Hypersensitivity to pain in congenital blindness

Abstract

Vision is important for avoiding encounters with objects in the environment that may imperil physical integrity. We tested whether, in the absence of vision, a lower pain threshold would arise from an adaptive shift to other sensory channels. We therefore measured heat and cold pain thresholds and responses to suprathreshold heat stimuli in 2 groups of congenitally blind and matched normal-sighted participants. We also assessed detection thresholds for innocuous warmth and cold, and participants' attitude toward painful encounters in daily life. Our results show that, compared to sighted subjects, congenitally blind subjects have lower heat pain thresholds, rate suprathreshold heat pain stimuli as more painful, and have increased sensitivity for cold pain stimuli. Thresholds for nonpainful thermal stimulation did not differ between groups. The results of the pain questionnaires further indicated that blind subjects are more attentive to signals of external threats. These findings indicate that the absence of vision from birth induces a hypersensitivity to painful stimuli, lending new support to a model of sensory integration of vision and pain processing.

Enhanced heat discrimination in congenital blindness

“…We propose that blind individuals have learned to better use these thermal cues in order to prevent thermal injuries. This is supported by our recent findings that congenitally blind individuals are hypersensitive to thermal pain [18,19]. The same studies, however, indicated that thresholds for innocuous thermal perception in congenitally blind and sighted participants were not different.…”

“…Since we tested the volar forearm, a body region that is unlikely being used extensively by the blind in temperature discrimination tasks, it seems rather unlikely that our results are due to training-induced plasticity. Alternatively, the increased thermal sensitivity in congenital blindness might be explained by their hypersensitivity to nociceptive stimulation [18,19]. Indeed, a more efficient computing of rapid temperature raises will help in avoiding possible encounters with noxious thermal stimuli.…”

“…Indeed, congenitally blind individuals have supra-normal discrimination skills in tactile [2][3][4], auditory [5][6][7] and olfactory [8][9][10] modalities. In a previous study, we measured warmth and cold detection thresholds as well as heat and cold pain thresholds and responses to supra-thresholds heat stimulation in congenital blind subjects [18]. Although blind individuals showed increased responses to pain stimulation, thresholds for innocuous warmth and cold were not different from normal sighted controls.…”

“…Therefore, a rapid increase in temperature, even within the innocuous range, can be encoded as dangerous. Since congenitally blind individuals have lower heat pain thresholds compared to the sighted [18,19], they may be more attentive to temperature shifts that may be indicative for an impeding painful stimulus.…”

Pain Perception Is Increased in Congenital but Not Late Onset Blindness

“…In a recent study we showed that congenitally blind individuals have reduced thresholds to heat and cold pain, and rate supra-threshold nociceptive stimuli as more painful compared to normally sighted individuals [1]. In sharp contrast, thresholds for innocuous cold and warmth perception were not altered, suggesting a specific effect for noxious thermal processing.…”