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In 1998, researchers Matthew Botvinick and Jonathan Cohen of the University of Pittsburgh, PA, detailed an experiment that people would later refer to as the “rubber hand illusion” (RHI).

In the experiment, 10 people sat down, resting their left arm on a table. A screen hid each participant’s arm from view, and instead, they could see a life-sized rubber hand model.

The researchers placed the hand right in front of the person so that they could see it from the same angle as they would their own hand.

After asking each participant to fix their gaze on the rubber hand, the experimenters used two small paintbrushes to stroke the rubber hand and the participant’s actual hand at the same time.

After 10 minutes, the participants reported feeling the rubber hand as though it were their own.

Now, new research has used the RHI to help people with contamination-related OCD overcome their fears.

Baland Jalal, a neuroscientist in the department of psychiatry at the University of Cambridge, United Kingdom, is the first author of the new paper, which appears in the journal Frontiers in Human Neuroscience.

In contamination-related OCD, the fear of touching a doorknob, for example, may cause people with the condition to spend hours washing and scrubbing their hands to an excessive degree afterward.

Doctors and mental health professionals often recommend “exposure therapy” to treat this and other forms of OCD.

Exposure therapy encourages people with OCD to start touching potentially contaminating surfaces without washing their hands afterward.

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

This limitation is what made him and his colleagues want to explore other options, such as contaminating a fake hand instead.

Using a fake hand to treat OCD

The new research builds on previous RHI experiments that Jalal carried out together with fellow neuroscientist Vilayanur S. Ramachandran, who is a co-author of the new study.

In these previous studies, Jalal and Ramachandran contaminated the fake hand with fake feces, and the participants reported feeling disgusted in the same way that they would if they had used their own hand.

For the new study, the researchers recruited 29 people with OCD from the McLean Hospital Obsessive Compulsive Disorder Institute in Belmont, MA.

Of these participants, 16 experienced the paintbrush stroking on both their real hand and the dummy hand at exactly the same time, whereas 13 controls experienced the stroking out of synch.

After 5 minutes, the experimenters asked how real the dummy hand felt to the participants. Then, they used a tissue to smear the dummy hand with fake feces while simultaneously touching the real, hidden hand with a damp paper towel to mimick the feeling of them having feces on their hand.

The experimenters again asked the participants to rate their level of disgust, as well as how anxious they were and how strongly they felt the urge to go and wash their hand.

RHI may ease OCD contamination fears

At first, both groups reported feeling the illusion, regardless of whether or not the stroking of the two hands was simultaneous.

Then, the researchers took away both the clean paper towel and the fake feces tissue, leaving fake feces on the dummy hand. After this, they stroked the rubber hand and the real hand for another 5 minutes, still either synchronously or asynchronously.

In this condition, the participants in the intervention group reported feeling more disgusted than those in the control group.

In the next step, the stroking stopped, and the researchers placed fake feces on the real right hand of each of the participants.

This time, the people in the control group rated their anxiety, disgust, and urge to wash at seven on a 10-point Likert scale, whereas the intervention group reported these factors as a nine.

“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,” reports Jalal.

“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.”

Baland Jalal

Replacing traditional exposure therapy

In other words, the researcher believes that it is safe to conclude from these findings that after 30 minutes, participants would experience a drop in feelings of anxiety, disgust, and washing urge, based on the proven success of exposure therapy.

“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,” continues the scientist.

He adds, “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.”

In the near future, the researchers plan to compare this technique with existing treatments in randomized clinical trials.

Ramachandran agrees that the findings are strong, but also points out that more research is necessary before moving on to clinical trials.

“These results are compelling but not conclusive,” he says. “We need larger samples and to iron out some methodological wrinkles.”