.; FURTADO, V.; VEIGA, H.; PIEDADE, R.; RIBEIRO, A.P. Sensory-motor integration and synaptic
plasticity in the cerebelar cortex. Fitness & Performance Journal, v.2, n.2, p. 91-96, 2003.
ABSTRACT: The present study aims to investigate the synaptic plasticity in the cerebellum as a result of the learning process of
complex (acrobatic) motor skills. It begins with an anatomical and physiological description of the cerebellum, which includes its
division into lobes, the relationship with other areas of the Central Nervous System, and a detailed analysis of its internal circuits.
Next, an approach regarding disitnct models which attempt to explain how the cerebellum functions as it incorporates new motor
patterns to the system is made. Finally, results of different experimental studies which investigated the cerebellar synaptic remodelling
in acrobatic trained rats are assembled. The acrobatic training consisted of activities demanding a high level of coordination and
balance. The trainned rats were compared to others submitted to simple exercises and to inactive groups. The three groups of rats
were sacrifi ced and studied with an electronic microscope.
Keywords: Cerebellum, Sensory-Motor Integration, Motor Learning, Sinaptic Plasticity
Correspondence to:
Rua Antonio Carlos, 97 – Porto Velho – São Gonçalo – RJ
Submitted:
January / 2003 Accepted: February / 2003
Copyright© 2003 por Colégio Brasileiro de Atividade Física, Saúde e Esporte
Fit Perf J Rio de Janeiro 2 2
91-96
Mar/Apr 2003

RESUMO
Integração sensório-motora e plasticidade sináptica no córtex cerebelar
O presente artigo revisa o fenômeno de plasticidade sináptica no cerebelo
estimulada pelo processo de aprendizagem de habilidades motoras complexas
(acrobáticas). Inicia com uma descrição anatômica e fisiológica do cerebelo
que inclui, sua divisão em lobos, relação com outras áreas do sistema nervoso
central e uma análise mais refinada dos seus circuitos internos. A seguir é feita
uma abordagem sobre diferentes modelos que tentam explicar como o cerebelo
atua ao incorporar novos padrões motores ao sistema. Por último são reunidos
os resultados de diferentes estudos experimentais que investigaram a remodelagem
sináptica cerebelar em ratos treinados com atividades acrobáticas exigindo
elevado grau de coordenação e balanço. Eles foram então comparados com
outros grupos submetidos a exercícios de natureza simples e a um grupo inativo,
que igualmente aos primeiros, foram sacrificados e estudados ao microscópio
eletrônico.
Palavras-chave: Cerebelo, Integração Sensório-Motora, Aprendizagem
Motora, Plasticidade Sináptica
RESUMEN
Integración Sensório-motora y plasticidad sináptica en la corteza
cerebelar
Lo presente artículo revisa el fenómeno de plasticidad sináptica en el cerebelo
estimulada por el proceso de aprendizaje de habilidades motoras complejas
(acrobáticas). Inicia con una descripción anatómica y fisiológica del cerebelo
que incluye, su división en lobos, relación con otras áreas del sistema nervioso
central y un análisis más refinada de sus circuitos internos. La seguir es hecha un
abordaje sobre diferentes modelos que intentan explicar como el cerebelo actúa
al incorporar nuevos patrones motores al sistema. Por último son reunidos los
resultados de diferentes estudios experimentales que investigaron la remodelaje
sináptica cerebelar en ratones entrenados con actividades acrobáticas exigiendo
alto grado de coordinación y balance. Ellos fueron entonces comparados con
otros grupos sometidos la ejercicios de naturaleza simple y el un grupo inactivo,
que igualmente a los primeros, habían sido sacrificados y estudiados al
microscopio electrónico.
Palabras clave: Cerebelo, Integración Sensorio-Motora, Aprendizaje Motora,
Plasticidad Sináptica
INTRODUCTION
Scholars from the motor learning area fi nd in the cerebellum a
great prominence object of research. Reports state that in the 19 th
century, lesion studies showed the importance of cerebellum to
the coordination of movements. (HOUK, 1996). Another study
mentions that lesions in the cerebellum are responsible for breaking
with the coordination of limb and eye movements, disturbing
the balance and decreasing muscular tonus. (KANDEL, 1995).
Recently, it was discovered that the cerebellum not only acts on the
control of movements but also participates in mental functions of
the individual during superior motor tasks as: language, learning
of complex movements, emotional movements’ execution, etc.
(LENT, 2001).
The considerations about this nervous structure go on as a number
of experimental studies have demonstrated a kind of cerebelar
synaptic plasticity induced by the learning of complex motor abilities
in animals. (ANDERSON, 1996; KLEIM, 1998b). A huge
attention has been attributed to neurophysiologic mechanisms
that rule the referred plastic capacity that will be embodied as
the main subject of the present study.
LITERATURE REVIEW
Anatomic description of the Cerebellum
The cerebellum consists of a globose structure located in the
posterior cranial fossa, the hindbrain. It occupies about onequarter
of man’s cranial volume, (LENT, 2001). This structure
draws an analogy with the brain: divided in two hemispheres, its
external part constitutes of grey matter (cerebelar cortex) and the
inner one, of white matter, where the nervous nuclei are (deep
cerebellar nuclei). The analogy goes on as the cerebellar cortex is
also divided into lobes: the anterior lobe, the posterior lobe and
the fl occulonodular lobe. (KANDEL, 1995). There are four deep
nuclei in each hemisphere: the fastigial nucleus, the interposed
(globose and emboliform) and the dentate nucleus. These nuclei
receive afferents from different parts of the cerebellar cortex and
compose its main efferent pathways.(KANDEL,1995).
Analysis of connective relationships between deep nuclei and
cerebellar cortex states that the cortex from the fl occulonodular
lobe connects to vestibular nuclei, located in the cerebral trunk.
So, apart from their localization, from a connective viewpoint
vestibular nuclei can also be considered deep cerebellar nuclei.
(LENT, 2001). The fastigial nucleus receives afferents from the
median region of the brain, named vermis (due to its length and
segmented aspect). Vermis region divides the cerebellum into
two hemispheres, right and left one, and it is more prominent
on the lower surface of the posterior lobe (KANDEL, 1995). The
interposed nuclei receive afferents from the intermediate zone that
lies between the vermis and the more lateral portion of the hemispheres.
The dentate nucleus, as it is, receives its connections from
lateral hemispheres (LENT, 52001). The result of these analyses
was a proposal of a new organization of the cerebellum, dividing
it in four regions in each side: vermis, intermediate zone, lateral
hemispheres and fl occulonodular lobe. (LENT, 2001).
Varied information of CNS is reunited in the
Cerebellum
The cerebellum is composed by three pathways that promote its
contact with all parts of central nervous system (cerebral cortex,
encephalic trunk and spinal medulla). The Vestibulocerebellum
consists of a pathway where a reciprocal connection between
vestibular nuclei located in the encephalic trunk and fl occulonodular
lone is established. (KANDEL, 1955. DAZ; PUELLES, 2003).
This pathway is responsible for controlling eye movement and
maintaining posture and balance. The Spinocerebellum is another
pathway; its main inputs originate from spinal medulla and bring
sensorial data from the outer part. (KRUTKI, MROWCZYNSKI,
2002). All data arrives at the cerebellum in the vermis region
and intermediate zone being, thus, transmitted to fastigial and
interposed nuclei. These nuclei extend over the encephalic trunk
and mesoencephalon, and will innervate the medial descendent
92 Fit Perf J, Rio de Janeiro, 2, 2, 92, Mar/Apr 2003

system (vestibular nuclei, reticular formation and superior colliculus)
and lateral nuclei (red nucleus), respectively. The lateral
system is very important in the controlling limb movements in
real time. (HANDEL, 1995). At last, the cerebrocerebellum which
begins in the frontal, parietal and occipital areas of cerebral
cortex projects them to the nucleus’ basis and from the nucleus’
basis to the lateral hemispheres of the cerebellum. (SERAPIDE,
2001). This pathway is involved in planning and coordinating the
most complex movements, integrating sensorial data to mental
commands (cognitive and emotional).
Refined anatomy and intrinsic circuitry of the
Cerebellum
The cerebellar cortex is organized in three layers; from outer to inner
layers, these are: the molecular, Purkinje, and granular layers.
Each one contains specifi c types of neural cells whose functional
properties are shown through more refi ned microscopic analyses.
(LENT, 2001). Two pathways towards the cerebellum are observed,
these are the mossy and the climbing fi bers. The fi rst ones
originate from neurons in the medulla forming the spinocerebellar
tract and from various nuclei of encephalic trunk. They are the
main input system of cerebellar circuit due to the large diversity
of information they carry. (METZGER, TAKACS, 2002). In its turn,
the climbing fi bers originate from the inferior olive nuclei. (HOUK,
1996; HUESA,2003; LANG, 2001). The inferior olive also sends
collateral projection to cerebellar nuclei. (RUIGROK; VOOGD,
2000). MF and CF secrete the glutamate neurotransmitter exercising,
thus, excitatory infl uence on the areas of immediate contact
with the cerebellum. (BROBELF; GARTHWAITE, 1990). Mossy
and climbing fi bers reach the cerebellum in different areas and
pass through different ways, one in relation to the other, which
gives them a differential in functional properties. (THACH, 1998).
Firstly, mossy fi bers reach the granular layer of the cerebellar cortex
but they send collateral branches to deep nuclei. (ITO, 2000).
In the granular layer, they have contact with granular cells from
specialized zones named glomerulus, which provides high effi -
ciency in electric transmission. The glomerulus is formed by mossy
fi bers axonal terminal, Golgi cells inhibitory terminals and granule
cells dentrites. This arrangement is surrounded by glial cells that
promote electric signal isolation and, as a consequence, a huge
activation of granular cells. These cells will extend their axon over
the molecular layer (outer part) where a system of parallel fi bers
destined to the dendritic tree of other cellular type, the Purkinje
cell, whose body is placed in the layer below. (ITO, 2000).
Although there is excitatory activation, the Purkinje cell provides
inhibitory synapses from GABA neurotransmitter, and its target is
the deep cerebellar nuclei. (ITO, 2000).
The climbing fi bers address to the cerebellar cortex and connect
to Purkinje cell. (THACH, 1998). Each Purkinje cell receives only
one climbing fi ber that surrounds its body and the portions near the
dentrites, denoting excitatory synapses. One climbing fi ber is able
to connect to 1-10 Purkinje cells transmitting strong electric power
and these Purkinje cells send their axons with inhibitory activity
to deep nuclei. There is indication that like the mossy fi bers, the
climbing fi bers would send excitatory collaterals straight to deep
cerebellar nuclei. (HANDEL, 1995). According to some reports,
climbing fi bers’ inputs to Purkinje cells may provide modulation
on the effect of mossy fi bers, which is processed in one out of two
ways: emphasizing transiently the effect of mossy fi bers inputs to the
Purkinje cells (MARR,1969) or producing a long lasting depression
of the effi cacy of selected mossy fi bers inputs (ALBUS, 1971). The
last aspect would occur through a hetero-synaptic action, that is,
an alteration in a pathway activity due to other pathway activity.
(KANDEL, 1995).
Functional Analysis of the Cerebellar cortex
Here a fundamental question emerges: How does the cerebellar
cortex organize its internal computations in order to rule the premotor
pathway responsible for fi ne limb movements? To answer
this question some authors adopted the following idea: to have
one excitatory pathway circulating between the motor cortex and
the deep cerebellar nuclei. (TSUKAHARA, 1968). So they made it
offi cial that the motor cortex began its movements by activating a
group of cortical neurons that sent more commands than the really
necessary ones. These commands depended on the feedback
circulation in deep nuclei. Whenever the Purkinje cells spike, the
unnecessary commands were eliminated through an inhibition of
deep discharges nuclei. (BLOMFIELD, MAE, 1970).
Seeing that the outputs coming from the cerebellar cortex are
exclusively inhibitory, the deep nuclei (including the vestibular),
which are inhibited by Purkinje cells must be regulated by any noninhibitory
action. It could be one that competes with the activation
of the Purkinje cell or an excitatory infl uence from another source.
(HOUK, 1996). It’s worth highlight that the Purkinje cells receive
inhibitory inputs from cells in basket and stellate cells scattered
around the brain. Beyond the fact that a report stated that mossy
and climbing fi bers that carry excitatory infl uence to the Purkinje
cells send lateral branches straight to deep cerebellar nuclei during
their way. (KANDEL, 1995). Both proposals need to be analyzed
in experiments.
Cerebellum participation in the process of motor
learning
The cerebellum is considered a structure of the central nervous
system that associated with other ones (inferior olive, premotor
system, basal ganglia and cerebral cortex) help to provide a
profi table environment to many forms of motor learning. (HI-
ROSAKA 2002; HOUK, 1996). The experience of movements
promotes alterations in cerebelar circuitry, forming the learning
basis (HANDEL, 1995). Such alterations motivated researchers
like Marr (1969) and Albus (1971) to make offi cial the models
that defi ne motor learning strategies. The fi rst author suggested
a mechanism of long-term potentiation which would occur when
one Purkinje cell spiked at the same time as the parallel fi bers
were activated. This would cause an increase in synaptic strength
between parallel fi bers and the respective Purkinje cells. Climbing
fi bers were in charge of activating Purkinje cells facilitating the
process, unconditionally. (HOUK, 1996).
Albus proposed the opposite, stating that synaptic strength would
be lowered by a mechanism called long-term depression dependant
on three events that would occur simultaneously: climbing
fi ber input (training signal), Purkinje cells spikes and climbing fi bers
synaptic activity. This idea was reinforced by some fi ndings which
demonstrated that climbing fi bers’ activity is modulated during
learning process and that this modulation, by hetero-synaptic
Fit Perf J, Rio de Janeiro, 2, 2, 93, Mar/Apr 2003 93

inhibition, reduces the strength of mossy fi bers input to Purkinje
cells. (KANDEL, 1995). Purkinje cells activity provides a noninhibition
of deep cerebellar nuclei (exit circuitry) when reduced,
which will infl uence movement execution. To sum up, it is more
likely that climbing fi bers activity produces long-term depression
rather than long-term potentiation, when they are associated to
other factors. (ITO,1989).
Mossy and climbing fi bers function has been examined in some
studies. These fi bers’ activity was picked up in different phases of
the training expressing particular aspects in each one (STRIEDFER,
1998; THACG, 1998). In constant and predictable condition, the
movement was followed by stereotypical fl ows of simple spikes,
from mossy fi bers inputs with complex spikes, from climbing fi -
bers, occurring occasionally and one at a time. (THACH, 1998).
When the condition was suddenly altered (evoking learning),
complex spikes frequency increased drastically at the same time
that simple spikes’ gradually decreased. After many attempts,
with the subjects’ (monkeys) adjustment to the new condition,
complex spikes frequency returned to control levels. However,
simple spikes remained under base level (KANDEL, 1995), which
suggests that the modulation of climbing fi bers activity, during
learning process, reduces the strength of mossy fi bers inputs to
Purkinje cells, by means of hetero-synaptic inhibition, adjusting
them to the new condition of movement. (BARMACK; EBNER,
1998); YAKHNITSA, 2002).
Training signal of climbing fibers
As it was previously described, climbing fi bers come from the
inferior olive nuclei and reach the cerebellar cortex where they
contact Purkinje cells directly (HOUK, 1996). Many theories
around the cerebellum acknowledge that these fi bers transmit
training information that guides motor learning process (HOUK,
1996; STRIEDTER, 1998). However, there are some disagreements
between theory and the specifi c nature of this data. Marr (1969)
assumed that through climbing fi bers, the inferior olive transmits
specifi c instructions of the motor cortex, appointing what elementary
movements must be executed. But such proposal does not
clarify the way motor cortex acquires the knowledge elaborated
upon a vast group of required movements (HOUK, 1996). Albus
(1971) assumed that the inferior olive compares sensorial feedbacks
to required pathways of movement, in order to signalize the
performance. Both theories are questionable as they do not state
how internal patterns can be acquired (HOUK, 1996).
Ahead, electrophysiological analysis, from the neurons of the
inferior olive or from its climbing fi bers (axons), provided useful
data about the kind of training discussed here. In different regions
of the inferior olive, combinations of sensorial fi bers and
collateral branches of motor fi bers arrive and bring a copy of the
efferent data which is translated into motor responses. (BLOEDEL;
COURVILLE, 1981). Such fi nding, added to other factors, led to
the hypothesis that the inferior olive calculates error signals that
come from the efferent copy (OSCARSSON, 1980). Nevertheless,
such model is limited in relation to its possibilities of demonstration.
Another hypothesis attributes to motor cortex the function
of controlling simple feedbacks, receiving itself the signals of the
objective pathway. (associated cortex) and comparing to data
from the current pathway given through sensorial feedback. The
difference between pathways allows the motor cortex to generate
an error reference that will be spread through the inferior olive,
providing signal training to the cerebellum (GOMI; KAWATO,
1992). This model raises questions as it does not consider the
sensorial nature of the inferior olive as it is suggested by electrophysiological
analysis.
In the model generator of adjusted pattern, Houk and Barto (1992)
considered the sensorial nature of the inferior olive signalizing it as
a base to the generation of training information. They have considered
that such training signal derived from simple somatosensory
properties, which explains how internal patterns are generated.
(HOUK, 1996). Touch cells are answerable to the contact on
a receptive fi eld on the surface of the limb and proprioceptive
cells are answerable to limb movement in a particular direction.
These responses are repressed during some movement phases,
and the repression is attributed to a refi nement mechanism, by
inhibitory action that is controlled by the efferent copy signal.
Touch responses are inhibited right after a motor command stops,
eliminating responses of a command that, in another way, would
remain until the last precise movement. So, the responses may be
inhibited when a limb collides in an object during the movement,
constituting a simple indicative of motor error. (HOUK, 1996).
Regarding the touch responses, they are inhibited during the
movement that happens in the primary phase of the movement
and the responsible for the correction of secondary movements is
the inferior olive. As proprioceptive neurons are geared towards
different movement directions, different system units detect different
directions of corrective movements. This way, it’s possible to
supervise training data in the respective model (HOUK, 1996).
Motor learning inducing cerebellar plasticity
A huge number of tests have shown the aspect of synaptic plasticity
in adult population of rats under complex motor tasks that
required coordination and balance. These tasks’ learning (acrobatics)
is seen as the one able to produce a deep remodeling
in the intrinsic interconnectivity of the cerebellar cortex (KLEIM,
1998). Such aspect was investigated in an area of the cerebellar
cortex that receives somatosensory and proprioceptive inputs
from anterior and posterior limbs of the animal: the paramedian
lobe (ANDERSON, 1996; KLINTSOVA,2002; KRUTKI; MRO-
WCZYNSKI, 2002). Among the tests there are some that have also
investigated whether the similar alterations would occur in some
of the primary targets of the area’s outputs, the dentate nucleus;
however no nucleus modifi cations were found. (KLEIM, 1998a).
The result suggests that structural synaptic alterations related to the
cerebellum are selective about cortical regions and that dentate
nuclei participation would be that of retransmit the commands
resulting from the possible cortical reorganization.
Application of experimental tasks
Among the various tests, the animal models are generally subject
to one among four training conditions and the duration is
of about 15 to 30 days. (ANDERSON, 1996; KLEIM, 1998). In
the acrobatic condition, the tasks consisted of crossing obstacles
that required some degree of coordination and balance as: plane
bridges that progressively became narrow, vertical stretched ropes
(“hand-stair”), mobile bridges using a rope (stretched in each
side), paths with barriers in elevation, etc. The obstacles increase
in number and diffi culty during the training, in a way that the fi rst
94 Fit Perf J, Rio de Janeiro, 2, 2, 94, Mar/Apr 2003

day begins with a simple task and progress into a total of seven
complex activities until the last day. (ANDERSON, 1996). The
intense exercise condition involved a fast walk (10m/min) on a
motor treadmill, starting with a 5 minute-walk in the fi rst day and
gradually increasing to a 60 minute-walk throughout the days.
Another one was the volunteer exercise condition where the rats
were kept in cages that allowed them to exercise in running wheels.
They were free to run at their own will (ANDERSON, 1996).
At last, the inactive condition when the rats did not have the
opportunity of learning or other exercises than those which were
possible in the cages.
Variant behavior dependents
One of the variants here analyzed refers to the quantity of errors
made by the animals during the process of learning the acrobatic
tasks. The effect of the training on the rats’ performance was
stated (JONES, 1999; KLEIM, 1998b). One of the studies reports
an average of 20 errors/ attempt in the fi rst day and less than 1
error/attempt in the last periods of treatment. (KLEIM, 1998a).
This indicates a considerable learning during all the training
period. Another variant that has been discussed was the time
required to do the task (latency) that as an analogy to the fi rst, is
reduced throughout the training (JONES, 1999; KLEIM, 1998a;
KLEIM, 1998b). Registers from the fi rst day of training report an
average latency of 45 seconds for the conclusion of a task (group
CA), decreasing to less than 20 seconds on the 30 th day (KLEIM,
1998b). Another study compared the group of rats with lesions
produced in the sensorymotor cortex areas that represent the
anterior limbs, with the respective control group. The reductions
in the number of error and latency as a result of the treatment of
acrobatic abilities were observed from this study. (JONES, 1999).
Variant cellular dependents
When the training phase is over the following procedure is the
removal of left and right paramedian lobes of the animal and
preparation for the analysis on electronic microscope. Helped by
a lucid camera, a strip of molecular layer was removed. This layer
was located between the piamater and the Purkinje layer where
the data was collected from. (Anderson, 1996). Variants like: the
total number of synapses, the number of parallel fi bers synapses
and the number of climbing fi bers synapses, being them based on
the volume equivalent to one Purkinje cell, showed to be the most
conclusive variants to this part of the study. The classifi cation of
the different synaptic types of cerebellum has been carried out by
means of morphological characteristics of different pre-synaptic
and pos-synaptic components. The most utilized primary forms
are: Palay; Chan Palay (1974), Larramendi; Victor(1967) and
Ecles; Ito, Szengothai (1967).
Regarding the classifi cation of pre-synaptic components, there are
parallel fi bers terminals which are identifi ed by its light cytoplasm,
2-3 micro tubes cut transversally and small mitochondria. Such
terminals are small or medium in their size and have small spherical
vesicles (ANDERSON, 1996). Climbing fi bers terminals have
big spherical vesicles densely joined. They often contact several
spins in a plan section. In the inhibitory category there are basket
cell terminals, wide and full of microfi laments; their spherical and
ellipsoidal vesicles are loosely joined and the synaptic cleft is as
big as the intersciatic space. The stellate cells also have spherical
and ellipsoidal vesicles, but their differential is the crack space
that, in this case, is bigger than the normal intersciatic space. At
last the Purkinje cells terminals have fl atten and spherical vesicles
through wide terminals.
Concerning the classifi cation of pre-synaptic components, it
talks about the dentrites of Purkinje cells and the ones that come
from inhibitory interneurons (KLEIM, 1998b). The fi rst ones are
intensively surrounded by glias creating a “hem” and present
an extensive submembrane cavity. Whereas the interneurones
dentrites are surrounded by a small amount of glias and their
cavities have an interval in between. (KLEIM, 1998b). It is also
mentioned that the dentrites from the interneurons have a dark
cytoplasm with higher micro tubes density than that of the Purkinje
cells. (ANDERSON, 1996). The profi les that could not fi t any of
the mentioned categories may be classifi ed as pre or pos unknown
synaptic processes.
Remodeling of the cerebellar cortex associated
to the task’s nature
In a consensus, studies evidenced the substantial increase in the
number of parallel / Purkinje cells synapses, in groups of AC in
relation to the ones of IE, VE and IC (ANDERSON,1996; KLEIM
1998B). Concerning the climbing / Purkinje cells synapses, studies
showed different results. Anderson (1996) observed a considerable
increase in the number of these synapses between group AC,
compared to the others in his study. On the other hand, Kleim
(1998b) reports not having observed alterations of other type of
synapse apart from the parallel fi bers. A reasonable explanation
to the discrepancy is that only in the study done by the fi rst author
the molecular layer was observed from the out parts to the deepest
ones. Because of that, the author may have found regions rich in
climbing fi bers synapses, which could not be observed through
the strategies of the second test. (KLEIM, 1996). The total number
of synapses in the tissue volume equivalent to one Purkinje cell
had a considerable increase, mainly because of parallel fi bers
synapses. They represent the most abundant kind of the ones
present in the cerebellar cortex and their original distribution in
the reference of volume utilized represented 78% of the synapses
(ANDERSON, 1996). Climbing fi bers synapses could have
contributed modestly, as they, initially, represented only 2% of the
total. Increases in other synaptic types were not evidenced. (KLEIM,
1998b; ANDERSON, 1996).
CONCLUSION
According to the fi ndings, the cerebellum consists of a structure
importantly related to the acquisition of new movement patterns.
Its integrating properties between sensorial and motor aspects, on
behalf of effective motor executions, give it a status of an essential
structure in daily tasks. Beyond the fact that its functions showed
to be feed back to its own movement execution with a particular
nature. Many studies point out at the possibility through the learning
of complex motor abilities (acrobatic activities that asked
for balance and coordination), but not the simplest ones, those
of promoting adaptations located in the cerebellar cortex. Such
adaptations are responsible for improving the environment that
conducts the coordinates on the motor patterns to be executed
in response to the demands of learnt tasks. Considering neuro-
Fit Perf J, Rio de Janeiro, 2, 2, 95, Mar/Apr 2003 95

physiologic mechanisms of this plastic aspect, the experimental
results indicated an increase in the number of parallel fi bers’ synaptic
contact with the Purkinje cell as the responsible factor. The
confi rmation of this hypothesis invalidates the idea that the motor
learning is due to the increase in the effi ciency of individual synapses
as proposed by Marr and Albus. At last, the increase in the
number of climbing fi bers and Purkinje cells’ synapses, observed
in one of the experiments, is something to be better investigated.
If it is confi rmed, such aspect could represent an increase in the
speed that new motor patterns are incorporated by the system.
REFERENCES
Albus, J. (1971). A theory of cerebellar function. Biosci, 10: 25-61.
Anderson, B., Alcântara, A. & Greenough, T. (1996). Motor-skill learning: changes in
synaptic organization of the rat cerebellar cortex. Neurobiology of learning and memory,
66: 221-229.
Baker, M., Javid, M. & Edgley, S. (2001). Activation of cerebellar climbing fibres to rat
cerebellar posterior lobe from motor cortical output pathways. J physiol, 536 (3): 825-839.
Barmack, N. & Yakhnitsa, V. (2002). Vestibularly evoked climbing-fiber responses modulate
simple spikes in rabbit cerebellar Purkinje neurons. Ann NY acad sci, 978: 237-254.
Bloedel, J. & Courville, J (1981). Cerebellar afferent systems. In: J. Brookhart., V. Mountcastle.,
V. Brooks. & S. Geiger (eds) Handbook of physiology, V. 2. American physiological
society, pp 735-829.
Blomfield, S. & Marr, D. (1970). How the cerebellum may be used. Nature, 227: 1224-1228.
Daz, C. & Puelles, L. (2003). Plurisegmental vestibulocerebellar projections and other
hindbrain cerebellar afferents in midterm chick embryos: biotinylated dextranamine
experiments in vitro. Neuroscience, 117 (1): 71-82.
Ebner, T. (1998). A role for the cerebellum in the control of limb movement velocity. Curr
opin neurobiol, 8 (6): 762-769.
Eccles, J., Ito, M. & Szengothai, J. (1967). The cerebellum as a neuronal machine. New York:
Springer-Verlag.
Gartwaite, J. & Brodbelt, A (1990). Glutamate as the principal mossy fibre transmitter in
rat cerebellum: pharmacological evidence. Eur j neirosci, 2 (2): 177-180.
Houk, J. & Barto, A. (1992). Distributed sensorimotor learning. In: G. Stelmach & J. Requin
(eds). Tutorials in motor behavior II. Amsterdam, Elsevier, pp 71-100.
Houk, J., Buckingham, J. & Barto, A. (1996). Models of the cerebellum and motor learning.
Behavioral and brain sciences, 19 (3): 368-383.
Huesa, G., Anadon, R. & Yanez, J. (2003). Afferent and efferent conections of the cerebellum
of the chondrostean acipenser baeri: a carbocyanine dye (Dil) tracing study. J.
comp neurol, 460 (3): 327-344.
Ito, M. (1970). Neurophysiological aspects of the cerebellar motor control system. Int j
neurology, 7: 162-176.
Ito, M. (1989). Long-term depression. Ann rev neurosc, 12: 85-102.
Ito, M. (2000). Mechanisms of motor learning in the cerebellum. Brain research, 886:
237-245.
Jones, T., Chu,C., Grande, L. & Gregory, A. (1999). Motor skills training enhances lesioninduced
strutural plasticity in the motor cortex of adult rats. The journal of neuroscience,
19 (22): 10153-10163.
Kandel, E., Scwartz, J. & Jessell, T. (1995). Essential of neural science and behavior. Rio de
Janeiro: Prentice Hall.
Kawato, M. & Gomi, H. (1992). A computational model of four regions of the cerebellum
based on feedback-errorlearning. Biological cibernetics, 68: 95-103.
Kleim, J., Pipitone, M., Czerlanis, C. & Greenough, T. (1998 a). Strutural stability within
the lateral cerebellar núcleos of the rat following complex motor learning. Neurobiology
of learning and memory, 68: 290-306.
Kleim, J., Swain, R., Armstrong, K., Napper, R., Jones, T. & Greenough, W. (1998b). Selective
sinaptic plasticity within the cerebellar cortex following complex motor skill learning.
Neurobiology of learning and memory, 69: 274-289.
Klintsova, A., Scamra, C., Hoffman, M., Napper, R., Goodlett, C. and Greenough, W.
(2002). Therapeutic effects of complex motor training on motor performance deficits
induced by neonatal binge-like alcohol exposure in rats: II. A quantitative stereological
study of synaptic plasticity in female rat cerebellum. Brain research, 937: 83-93.
Krutki, P. & Mrowczynski, W. (2002). Afferent input from distal forelimb nerves to branching
spinoreticular-spinocerebellar neurones in the cat. Acta neurobiol exp, 62 (4): 271-276.
Lang, E. (2001). Organization of olivocerebellar activity in the absence of excitatory
glutamatergic input. J neurosci, 21 (5): 1663-1675.
Larramendi, L. & Victor, T. (1967). Sinapses on the Purkinje cell spines in the mouse: a
electron microscopic study. Brain research, 5: 15-30.
Lent, R. (2001). Cem bilhões de neurônios: conceitos fundamentais da neurociência. São
Paulo: Atheneu.
Marr, D. (1969). A theory of cerebellar cortex. J physiology London, 202: 437-470.
Oscarsson, O. (1980). Functional organization of olivary projection to cerebellar anterior
lobe. In: J. Courville., C. de Montigney., Y. Lamarre (eds). The inferior olivary nucleus: anatomy
and physiology. New York: Raven press, pp 279-289.
Palay, S. & Chan- Palay, V. (1974). Cerebellar cortex: citology and organization. New York:
Springer-Verlag.
Ruigrok, T. & Vood, J. (2000). Organization of projection from the inferior olive to the
cerebellar nuclei in the rat. J comp neurol, 426 (2): 209-228.
Serapide, M., Panto, M., Parenti, R., Zappala, A. & Cicirata, F. (2001). Multiple zonal
projections of the basilar pontine nuclei to the cerebellar cortex of the rat. J comp neurol,
430 (4): 471-484.
Striedter, G. (1998). A comparative perspective on motor learning. Neurobiology of learning
and memory, 70: 189-196.
Takacs, J. & Metzger, F. (2002). Morphological study of organotypic cerebellar cultures.
Acta biol hung, 53 (1-2): 187-204.
Thach, W. (1998). A role for the cerebellum in learning movement coordination. Neurobiology
of learning and memory, 70: 177-188.
Tsukahara, N., Korn, H. & Stone, J. (1968). Pontine relay from cerebral cortex to cerebellar
cortex and nucleus interpositus. Brain res, 10: 448-453.
Ungerleider, L., Doyon, J. and Karni, A. (2002). Imaging brain plasticiy during motor skill
learning. Neurobiology of learning and memory, 78: 553-564.
96 Fit Perf J, Rio de Janeiro, 2, 2, 96, Mar/Apr 2003