Nucleus Accumbens: What is it, functions, anatomy, diseases.

 

The nucleus accumbens is a brain structure that is part of our pleasure and reward system. It activates our motivation and allows willpower to translate into action. It has an essential role in learning and memory, in laughter, fear, aggression, addictions, the placebo effect, sex, food intake, etc. Discover all about nucleus accumbens: What it is, functions, anatomy, disorders, and more. 

nucleus accumbens

Nucleus Accumbens

 

What is Nucleus Accumbens? Definition

The nucleus accumbens is a brain part involved in functions such as motivation, reward or positive behavioral reinforcement.

The role of nucleus accumbens is to integrate motivation along with the motor action. Its function is to transfer relevant motivational information to the motor cells in order to obtain a certain reward or satisfaction.

An imbalance is related to many psychiatric and neurological disorders such as depression, obsessive-compulsive disorder, bipolar disorder, anxiety disorders, Parkinson’s disease, Huntington’s disorder, obesity and drug abuse.

How is the nucleus accumbens activated? Through natural positive behavioral enhancers such as pleasant food intake, sex, money, etc. They activate the group of neurons that make up this region and an automatic release of dopamine occurs which is what gives an immediate pleasure effect. However, it can also be generated through repeated drug use (cocaine, heroin, ecstasy, nicotine, etc.). Maintaining the mechanisms involved in addiction.

Basic Neurobiology of Nucleus Accumbens

Anatomy and structure of the nucleus accumbens. This brain part is located in an area called the basal. Each cerebral hemisphere has a nucleus accumbens. This structure is part of the so-called basal ganglia and receives connections from the ventral tegmental area, which has dopamine. Its full name is nucleus accumbens septi, which means nucleus lying on the septum. This is because it is situated where the caudate nucleus and putamen (other basal ganglia) are attached to a third structure called septum.

Anatomically it has two components: the shell and the core. The functions of these two parts are different. The shell is more related to the limbic system (the emotions) and the core has to do with the motor system (the execution of motor actions). However, in rodents, these areas are more differentiated than in humans.

1. Shell

The Shell contains a high number of neural connections that connect this area with other parts of the brain, such as the limbic system and the hippocampus. Both the limbic system and the hippocampus are responsible for receiving dopamine, serotonin, and glutamate. The Shell is linked to the emotions. In addition, it also contains important neural connections from the frontal lobe, which is responsible for sending information collected from the thalamus to the central area of the nucleus accumbens.

2. Core

The Core presents functions mainly related to the motricity. The Core is connected to the basal ganglia, substantia nigra, and motor cortex. These areas of the brain are activated when an action with an emotional content is aimed at achieving a specific goal.

Nucleus-Accumbens-Shell and Core

Nucleus Accumbens Shell and Core

Functions of the nucleus accumbens

The anatomical structure of the nucleus accumbens indicates that its function is the limbic-motor integration.

  • Emotions: This organ receives connections from brain areas related to emotions, such as the amygdala and hypothalamus.
  • Memory and motor areas: It also connects to memory and motor areas.

All this makes it a fundamental organ for the learning of behaviors that lead us to pleasurable sensations and to avoid negative experiences.

1- Nucleus accumbens: Dopamine and its function in the reward system

The most well-known function is its role in the reward circuit. When we perform some pleasurable activity, whether eating or having sex, dopamine neurons (among other neurons) are activated in the ventral tegmental area. These neurons cause the dopamine levels of the nucleus accumbens to increase, causing a sensation of pleasure.

The association between pleasurable experiences and levels of dopamine has long led neuroscientists to believe that the function of this organ was based on reward, therefore, involved in addiction and addictive processes. The nucleus accumbens is still considered the pleasure center of the brain.

However, this study found that nucleus accumbens is related to both reinforcing and aversive stimuli. According to the article, the levels of dopamine in the accumbens increase in response to reinforcing stimuli and descend drastically with the aversives.

Therefore, the dopamine circuit is involved in the storage of information about both positive and negative environmental stimuli. This helps us remember how to repeat pleasant experiences and how to avoid aversive experiences.

This is why it is essential for our learning. Thanks to this organ we are able to create associations with that which gives us pleasure and/or gives us pain, to look for one and avoid the other.

2- Nucleus accumbens and placebo effect

According to this study, nucleus accumbens may play a key role in the placebo effect.

The placebo effect is defined as a psychological experience of improvement in health following administration of a substance, treatment or surgery that does not provide any effect (such as homeopathy and other pseudotherapies), accompanied by the promise of real benefit from it.

It is such a powerful effect that when testing the efficacy of drugs, the placebo effect is very carefully controlled.

The aforementioned study, using healthy subjects, examined its role in the formation of placebo responses. They observed the release of dopamine in the nucleus while administering a placebo substance.

The researchers found that the more participants anticipated the benefits of the placebo substance, the more dopamine was released in the nucleus accumbens and the more relief they perceived later.

3- Nucleus accumbens and relationship with love and attachment

The basic function of the reward system and the nucleus accumbens is to ensure the vital behaviors for us, such as food, attachment, and sex. Although it is also activated with many other behaviors, this is the most primitive function.

Therefore, one of the functions is to generate pleasure and attachment within affective relationships. The nucleus accumbens intervenes in creating bonds of affection, in love (partner, family or friend) and also becomes active when we are rejected. Humans are social beings, we need each other and it is very important to maintain a solid support group. Therefore, his activity also tries to keep us from separating (physically and psychologically) from those we love. By seeing a photograph of a loved one (couple, family or friend) increases the activity of the nucleus accumbens.

According to a study, this brain area along with the orbitofrontal cortex is associated with the evaluation of the gains and losses that entails love and rejection.

In romantic love, when we are with a person that attracts us, dopamine activity increases, encouraging us to spend more time with it, giving us pleasure with its mere presence and enabling, evolutionarily, the continuation of the species.

4- Nucleus accumbens and its role in addictions

The nucleus accumbens plays a fundamental role in addictions. Drug or substance abuse causes an exorbitant amount of dopamine to be released, making us feel pleasure. Therefore, we are able to make an association between the substance and feeling good so we will tend to continue to consume.

One of the functions of the accumbens is the impulse for action, in the planning and inhibition of behaviors, due to its connections with the prefrontal cortex.

5- Nucleus accumbens and the motivational system

The key neurotransmitter for motivation is dopamine. As we have said, the dopamine and nucleus accumbens are the perfect match for the rewarding sensations of positive stimuli. But they not only work when we have received that reward, but also predicting it. When we anticipate some reward or something pleasurable, dopamine is released. Due to the connections of the nucleus with the prefrontal cortex, we are able to generate plans of action to obtain that reward.

That is, the nucleus accumbens has the function of making us anticipate the prize to encourage us to achieve it.

Nucleus Accumbens Reward Circuit

Nucleus Accumbens: Reward Circuit

Can you enhance the nucleus accumbens and the motivational system?

Is it possible to increase our motivation by enhancing the nucleus accumbens circuit? You can train your brain to have more motivation and produce more dopamine in the accumbens. How?

Give yourself frequent positive feedback from your progress by setting up goals. That is, divide the task into parts and treat yourself for each one. You don’t have to take a piece of cake every time you finish one. It would be excessive and harmful to your health. But give yourself a break and say positive things like: “This is how it is done!” “You can do it!”

For example, if you have to study a very extensive syllabus divide it into sections and reward yourself for each section completed.

6- The function of nucleus accumbens in learning and memory

As we mentioned the dopamine reaches the nucleus accumbens making us feel pleasure. But when we are faced with something negative, the dopamine in that area descends drastically. This helps us to learn what we have to avoid and what we have to repeat. For example, if I burn myself with a hot pan, the nucleus accumbens will receive a response that allows us to learn that we should not get that close to a hot pot. On the contrary, if a child draws a picture to his father and he responds with joy and affection, the dopamine in the nucleus accumbens will work as a reward. So the child will learn that by drawing pictures he is more likely to get affection.

7- The nucleus accumbens and music

Listening to music is one of the most enjoyable experiences for humans. According to this theoretical review, listening to music influences the activity of the accumbens. Musical stimuli can significantly increase dopamine levels, along with other neurotransmitters. Even the passive listening of music that we like even if it is not familiar to us increases the activity of this nucleus.

How does the nucleus accumbens intervene in psychological disorders?

As we have said, the main function of the nucleus accumbens is its intervention in the reward system. But when it does not work well, either because of genetic causes or certain vital experiences, it results in psychological disorders.

Nucleus accumbens and depression

According to this study neuronal activity in the nucleus accumbens, neurotransmitter-related acetylcholine regulates depressive behaviors. Researchers found that when levels of this neurotransmitter go down, depressive symptoms can be observed. This suggests that such activity is essential for regulating mood and motivation.

Nucleus accumbens and psychopathy

According to this study, psychopaths, or people with antisocial personality disorder, have a hyper-reactive reward system. That is, before the anticipation of a reward, a large amount of dopamine (more than all other people) is released in the nucleus accumbens. This may explain that they exhibit abusive behavior and the pursuit of personal satisfaction without thinking about other people.

Nucleus accumbens and ADHD

In ADHD the nucleus accumbens is also altered, as this study says. Attention deficit hyperactivity disorder is related to a reduction of dopamine in the accumbens. This has to do with the symptoms of inattention. As we have seen, accumbens is related to motivation. If this is not active enough, children with ADHD will not be able to focus their efforts on those action plans that lead to medium-and long-term rewards. They will then seek immediate reinforcement.

This article is originally written in Spanish by Andrea García Cerdán.

Alejandra is a clinical and health psychologist. She is a child specialist with a diploma in evaluation and intervention in autism. She has worked in different schools with young children and private practice for over 6 years. She is interested in early childhood intervention, emotional intelligence, and attachment styles. As a brain and human behavior enthusiast, she is more than happy to answer your questions and share her experience.