Mesolimbic pathway (brain): anatomy and functions

The human nervous system is made up of millions of neurons, which connect to each other forming complex neural networks.

Different networks are usually responsible for transmitting different information, allowing the operation of different systems with distinctive functions. One of the most important pathways for our survival is the mesolimbic pathway., which we will analyze throughout this article.

The mesolimbic pathway: one of the main dopaminergic pathways

The mesolimbic pathway is understood to be one of the main brain dopaminergic circuits, which connects the midbrain with the limbic system going from to ventral tegmental area until the nucleus accumbens, connecting with other structures such as amygdala and even the prefrontal cortex.

The mesolimbic pathway has been identified with the brain's reward mechanism, including most of the structures that are part of it. Thus, it is a circuit of great importance for the development and functioning of the being. human being, being fundamental in the capture and experimentation of sensations of pleasure and gratification.

This allows us to get closer to stimulation, allowing for example that we want to eat or have relationships due to the experience of satisfaction. In the same way. Its correct functioning of this path allows us to learn by reinforcing our behavior, seeking to repeat the same actions in those stimulating situations similar to those that provoked his activation of the sensations of gratification. With this, it allows us to a great extent the learning and the conditioning of the behavior. It also plays an important role in aspects such as the management of emotions and the physiological reactions that derive from them, behavioral control, impulsivity and motivation.

Main structures involved

The mesolimbic pathway is not a structure in itself, but rather a set of them that work together to form a network through which information circulates.

There are numerous cortical and subcortical structures that are part of this pathway, the following being some of the most notable.

1. Ventral tegmental area

This brain region is the starting point of the mesolimbic pathway, located in the brain stem.. It is one of the areas that receives the greatest number of dopamine owns, participating in both the mesolimbic and mesocortical pathways. The ventral tegmental area plays an important role in the maintenance of motivation, emotion and cognition, as well as in the experience of pleasure. Neurons in this area modulate dopamine release in other areas of the mesolimbic pathway.

2. Nucleus accumbens

Part of the basal ganglia, the nucleus accumbens is one of the most important structures in the brain's reward circuitry and mesolimbic pathway. And it is that this nucleus largely controls the release of dopamine in the brain. It is in this area that most drugs act, as well as one of the most linked to the processes of habituation and acquisition of addictions. Participate in the integration of emotion and motivation to transform them into actions, in addition to contributing to the management of aggressiveness, memory and behavior planning (through its connection with the prefrontal).

3. Amygdala

The tonsillar complex is an important part of the mesolimbic pathway, linking emotion with physiological responses and behavioral characteristics of their experimentation. It is the main nucleus that is responsible for emotional management, especially in the case of fear (something that partly explains the feelings of fear generated by the hallucinations of the subjects with schizophrenia) and the aggressiveness. It also influences sexuality and feelings of satiation.

4. Hippocampus

The hippocampus is one of the regions of the limbic system that is most associated with memory and learning, allowing the formation and recovery of memories and associating them with the emotional assessment that is made of the experience.

5. Nucleus of the terminal stria

Part of the limbic system, this nucleus groups together the set of fibers that connect the thalamus and the amygdala. It is linked to stress management and sexuality (there are differences between the sexes and sexual identities in this area).

6. Prefrontal cortex

The prefrontal cortex is one of the areas that govern the cognitive aspects of behavior, allowing the use of skills such as planning and impulse inhibition. The mesolimbic pathway also connects with this part of the cerebral cortex.

Role in different disorders

A malfunction of the mesolimbic pathway, either due to hyperfunction or hypofunction of it, has been frequently linked to the experimentation of different mental disorders and behavioral disturbances. Specifically, some of the disorders to which this pathway has been most linked are the following.

1. Schizophrenia and other psychotic disorders

The main disorder with which it is associated, in schizophrenia it has been observed that the presence of hyperarousal of the mesolimbic pathway due to an excess of dopamine is linked to the appearance of hallucinations and other positive symptoms, such as restlessness, impulsiveness, and chaotic behavior and disorganized.

But not only in the schizophrenia, but this pathway has also been found to be associated with the symptoms of other psychotic disorders such as chronic delusional disorder, schizophreniform disorder or acute psychotic disorder, among others. The mesolimbic pathway is in fact the main objective to which most neuroleptics aim, being essential to work with it in order to solve problems of a psychotic nature.

2. Substance addictions and withdrawal

As we have indicated previously, the mesolimbic pathway is also part of the brain's reward circuit, which is associated with experiencing sensations of pleasure. In this sense, it highlights its importance when explaining the addictive process of drug addicts, the which is due to the facilitation and agonism of dopamine that tend to generate a large number of substances.

In withdrawal, the level of dopamine produced by the brain naturally, unlike in schizophrenia, is insufficient to maintain a normative functioning, with which symptoms such as discomfort appear and the craving or desire for consumption.

3. Eating disorders

As a fundamental part of the brain's reward circuit, the mesolimbic pathway also participates in the process of feeding and it is linked to the sensations of pleasure we feel when we eat. The activation of this pathway is closely linked to the presence of eating disorders that involve a loss of impulse control, as occurs with binge eating in cases of bulimia and Binge eating disorder.

Although obesity is not in itself a mental disorder, excessive food intake despite having satiated or eating response to the perception of anxiety and stress is also due in large part to the pleasure obtained thanks to the activation of this via.

4. Other disorders

Mesolimbic pathway dysfunction has also been linked to the presence of problems related to aggressiveness and impulse control. In general, it is also linked to compulsive behavior, and this pathway can be affected by other disorders such as OCD or paraphilias.

Bibliographic references:

• Adams R, Victor M, Ropper A. (1999). Principles of Neurology Sixth Edition. México D.F.: Mac Graw-Hill Interamericana.
• Haaga J, Lanzieri C, Sartoris D, Zerhouni E. (1996). Computed Tomography and Magnetic Resonance-Total Body Imaging Diagnosis. Third edition. Barcelona: Mosby / Doyma Libros.