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The tremendous complexity of the human brain makes it difficult for psychologists to pin down exactly how and why things go wrong, so how do we define and diagnose disorders?

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Do you ever feel really bummed?

Okay, maybe that's a silly question because, like, everyone's gonna have a crappy day at some point. Right?

But how do you know if you're just feeling sad, or if you've crossed over into something like clinical depression? The answer to that depends on how researchers define psychological disorders, which isn't always the clearest thing— especially because these definitions have changed over time as our scientific understanding improves. One main approach to studying disorders is based on the medical model, which says that a mental disorder is like a physical illness: it has a specific cause, set of symptoms, and a best way to treat it.

So if a patient comes into a psychiatrist's office, for instance, the doctor is going to look at signs and symptoms to figure out a diagnosis and possible treatments. Signs are the objective, outward indications that something is wrong. Like if a patient has dry, red, and cracked skin on their hands, there's a chance that could be the result of excessive hand-washing— something patients with obsessive compulsive disorder might do.

On the other hand, symptoms are more subjective things that are reported by the patient, like if they say they're feeling sad or anxious. So professionals like psychologists and psychiatrists, plus policymakers, and health companies, and the legal system, need to be aware of all of the disorders that scientists know about. And for that, many turn to the Diagnostic and Statistical Manual of Mental Disorders, or DSM.

It's a resource that describes known disorders and how you'd diagnose them. And as of 2013, we're on the fifth revision of it, the DSM-5. It's really hard to standardize and measure mental health because it's so complex, but for the most part, all disorders have a couple major ingredients.

First, a patient has to have thoughts, feelings, or behaviors that are ongoing and unusual. Like, in the DSM-5, major depressive disorder is defined as experiencing things like sadness, fatigue, loss of appetite, and feelings of worthlessness—all for at least two weeks. Unusual can also mean things that don't necessarily fit into societal norms, which can vary depending on the culture you're a part of.

And then, this unusual ongoing thing needs to create distress or impairment. Basically, some people might be sad a lot of the time, and they're cool with that. They're still meeting their responsibilities, and have social lives that work for them.

But other people might feel like there's something really wrong—that's distress. And their symptoms can start messing with their ability to live their normal lives— that's impairment. That's why it's so important for people who are experiencing distress to seek help, because psychologists need to understand that you're having problems, and you want to fix them.

There are other cases where people might not be feeling distressed by symptoms, but that's part of the problem. Something like antisocial personality disorder, for example, may involve aggressive or violent behavior, so there's a chance you could be a risk to others. Or schizophrenia can cause false beliefs or sensations.

So psychologists would consider these to be disorders and try to help treat them. Looking at mental health with the medical model and the DSM has helped a lot of people, but there are some problems with it too. For one thing, the medical model presumes that there are clear boxes that signs and symptoms fall into— like a checklist that will lead to a surefire diagnosis.

Problem solved! But that's not reality. Multiple disorders might share the same causes.

Like, if you have a major depressive disorder, several surveys have found that the chance of having an anxiety disorder too is around 60%. Plus, there might be many different causes for the same disorder, which could be explained by the diathesis-stress model. The idea here is that some people might have more biological risk of developing a disorder, but they could live perfectly healthy lives if they don't experience psychological influences like stress that can trigger the symptoms.

A good example of this is post-traumatic stress disorder— the anxiety, fear, and panic that people might suffer after they have a traumatic experience, like abuse or exposure to war. One 2006 study found that war veterans who developed PTSD had a smaller hippocampus, a brain region that's associated with memories and emotion, than those who never developed the disorder. It's not like war shrank part of their brains, because the study looked at 130 pairs of veterans and their identical non-military twins.

And they also had similar-sized hippocampi. So, according to this research and similar studies, having a smaller hippocampus may be a risk factor for developing PTSD. Another big problem with these systems is that the DSM is written by humans, and humans make mistakes.

Every decade or two the American Psychiatric Association recruits dozens of psychiatrists, psychologists, neuroscientists and the like to review the best scientific evidence and decide what changes should be made to reflect our current understanding of mental illness. But that panel of experts doesn't always agree, so there's flaws and controversy. For example, the definition of major depressive disorder in the DSM-IV had an exception for people who were grieving the death of a loved one.

A patient wouldn't be diagnosed with depression, as long as their sadness and other symptoms went away eventually. But in the latest edition of the DSM, that exception is gone. Some people in the field don't agree with this decision, because losing a loved one is sad for anyone!

That's not your brain doing something wrong, or indicating a depressive disorder. It's kinda doing exactly what it should be. Others argue that death can be a stressor that can lead to depression, just like other factors.

And people who want to get treatment should be able to get support for it. The boxes and lines aren't always clear when it comes to diagnosing disorders, but plenty of scientists are working on tools like the DSM and different models of mental health to get people help when they need it. Thanks for watching this episode of SciShow Psych, especially if you're a patron on Patreon!

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