Gender and laterality differences in thermosensation throughout the perceptible range.

Several studies suggest that females exhibit greater sensitivity to experimentally induced thermal pain than males. These investigations have focused mainly on the sensory-discriminative rather than the affective aspect of pain. Moreover, potential gender differences for the affective components of innocuous thermal sensations have yet to be examined. The primary aim of the present study was to evaluate gender differences in the sensory and the affective dimensions of the entire thermosensory system, including warmth, coolness, heat pain and cold pain. The secondary aim was to evaluate laterality differences in these same perceptual dimensions and ranges. Twenty healthy females and 20 healthy males immersed their hands in water baths maintained at temperatures ranging from 10 to 47 degrees C, and rated their perceived thermal intensity, (un)pleasantness, and pain intensity. There was a progressive growth in the thermal intensity ratings as bath temperatures either increased or decreased from the adapting temperature of 33 degrees C. No gender differences emerged for these thermal intensity ratings. However, a significant sex effect emerged for the pain intensity ratings (P<0.01), and a significant sex x temperature interaction for the affective ratings (P<0.01). Females provided higher unpleasantness and pain intensity ratings for the more extreme temperatures (10, 15 and 47 degrees C), compared to males. Moreover, women perceived the milder temperature baths as more pleasant than men did. For a given painful temperature, unpleasantness ratings were higher than pain intensity ratings. This relationship between unpleasantness ratings and pain ratings was not significantly different between the sexes. No laterality differences emerged for the thermal intensity ratings. However, perceived pain intensity was significantly higher for the left as compared to the right hand (P<0.01). Ratings of unpleasantness also tended to be higher for the left vs. right hand, but this difference fell just short of statistical significance (P=0.06). These findings indicate that sex differences in thermosensory perception are not general, but occur only for the painful and affective components. Of particular note is the sex difference for affective but not intensive ratings of innocuous temperatures, revealing sex differences in thermal perception outside the nociceptive system.