LAUSR

We read with great interest the recently published paper by Slimani et al. [2] in PAIN . The authors investigated pain sensitivity in congenitally blind individuals, and found reduced pain thresholds as well as increased pain report to suprathreshold pain stimuli in blind participants compared with sighted controls. Based on these findings, the authors come to the conclusion that the absence of vision from birth leads to a permanent state of pain hypersensitivity. Although their findings undoubtedly corroborate such a conclusion, we were somewhat surprised that the authors completely disregarded a recently published study of our group [1], where we used very similar methods to study pain responses in congenitally blind individuals and found—in contrast to Slimani et al.—no changes in pain threshold or in suprathreshold pain ratings in blind individuals compared with sighted individuals. This neglect of our findings is quite surprising, since our study is the only other study (to our knowledge) that has investigated pain responses to experimentally induced pain in congenitally blind individuals. We used similar pain induction methods (Peltier-based thermotester, TSA-II, Medoc, Haifa, Israel) and studied similar samples of individuals (as regards onset and cause of blindness, as well as sample size) but found no clear indication of pain hypersensitivity. Reasons for the discrepancy might lie in the methods used to assess pain thresholds. Slimani et al. applied the method of limits whereas we used the method of adjustment to assess pain thresholds. Having to respond (by pressing a button) to a rather quickly ascending temperature increase (3 C per second; method of limits as used by Slimani et al.) might have elicited more anxiety in blind individuals than if they had been able to adjust the stimulus temperature at their own pace (method of adjustment that we used). Thus, heightened anxiety might have contributed to the pain hypersensitivity in congenitally blind individuals reported by Slimani et al. The same might hold true for the increased pain report to suprathreshold pain stimuli in blind participants. Slimani et al. used phasic laser stimuli (3 seconds duration) with a very rapid onset/increase, whereas we used tonic heat stimuli (6 minutes duration) that are very predictable in their time course. Thus, the suprathreshold protocol used by Slimani et al. might have elicited more anxiety in the participants than our protocol and, given that blind individuals had higher scores on pain anxiety and pain vigilance questionnaires, it is likely that the factor of anxiety contributed to the group differences found by Slimani et al. In summary, the absence of vision from birth does not seem to lead automatically to a generalized state of pain hypersensitivity. Instead, the occurrence of increased pain sensitivity in congenitally blind individuals might depend on factors like the protocol used to induce pain, the methods used to assess pain sensitivity and the level of anxiety that accompanies the pain experience. References