The nucleus accumbens is a relatively small portion of the brain. It provides a connection between the putamen and the caudate nucleus. Its main function is to regulate the reward system.
What is nucleus accumbens?
The nucleus accumbens is classified as part of the mesolimbic system. The mesolimbic system is the reward system for positive stimuli. In it, positive emotions are localized and identified by external stimuli. Appropriate responses to the stimuli are planned and executed in this brain region. The triggering stimuli can be based on experienced events, but can also be triggered by the ingestion of substances. For this reason, the nucleus accumbens is considered the region that plays an essential role in the development of addiction. The nucleus accumbens is a part of the putamen. The putamen provides an important function in the control of voluntary motor activity. Together with the caudate nucleus, the plutamen forms the striatum. The striatum belongs to the basal ganglia. These take over part of the motor, cognitive and limbic functions. The nucleus accumbens is a section of this region that cause a conversion of motivational intent into action. The perceived emotion is transformed into a so-called locomotion by the influence of the nucleus accumbens. Thus, the nucleus accumbens is the instance that represents the transition from the motivational system to the activation system.
Anatomy and structure
The nucleus accumbens is considered the inner core area of the telencephalon. This is the cerebrum. The nucleus accumbens is included in the corpus striatum. It is a nucleus in the basal ganglia in which a group of endbrain and diencephalic nuclei are located. The nucleus accumbens forms a small region in the ventrorostral area of the striatum. The striatum is a switch point in the extrapyramidal motor system. The nucleus accumbens is the area where the caudate nucleus and plutamen merge. Its fiber connections resemble those of the rest of the striatum. In the limbic system area, it is characterized by a particularly afferent fiber structure. For this reason, this part of the basal ganglia is a special relay site for the implementation of motivation and emotion. Thus, the nucleus accumbens is a link between the basal ganglia and the limbic or psychomotor system. The nucleus accumbens contains D2-type dopamine receptors. These receptors receive signals from the neurotransmitter dopamine. This has an excitatory effect.
Function and tasks
The nucleus accumbens performs an important function in social behavior. Functionally, the nucleus accumbens represents a switching point between the emotional and locomotor systems. This means that perceived emotions produce actions that are regulated by the nucleus accumbens. The dopamine receptors present in the nucleus accumbens trigger positive emotions. These include feelings of happiness, the experience of success, or euphoria. Substances such as opiates or amphetamines also act on the receptors and trigger the same positive emotions. Synaptic transmission therefore works for experienced emotions as well as for artificially induced emotions. The nucleus accumbens represents the reward center. Thus, it plays an important role in classical conditioning. This involves learning simple stimulus-response patterns. For example, conditioning causes salivation at the sight of food. The nucleus accumbens is the region in the brain where the development of addiction is located. This can be addiction to substances such as cocaine, amphetamines or opiates. However, addiction to milder substances such as tobacco or nasal spray also originates in the nucleus accumbens. Efferents from the nucleus accumbens travel to the limbic system and the hypothalamus. The incoming information is processed cognitively-psychologically in this brain region. The processing process causes the vegetative response of happiness.
Diseases
Lesions and damage to the nucleus accumbens have direct effects on the sensation of positive feelings as a result of reward. Impairments can occur in brain hemorrhage, due to inflammation, or after accidents. Likewise, damage to the nucleus accumbens is possible after surgical procedures or in tumor diseases. In the case of lesions of the nucleus accumbens, the release of so-called feelings of happiness can no longer be regulated by feedback mechanisms.The D2-type dopamine receptor mediates positive and negative symptoms of schizophrenia. Thus, all disorders due to schizophrenia are influenced via the nucleus accumbens. Dysfunction of the nucleus accumbens can negatively affect the functionality of the reward system. Thus, dysfunction can have an important influence in disorders such as depression. The disorder may be exacerbated or depressive episodes may be triggered. Bipolar affective disorder is characterized by a disturbed experience of emotions. Sufferers suffer from an interplay of positive and negative feelings. The nucleus accumbens plays a decisive role in this. Its influence can weaken or intensify the experience of emotions. If the functional activity of the nucleus accumbens is impaired, this can make it impossible to learn classical conditioning. Thus, stimulus-response is impaired. Many anxiety disorders are stored in the brain through classical conditioning. Damage to the nucleus accumbens can cause an already learned fear experience to be minimized. In this case, the fear conditioning must have occurred before the lesion of the nucleus accumbens. An addictive disorder is significantly influenced by the activity of the nucleus accumbens. This is a chronic disease in which a permanent increase in dopamine levels causes insensitivity to the substance in question. Discontinuation of the substance leads to severe withdrawal symptoms.
