Here are definitions of medical terms related to depression
Aerobic exercise: Physical activity that requires extra effort of the heart and lungs to meet the body's increased demand for oxygen; examples include running, swimming, cycling, and vigorous dancing.
Biochemistry: The chemistry of living organisms and life processes.
Bipolar disorder: Also known as manic depression, this disorder involves mood swings that soar to mania, or unusual elation, and then plummet to depression.
Dysthymia: A chronic (ongoing), low-grade depression that often begins in childhood or adolescence and may last for many years in adulthood if not treated.
Neurotransmitters: Chemical messengers that carry messages or signals between the various nerves in the brain; the neurotransmitters serotonin, dopamine, and norepinephrine are believed to be the chemical messengers responsible for moods and emotions.
Retina: A 10-layered tissue membrane of the eye that transmits visual impulses through the optic nerve to the brain.
Seasonal affective disorder (SAD): A form of depression thought to be triggered by a decrease in exposure to sunlight.