It has become popular in recent years to describe mental disorder as a chemical imbalance in the brain, a neural jumble that needs sorting out. The idea that anxiety, depression and OCD (of the catatonic, crippling, world shattering forms) can be attributed to a simple failure in the body's homeostasis is, for many, comforting and affirming. It is seductive, too, in its reductionism - mental disorder is always messy; thinking about it as a neural mishap helps us to reclaim some power over it - 'my disorder is not me, it is a misfiring in my brain.'
It was Hippocrates, a physician and contemporary of Socrates, who first thought that our bodies being a bit out of whack could have serious consequences for our health. He hypothesised that all illnesses were the result of an imbalance of the four elements or 'humours' that make up a human being: blood, phlegm, yellow bile and black bile. Too much blood, and you were prone to rousing angrily; too little blood, and you were likely to succumb to cowardice.
And this line of thought was maintained for the next couple of thousand years, with medical practice continuing to be informed by it until well in to the 19th century. Our modern approach to medicine is based off a much more complex model, but relics of the Hippocrates' hypothesis can still be seen today in our discourse about mental disorder. (The idea of chemical imbalance is also used in pseudoscience and homeopathy.)
And whilst it is worth acknowledging the usefulness of reducing something as complex as mental disorder, we must be careful that we don't leave out something essential in the process.
It is useful for me to know that the feelings I get around my partner are because of chemicals like dopamine and oxytocin circulating my brain, but taking this view does not help me identify how it feels to be in love. It removes me from the picture; and the same happens when my depression is described as a lack of serotonin in my brain - I become a passive observer of a process that might as well not be happening to me, because I don't feel like a serotonin deficiency; I feel like me, in a world that has become slow and grey.
The reason why the comparison fails is for the same reason that figuring out the problem of consciousness is so tricky; our subjective experiences are always tied to a particular point of view. We don't have experiences along side our mental disorder; our experience is our mental disorder - it filters our perception of the world.
Thinking of our mental disorder as a chemical imbalance makes it somehow not us. In the same way that somebody who has diabetes must endure the consequences of a faulty pancreas, somebody who has depression must endure the consequences of a faulty brain. This makes sense - the brain is the epicentre of our thoughts and feelings; but thinking in this way results in a short sighted view of what it is really like to be depressed.
Mental disorder doesn't just affect one particular, medically identifiable, function of the body. And whilst it may reside in the brain, it doesn't only produce physical symptoms like those produced by other, physical illnesses. Mental disorder hijacks our whole sense of self: the speed at which time seems to pass; how far in to the future we can project ourselves; what things in the world we care about - mental disorder changes all of these in the most radical way. And it doesn't just affect the function of a particular body part, it changes the very conditions that make it possible for us to live a meaningful life.
The language that we use in our current discourse on mental disorder is, in many ways, fitting. We now have medicines that can effectively help thousands of people to manage and, in some cases, overcome their mental disorder. But in focusing our discourse on the chemical aspect of mental disorder we blinker ourselves from the real power of mental disorder - the power to change what it means to be human. That is something that can't be reduced.