If you have you ever been addicted to a behavior, such as shopping or gambling, you've lacked focus or motivation to complete a task, or you've suffered from depression, brain chemicals may be the cause. At the center of these complex behaviors are two powerful neurotransmitters, dopamine and serotonin. These naturally occurring chemicals in your brain help your body move fluidly, your mind stay calm and focused on a task, and help you to resist depression and other mood disorders. Their levels are affected by your lifestyle, and understanding how they work may help you improve your mood, concentration and health.
Your body requires dopamine for normal movement such as walking and balance. Low levels of dopamine, as seen in people with Parkinson disease, cause a lack of fluid movements. People become stiff and "frozen" in their bodies. Levodopa is a medication used to increase dopamine levels and restore normal movement in people with Parkinson disease. The dose is difficult to adjust, and too much dopamine can cause uncontrolled movements such as tremors and jerking.
Unlike dopamine, the role of serotonin in movement is not as clear. Serotonin is needed for normal movement and may manage the effects of other neurotransmitters.
Dopamine may have a role in addiction and impulse control. Some people with Parkinson disease treated with dopamine replacement therapy develop addictive behaviors, which may include compulsive gambling and shopping, aimless repetitive behaviors and hypersexuality. Dopamine is implicated in other impulse control disorders, such as attention deficit hyperactivity disorder. But the relationship between dopamine and impulse control is complex, and it is not clear why dopamine-increasing medications improve symptoms for some people with ADHD, yet worsen them for others.
In contrast, decreased serotonin is linked to drug abuse. Serotonin may contribute to the altered state seen after cocaine use and increase cocaine craving. Some of serotonin's effects may be due to its influence on other neurotransmitters.
Dopamine is important for attention, motivation and goal-directed behavior -- it acts to reinforce behaviors that make you feel good. Cocaine and amphetamines, for example, increase dopamine and may make these drugs more addictive. In contrast, serotonin is important for calmness and emotional well-being.
While imbalances in serotonin and dopamine are linked to depression and anxiety disorders, lower serotonin is linked to greater impulsivity and an increased risk of suicide. Enhancing serotonin may reduce impulsiveness and serotonin replacement therapies are widely used to reduce suicide risk.
As with the dopamine studies, there are inconsistencies among studies with reports of serotonin replacement therapies increasing the risk of suicide in adolescents. MDMA (ecstasy), which increases both serotonin and dopamine and causes mood elevation, likely causes its effects through a large release of serotonin.
Regular physical activity is important for normal brain function and mental health. Sustained exercise increases the level of serotonin in your brain and serotonin may play a key role in preserving brain function. As you age, the amount of serotonin in your brain decreases, which this is linked to an increase in depression.
Exercise can increase brain serotonin, even for older adults, suggesting that regular exercise may act as a natural antidepressant and anti-aging strategy for the brain. While exercise relieves some symptoms in people with ADHD or early Parkinson disease, larger studies are needed to confirm the link between exercise and dopamine release in the brain.
Bright light, which is used to treat seasonal depression, may increase serotonin levels, and it has been suggested that as people spend more time indoors, serotonin levels may lower while depression increases. Bright light also regulates circadian rhythms -- the internal clock -- and some studies suggest dopamine is necessary for this. Low dopamine is often associated with sleep disorders and problems with staying awake.
A number of studies have also looked at the effect of diet additives on serotonin and dopamine levels but the data remain inconclusive. Your doctor can provide the best guidance regarding maintaining a healthy balance of your neurotransmitter levels.
- National Parkinson Foundation: Parkinson’s Disease
- Pharmacological Reviews: The Pharmacology of L-Dopa-Induced Dyskinesia in Parkinson’s Disease
- Journal of Neuroscience: Serotonin 1A Receptors Alter Expression of Movement Representations
- Parkinsonism & Related Disorders: Association Between the Dose of Dopaminergic Medication and the Behavioral Disturbances in Parkinson’s Disease
- The Journal of Neuroscience: Dopamine, Time, and Impulsivity in Humans
- Neuroscience: Dopamine, Serotonin and Impulsivity
- Neuropharmacology: Serotonin at the Nexus of Impulsivity and Cue Reactivity in Cocaine Addiction
- Trends in Pharmacological Sciences: Mechanisms of Dopamine Transporter Regulation in Normal and Disease States
- Cochrane Database of Systemic Reviews: Newer Generation Antidepressants for Depressive Disorders in Children and Adolescents
- National Institute on Drug Abuse: Drug Facts: MDMA (Ecstasy)