Lateral Cerebellar Hemispheres Research Articles

Lateral cerebellar hemispheres actively support sensory acquisition and discrimination rather than motor control.

This study examined a new hypothesis proposing that the lateral cerebellum is not activated by motor control per se, as widely assumed, but is engaged during the acquisition and discrimination of tactile sensory information. This proposal derives from neurobiological studies of these regions of the rat cerebellum. Magnetic resonance imaging of the lateral cerebellar output nucleus (dentate) of humans during passive and active sensory tasks confirmed four a priori implications of this hypothesis. Dentate nuclei responded to cutaneous stimuli, even when there were no accompanying overt finger movements. Finger movements not associated with tactile sensory discrimination produced no dentate activation. Sensory discrimination with the fingers induced an increase in dentate activation, with or without finger movements. Finally, dentate activity was greatest when there was the most opportunity to modulate the acquisition of the sensory tactile data: when the discrimination involved the active repositioning of tactile sensory surface of the fingers. Furthermore, activity in cerebellar cortex was strongly correlated with observed dentate activity. This distinct four-way pattern of effects strongly challenges other cerebellar theories. However, contrary to appearances, neither our hypothesis nor findings conflict with behavioral effects of cerebellar damage, neurophysiological data on animals performing motor tasks, or cerebellar contribution to nonmotor, perceptual, and cognitive tasks.

Long-term effects of parallel fiber loss in the cerebellar cortex of the adult and weanling rat

Short- and long-term effects of parallel fiber deafferentiation of adult and weanling cerebellar cortex were investigated following parasagittal transections of the lateral cerebellar hemisphere. Short-term electron microscopic examination revealed that parallel fibers undergo rapid electron-dense degeneration within 5 days of axotomy. These axons were the only neuronal elements immediately affected by the lesion. The continued maintenance of Purkinje cell terminal branchlets and stellate cell dendrites is dependent upon the presence of an adequate parallel fiber milieu. Morphological evidence is provided which suggests that Purkinje cell dendritic spines may be phagocytically removed by Bergmann glial cells following parallel fiber loss. Although a marked decrease was reported in the number of spines projecting from terminal branchlets following deafferentation of both adult and weanling rats, these data suggest that some spines are capable of increasing their length. The elongation of these spines may represent a form of dendritic plasticity. No evidence was found to suggest that deafferentated terminal branchlets are receptive to forming heterologous synaptic contacts. The primary response to parallel fiber deafferentation for both the adult and weanling cerebellum therefore appears to be transneuronal degeneration.

Neurogenesis of the climbing fibers in the human cerebellum: a Golgi study.

The prenatal and early postnatal neurogenesis of the human climbing fibers of the lateral cerebellar hemispheres have been studied, with the rapid Golgi method, and correlated with the developmental stages of Purkinje cells. A transitional phase has been established in the neurogenesis of the human Purkinje cell between the second and third stages of Cajal. This phase coincides with the arrival of the climbing fibers. It is characterized by the reabsorption and subsequent transformation of Purkinje cell's basal dendrites into somatic spines. Following the arrival of the climbing fibers and the establishment of contacts, the Purkinje cell is progressively transformed from an immature stellate and nonoriented cell into a monopolar and spatially oriented one which acquires all of its mature morphological and functional features. The human climbing fibers arrive at the Purkinje cell plate by the 28th week of gestation and establish a transient paraganglionic plexus before contacts with these neurons can be recognized. They start to form pericellular nests by the 29th week, and by the 31st week of gestation all Purkinje cells of the lateral hemispheres have pericellular nests around their bodies. These pericellular nests are progressively and rapidly transformed into supracellular "capuchones" which themselves are also short-lived because the climbing process starts readily in them. Supracellular "capuchones" are recognized by the 34th seek and their fibrils start to climb the dendrites of Purkinje cells (young climbing phase) by the 36th week of gestation. The process of climbing the dendrites of the Purkinje cells will continue through late prenatal and early postnatal life. The human climbing fibers are distributed, in the internal granular layer, within narrow and long vertical territories which are transverse to the long axis of the follium. A single climbing fiber is (1) able to establish contacts with many Purkinje cells located within its narrow territory of distribution; (2) has a tendency to establish contacts with small groups of Purkinje cells rather than with isolate neurons; (3) able to send collaterals to several contiguous cerebellar folia; and (4) able to send collaterals to the internal granular layer and to form pericellular nests in it. The human cerebellum may be considered to be subdivided into a series of parallel, narrow, and transverse structural/functional planes, each one characterized by the distribution of a climbing fiber.(ABSTRACT TRUNCATED AT 400 WORDS)

Intra- and interhemispheric collateral branching in the rat pontocerebellar system, a fluorescence double-label study

A double-labeling method which employed the injection and subsequent retrograde transport of two different fluorescent dyes was utilized to investigate the possibility that some pontocerebellar neurons might give rise to collateral branches which distributed to more than one lobule of the contralateral lateral cerebellar hemisphere (intrahemispheric branching) or bilaterally to homotopic or heterotopic lobules in both lateral hemispheres (interhemispheric branching). With regard to intrahemispheric branching, these studies revealed the largest number of double-labeled neurons when the dye injections involved a combination of crus I and the paraflocculus. A considerable number of double-labeled cells were also observed in simplex-crus II cases while a modest number were noted in crus I-paramedian and simplex-paramedian combinations. Evidence for interhemispheric branching was also apparent but the number of double-labeled cells was generally less than that observed in the intrahemispheric experiments. Following bilateral injections, a modest number of double-labeled cells was noted with simplex-simplex and crus I-Crus I homotopic injections and crus II-paramedian heterotopic combinations. In contrast to those cases with unilateral injections, not all bilateral injection combinations produced double-labeling, the most conspicuous in this regard being homotopic and heterotopic injections involving the paraflocculus. Overall, the population of double-labeled cells included many varieties of pontine neurons ranging from small, spindle-shaped to large multipolar. No clear topographic patterns emerged when the location or distribution of either intrahemispheric or interhemispheric double-labeled cells was compared. It was noted, however, that most double-labeled neurons were situated in zones of overlap that occurred between single-labeled neurons projecting to one or the other of the injected lobules. Conversely, in some situations, sharp borders were maintained between adjacent groups of single-labeled neurons. These studies have demonstrated the existence of both intrahemispheric and interhemispheric branching in the pontocerebellar system. The interhemispheric category included pontine neurons which distributed bilaterally to either homotopic or heterotopic lobules in each hemisphere. The overall distribution pattern of double-labeled pontine neurons, those whose axons distribute to more than one hemispheral lobule, is extremely complex and, although some trends were noted, no system-wide topographic organization was apparent. The category of double-labeled neurons included a wide variety of shapes and sizes ranging from the smallest to the largest types of pontine neurons. Most double-labeled neurons were intermixed with single-labeled pontine cells which projected to one or the other of the two injected lobules. No cluster of pontine neurons composed exclusively of double-labeled cells was ever observed although on some occasions, only one population of single-labeled pontine neuron was interspersed with double-labeled cells.

The cerebellopontine system in the rat. I. Autoradiographic studies.

This study utilized light microscopic autoradiographic procedures to describe the projections from the three major subdivisions of the deep cerebellar nuclei (DCN) to the basilar pontine nuclei (BPN). Although the vast majority of cerebellopontine axons reached the BPN via the descending limb of the brachium conjunctivum (BC) after crossing the midline within the midbrain, a relatively small number of ipsilaterally projecting fibers was also observed. Fascicles of cerebellopontine axons left the main bundle of descending limb fibers throughout much of the rostrocaudal length of the BPN and passed around and through the medial lemniscus and cerebral peduncle to enter the pontine gray. The lateral cerebellar nucleus gave rise to the largest number of cerebellopontine fibers, whose terminal fields exhibited both diffuse and patchlike labeling patterns within each of the major subdivisions of the BPN including medial, ventral, lateral, and dorsal areas. Projections from the interpositus complex exclusive of its posterior division were fewer and less widely distributed than those from the lateral nucleus. Interpositopontine fibers terminated primarily in the caudal one-half of the BPN in medial, ventral, and lateral regions and overlapped somewhat with projections from the lateral cerebellar nucleus. Pontine projections emanating from the medial cerebellar nucleus were the fewest and most restricted in distribution relative to the other two cerebellar efferent systems. Such fibers formed a patchlike network of terminal fields which extended throughout much of the rostrocaudal length of the BPN in medial and dorsomedial regions. A relatively small but considerable number of ipsilateral cerebellopontine fibers terminated in pontine regions, which often mirrored the typical contralateral projection fields. Although it proved difficult to determine the precise origin of the ipsilateral fiber systems, it appeared that each of the three major DCN subdivisions made some contribution. Also it was apparent that considerable overlap existed between cerebellopontine projection zones and those of other pontine afferents including sensorimotor, visual, and auditory cortices, the superior colliculus, and the mammillary nuclei of the hypothalamus. Moreover, cerebellopontine terminal fields were congruent in some instances with discrete clusters of BPN neurons which serve as the source of pontocerebellar fiber systems, reaching portions of the lateral cerebellar hemispheres, posterior vermis, and the paraflocculus.

Biochemical effects of thiethylperazine (Torecan) on the vestibular system of rabbits.

Albino rabbits were subjected to unilateral vestibular neurotomy and sacrificed 7 days later. One group received intravenous injections with thiethyl-perazine (Torecan) 6.5 mg in 1 ml solution twice daily. Controls were injected with Ringer's solution. Succinoxidase activity was determined in Deiters' giant cells and RNA content in Purkinje cells from hemisphere lobulus III. Incorporation of 3H-leucine into protein from cerebral cortex, lateral vestibular nuclei and cerebellar nodulus and hemisphere lobulus III was determined in neurotomized rabbits and in rabbits given thiethylperazine. Neurotomy caused pronounced vestibular disturbances and the animals had higher succinoxidase activity on the operated side than on the non-operated side. Rabbits treated with thiethylperazine showed minor signs of vestibular disturbance and the Deiters' cell succinoxidase activity was similar on both sides as well as the Purkinje cell RNA content 1 week after the operation. The 3H-leucine incorporation into protein from c...

Management of the large acoustic tumor.

THE TECHNIQUE of the transsigmoid approach to the cerebellopontine angle for the management of large acoustic tumors has previously been reported. 1 It will be the purpose of this paper to summarize those cases in this series who underwent this operation. Evolution of the Transsigmoid Operation The authors have felt that in those patients harboring large acoustic tumors extending below the level of the jugular bulb and associated with multiple cranial neuropathy, the translabyrinthine, middle fossa, and suboccipital operations all have deficiencies. Basically, a procedure has been needed which would allow access to the inferior pole of the tumor, decompression of the posterior fossa, preservation of the facial nerve, and total removal of the tumor. The suboccipital approach allows access to the inferior pole of the tumor and decompression of the posterior fossa, but usually at the price of retraction or resection of the lateral cerebellar hemisphere. In addition, of