Dopamine's Role in Mental Illness

Dopamine is a neurotransmitter (a chemical released by nerve cells) that plays an important and diverse role in how your brain functions. 

Dopamine neurons (nerve cells) have cell bodies in the midbrain with nerve fibers (called axons) that extend into a number of other sites in the brain. This allows for dopamine to be transmitted from one brain site to another, and these connections are called dopaminergic pathways. 

One dopaminergic pathway projects from an area of the midbrain called the substantia nigra to the basal ganglia, which coordinates movement in the body. When there is a loss of dopamine neurons in the substantia nigra, Parkinson's disease occurs—a neurological disease characterized by slowed movements, a rigid appearance, and a resting tremor.

Other sites of dopamine signaling include the prefrontal cortex, an area of the brain that is important for problem-solving, complex thinking, memory, intelligence, and language. Minor dopamine signaling pathways include the amygdala, which plays an important role in emotion processing, and the hippocampus, which is important for memory.

In addition to movement, emotion, memory, and thinking, dopamine neurons play a critical role in motivation and reward. This is why certain substances of abuse, especially cocaine and nicotine, are addictive—as these substances stimulate the dopamine-mediated reward system in the brain. 

Besides Parkinson's disease, a number of psychiatric illnesses have been linked to dopamine dysregulation like schizophrenia, attention deficit disorder (ADD), bipolar disorder, and depression.

The manner in which dopamine has affected these psychiatric illnesses is unique. For example, in ADD, impairment in the dopamine system causes poor attention. This is why stimulants, like Ritalin (methylphenidate) or Adderall (amphetamine), which increase dopamine levels in the brain, help improve attention and alertness.

On the other hand, in schizophrenia, the dopamine system is overactive. This is why medications that block dopamine receptors in the brain (called antipsychotics) are used in its treatment.

Some researchers believe that dopamine dysfunction may be involved in the development of borderline personality disorder (BPD). This mainly stems from studies that support dopamine's role in thinking, regulating emotions, and impulse control—all of which are impaired in people with BPD. Also, antipsychotic medications seem to reduce some BPD symptoms, especially those of anger and cognitive problems (like paranoid thinking).

That being said, other experts argue that the manner in which antipsychotics benefit patients with BPD is through non-dopamine pathways. Overall, it's hard to say at this time how critical dopamine is in the development or course of BPD. More research will be helpful in elucidating this connection. 

The dopamine system is an intricate, fascinating system that participates in a number of different neurological and mental functions. By further examining dopamine's role in the brain, scientists will hopefully gain the information they need to develop more targeted dopamine medications—so people with dopamine-mediated illnesses, like schizophrenia, can get well and avoid undesirable side effects.