OCD sufferers fail to learn when something is safe
OCD or excessive compulsive disorder affects about one person in 50. Patients with the condition often feel compelled by anxiety to perform repetitive, ritualistic behaviours, like washing their hands a certain number of times or getting dressed in a certain way. If they don’t comply, they experience an overwhelming sense of dread that something terrible will happen. One way to treat the problem is to prevent sufferers from fulfilling their rituals - for instance, making them touch a toilet seat and then stopping them from washing their hands more than once. But this only works for about half of patients, so what’s needed is a deeper understanding of what causes OCD in the first place so that better therapies can be developed. Now Annemieke Apergis-Schoute, at Cambridge University, has discovered that OCD patients are very good at learning when things are unsafe or a threat, but they fail to be flexible and learn when something is actually safe, as she explained to Chris Smith...
Annemieke - We used an experiment where you had one threatening stimulus. That meant it was a stimulus that was sometimes paired with a mild electric shock, and another stimulus that was always safe, so it was never paired with a shock. The nice thing about this experiment is that we can measure very small changes in sweat in the skin so we know exactly when the participant is expecting a shock and when they are not, because you see a difference in the amount of sweat that comes on. And then unannounced in the middle of this experiment, the threatening stimulus became the safe one, and the safe one became the threatening one.
Chris - Right. So let’s say, for the sake of argument, I show them a picture of an orange and I give them an electric shock whenever they see it. I show them a picture of an apple and I never give them an electric shock. So you’re measuring how much they sweat when I’m presenting this sequence of pictures at them randomly and then, all of a sudden, you flip round so the orange, which was I’m going to get a shock now becomes no shock, and the apple, which was safe now gets an electric shock?
Annemieke - Exactly.
Chris - If a person who is not affected by OCD does this, what do you see in a normal person first?
Annemieke - What we see there is that they’re very flexible. They have increased amounts of sweat, which we call skin conductance, to the threatening stimulus compared to the safe stimulus. And then when this reverses, so when the threatening one becomes safe and the safe one becomes threatening, they very easily adapt to this. So that in a few trials, the one that has now become threatening, which was previously safe, leads to more sweat than the newly safe one.
Chris - Right, and what happens when you do the same thing with someone who has got OCD?
Annemieke - What we found in this study is that although they initially learn that one of the stimuli is threatening, when this changes they can’t learn that stimulus that was previously threatening is now safe.
Chris - If one looks at the brain when it is in the process of doing this reversal, when you take something that was a threat that had something unpleasant attached to it and you flip it round and make it un-nasty, how does it compare when you look at someone who’s normal and someone who’s got OCD?
Annemieke - Because we performed this experiment while the participants were in the brain scanner, an area called the ventral medial prefrontal cortex that we know is specifically involved with learning safety of stimuli, and we already know that this area gives a larger signal to when a stimulus is safe. What we found was that this signal was entirely absent in OCD patients from the get go, meaning they did the initial learning based on just learning about the threatening stimulus in absence of learning most likely about the safe stimulus.
Chris - Is it that there’s physically some kind of circuitry missing that enables them ascrib safety to things, or is it that they’re just very good at rendering things unsafe?
Annemieke - I have my own theory about this. I believe that this area of the brain might be too concerned with their kind of self-referential kind of thinking about their own obsessions and, perhaps, unavailable to pay attention when things are rewarding or safe in the environment.
Chris - Does this help that 40 percent or so of people for whom the exposure therapy does not work at the moment? Have we got some clues on the basis of what you’ve found as ways we can intervene more meaningfully for those people?
Annemieke - So, yeah. We think that we can come up now with new therapies. For example, in terms of the exposure with response prevention therapy, we could augment a therapy by enhancing the experience of the safety. So when they actually touch the toilet seat that they feel more of a reward, that they feel oh yes indeed, nothing went terribly wrong when I didn’t wash my hands right afterwards. So this experience can be more meaningful and, perhaps, is easier for them afterwards to overcome the urge of performing the compulsion.