The substania nigra is an area of pigmented cells in the midbrain which is responsible for producing the neurotransmitter dopamine. This section of the brain plays an important role in the control of movement, and it also appears to interact in the process of addiction, as well. If you view a brain in cross-section, the substantia nigra is located in the midbrain, right at the tip of the brainstem.
In Latin, substantia nigra literally means “black substance,” emphasizing the distinctive coloration of the cells in this part of the brain. You may also hear the substantia negra referred to as the locus niger. In addition to being considered part of the midbrain, this region is also part of the basal ganglia, a complex network which controls movement, learning, emotion, and several other important bodily functions.
Because the substantia nigra is so critical to movement, having a healthy one is important. If lesions appear on this region of the brain, people can experience movement disorders. Parkinson's, for example, is linked with lesions and decreased activity in the substantia nigra. Depending on how severe the damage is, patients may simply have difficulties with coordination, or they may experience severe tremors and other movement problems.
Dopamine plays an important role in the motivation and reward cycle for the brain, which means that it can play directly into addiction. When your brain learns that a behavior will be rewarded, it will encourage you to engage in that behavior as often as possible, with dopamine receptors becoming more active whenever you engage in that behavior. Dopamine is also involved in mood and sleep regulation.
When the substantia nigra is damaged, supplementary dopamine may be offered to the patient to make up for the shortfall in production. Because dopamine is incapable of crossing the blood-brain barrier, usually a precursor to dopamine is given, with the body converting the substance into dopamine over time.
This section of the brain is only one small aspect of a very large and complex organ, and it is entirely possible that additional functions of the substantia nigra may be uncovered over time, as researchers learn more about the brain. This area also doesn't work in a vacuum; it is affected by the health and activities of other areas of the brain which can disrupt or deregulate its function.