He cerebellum Human is one of the larger brain structures that is part of our nervous system. It accounts for approximately 10% of brain weight and may contain approximately more than half of brain neurons.
Traditionally, it has been given a prominent role in the execution and coordination of motor acts and the maintenance of muscular tone for the Control of balance, due to its position close to the main motor and sensory pathways.
However, over the last few decades, clinical neuroscience has considerably broadened the traditional view of the cerebellum as a mere Coordinator of the motor functions.
The interest of current research centers on the involvement of the cerebellum in complex cognitive processes, Such as executive functions, learning, memory visuospatial functions or even contributing to the emotional sphere and the linguistic area.
This new vision of the functioning of the cerebellum is based on the detailed study of its structure, as well as the analysis of studies of lesions Both in animals and in humans through different current neuroimaging techniques.
Anatomy: Structure of the cerebellum
This broad structure is located caudally, at the level of brain stem, below the occipital lobe And is supported on three stalks Cerebellar (upper, middle and lower) through which it connects with the brainstem And the rest of the encephalic structures.
The cerebellum, like the brain, is covered in all its external extension by a Cortex or cerebellar cortex That Located highly folded.
With respect to the external structure, there are different classifications depending on their morphology, functions or phylogenetic origin. Generally, The cerebellum is divided into two main portions.
In the middle line is the Vermis Which divides and connects the two Lateral lobes T the Cerebellar hemispheres (right and left). In addition, the lateral extensions of the vermis in turn Are divided into 10 lobes numbered from I to X, being the most superior. These lobes can be grouped into:
- Anterior lobe : Lobes I-V.
- Upper posterior lobe : VI-VII
- Lower posterior lobe : VIII-IX
- Floculonodular lobe : X.
In addition to this classification, recent research suggests a division of the cerebellum based on the different functions it modulates. One of the Schemas is the one proposed by Timman et al., (2010), hypothetically assigns cognitive functions to the lateral area, motor to the intermediate area and To the medial area of the cerebellum.
Surface of cerebellum.
With respect to the internal structure, the cortex of the cerebellum presents a uniform cytoarchitectonic organization throughout the structure and Consists of three layers:
- Molecular or outer layer: In this layer are stellate cells and cells in basket, in addition to the arbolizations Dendritic cells from Purkinje cells and parallel fibers. Starry cells establish Synapses With the dendrites of the Purkinje cells and Receive stimuli of the parallel fibers. On the other hand, the cells in the basket extend their axons above the Purkinje cellular sums emitting Ramifications on these and also receive stimuli of the parallel fibers. In this layer also are Golgi dendrites whose
Are located in the granular layer.
- Purkinje or intermediate cell layer : Is formed by the sums of the cells of Purkinje, whose dendrites are in the Molecular layer and its axons are directed towards the granular layer through the deep nuclei of the cerebellum. These cells are the main route of Exit towards the cerebral cortex.
- Granular or internal layer : It is composed mainly of granular cells and some interneurons of the Golgi. Granular cells Extend their axons towards the molecular layer, where they bifurcate to form the parallel fibers. In addition, this layer is a Information from the brain through two types of fibers: mosses and climbers.
In addition to the cortex, the cerebellum is also composed of a White matter In its interior, within which four pairs of Deep cerebellar nuclei Fastigial nucleus , Globular, emboliform and toothed . Through these Nuclei the cerebellum sends its projections outwards.
- Fastigial nucleus : Receives projections of the medial region of the cerebellum, vermis.
- Interposed nucleus (Globose and emboliform): receives projections of the regions contiguous to vermis (paravermal region or paravermis).
- Toothed core: Receives projections of the cerebellar hemispheres.
Cerebellar afferents and efferences
To the cerebellum comes information from different points of the nervous system: cerebral cortex, brain stem and spinal cord And also, that access Mainly by the middle peduncle and to a lesser extent by the lower peduncle.
Almost all the afferent pathways of the cerebellum terminate in the granular layer of the cortex in the form of Mossy fibers . This type of fiber Is the main input of information to the cerebellum and originates in nuclei of the brainstem and establish synapses with the dendrites of the Purkinje cells.
However, the lower olive core extends its projections through the Climbing fibers That establish Synapses with the dendrites of granular cells.
In addition, the main cerebellum information pathway runs through the deep cerebellum nuclei. These extend their projections To the superior cerebellar peduncle that will project both areas of the cerebral cortex and motor centers of the brainstem.
Functions of the cerebellum
As we have pointed out, initially, the role of cerebellum was highlighted by its motor involvement. However, recent research offers Evidence on the possible contribution of this structure to non-motor functions.
These include cognition, emotion, or behavior; Functioning as a coordinator of cognitive and emotional processes, since this structure presents wide connections with cortical regions and Subcortical that are not only directed towards motor areas.
Cerebellum and motor functions
The cerebellum stands out for being a center of coordination and organization of the movement. Together, it works by comparing orders and motor responses.
Through its connections it receives the motor information elaborated to cortical level and of the execution of the motor plans and it is in charge to compare and To correct the development and evolution of motor acts. In addition, it also acts by strengthening the movement to maintain adequate muscular tone Changes of position.
Clinical studies examining cerebellar pathologies have consistently shown that patients with cerebellar Disorders that produce motor syndromes, such as Cerebellar ataxia , Which is characterized by a lack of coordination of balance, gait, movement Of the extremities and of the eyes and dysarthria among other symptoms.
On the other hand, a large number of studies in humans and animals provide ample evidence that the cerebellum is involved in a form Specific associative learning engine, classic blink conditioning. In particular, the role of the cerebellum in the learning of Motor sequences.
Cerebellum and cognition
Since the 1980s several anatomical and experimental animal studies, patients with cerebellar damage, and neuroimaging studies suggest that the Cerebellum has broader functions, involved in cognition. The cognitive role of the cerebellum, therefore, would be related to the existence of Anatomical connections between the brain and regions of the cerebellum supporting the higher functions.
Studies with injured patients show that many cognitive functions are affected, associating with a broad spectrum of symptoms Such as impairment of attentional processes, executive dysfunctions visual and spatial alterations, learning and a variety of Language disorders.
In this context, Shamanhnn et al (1998) proposed a syndrome that would encompass these non-motor symptoms that presented patients with focal damage Cerebellar, denominated Cerebellar Cognitive affective Syndrome (SCCA) that would include the deficiencies in the executive function, visual-spatial abilities, Language skills, affective disturbance, disinhibition or psychotic features.
Specifically, Schmahmann (2004) proposes that symptoms or Motor syndromes appear when the Cerebellar disease Affects sensorimotor areas and the SCCA syndrome when the pathology affects the posterior part Of the lateral hemispheres (involved in cognitive processing) or vermis (which participates in emotional regulation).
Cerebellum and emotional area
Due to their connections, the cerebellum can participate in neural circuits that have a prominent role in emotional regulation and functions Autonomous regions. Different anatomical and physiological studies have described reciprocal connections between the cerebellum and the Hypothalamus , The thalamus system Reticular, limbic system and neocortical areas of association.
Timmann and collaborators (2009) in their investigations found that vermis maintained Connections with the limbic system , Including amygdala and the hippocampus , Which would explain their relationship with fear. This matches the findings Raised a few years ago by Snider and Maiti (1976), which demonstrated the relation of the cerebellum to the Papez circuit.
In sum, studies in humans and animals provide evidence that the cerebellum contributes to emotional associative learning. The vermis contributes To the autonomic and somatic aspects of fear, while the postero-lateral hemispheres may play a role in emotional content.
The growing experimental evidence suggests that cerebellar pathology may be associated with alterations mainly in the cognitive sphere in Place of motor performance. On the other hand, studies have also shown that the cerebellum is involved in many psychiatric disorders such as Schizophrenia, bipolar disorder and autism among others.
Although these evidences are widely supported by functional and structural imaging studies, they are still Necessary to clarify the specific role of the cerebellum in the different functions and neuropsychiatric disorders in which Finds implied.
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- Mediavilla, C., Molina, F., & Puerto, A. (1996). Non-motor functions of the cerebellum. Psicothema , Referring to Fig. (3), 669-683.
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