Thalamus: anatomy, structures and functions

the thalamus it 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 center of the brain, as the name suggests, which comes from the Greek word thalamos (or “inner chamber”).

By occupying so much and being so well communicated with other parts of the brain, the thalamus is involved in a large number of mental processes which shape the way we perceive things and act on the environment. that surrounds us … even if we don’t realize it.

What is the thalamus?

The thalamus is basically a set of gray matter (Neural bodies) formed by two brain egg-shaped structures located below the cerebral cortex. These structures are located next to each other, and more than being the same shape and size retain 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 an interthalamic connection.

The thalamus is part of an area called diencephalon. The diencephalon is located between the cerebral cortex (and all lobes of the brain) and the top of the brainstem. In turn, the diencephalon is made up of the thalamus, the hypothalamus (located just below the first), and a few other smaller structures.

In addition, the thalamus has a symmetrical shape and being located just below the space between the two cerebral hemispheres, it presents an exit on either side 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 within it.

The structures of the thalamus

The thalamus is essentially a cluster of neuronal bodies, that is, a structure of gray matter, just like the cerebral cortex. But within this set of neuronal groups a number of nuclei of the thalamus can be distinguished:

  • Specific connection kernels. These send sensory information to specific areas of the cerebral cortex that specialize in working with that particular type of data coming from a specific sense.
  • Non-specific connection cores. They send information to very large areas of the cerebral cortex, without being discriminated against by specialization.
  • Association kernels. They are part of an information circuit that communicates the cerebral cortex with the subcortical structures.

The neurons of the thalamus

the thalamus it is made up of many other specialized substructures, but all are, after all, neurons and glial cells. Like any other part of the brain, the thalamus is only right if it is connected to other areas of the nervous system, and this is reflected in the type of neurons that make it up. In the distribution of these, we note that they are associated with many other bundles of neurons from many parts of the central nervous system.

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

  • local interneurons. These nerve cells are basically responsible for processing information from other parts of the nervous system in the thalamus, turning it into a new set of data. Therefore, its main function is to send nerve impulses to other interneurons in the thalamus. They represent about 25% of the neurons of the thalamus.
  • Projection neurons. These nerve cells are responsible for sending information from the thalamus to the cerebral cortex. These are 75% of thalamic neurons.

The functions of the thalamus

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

1. Integration of sensory data

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

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

Thus, it facilitates the integration of sensory information to pass raw data in relatively complex information units and capable of making sense to us. However, it should be clear that this process not only takes place in the thalamus, but also involves multiple neural networks spread throughout virtually the entire brain.

2. The sleep-wake cycle

The thalamus, like its younger brother the hypothalamus, is involved in regulating the rate with which the sensation of sleep comes and goes. This function, besides being essential to regulate all nervous activity in general, is also linked to the following ones.

3. Attention and awareness

Recent research indicates that the thalamus it could play a very important role in the emergence of consciousness and all that is related to it; from the ability to reflect on one’s own thoughts, the use of language, the ability to focus attention on specific information according to the goals one has at a given time.

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

Moreover, all of these mental processes are so complex and related to abstract thinking they require the participation of many areas of the brain, not just the thalamus; this part of the brain is a necessary but insufficient component to accommodate thought, attention and language (which can be said of virtually every part of the brain, as they all work in an interconnected whole).

Since 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 to maintain the level of consciousness. Without it, the rest of the brain becomes non-functional, at least in the vast majority of cases. Exceptions may always appear for people born without a thalamus or with a very underdeveloped person who can still live for many years; in such cases, the rest of the brain would have learned to reconfigure itself to perform the tasks of this missing structure using other neural networks.

4. The regulation of emotions

The thalamus is not only connected to circuits that carry sensory information, but it also interacts with neural pathways which are directly involved in the appearance of emotional states. It is not in vain that the thalamus is surrounded by the limbic system.

Thus, the thalamus integrates these two pathways and works by combining these two types of information, causing the 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 segregation of different types of hormones in 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 which are neither too much alike nor much alike at first glance.

However, this reflects the proper functioning of the nervous system, in which all the time, whether we are sleeping or awake, many processes are taking place in parallel and at the same time in a coordinated manner.

He plays also a very important role in the emergence and maintenance of responsible brain activation states that keep us aware of our own existence and what is happening around us. This made the thalamus came to be seen as “the change of consciousness”.

However, the thalamus itself is not the part of the brain in which consciousness “resides”. Assuming that would be like thinking that in our head is a goblin with the awareness of himself that he is surrounded by unconscious matter like the pilot of an airplane; that is to say, it would make us fall into the dualism of philosophers like René Descartes.

It is currently understood that consciousness is the result of the activity of various parts of the brain (including the thalamus) working with each other at high speed and in a coordinated manner, and therefore this mental state cannot be reduced. to a single structure.

Bibliographical references:

  • Boutros, NJ (2008). The thalamus. Clinical EEG and Neuroscience, vol. 39 (1), p.IV
  • Percheron, G. (1982). The arterial supply of the thalamus. At Schaltenbrand; Walker, AE (ed.). Stereotaxis of the human brain. Stuttgart: Thieme. p. 218 – 232.
  • Perea-Bartomeu. MV and Vessant-Fernández, V. (2004). The thalamus: neurofunctional aspects. Journal of Neurology, 38 (7), p. 697-693.
  • Sherman, S. Murray; Guillery, RW (2000). Explore 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.

Leave a Comment