Depression is seen as both a genetic and learned (or environmental) condition. At times, depression is due to a lack of neurotransmitters released between the synapses of brain cells. At other times, depression can be due to environmental conditions, such as broken relationships, financial stress, and abuse.
Midstream approaches are those that are used with populations that are at risk, or are likely to be at risk, of depression. The midstream approach has a focus on lifestyle and behavior of an individual. It includes both health promotion and prevention using a behaviourist approach. It would not include the prescription of drugs.
Behaviourists believe that people learn through classical and operant conditioning. Classical conditioning occurs when two stimuli occur together. Over time, people learn to associate the two stimuli. Operant conditioning is when people learn behaviors due to consequences that follow such behaviors (negative consequences would deter the behavior, while positive consequences would reinforce the behavior).
Applying a behaviorist approach to depression entails cognitive behavior therapy (CBT). CBT is both educational and goal oriented. During CBT, a person learns to realize when he/she is thinking negatively. The person then reflects on the validity of the thought. If the thought is deemed invalid, the person learns how to replace the thought with healthier ways of thinking.
Mainstream approaches also promote lifestyle changes. Lifestyle changes that can be used to prevent depression would be increased sleep, relaxation and breathing exercises (such as yoga), increasing exercise (which is proven to increase endorphins- a neurotransmitter that increases the sensation of happiness and well-being), eating a healthy diet, surrounding yourself with positive people, finding a hobby that one enjoys, and finding a strong support system.