– Neurotransmitter Imbalances
Neurotransmitter imbalance in the brain is one of the depression causes widely accepted by those in the psychiatry field.
Importance of neurotransmitters
Neurotransmitters are actually chemicals in our bodies that serve to transmit signals from one nerve cell to another (across synapses). When neurotransmitters in our body are in good balance and function normally, there is effective communication between the brain and the central nervous system, the immune system, the endocrine system and the rest of the body.
Through their direct or indirect effect on the various cells, tissues and organs in the body, neurotransmitters bring about our emotions, thoughts, memories, moods, behaviors, sleep and learning abilities. 
So when our neurotransmitters are in imbalance, it is no surprise that we suffer from a depressed mood that can be hard to uplift even with a happy event.
The mentioned of neurotransmitter imbalance in depression causes usually brings to mind the relatively well-known monoamine hypothesis.
In fact, some proponents of the monoamine hypothesis go as far as to suggest that the different monoamine deficiencies bring about specific corresponding features of depression. 
For example serotonin deficiency brings about anxiety, obsessions, and compulsions; dopamine deficiency brings about a lack in attention, motivation, pleasure, and reward, as well as interest in life; and norepinephrine deficiency brings about shortage in alertness, attention, interest in life and energy, as well as brings about anxiety. 
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