Both experimental and clinical studies have shown that psychological manipulations, such as hypnosis, behavioral modification and cognitive-behavioral therapy, can reduce reports of pain. Although these are complex procedures, one important variable common to each is direction of attention. We have previously demonstrated in both humans and monkeys a method for monitoring and manipulating attention toward or away from a painful stimulus and have shown that changes in the direction of attention alter the ability to discriminate noxious heat stimuli. The present study assessed whether these changes in discrimination were accompanied by changes in the perception of pain intensity and/or unpleasantness. These data confirm that both the speed and accuracy of detecting changes in noxious heat stimuli are decreased when the subject attends to another stimulus modality. In addition, they show that direction of attention affects the perceived intensity and unpleasantness of painful stimuli in a similar manner. Our previous findings of attention-related modulation of nociceptive neuronal activity in the medullary dorsal horn suggest that these attention-dependent changes in sensory-discriminative and affective components of pain are mediated at early stages of sensory processing.

Summary. The ability of subjects to perceive innocuous stimuli in the presence and absence of movement was evaluated using electrical stimulation of the skin. The subjective intensity of suprathreshold stimuli was unchanged during movement. Discrimination of small differences in the intensity of suprathreshold stimuli (difference thresholds) was also not altered by movement while, in the same subjects, detection thresholds were increased during movement of the stimulated arm. These results suggest that the elevation of detection thresholds during movement can be explained by masking. Both active and passive movement of the stimulated limb increased detection thresholds, with active movement having a slightly greater and more consistent effect than passive movement. Thus, both central and peripheral feedback factors appear to play a role in diminishing one's ability to detect weak stimuli during movement. Attention was also shown to influence performance of the detection task.

This study compared pain perception in young male and female subjects, using experimental noxious heat stimuli. During 2 sessions, each of 40 subjects rated the magnitude of 120 heat stimuli, ranging from 45 degrees C to 50 degrees C. The study included a comparison of visual analogue and magnitude matching rating procedures, as well as a test of simulated analgesia, in which the range of stimuli presented during the 2 experimental sessions was shifted by 1 degree C. We found that females rated noxious heat stimuli as more intense than did males, independent of the gender of the experimenter or the type of rating scale. In addition, the data suggest that females discriminate among the painful heat intensities better than males. For example, female subjects showed significant between-session discrimination of noxious heat stimuli, while male subjects did not, and females produced steeper within-session stimulus-response functions than did males. These observed differences in nociceptive discrimination between males and females indicate that the sex-related variation in pain perception is probably related to sensory factors rather than differences in attitude or emotional response.

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