Nucleus accumbens is a small brain structure that performs some of the major functions in the cerebral cortex. It connects the basal ganglia and the limbic system, thus participating in the reward system of the brain.
This cluster of neurons is involved in the cognitive processing of the motor functions related to the analysis and processing of rewards and reinforcing stimuli. The nucleus accumbens cluster is also responsible for the regulation of slow-wave sleep.
Located close to the amygdala as a part of the mesolimbic system, the nucleus accumbens is involved in the regulation of emotions, particularly in the development of motivation, the reward and reinforcement processes, feelings of happiness, as well as addictions.
Anatomy of the Nucleus Accumbens
According to its position, this structure of the brain is considered to be a part of the basal ganglia. The basal ganglia are one of the most important and fundamental processing units of the brain, responsible for a broad spectrum of functions, including the control of voluntary motor movements, procedural and habit learning, movements of the eyes, cognition, as well as emotion.
The nucleus accumbens is located in each of the brain’s hemispheres, i.e. between the caudate nucleus and the putamen.
Caudate nucleus refers to a cluster of neurons that directly contributes to decision-making, action selection, and initiation. It also plays a vital role in how the brain learns, especially when it comes to storing and processing memories.
By using information from past experiences, the caudate nucleus regulates and controls future actions and decisions. This is important for the development and use of language.
The putamen is a large structure in the outermost part of the brain that plans and aids the movement of the extremities. This group of nuclei is interconnected with the cerebral cortex, the thalamus, and the brainstem.
Structure of the Nucleus Accumbens
The nucleus caudate can be divided into two structures:
- The nucleus accumbens core,
- The nucleus accumbens shell.
The nucleus shell is also called the NAcc shell, and it represents the outer part of the nucleus accumbens. On the other hand, the nucleus accumbens core is also known as the NAcc core, which refers to the inner part of this brain structure.
These two structures have different inputs and outputs. However, they harmonize their functions in order to mobilize information so that they could guide behavior.
What Is the Function of the Nucleus Accumbens?
This small brain structure performs a variety of functions. The main function of the nucleus accumbens is to receive information from the cortex related to the reward and positive reinforcement processes of the brain, maternal behavior, aversive behavior, voluntary motor movements, procedural learning, emotions, cognitive processes, as well as sleep.
Furthermore, that information is transferred to the motor centers, which, in turn, send it to the parts of the cerebral cortex which are responsible for the control, planning, and regulation of the voluntary motor movements of our body.
The balance of all these functions of the nucleus accumbens results in a stable and balanced personality with rational actions. In cases where the nucleus accumbens is dysfunctional, it can lead to various addictions, as well as motivational salience.
Nucleus Accumbens and the Reward System
The nucleus accumbens is involved in the reward system of the human brain. Namely, when we do something that we consider a great pleasure (like eating ice cream, dancing, or traveling to exotic countries), the dopamine neurons in this ventral tegmental area of the brain are activated.
They project their axons to the nucleus accumbens and increase the dopamine levels in this structure of the brain when activated by a previously assumed reward for our actions. These actions are mainly based upon two neurotransmitters – dopamine and serotonin.
Because of this association between the levels of dopamine in the brain and the rewarding experiences, in cases of damaged or dysfunctional nucleus accumbens, all addictions become a real possibility.
Neurochemistry of the Nucleus Accumbens
The neurochemical operations performed by the nucleus accumbens are largely based upon neuromodulators, hormones, and two neurotransmitters: dopamine and serotonin.
The nucleus accumbens cluster of neurons is responsible for the addictive behavior of an individual, because all drugs increase the production of dopamine in the nucleus accumbens, while reducing the production of serotonin.
What Is the Difference Between Neuromodulators and Neurotransmitters?
Activity in the human brain is governed by a multitude of complex chemical processes. Neurotransmitters are chemical molecules in the central nervous system that relay the nerve impulse when nerve cells, or neurons, are stimulated; they undergo chemical changes that produce nerve impulses.
On the other hand, neuromodulators change the way in which both presynaptic and postsynaptic neurons interact with the neurotransmitters. This is the reason why the effect of the neuromodulators lasts longer than the effect of the neurotransmitters.
What Is Dopamine and How Does It Help the Nucleus Accumbens Perform Its Function?
The neurotransmitter dopamine is a chemical that supports the brain processes developed in the nucleus accumbens which control and regulate motivation, desire, and cravings.
It’s also in charge of our mood, the regulation of the control and reward systems in the brain, as well as movement and muscle contraction.
Dopamine influences the following functions of the body:
- mood;
- sleep cycles;
- cognitive processes;
- movement of muscles;
- alertness and concentration;
- blood flow.
High levels of dopamine in the blood can result in:
- euphoric feelings;
- increased concentration and motivation;
- irregular heartbeats;
- nausea;
- vomiting;
- anxiety;
- headache;
- chills;
- goosebumps;
- shortness of breath.
What Is Serotonin and How Does It Help the Nucleus Accumbens Perform Its Function?
Serotonin is a neurotransmitter hormone that is responsible for the transmission of information among the neurons of the brain. It supports the cognitive processes, as well as the formation of memory.
The levels of serotonin also influence the following functions of the body:
- hormonal activity;
- concentration;
- body temperature;
- appetite;
- the sleep-wake cycle;
- mood and emotions;
- metabolism and appetite.
If the levels are higher than normal, they can result in:
- agitation or restlessness;
- confusion;
- rapid heart rate and high blood pressure;
- dilated pupils;
- loss of muscle coordination or twitching muscles;
- muscle rigidity;
- heavy sweating;
- diarrhea.
What Is Phenethylamine and How Does It Help the Nucleus Accumbens Perform Its Function?
Phenethylamine is an organic compound that works as a stimulant for the central nervous system. It’s a hormone-like substance that functions as a neurotransmitter.
The levels of phenethylamine also influence attention, goal-directed behavior, and they can improve depression and task-completion and heighten focus.
A large quantity of accumulated phenethylamine can result in side effects similar to the drug amphetamine, such as:
- rapid heart rate;
- anxiety;
- agitation.
Phenethylamine can be substituted by:
- hormones;
- monoamine neurotransmitters;
- dopamine;
- norepinephrine;
- adrenaline;
- tyramine.
What Is Tyramine and How Does It Help the Nucleus Accumbens Perform Its Function?
Tyramine is a type of so-called false neurotransmitter (a chemical molecule that imitates the action of neurotransmitters in the central nervous system).
This false neurotransmitter is an amino acid that supports healthy blood pressure, and it can be naturally found in some types of food, like:
- aged chicken liver;
- beer;
- meats that have been fermented or air-dried, such as summer sausage;
- red wine;
- sauerkraut;
- soy sauce;
- sauces containing fish or shrimp;
- strong or aged cheeses, such as aged cheddar, Swiss, and Parmesan;
- blue cheeses, such as Stilton, Gorgonzola, and Camembert;
- summer sausages;
- pepperoni and salami.
A large quantity of accumulated tyramine can result in:
- migraine;
- life-threatening blood pressure;
- nausea and vomiting;
- sweating and severe anxiety;
- nosebleeds;
- fast heartbeat.
- chest pain;
- changes in vision;
- shortness of breath.
What Are Glucocorticoids and How Do They Help the Nucleus Accumbens Perform Its Function?
Glucocorticoids are cortico-steroid hormones that aid reduction of inflammation, like prednisone, dexamethasone, and hydrocortisone.
They are produced by the adrenal gland, but if their levels are too high, that can lead to the following side effects:
- increase of blood pressure;
- increase of triglycerides;
- increase of cholesterol;
- increase in glucose levels;
- water retention (swelling in the feet, ankles, lower legs, or hands);
- increased appetite and weight gain;
- unwanted hair growth;
- headache;
- dizziness;
- mood changes
- osteoporosis.
What Are GABA Receptors and How Do They Help the Nucleus Accumbens Perform Its Function?
GABA receptors are chemical messengers found in the brain structures, more specifically on the Schwann cells. Their function is to reduce the activity of the neuron they bind to by slightly changing their shape. In this way, they allow the ions to pass through their channels.
This type of chemical messengers is also responsible for maintaining the proper functions of the brain.
The following drugs bind to the GABA receptors:
- Alcohols (e.g., ethanol, isopropanol);
- Avermectins (e.g., ivermectin);
- Barbiturates (e.g., phenobarbital);
- Benzodiazepines (e.g., diazepam, alprazolam);
- Bromides (e.g., potassium bromide);
- Carbamates (e.g., meprobamate, carisoprodol);
- Kavalactones;
- Loreclezole;
- Neuroactive steroids (e.g., allopregnanolone, ganaxolone);
- Nonbenzodiazepines (e.g., zaleplon, zolpidem, zopiclone, eszopiclone).
What Is Glutamate and How Does It Help the Nucleus Accumbens Perform Its Function?
The neurotransmitter glutamate is found in both the brain and the spinal cord. This powerful neurotransmitter supports the transmission of signals between the two neuron cells.
It also plays a vital function in the early development of the brain, the cognitive processes (especially learning), perception, as well as memory.
When the concentration of glutamate is too small, it can lead to coma, psychosis, or even death. On the other hand, an extremely high concentration of this neurotransmitter can cause seizures and brain cell death.
Fun Facts
Did you know?
- Physical exercises give the biggest dopamine release.
- Chocolate can really give us happiness – it contains dopamine and serotonin, but also a small dose of tyramine.
- Anhedonia is a state of joylessness, which occurs as a result of a dysfunctional nucleus accumbens.
- Dopamine is called the ‘hormone of happiness’, because it’s responsible for our experience of happiness. It is produced in several areas of the brain, including the substantia nigra and the ventral tegmental area, during a pleasurable experience. It is also responsible for our mental and emotional responses, as well as the motor reactions of our bodies.
- Unlike animals that walk on all four legs, humans walk on two legs thanks to the functions regulated in the basal ganglia.
- The putamen regulates our automated learning, which we use in activities such as riding a bike, driving a car, as well as all other repetitive actions which do not require upper-level thinking.
- Motivational salience is a cognitive process processed in the nucleus accumbens shell, and refers to a reward motivation triggered by a previously learned association.
- Tyramine can be found in chocolate, red wine, ripe fruits, bananas, raisins, citrus fruits, and cheese.
- Glucocorticosteroids increase the levels of sugar (glucose) in blood.