What is the function of the nucleus accumbens (NAc)?

From the Guidelines

The nucleus accumbens plays a crucial role in the development of opioid addiction by triggering the release of dopamine in response to the pleasurable effects of opioids, leading to a learned association between the drug and the experience of pleasure. This process is referred to as conditioning, and it can result in the desire for the drug's effects and the strong motivation to seek them 1. The nucleus accumbens is a key brain structure located in the basal forebrain that processes information related to pleasure, motivation, and reinforcement learning. It receives dopaminergic input from the ventral tegmental area and glutamatergic signals from regions like the prefrontal cortex, amygdala, and hippocampus.

The development of addiction to opioids involves several neurobiological processes, including learning mechanisms that consolidate automatic behaviors in response to the drug and stimuli associated with it. The pleasurable effects of opioids are triggered by release of dopamine in the nucleus accumbens, a key reward region 1. This in turn results in a learned association between the drug administration and the experience of pleasure. Repeated exposures to opioid medications will strengthen these learned associations and, with time and repetition, can result in the desire for the drug's effects and the strong motivation to seek them.

Some key points to consider about the nucleus accumbens and opioid addiction include:

• The nucleus accumbens is involved in the brain's reward system and plays a central role in the development of opioid addiction
• The release of dopamine in the nucleus accumbens triggers the pleasurable effects of opioids, leading to a learned association between the drug and the experience of pleasure
• Repeated exposures to opioid medications can strengthen this learned association, leading to the desire for the drug's effects and the strong motivation to seek them
• Dysfunction of the nucleus accumbens is implicated in various conditions, including addiction, depression, and obsessive-compulsive disorder
• The nucleus accumbens represents an important target for treatments addressing addiction and certain psychiatric disorders 1.

From the Research

Nucleus Accumbens Structure and Function

• The nucleus accumbens is the most inferior part of the striatum and is mainly connected to the limbic system 2.
• It is neurochemically and immunohistochemically divided into a shell laterally and a core medially 2.
• The nucleus accumbens plays a modulative role in the flow of information from the amygdaloid complex to other regions, including the basal ganglia, mesolimbic dopaminergic regions, mediodorsal thalamus, and prefrontal cortex 2.

Role in Psychiatric Disorders

• The nucleus accumbens is involved in several cognitive, emotional, and psychomotor functions, altered in some psychopathology 2.
• It is involved in various psychiatric disorders, such as depression, schizophrenia, obsessive-compulsive disorder, anxiety disorders, addiction, bipolar disorder, attention deficit/hyperactivity disorder, and post-traumatic stress disorder 2, 3.
• Neuromodulation interventions targeting the nucleus accumbens have been applied in patients suffering from treatment-resistant depression, obsessive-compulsive disorder, Tourette syndrome, and addiction to drugs or alcohol 2, 3.

Neuroplasticity and Connections

• The nucleus accumbens has a unique role in the brain reward system due to its hierarchical connections with other brain areas, morphological and functional plasticity, and cooperation among several neurotransmitter systems 4.
• The nucleus accumbens and its corticolimbic connections to other brain regions are involved in reward and pain processes, with distinct functional circuitry between the shell and core in healthy patients 3.
• Glutamate homeostasis in the nucleus accumbens plays a crucial role in addiction-related behaviors, and alterations in glutamatergic transmission occur after withdrawal from chronic drug exposure 5.

Clinical Studies and Outcomes

• Neuromodulation studies have provided promising clinical results in the context of addiction and substance misuse, obsessive-compulsive disorder, and mood disorders 3.
• The most common complications of nucleus accumbens neuromodulation are impaired memory or concentration, and a notable serious complication is hypomania 3.
• Deep brain stimulation of the nucleus accumbens has been associated with antidepressant and anxiolytic effects, as well as quality of life improvement in patients suffering from severe resistant depression 2.