Depression has been linked to problems or imbalances in the brain, specifically with regard to the neurotransmitters serotonin, norepinephrine, and dopamine. The evidence is somewhat indirect on these points because it is very difficult to actually measure the level of neurotransmitter in a person’s brain. What we do know is that antidepressant medications (used to treat the symptoms of depression) are known to act upon these particular neurotransmitters and their receptors.