Many of us are guided by a firm belief in mind-body dualism, a philosophy that Wikipedia defines thus: the assumption that mental phenomena (thinking and feeling, for example) are non-physical, or that the mind and the body are distinct. Research in the neurosciences over the last half-a-century has finally debunked this philosophy for good: what we refer to as "mind" is very much a product of brain function. Thinking and feeling are not merely psychological; they are also neurochemical. The brain chemicals that underlie these mental phenomena are called neurotransmitters.
What are neurotransmitters? Neurotransmitters are vital chemicals in our body that communicate information throughout our brain and body. They relay signals between nerve cells (called neurons) and are important for a large array of physical functions. The brain uses neurotransmitters to tell our heart to beat, our lungs to breathe, and our stomach and intestines to digest. Without neurotransmitters, there would be no communication between neurons. The heart wouldn't get a signal to beat, our arms and legs wouldn't know to move and so on.
Not only are neurotransmitters important for our physical health but they also play a significant role in our mental health, affecting our thoughts, mood, sleep, memory and concentration. When they are out of balance (or when receptors on cells responsible for receiving neurotransmitter signals are impaired) they have a significant impact on our mood and behavior.
Neuroscience research has identified over fifty neurotransmitters in the brain. Research has also revealed that several neurotransmitters are related to mental health problems - dopamine, serotonin, norepinephrine and GABA are the most significant of these. Too much or too little of these neurotransmitters are now accepted to play a major role in psychiatric conditions such as
schizophrenia, depression, bipolar disorder, obsessive-compulsive disorder and ADHD among many others.
Unfortunately, there are no simple lab tests for neurotransmitters, at least ones that are inexpensive enough for routine psychiatric practice. There are advanced imaging techniques such as Positron Emission Tomography (PET) that are being utilized in research and in the development of medications that directly influence changes in specific neurotransmitters, but these are still a decade or two away from being applied for diagnosis of psychiatric illnesses. Psychiatrists evaluate neurotransmitter levels by looking for indicators in thought, behavior, mood, perception and speech that are known to be related to levels of certain neurotransmitters.
The technical aspects of neurotransmitter levels, the psychiatric symptoms they produce and the medications have been developed to raise or lower the brain levels of these neurotransmitters is complex. For this reason, the same procedure of explaining other medical conditions where medication brings symptoms back to the "normal range" is often used. Medical patients with high blood pressure, high blood sugar or high cholesterol are informed that their body chemistry is too high, or in some cases, too low and must be corrected with medication.
For many years, mental health professionals have used the term neurochemical imbalance to explain the need for medications that are used to treat mental health conditions. This simple and commonly used explanation recognizes that the condition is a medical problem and that it can be treated with medication. The "chemical imbalance" explanation also reflects the overall focus of treatment – identifying what neurotransmitters are involved in the clinical symptom picture and, with medication, attempting to return that neurotransmitter level back to the "normal range".