Big Think and the Mental Health Channel are proud to launch Big Thinkers on Mental Health, a new series dedicated to open discussion of anxiety, depression, and the many other psychological disorders that affect millions worldwide.

In the second video in the series, Dr. Helen Blair Simpson, director of the Center for Obsessive-Compulsive and Related Disorders at Columbia University, paints a vivid portrait of the many different versions of OCD. Even though it’s a well-known anxiety disorder, OCD is also one of the most misunderstood, so it’s important to educate ourselves on what our peers who suffer from it are going through. Dr. Simpson runs through variations of OCD, offers some extreme examples from her patients, and details what we’ve learned from brain scans of OCD sufferers.

Dr. Helen Blair Simpson: We all have intrusive thoughts from time to time and many of us, for example, will check whether we have our airplane ticket before going to the airport more than once. That isn’t OCD.

To have OCD, you have to have obsessions and compulsions that impair your life and are highly distressing. And a sort of a rulebook would be maybe at least an hour a day, but most of the patients that I work with will obsess and compulse for hours a day and really their life can be ruined. I have some patients that will come to me and say look, I know I don’t need to be washing my hands like this, but I can’t stop. And I have other patients who are really not sure, really not sure — I mean they really believe that if they don’t wash maybe they’ll actually get ill.

So there’s that sort of range of insight. It’s also true that someone in my office can say, you know, I know the subway is safe and I could touch that pole, but if I walk onto the subway with them doing an exposure and ask them to touch the pole in front of me they lose their ability to, you know, remember that this isn’t going to kill them.

So Obsessive-Compulsive Disorder or OCD is a disorder where patients have obsessions and compulsions. And obsessions are intrusive thoughts, images, or urges that they find very distressing and are very repetitive. And compulsions are behavioral acts or mental acts, things they do in their head over and over again to try to reduce the distress that obsessions cause or to follow specific rules. So while all patients with OCD have obsessions and compulsions, the content of the obsessions and compulsions can really vary.

So one type of patient can have intrusive concerns about contamination and they may be washing, doing elaborate washing rituals. A different patient might have intrusive thoughts about harming either other people or harm befalling themselves. And they, for example, might have rituals of checking to make sure that the harm didn’t happen. Yet another type of OCD patient might have what’s called just-so OCD where everything has to be either arranged or ordered in a certain way or they have to actually do things in a certain way. And they may be repeating and rearranging and organizing all day long. And finally there’s a group of people who have what we call intrusive taboo thoughts. It can be about sex or religion or violence. And often these are images that they have and again they might have elaborate rituals to reassure themselves that they actually didn’t actually commit any of these acts.

Now it’s not like OCD patients only have one, you know. Often OCD patients have more than one of these types of obsessions and compulsions together. But that’s sort of a flavor. So there’s a sort of a simple version, right. Fear of contamination with washing rituals. But OCD can get really, you know, sort of far out so, for example, I once worked with someone who believed California was contaminated. And so what it meant was she couldn’t have anything in her apartment that had the name California in it. If an envelope had once arrived to her mailbox that had California on it her mailbox then became contaminated. Or, for example, intrusive harm befalling.

I’ve had patients who worry that maybe they’ve driven over someone as they drive and so they can’t make it to work because they’re going around and around the intersection to make sure that they haven’t run someone over. But the harm can also be very, very abstract — not as concrete as that, but very, very abstract. So, you know, there are many, many, many versions of OCD. What we know is that when you do brain-imaging studies of people with OCD and you compare their brain to the brain of people who don’t have OCD, that there’s a hyperactive circuit in the brain that’s been linked to OCD and that hyperactivity in that circuit has been confirmed through animal studies. And we don’t think it’s only that circuit.

We think there are other circuits that are likely involved as well, but there’s a real clear neuroscience of this behavior of obsessions and compulsions. How did the brain get that way? And here we know less about that. What we do know is that in some families, but not in all families, OCD seems to run in those families. And certain genetic studies suggest that there is a familial contribution to OCD, but again, not in all cases. But exactly how that particular brain circuit went awry in that particular patient, we don’t know that. We’re working on it, but we don’t know yet.