Do you know what your back looks like? And if you now compare your back to your hands, what appears more familiar to you? In contrast to other body areas, one’s own back cannot be seen directly, so you always have to use mirrors. The back is only perceived when it causes trouble. In most chronic back pain patients the exact localization of their pain is often difficult. This diffuseness of pain and its shifting locations are central to musculoskeletal pain syndromes, and there is evidence, especially of Lorimer’s work, that their body image has become disrupted.
What we do not know is how seeing one’s own back during painful stimulation influences pain perception. For this we implemented online video feedback using a video camera to film the back or the dorsum of the hand and present the film on a monitor in front of the participants. The participants were always stimulated on the back but saw in one condition the online film of their hand and in the other condition the online film of that part of the back, where the painful stimuli were applied. Participants had to rate pain intensity. Painful stimulation was adjusted to subjectively equal intensity in chronic back pain patients and healthy controls.
We found higher pain ratings for the chronic back pain patients although the stimulation intensity was subjectively identical beforehand. Most interestingly we found higher pain ratings during feedback of the hand compared to feedback of the back. The unpleasantness ratings were not different between the groups but were again higher during video feedback of the hand. In the chronic back pain patients higher habitual pain severity and interference values were related to lower site-specific feedback–related reduction.
We observed that visual feedback of one’s own back reduces the perceived intensity of acute painful stimuli applied to it. In chronic back pain patients, both habitual pain severity and interference related to pain was associated with an reduced ability to profit from site-specific feedback. This suggests that the experimental pain and habitual pain interact, and that patients with less intense pain and interference may profit most from the visual feedback. The underlying mechanisms need to be investigated because this may influence how pain treatments are planned. Thus, we suggest that visual feedback of the site of pain may be beneficial to boost the effects of other interventions, such as physiotherapy or joint manipulation. We do expect that repeating such short manipulations might induce lasting effects on perceived pain intensity and perhaps also on the unpleasantness of chronic pain.
About Martin Diers
Martin Diers, PhD, is a psychologist in the Department of Cognitive and Clinical Neuroscience at the Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, in Mannheim, Germany. He was trained in neuroscientific pain research and has an additional clinical training in behavioral treatment. Any questions about his work can be directed to him at martin.diers@zi-mannheim.de
Reference
Diers M, Zieglgänsberger W, Trojan J, Drevensek AM, Erhardt-Raum G, & Flor H (2013). Site-specific visual feedback reduces pain perception. Pain, 154 (6), 890-6 PMID: 23582151