BASAL GANGLIA: FUNCTIONS, ANATOMY AND PATHOLOGIES - NEUROPSYCHOLOGY - 2024

The basal ganglia or basal ganglia are brain nuclei found within the telencephalon characterized by being accumulations of nerve neurons. It is located at the base of the brain, where they allow connecting lower and higher regions.

The basal ganglia are made up of various nuclei: caudate nucleus, putamen, globe pallidus, lenticular nucleus, nucleus accumebns, striatum, neo-striatum, brain amygdala, and substantia nigra.

Basal ganglia in orange

These neuronal structures form a circuit of nuclei that are interconnected with each other. The main functions they perform are related to the initiation and integration of the movement.

The basal ganglia receive information from both the cerebral cortex (above) and the brainstem (below). Likewise, they process and project information to both brain structures.

The different nuclei of the basal ganglia are cataloged and categorized according to their anatomy, their mechanisms of action and the functions they perform.

Basal ganglia characteristics

Basal ganglia. Source: BruceBlaus (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine. via Wikimedia Commons

The basal ganglia are large subcortical neural structures that form a circuit of nuclei that continuously exchange information.

Likewise, these brain structures that are found at the base of the brain, allow to connect the lower regions (the brain stem and the spinal cord), with the upper regions (cerebral cortex).

Anatomically, the basal ganglia are made up of masses of gray matter from the telencephalon, the fibers of which run directly to the spinal column and link to the supraspinal motor center.

These structures are associated with the performance of voluntary movements performed unconsciously by the subject. That is, those movements that involve the entire body in routine and everyday tasks.

The basal ganglia are located in an area known as the striatum. It consists of two regions of gray matter that are separated by a bundle of fibers called the internal capsule.

Features

The basal ganglia are made up of various nuclei that constitute a series of well-defined cells or sets of neurons. Each nucleus basalis is related to a different function.

The basal ganglia contain both sensory neurons as well as motor neurons and internuncial neurons. Each of them performs a series of specific functions and has a specific anotomy and structure.

The basal nuclei referring to the basal ganglia are: the caudate nucleus, the putamen nucleus, the globus pallidus, the lenticular nucleus, the nucleus accumbens, the corpus striatum, the corpus neostriatum, the tonsil corpus and the substantia nigra.

The nuclei that are part of the basal ganglia and their functions are explained below:

Caudate nucleus

Caudate nucleus in yellow

The caudate nucleus is a region that is located deep in the cerebral hemispheres. This nucleus mainly participates in the modulation of movement in an indirect way. That is, connecting the thalamic nuclei with the motor cortex.

It is characterized by presenting a C shape with three portions. The first of these constitutes the head of the nucleus and is in contact with the lateral ventricles. The other two portions are the body and tail of the caudate nucleus.

It has a close functional relationship with another basal nucleus, the putamen nucleus. Likewise, a brain structure is widely innervated by dopamine neurons, which have their origin in the ventral tagmental area.

When the existence of the caudate nucleus was described, it was postulated that this region of the basal ganglia participated only in the control of voluntary movement. However, it has recently been shown that the caudate nucleus is also involved in learning and memory processes.

Putamen nucleus

Putamen in light blue

The nucleus putamen is a structure that is located in the center of the brain. Specifically, it is right next to the caudate nucleus.

It is one of the three main nuclei of the basal nuclei of the brain, which are mainly responsible for motor control of the body. It is the outermost portion of the basal ganglia and appears to play an important role in operant conditioning as well.

Finally, the latest research on this brain structure relates it to the development of feelings. Specifically, it is postulated that the putamen nucleus could intervene in the appearance of feelings of love and hate.

Pale balloon

Pale balloon.

Along with the caudate nucleus and the putamen nucleus, the globe pallidus is the third main structure of the basal nuclei. It is responsible for transmitting the information projected by the putamen and caudate nuclei towards the thalamus.

Anatomically, it is characterized by presenting a narrow wall of the wedge, which is directed medially from the lenticular nucleus. Likewise, it is divided into two portions (internal and external portion) through a medial medullary lamina.

Lenticular core

Lenticular nucleus.

The lenticular nucleus, also known as the extraventicular nucleus of the striatum, is a structure that is located below the caudate nucleus, in the oval center.

This structure does not form a nucleus per se, but refers to the anatomical region constituted by the union between the globus pallidus and the putamen nucleus.

It is a large nucleus, since it is about five centimeters long. And its functions include both the activities performed by the globe pallidus and the nucleus putamen.

Nucleus accumbens

The nucleus accumbens is a group of neurons in the brain located between the caudate nucleus and the anterior portion of the putamen nucleus. Thus, a brain structure formed by specific regions of the two basal nuclei results.

It is part of the ventral region of the striatum and performs activities related to emotional processes and the elaboration of feelings.

Specifically, the nucleus accumbens is attributed an important function of pleasure, including activities such as laughter or reward experimentation. Likewise, it also seems to be involved in the development of emotions such as fear, aggression, addiction or the placebo effect.

Striated body

Striated body in red

The corpus or striatum is a subcortical part of the forebrain. It forms the main information pathway to the basal ganglia, since it is connected to important regions of the brain.

The dorsal striatum is divided by a section of white matter known as the internal capsule, thus forming two sectors: the caudate nucleus and the lenticular nucleus, which in turn is made up of the globe pallidus and the putamen nucleus.

Thus, the striatum is interpreted as a structure referring to the basal ganglia that encompasses a great variety of nuclei and regions.

Present medium spiny neurons, Deiter neurons, cholinergic interneurons, interneurons that express parvalbumin and catelcholamines, and interneurons that express somatostatin and dopamine.

Neostriate body

Striated nucleus (striatum)

The neostriated body is the name given to the brain structure that includes the caudate nucleus and the putamen nucleus.

Its characteristics are based on the attributes of the two basal ganglia. Likewise, the functions attributed to the neostriate body are defined through the activities carried out by the caudate nucleus and the putamen nucleus.

Tonsil body

Brain tonsil.

The tonsil body, also known as the tonsil complex or brain amygdala, is a set of nuclei of neurons that are located deep in the temporal lobes.

This structure is part of the limbic system and performs vital actions for the processing and storage of emotional reactions. Likewise, it is a basic region of the brain's reward system and is related to addiction and alcoholism.

Within the tonsil complex a large number of anatomical divisions can be detected. The basolateral group, the centromedial nucleus and the cortical nucleus are the most important.

This structure makes it possible to connect the hypothalamus, which projects information regarding the autonomic nervous system, with the reticular nuclei, the nuclei of the facial trigeminal nerve, the ventral tagmental area, the locus coerelus and the laterodrosal tagmental nucleus.

Finally, the most recent research shows that the tonsil body is a basic structure for the development of emotional learning. It is responsible for modulating memory and allows the development of social cognition.

Black substance

Black-substance.

Finally, large regions of substantia nigra are also seen in the basal ganglia. The substantia nigra is a heterogeneous portion of the midbrain and an important element of the basal ganglia system.

It presents a compact part that contains black neurons due to the neuromelanin pigment, which increases with age. As well as a crosslinked part of much lower density.

The function of this substance is complex and seems to be closely related to learning, orientation, movement and oculomotion.

Ways of association

The different nuclei that are part of the basal ganglia have multiple connections both between them and with other structures in the brain. However, research on the basal ganglia has established two main types of association pathways for this structure.

Specifically, this region of the brain would present a direct association pathway and an indirect association pathway. Each of them presents a different operation and carries out different activities.

Direct way

The direct pathway to the basal ganglia is activated through type 1 dopamine receptors. The median spinous neurons of the striatum generate a GABAergic inhibition, which inhibits the thalamus.

In this way, the direct pathway to the basal ganglia is exciting and stimulates the frontal cortex of the brain. When the striatum receives dopaminergic projections, it activates the direct pathway to stimulate the motor cortex and produce movement.

Indirect route

The indirect route of the basal ganglia functions totally contrary to that of the direct route. This is usually inhibited by dopaminergic projections through dopamine D2 receptors. Thus, when lit, it inhibits the frontal cortex through GABAergic projections.

Related diseases

Coronal sections of the human brain that mark the basal ganglia. Blue = striatum, green = pale globe (outer and inner segments), yellow = subthalamic nucleus, red = black substance (pars reticulata and pars compacta). The right section is deeper, near the brain stem. Source: Andrew Gillies via Wikimedia Commons

The basal ganglia perform important functions in the brain. Thus, the alteration of both the anatomy and the functioning of these structures is usually associated with the appearance of pathologies.

In fact, currently several diseases have been detected that are etiologically related to the state of the basal ganglia. Most of them are serious and degenerative pathologies.

The main diseases related to the basal ganglia are: Parkinson's disease, Huntington's disease, cerebral palsy, and PAP syndrome.

Parkinson's disease

Parkinson's disease is a degenerative pathology characterized by the presentation of tremors, muscle stiffness, difficulty in making quick and smooth movements, standing or walking.

Likewise, as the pathology progresses, Parkinson's disease usually causes mood disturbances, depression, apathy, anxiety, memory loss, cognitive impairment and dementia.

It usually appears during old age, although there are cases of early onset. This disease has its origin in the death of the cells of the substantia nigra of the basal ganglia.

The neurons in this brain region progressively deteriorate and die, causing a gradual loss of dopamine and brain melanin, a fact that motivates the appearance of symptoms.

Huntington's disease

Huntington's disease is also a degenerative pathology. It is characterized by progressive memory loss and the appearance of strange and jerky movements known as "chorea."

It is a hereditary disease, the etiology of which involves the death of neurons in the caudate nucleus. It usually begins at age 30, although it can start at any age.

At present there is no cure for this disease, since no intervention has managed to eradicate the deterioration of the caudate nucleus that causes the pathology.

Cerebral palsy

Cerebral palsy causes serious motor problems, such as spasticity, paralysis, or even stroke of the body.

Spasticity occurs when the muscles of the body are constantly tense, which prevents the adoption of normal movements and posture.

This disease seems to be related to the generation of brain damage during pregnancy. Causes can include fetal infection, environmental toxins, or lack of oxygen, and damage often affects the basal ganglia, among other structures in the brain.

PAP syndrome

PAP syndrome is a pathology characterized by the development of an unusual lack of motivation.

Due to the importance of the caudate nucleus in the development of this type of feelings, several studies suggest that the etiology of the disorder is related to alterations in the functioning of this brain region.

References

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