THALAMUS: NUCLEI AND FUNCTIONS - NEUROPSYCHOLOGY - 2025

The thalamus is a large mass of gray matter located in the dorsal part of the diencephalon, within the brain. It is a part of this organ that fulfills several functions of vital importance and is the most voluminous structure in the area in which it is found. It is located just above the hypothalamus, being separated from it by the Monroe sulcus.

The thalamus is responsible for several functions of vital importance to us. Among other things, it is in charge of regulating processes such as sleep, consciousness or attention. In addition, all information from the senses (except smell) first passes through this organ, before reaching the areas of the brain where it is processed.

The main function of the thalamus in this regard is to decide which stimuli are important and which are not. If certain sensory information is considered irrelevant, it is discarded in this area. On the contrary, if it seems something significant, this nucleus sends the information back to the areas of the brain where it will be translated into sensations.

Situation of the thalamus. Source: commons.wikimedia.org

Anatomically, it is divided into two parts, and it is the most important subdivision of an area known as the diencephalon. In this article we will study in more depth its anatomy, its functions and the way it develops during the gestation process of a person.

Thalamus nuclei

The thalamus is an egg-shaped mass of gray matter that is part of the diencephalon. It is divided into two equal parts, each one located on one side of the third ventricle of the brain. The two are connected to each other by a band of gray matter known as the interthalamic connection.

Each of the thalamus is clearly separated from the rest of the brain. Thus, in its anterior part, it ends in the interventricular foramen; and in the later, in an expansion known as pulvinar. Below, it borders the tegmentum, and medially, it collides with the lateral wall of the third ventricle.

The internal structure of the thalamus is quite complex; therefore, it is usually divided into several nuclei, which are connected to each other. Nuclei are special areas of the thalamus where the cell bodies of neurons are especially densely packed.

Thalamus nuclei anatomy

Source: By Ben Brahim Mohammed, from Wikimedia Commons

If you examine a horizontal section of each of these nuclei, they would look like an egg-shaped collection of gray matter. Each of them is located in a very specific section of the thalamus: mainly, in the lateral, medial and anterior sections.

These parts are divided by a wall of white matter known as the internal medullary lamina, which separates the different sections of the thalamus. Due to the shape of this sheet, the division becomes Y-shaped.

In general, the nuclei of the thalamus are connected to the cerebral cortex in a two way. Thus, they can both transmit information to this area of ​​the brain and receive responses from it. On the other hand, each of the three areas of this structure is divided into smaller ones, which would be the nuclei themselves.

Although there are a large number of them, they can be divided into three types: relay nuclei (which receive sensory information and send it to the cortex), association nuclei (which obtain information from the cortex and forward it to other areas of the same) and non-specific nuclei (which seem involved with the maintenance of attention).

Next we will see a list of the main nuclei of the thalamus and their functions.

Anterior part

This part contains the anterior thalamic nucleus. This, in turn, is divided into three sections: anteroventral, anteromedial, and anterodorsal. All of them receive information from the limbic system, that is, from the part of the brain in charge of processing our emotions.

Therefore, its functions are directly related to our sentimental states, in addition to processes such as memory, attention and alertness levels. Some of its most important connections are with the mammillary nuclei, with the cingulate gyrus, and with the anterior limbic area.

Medial part

The medial part of the thalamus has only one component, known as the dorsomedial nucleus. It borders laterally with the medullary lamina and with the intralaminar nuclei. On the other hand, it is usually subdivided into two parts: the anteromedial magnocellular, and the posterolateral parvocellular.

Anterior medial magnocellular part

The anteromedial magnocellular part communicates with different parts of the brain. Some of these communications are one-way; that is, they only transmit or receive information. Others, on the other hand, are capable of doing both functions, so they are considered reciprocal.

Some of the areas of the brain with which the anteromedial magnocellular part communicates are the olfactory areas, the ventromedial cingulate gyrus, the inferior parietal cortex, the anterior insula, the mediobasal nucleus of the amygdala, and the lateral nuclei.

Posterolateral parvocellular part

On the other hand, the posterolateral parvocellular part has mainly reciprocal connections with different areas of the brain; among them are the prefrontal cortex, the anterior cingulate gyrus, and the supplementary motor area.

Through all these connections, the medial part of the thalamus is responsible for integrating motor, sensory, olfactory and visceral information; and relate it to the emotional state of the person. In general, its functions are very similar to those carried out by the prefrontal cortex.

Side

This set of nuclei is the largest in the entire thalamus. To facilitate its study, it is normally subdivided into a dorsal and a ventral part.

Dorsal group

This zone includes three subgroups of nuclei: the dorsal lateral, the posterior lateral, and the pulvinar. The dorsal nuclei communicate with different regions of the brain through afferent pathways. However, its functions are still not very clear.

Dorsal lateral nucleus

The dorsal lateral nucleus is the one that is located in a more anterior position. It is primarily connected to the pretect, the superior colliculus, the parietal cortex, the parahippocampal cortex, and the cingulum.

Lateral posterior nucleus

As for the lateral posterior nucleus, it borders the posterior ventral nucleus. Its communications include the superior colliculus, superior parietal lobe, medial parahippocampal cortex, cingulum, and inferior parietal.

Pulvinar nucleus

Finally, the pulvinar forms the posterior expansion of the thalamus. It is usually subdivided into three parts: the medial nuclei, the lateral nuclei, and the inferior nuclei. Each of them has several connections both afferent and efferent with different parts of the brain, as well as with some sensory organs.

The exact functions of the pulvinar are unknown, but due to the complexity of its connections, it is considered that it must fulfill several and very complicated. It appears to be involved in vision, but also in the modulation of perception, memory and cognition due to its connections with the temporal lobe.

Furthermore, it is also possible that the pulvinar nucleus is related in some way to the perception and modulation of pain. However, this function is the one that we understand the least of all today.

Ventral group

This part of the thalamus is also divided into three subgroups: anterior ventral, lateral ventral, and posterior ventral. Let's see each of them.

Anterior ventral nucleus

The anterior ventral nucleus is surrounded by the reticular nucleus, the lateral ventral nucleus, and the external medullary lamina. It is divided into the main body and the magnocellular part.

It is located on the path between the striatum and the motor areas of the premotor cortex, so it transmits information between the two.

Its main connections are with the globus pallidus, the premotor cortex, the substantia nigra, the intralaminar thalamic nucleus, the frontal lobe, and the anterior parietal complex. Thanks to all of them, it is able to influence the activities of the motor cortex, which is why it is in charge of planning and initiating movements.

Ventral lateral nucleus

This subgroup has two main divisions: the pars olaris, located anteriorly, and the pars caudalis, located posteriorly. The ventral lateral nucleus transmits information between different areas, such as the lateral premotor cortex, some nuclei of the cerebellum, the vestibular nucleus, and the motor cortex.

Thus, the ventral lateral nucleus is active during voluntary and involuntary movements produced by the contralateral (opposite) part of the body. It is also responsible for sending feedback on these movements from the cerebellum to the cerebral cortex.

Posterior ventral nucleus

This component of the thalamus is the main one in charge of transmitting somatosensory information between the different areas of the brain. It is subdivided into two parts: the ventral posteromedial and the ventral posterolateral.

One of its most important functions is to transmit information about the temperature and pain felt in the face, head and neck. In addition, it also receives data on the skin and joints. This area of ​​the thalamus is organized into sheets, each one taking care of the sensory "inputs" of a region of the body.

Finally, the efferent fibers emerging from the posterior ventral nucleus go to the corona radiata and the internal capsule, in the somatosensory cortex. This indicates that he is involved in sending sensory information so that it can be consciously processed.

Medial geniculate nucleus

The medial geniculate nucleus is located within the medial geniculate body. This is a kind of protrusion located on the ventrolateral surface of the thalamus, under the nucleus pulvinar.

This nucleus is divided into three parts: medial, ventral, and dorsal. Its main function is to transmit information related to hearing; and therefore you are responsible for the conscious processing of hearing.

Lateral geniculate nucleus

The lateral geniculate nucleus is found within the lateral geniculate body. It is ovoid in shape, and is located in the posterior thalamus. It consists of several sheets, separated by several intermediate areas, which receive visual information from the retina of both eyes.

Therefore, it is considered that the lateral geniculate nucleus plays a fundamental role in the interpretation of data related to the sense of sight.

Other cores

These are the main areas of the thalamus; however, they are not the only ones that exist. Thus, we can also find several specialized nuclei within the sheets of white matter that divide the different subsections of the same; or in the periphery of the main gray matter groups.

As you can see, the organization of the thalamus is extremely complex, and its connections encompass practically every other structure in the brain.

Therefore, there is still much to learn about this part of our mind and the functions it performs in relation to our senses, emotions and consciousness.

Features

The functions of a brain area are studied mainly by observing its connections with other cortical or subcortical areas. Because the thalamus has an immense number of inputs and outputs of information, it is very difficult to reduce the tasks that it performs within our brain to just a few.

However, most experts agree that it has to do primarily with three areas: emotional control, maintenance of attention and awareness, and interpretation of information received from the senses.

Emotional control

It seems that the thalamus is closely related to our feelings. Thanks to its function as an information exchanger, it is able to regulate the way we feel based on the inputs it receives from other areas.

Thus, thanks to the thalamus, our emotional state changes depending on the information that we interpret from both our senses and our cerebral cortex.

Maintenance of attention and awareness

On the other hand, the thalamus seems to be in charge of directing our conscious attention to what interests us. When it fails, it is impossible to stay focused on just one thing; therefore its function is essential for our correct operation during the day to day.

Interpretation of sensory information

Finally, the thalamus is the place where information from four of the five senses goes, all except smell. Once processed by this brain organ, it is redistributed and directed to other areas of the cortex, where it will be transformed into conscious sensations.

References

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4. "Thalamus" in: Britannica. Retrieved on: July 22, 2018 from Britannica: britannica.com.
5. "Thalamus" in: Wikipedia. Retrieved on: July 22, 2018 from Wikipedia: en.wikipedia.org.