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 various 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 the ventral tegmental area to the nucleus accumbens, connecting with other structures such as the amygdala and even the prefrontal cortex.
The mesolimbic pathway has been identified with the brain 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 human being, being fundamental in the capture and experimentation of sensations of pleasure and gratification.
This allows us to get closer to stimulation, allowing us, for example, to want to eat or maintain relationships due to the experience of satisfaction. In the same way. The correct functioning of this pathway allows us to learn by reinforcing our behavior, seeking to repeat the same actions in those stimulating situations similar to those that caused the activation of the sensations of gratification. With this, it greatly allows us to learn and condition behavior. It also plays an important role in aspects such as the management of emotions and the physiological reactions that arise from them, behavioral control, impulsivity and motivation.
The mesolimbic pathway is not a structure in itself, but a set of them that work together forming 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 has the greatest number of dopamine receptors, participating in both the mesolimbic and mesocortical pathways. The ventral tegmental area plays an important role in maintaining 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 reward circuit and the mesolimbic pathway. And this nucleus largely controls the release of dopamine in the brain. It is in this area where most drugs act, as well as one of the most linked to the processes of habituation and acquisition of addictions. It participates in the integration of emotion and motivation to transform them into actions, in addition to contributing to the management of aggressiveness, memory and behavioral planning (through its connection with the prefrontal).
3. Amygdala
The amygdaloid complex is an important part of the mesolimbic pathway, linking emotion with physiological responses and behavioral characteristics of their experimentation. This is the main nucleus that is responsible for emotional management, especially in the case of fear (which partly explains the sensations of fear generated by the hallucinations of subjects with schizophrenia) and aggressiveness. It also influences sexuality and the feeling of satiety.
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 made of the experience.
5. Nucleus of the stria terminalis
Part of the limbic system, this nucleus groups the set of fibers that connect the thalamus and amygdala. It is linked to stress management and sexuality (there are differences between sexes and sexual identities in this area).
6. Prefrontal cortex
The prefrontal cortex is one of the areas that governs the cognitive aspects of behavior, allowing the use of skills such as planning and inhibition of impulses. The mesolimbic pathway also connects with this part of the cerebral cortex.
Role in different disorders
A malfunction of the mesolimbic pathway, whether due to its hyperfunction or hypofunction, has frequently been linked to the experience of different mental disorders and behavioral alterations. 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 hyperactivation of the mesolimbic pathway due to excess dopamine is linked to the appearance of hallucinations and other positive symptoms, such as restlessness, impulsivity, and chaotic and disorganized behavior.
But not only in schizophrenia, a link of this pathway has also been found 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 targeted by most neuroleptics, making it essential to work with it in order to solve psychotic problems.
As we have indicated previously, the mesolimbic pathway is also part of the brain reward circuit, which is associated with the experience of sensations of pleasure. In this sense, its importance stands out when it comes to explaining the addictive process of drug addicts, which is due to the facilitation and dopamine agonism that a large number of substances tend to generate.
In abstinence the level of dopamine produced by the brain naturally, unlike what occurs in schizophrenia is insufficient to maintain normative functioning, which causes symptoms such as discomfort and generates craving or desire to consume.
3. Eating disorders
As a fundamental part of the brain reward circuit, the mesolimbic pathway also participates in the feeding process 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 a mental disorder in itself, excessive food intake despite being satiated or in response to the perception of anxiety and stress is also largely due to the pleasure obtained thanks to the activation of this pathway.
4. Other disorders
Dysfunction of the mesolimbic pathway has also been linked to the presence of problems related to aggression 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.
