Fake hand contamination treats OCD

UK and US researchers have found that the ‘rubber hand illusion’ could help those with OCD overcome their condition without the stress caused by exposure therapy.

Obsessive compulsive disorder (OCD) is treated using a combination of medication such as Prozac and a form of cognitive behavioural therapy known as ‘exposure and response prevention’. This exposure therapy often involves instructing OCD patients to touch contaminated surfaces, such as a toilet, but to refrain from then washing their hands. This experience can be so stressful that many patients cannot take part.

“OCD can be an extremely debilitating condition for many people, but the treatments are not always straightforward,” explained neuroscientist Baland Jalal, based in the Department of Psychiatry at the University of Cambridge.

“In fact, exposure therapy can be very stressful and so is not always effective or even feasible for many patients.”

Jalal said the rubber hand illusion may offer a way of treating OCD patients without the high stress levels that exposure therapy can cause.

“If you can provide an indirect treatment that is reasonably realistic, where you contaminate a rubber hand instead of a real hand, this might provide a bridge that will allow more people to tolerate exposure therapy or even to replace exposure therapy altogether,” he said.

“Whereas traditional exposure therapy can be stressful, the rubber hand illusion often makes people laugh at first, helping put them at ease. It is also straightforward and cheap compared to virtual reality, and so can easily reach patients in distress no matter where they are, such as poorly resourced and emergency settings.”

The rubber hand illusion and how it works

The technique builds on a famous trick known as the rubber hand illusion: an individual places both hands in front of them on a table, either side of a partition so that they cannot see their right hand. Instead, to the left of the partition they see a fake right hand. The illusionist simultaneously strokes both the fake hand and hidden right hand using a paintbrush. After several minutes of stroking the individual often reports ‘feeling’ touch arising from the fake hand as though it was their own.

In a previous study, carried out by Jalal and neuroscientist VS Ramachandran, once the illusion had begun to work, the researchers contaminated the dummy hand with fake faeces. The participants reported disgust sensations as if it were their own hand that had been contaminated.

In the current study — published in Frontiers in Human Neuroscience — Jalal and Ramachandran teamed up with researchers at Harvard University: Richard J McNally, Director of Clinical Training in Department Psychology and Jason A Elias and Sriramya Potluri in the Department Psychiatry.

The team recruited 29 OCD patients from the McLean Hospital Obsessive Compulsive Disorder Institute, an intensive residential treatment program affiliated with Harvard Medical School. Sixteen of these patients had their hidden and dummy hands stroked at the same time, while the remaining 13 patients (the control group) had their hands stroked out of sync.

After five minutes of stroking, the participant was asked to rate how much the rubber hand felt like their own. The experimenter then used a tissue to smear the fake faeces on the rubber hand while simultaneously dabbing a damp paper towel on the participant’s real right hand (to create the sensation of having the contaminant smeared on their real hand). The participant was then asked to rate their disgust, anxiety and handwashing urge levels, and the experimenter rated the participant’s facial expression of disgust.

The researchers found that patients in both the experimental and control groups felt an equally strong rubber hand illusion. In other words, even when their real and fake hands were being stroked asynchronously, they had still begun to sense the fake hand as their own. Unsurprisingly, therefore, patients in both groups initially reported similar levels of contamination.

The experimenter then removed the clean paper towel and the tissue that had been used to contaminate the rubber hand, leaving fake faeces on the rubber hand. The experimenter continued to stroke the rubber hand and the participant’s real hand for an additional five minutes, after which the participant again provided contamination ratings and the experimenter rated their facial expression.

Now, the patients in the experimental condition were more disgusted: 65% of participants in the experimental condition had a disgust facial expression compared to 35% in the control. This supports previous studies that show that the rubber hand illusion becomes stronger the longer the hand is stroked.

Next, the experimenter stopped the stroking and placed the fake faeces on the patient’s real, right hand and asked the participant once again to provide contamination ratings. Now the differences were much more pronounced in the experimental condition. While those in the control group had average disgust, anxiety and washing urge levels at nearly 7, the experimental group had levels of nearly 9 — that is, an overall 23% difference in contamination ratings.

“Over time, stroking the real and fake hands in synchrony appears to create a stronger and stronger and stronger illusion to the extent that it eventually felt very much like their own hand,” Jalal said.

“This meant that after 10 minutes, the reaction to contamination was more extreme. Although this was the point our experiment ended, research has shown that continued exposure leads to a decline in contamination feelings — which is the basis of traditional exposure therapy.”

Jalal said it can be safely assumed that the fake hand contamination procedure would lead to a similar fall in levels of disgust and contamination ratings, possibly after 30 minutes.

Jalal said the next step is to do randomised clinical trials and compare this technique to existing treatments.

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