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The nucleus accumbens(NAcc) is a region in the brain’s basal forebrain that plays a critical role in the reward circuit. It is involved inpleasure, reinforcement learning, and the processing of motivation and reward. Dysregulation of this area is often implicated in addiction, depression, and other psychiatric disorders.
Functions
Primary Function:The Reward Circuit
The nucleus accumbens (NAcc) is a component of themesolimbic dopamine pathway, which is stimulated during rewarding experiences.
When someone does something rewarding, such as eating a favorite food or engaging in an enjoyable activity, dopamine neurons in theventral tegmental area(VTA) are activated.
These VTA neurons project to the NAcc, resulting in increased dopamine levels. This activation tells us to repeat the rewarding experience.
However,research has shown thatdopamine levels in the NAcc increase in response to both rewarding and aversive stimuli, making its role more complex than simply processing rewards.
Additional Functions
The NAcc is involved inlearning about rewardsand the stimuli associated with them. It helps stimulate reward-seeking behaviors while suppressing actions that are less likely to obtain rewards.
Through its connection to the amygdala, itattributes feelingstowards rewarding or aversive experiences.
Its connection to thehippocampushelpsattribute memoriesand learning to these experiences.
Studies have shown the NAcc has greater activation for rewarding stimuli when they are unpredictable. The structure also plays crucial roles in:
Due to input from the limbic system and output similarity to the motor nuclei of the basal ganglia, the NAcc functions as an interface between the limbic and motor systems.
Location
The NAcc is situated in the basal forebrain, withone nucleus in each cerebral hemisphere.
It sits at the intersection of thecaudate(a neural region involved in learning and memory) andputamen(an area that regulates movement and motor learning), functioning as a specialized part of the striatal complex.
The nucleus accumbens is located in the basal forebrain, near the front of the brain. It is part of the ventral striatum and is situated close to the prefrontal cortex and the dopaminergic pathways.
Each region serves different but complementary functions. The shell maintains stronger connections tothe limbic system,processing emotional and motivational information, while the core connects more strongly to the motor system,influencing physical responses to stimuli.
This specialized architecture allows the NAcc to act as a crucial interface between emotional processing and motor control.
These neurons are particularly responsive todopamine, aneurotransmittercentral tomotivation, reward, and motor control.
The NAcc’s position and connections make it a key modulator of information flow between theamygdala, basal ganglia, and prefrontal cortex, allowing it to integrate emotional, motivational, and executive functions.
Conditions associated with the nucleus accumbens
Substance use disorders
Typically, with repeated exposure to a reward, the rewarding feeling will wane. However, with drugs of abuse, the functioning of the reward system can become overwhelming sincethe effects of these drugs do not wane after repeated exposure.
This can be one of the reasons why people develop substance use disorders. Drugs of abuse tend toincrease dopamine in the NAccor change synaptic plasticity, whereas non-abused drugs generally do not affect dopamine in the NAcc or synaptic plasticity.
The mesolimbic dopamine pathway can become hypofunctional in the addicted brain, resulting in decreased interest in non-drug-related stimuli and increased dependence on the drug to experience rewarding feelings.
Mood disorders
As the NAcc is involved with cognitive and emotional functions, it may be involved in psychiatric conditions such asmood disorders.People with mood disorders have been found to have reduced NAcc activation(Heller et al., 2009).
People with mood disorders were also found to have reduced NAcc volume in comparison to those without mood disorders (Baumann et al., 1999). A study used deep brain stimulation (a therapy for severe depression that proves resistant to other treatment methods) on the NAcc of those with depression.
They found that after 12 months,50% of the people had significant reductions in their depressive symptoms(Bewernick et al., 2010). This implies that the NAcc may play a role in symptoms of depression.
Anxiety disorders
Due to connections to emotional regions of the brain,specifically the amygdala, the NAcc may be linked toanxiety conditions, which are also thought to be related to emotional regions.
Deep brain stimulation has been applied to the NAcc of people with obsessive-compulsive disorder (OCD), an anxiety disorder,resulting in significant improvements in their symptoms and quality of life(Denys et al., 2010).
This further implies that anxiety disorders may be related to dysfunctions of the NAcc.
Parkinson’s Disease
Apathy, which is associated with a lack of interest and loss of initiative, is a complication of Parkinson’s Disease.
It has been found that these symptoms were associated with atrophy of the left NAcc in people with this disease (Carriere et al., 2014), suggesting that the NAcc may have some involvement with this condition.
Alzheimer’s Disease
The NAcc is believed to be a brain region that isassociated with cognitive impairments in people with Alzheimer’s Disease. Alterations of dopaminergic systems are frequently reported in those with Alzheimer’s, and these alterations are commonly linked with cognitive and non-cognitive symptoms.
It has been suggested that the VTA dopaminergic neuron degeneration results in lower dopamine outflow in the NAcc shell and hippocampus. This is said to be linked to impaired memory performance and dysfunctions of reward processing (Nobili et al., 2017).
Tourette Syndrome
The NAcc may also play a role in Tourette Syndrome. A study found that deep brain stimulation treatment has proved to be beneficial forreducing some of the syndrome’s motor manifestations,including alleviating tics and compulsions with the person’s self-injurious behavior (Zabek et al., 2008).
Chronic pain
It has been suggested that those with chronic pain mayhave smaller NAcc volumes compared to those without chronic pain.
It has been suggested that the smaller NAcc may play a part in the risk of developing chronic pain (Makary et al., 2020).
References
Berns, G. S., McClure, S. M., Pagnoni, G., & Montague, P. R. (2001). Predictability modulates human brain response to reward. Journal of neuroscience, 21(8), 2793-2798.
Bewernick, B. H., Hurlemann, R., Matusch, A., Kayser, S., Grubert, C., Hadrysiewicz, B., Axmacher, N., Lemke, M., Cooper-Mahkorn, D., Cohen, M. X., Brockmann, H., Lenartz, D., Sturm, V. & Schlaepfer, T. E. (2010). Nucleus accumbens deep brain stimulation decreases ratings of depression and anxiety in treatment-resistant depression. Biological psychiatry, 67(2), 110-116.
Denys, D., Mantione, M., Figee, M., Van Den Munckhof, P., Koerselman, F., Westenberg, H., Bosch, A. & Schuurman, R. (2010). Deep brain stimulation of the nucleus accumbens for treatment-refractory obsessive-compulsive disorder. Archives of general psychiatry, 67(10), 1061-1068.
Heller, A. S., Johnstone, T., Shackman, A. J., Light, S. N., Peterson, M. J., Kolden, G. G., Kalin, N. H. & Davidson, R. J. (2009). Reduced capacity to sustain positive emotion in major depression reflects diminished maintenance of fronto-striatal brain activation. Proceedings of the National Academy of Sciences, 106(52), 22445-22450.
Knutson, B., Adams, C. M., Fong, G. W., & Hommer, D. (2001). Anticipation of increasing monetary reward selectively recruits nucleus accumbens. Journal of Neuroscience, 21(16), RC159-RC159.
Makary, M. M., Polosecki, P., Cecchi, G. A., DeAraujo, I. E., Barron, D. S., Constable, T. R., Whang, P. G., Thomas, D. A., Mowafi, H., Small, D. M. & Geha, P. (2020). Loss of nucleus accumbens low-frequency fluctuations is a signature of chronic pain. Proceedings of the National Academy of Sciences, 117(18), 10015-10023.
Mavridis, I. (2015). The role of the nucleus accumbens in psychiatric disorders. Psychiatrike= Psychiatriki, 25(4), 282-294.
Mogenson, G. J., Jones, D. L., & Yim, C. Y. (1980). From motivation to action: functional interface between the limbic system and the motor system. Progress in neurobiology, 14(2-3), 69-97.
Neuroscientifically Challenged. (2014, June 13). KNOW YOUR BRAIN: NUCLEUS ACCUMBENS.https://neuroscientificallychallenged.com/posts/know-your-brain-nucleus-accumbens
Nobili, A., Latagliata, E. C., Viscomi, M. T., Cavallucci, V., Cutuli, D., Giacovazzo, G., Krashia, P., Romana Rizzo, F., Marino, R., Federici, M., De Bartolo, P., Aversa, D., Concetta Dell’Acqua, M., Cordella, A., Sancandi, M., Keller, F., Petrosini, L., Puglisi-Allegra, S., Biagio Mercuri, N., Coccurello, R., Berretta, N. & D’Amelio, M. (2017). Dopamine neuronal loss contributes to memory and reward dysfunction in a model of Alzheimer’s disease. Nature communications, 8(1), 1-14.
Salgado, S., & Kaplitt, M. G. (2015). The nucleus accumbens: a comprehensive review. Stereotactic and functional neurosurgery, 93(2), 75-93.
Volman, S. F., Lammel, S., Margolis, E. B., Kim, Y., Richard, J. M., Roitman, M. F., & Lobo, M. K. (2013). New insights into the specificity and plasticity of reward and aversion encoding in the mesolimbic system.Journal of Neuroscience,33(45), 17569-17576. https://doi.org/10.1523/JNEUROSCI.3250-13.2013
Wise, R. A. (1982). Neuroleptics and operant behavior: the anhedonia hypothesis. Behavioral and brain sciences, 5(1), 39-53.
Zabek, M., Sobstyl, M., Koziara, H., & Dzierzecki, S. (2008). Deep brain stimulation of the right nucleus accumbens in a patient with Tourette syndrome. Case report. Neurologia i neurochirurgia polska, 42(6), 554-559.
Saul McLeod, PhD
BSc (Hons) Psychology, MRes, PhD, University of Manchester
Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.
Olivia Guy-Evans, MSc
BSc (Hons) Psychology, MSc Psychology of Education
Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.
