Friday February 11 2011
The heat-based pain in the study may differ from needle pain
“Injections are less painful if you don't look away,” The Daily Telegraph reported.
The news is based on a study that tested pain responses in 18 people by applying heat probes to their left hand. The participants had their left hand obscured with a mirror that reflected their right hand in its place. Nine people who could see their right hand and its reflection had a better pain threshold than nine people who could see neither hand because their right hand was obscured by a block. When mirrors of different magnification were used, people had a better pain threshold when they viewed a magnified image of their hand, and a lower threshold when they viewed a reflection of reduced size.
This was a very small experiment in an artificial test scenario. These findings may or may not be relevant to the real-life experience of pain, such as having an injection. There is no harm in trying this technique, for example by looking at an injection being carried out. However, it is difficult to see how the technique could have a direct practical application.
Where did the story come from?
The study was carried out by researchers from University College London. Individual authors received funding from University of Milano-Bicocca, a Biotechnology and Biological Sciences Research Council project grant, a postdoctoral fellowship from the Economic and Social Research Council/Medical Research Council, funding from the EU’s Seventh Protocol project, and a Leverhulme Trust Major Research Fellowship. The study was published in the peer-reviewed scientific journal Psychological Science.
Contrary to the headlines in the Daily Mail and The Daily Telegraph, this scientific research did not involve injections. The findings may be relevant to other areas, but limited conclusions and implications can be drawn from this small experimental study in 18 people.
What kind of research was this?
This experimental scientific research aimed to further investigate how the subjective experience of pain can be influenced by many factors. The researchers were interested in the theory that viewing an affected body part can reduce the intensity of pain, known as “visually induced analgesia”. Specifically, they aimed to see whether visually altering the size of the affected body part had an effect.
While the results are of interest and further the understanding of the body’s physiological and psychological response to pain, limited conclusions can be drawn from such a small experimental study.
What did the research involve?
This study involved 18 healthy adults. The participants received heat stimulation to their left hand using a probe that increased in temperature over time. Probe temperature increased by 2°C a second from normal body temperature (32°C) until the participants’ pain threshold was reached.
The researchers then repeated the tests using a mirror-box technique. Participants sat at a table with a mirror just to the left of their head, obscuring their left arm and hand from view. The mirror was placed so that the participants could see both their right hand on the table and the reflection of their right hand in the position of their real left hand. As they would not be able to see their left hand (the one receiving pain), the brain would theoretically perceive the reflected right hand as being the left hand.
Nine participants looked at their normal right hand and its reflection. The other nine had a hand-sized wooden block placed over their right hand, blocking their direct view of their hand. This meant they also saw a reflection of the box obscuring their hand. Three different mirrors were then used in each of the two groups: a normal mirror, a mirror giving 2x magnification (enlarged image), and a mirror giving 0.5x magnification (reduced image). The researchers repeated the heat stimulus tests to see how the participants’ different visual perceptions of their “left” hand affected their pain threshold. A fake probe was simultaneously applied to their right hand, or to the block, to reinforce the visual perception of a heat probe touching their left hand.
To gain extra feedback, the researchers also used questionnaires to establish that the mirror made the participants feel that they were looking at their real left hand, and not at a reflection.
What were the basic results?
The questionnaire responses showed that the participants viewed the reflected hand image (in normal, enlarge and reduced size) as their own left hand rather than a reflection. Participants who had their direct view of their right hand obscured by a block did not consider its reflection to be their left hand.
The researchers found that, compared with viewing the block obscuring their hand, viewing the reflected right hand (perceived as the left hand) increased pain thresholds by an average of 3.2°C. Further to this, viewing an enlarged image of their hand gave the participants a better pain threshold. Visual reduction in the size of the hand decreased the pain threshold. An enlarged or reduced image of the block had no effect.
How did the researchers interpret the results?
The researchers concluded that their results demonstrate that pain perception depends on the person’s sensory perception of their body, and that visual distortion of the affected body part changes the pain experience.
This interesting experimental research highlights some of the body’s unusual physiological and psychological responses to pain.
However, limited conclusions can be drawn from such a small experimental study in 18 people, with only nine people testing each of the conditions. This means that, while it is possible that people who view the body part receiving a painful stimulus may experience less pain than if they turn away, this cannot be definitely concluded from the results. Also, the heat-induced pain used in this test may affect people differently to other forms of pain arising from cutting or pressure.
Many factors can influence the subjective experience of pain. When next having a procedure, such as injection, there is no harm in testing out this phenomenon and looking at your injection to see if it makes you feel better or worse.