Thalamus: anatomy, structures and functions

What is the thalamus and what is its function in our nervous system?

The thalamus is one of the most important parts of the brain. Not only is it one of the largest brain structures, but it is also located in the very center of the brain, as is reflected in its name, which comes from the Greek word thalamos (or "inner chamber").

Because it occupies so much of the brain and is so well communicated with the other parts of the brain, the thalamus is involved in all aspects of the brain, the thalamus is involved in a large number of mental processes that shape the way we perceive things and act on the environment around us... even if the thalamus is not the only part of the brain involved. around us... even if we don't realize it.

What is the thalamus?

The thalamus is basically a collection of gray matter (neuron bodies) formed by two egg-shaped brain structures that lie beneath the cerebral cortex. These structures are located next to each other, and in addition to having the same shape and size, they have a symmetrical arrangement, as do the two cerebral hemispheres that cover them. They communicate with each other through a kind of bridge that holds them together and is called the interthalamic connection.

The thalamus is part of an area called the diencephalon. The diencephalon is located between the cerebral cortex (and all the lobes of the brain) and the upper part of the brainstem. The diencephalon, in turn, is composed of the thalamus, the hypothalamus (located just below the first one) and some other smaller structures.

In addition, the thalamus has a symmetrical shape and being located just below the space separating the two cerebral hemispheres, it has an outlet on both sides of the brain. To see how it interconnects with these parts, we can take a look at the structures of the thalamus and the types of neurons in it.

The structures of the thalamus

The thalamus is basically a collection of neuron bodies, i.e. a gray matter structure, just like the cerebral cortex. But within this cluster of neuronal groups, a number of nuclei of the thalamus can be distinguished:

• Nuclei of specific connection. These send sensory information to specific areas of the cerebral cortex that are specialized in working with that specific type of data coming from a specific sense.
• Nonspecific connection nuclei. They send information to very broad areas of the cerebral cortex, without discriminating by specialization.
• Association nuclei. They are part of an information circuit that communicates the cerebral cortex with subcortical structures.

The neurons of the thalamus

The thalamus is made up of many other specialized substructures, but they are all, after all, neurons and glial cells. Like any other part of the brain, the thalamus only has a reason to exist if it is connected to other areas of the nervous system, and this is reflected in the type of neurons that compose it. The distribution of these neurons shows that they are associated with many other bundles of neurons coming from many parts of the central nervous system.

From the functional point of view, the classes of neurons of the thalamus are as follows:

• Local interneurons. These nerve cells are basically in charge of having the information arriving from other parts of the nervous system processed in the thalamus, transforming it into a new set of data. Therefore, their main function is to send nerve impulses to other interneurons in the thalamus. They account for approximately 25% of the neurons in the thalamus.
• Projection neurons. These nerve cells are responsible for sending information out of the thalamus to the cerebral cortex. They are 75% of the thalamic neurons.

Functions of the thalamus

We have seen that the thalamus is very well communicated, but its role is not that of a simple communication bridge between relevant parts of the brain. The thalamus itself is a structure that plays an active role in processing information coming to it from other areas. But... what are the functions performed by this brain structure?

1. Integration of sensory data

The best known and most studied function of the thalamus is that of being one of the first that of being one of the first stops in the brain for the information that reaches us through the senses, with the exception of the sense of smell.with the exception of smell.

The thalamus processes this sensory information, discards the parts that are not too important and sends the final result to the cortex of the brain, where this information will be further processed.

It thus facilitates the integration of sensory information to move from raw data to relatively complex information units. to relatively complex units of information information units capable of holding meaning for us. In any case, it should be clear that this process does not only take place in the thalamus, but involves several networks of neurons distributed throughout practically the entire brain.

2. The sleep-wake cycle

The thalamus, like its younger brother the hypothalamus, is involved in regulating the rhythm with which the sensation of sleep comes and goes. This function, in addition to being fundamental in regulating all nervous activity in general, is also related to the following.

3. Attention and consciousness

Recent research indicates that the thalamus may play a very important role in the emergence of consciousness and everything related to it, from the ability to think about one's own thoughts, to the use of language, to the ability to focus attention on specific informationThe thalamus may play a very important role in the emergence of consciousness and everything related to it, from the ability to think about one's own thoughts, to the use of language, to the ability to focus attention on specific information according to one's objectives at any given moment.

However, it is important to point out that these processes related to conscious states are not consciousness itself, although they appear in parallel. We cannot focus our attention on anything when we are not aware that we exist, nor can we speak or reflect; but when we are conscious, there are aspects of attention and language that are beyond consciousness.

In addition, all these complex mental processes related to abstract thinking require the participation of many areas of the brain, not just the thalamus; this part of the diencephalon is a necessary but insufficient component in making thought, attention and language happen.This part of the diencephalon is a necessary but insufficient component in making thought, attention and language take place (something that can be said of virtually all parts of the brain, because they all work in an interconnected way).

Because the thalamus is so well connected to many areas of the cortex at once, it may be able to intervene in the synchronization of neural activity necessary for the level of consciousness to be maintained. Without it, the other parts of the brain become non-functional, at least in the vast majority of cases. There can always be exceptions of people born without thalamus or with a very poorly developed thalamus who can nevertheless live for many years; in such cases, the rest of the brain would have learned to reconfigure itself to carry out the tasks of this absent structure using other networks of neurons.

4. Emotion regulation

The thalamus is not only connected to circuits that carry sensory information, but it also interacts with neural also interacts with neural pathways directly involved in the emergence of emotional states.. It is not for nothing that the thalamus is surrounded by the limbic system.

Thus, the thalamus integrates these two pathways and works by bringing together these two types of information, causing emotions to affect the perceived and vice versa. In addition, it receives information from the hypothalamus, which in turn is directly involved in the regulation of emotions and the secretion of different types of hormones into the bloodstream.

Conclusion

The thalamus is one of the largest parts of the brain and, moreover, it seems to play a role in a multitude of functions that neither look very similar nor have much to do with each other at first glance.

However, this is a reflection of the very functioning of the nervous system, in which all the time, regardless of whether we are asleep or awake, a multitude of processes are being carried out in parallel and at the same time in a coordinated manner.

It also plays a very important role in the appearance and maintenance of the brain activation states responsible for keeping us aware of our own existence and of what is happening around us. This has led to the thalamus has come to be considered "the switch of consciousness.".

However, the thalamus itself is not the part of the brain in which consciousness "resides". To assume this would be like thinking that inside our head there is a self-aware sprite with its own consciousness that is surrounded by non-conscious matter just as the pilot of an airplane would do; that is, it would make us fall into the dualism of philosophers such as René Descartes.

It is currently understood that consciousness is the fruit of the activity of several parts of the brain (among which the thalamus would stand out) working together at great speed and in a coordinated manner, and therefore this mental state cannot be reduced to a single structure.

Bibliographical references:

• Boutros, N. J. (2008). The thalamus. Clinical EEG and Neuroscience, Vol.39(1), p.IV.
• Percheron, G. (1982). The arterial supply of the thalamus. In Schaltenbrand; Walker, A. E. (eds.). Stereotaxy of the human brain. Stuttgart: Thieme. pp. 218 - 232.
• Perea-Bartolomé. M. V. y Ladera-Fernández, V. (2004). El tálamo: aspectos neurofuncionales. Revista de neurología, 38(7), pp. 697 - 693.
• Sherman, S. Murray; Guillery, R. W. (2000). Exploring the Thalamus. Academic Press.
• Sherman, S. (2006). Thalamus. Scholarpedia1 (9): 1583.
• Shimamura, K; Hartigan, DJ; Martinez, S; Puelles, L; Rubenstein, JL (1995). "Longitudinal organization of the anterior neural plate and neural tube". Development. 121 (12): 3923 - 3933.