[A study of itch intensity in relation to two-point tactual discrimination]

This study was designed to investigate whether or not the areas of the human body most sensitive to itch stimuli are identical with the body parts least sensitive to tactual discrimination, a hypothesis which arouse from our previous studies of itching. Subjects were 12 college students (six males and six females). The itching was induced by grated Japanese yam. The body areas were the upper arm (with large two-point thresholds), the lower leg (with intermediate two-point thresholds), and the middle finger (with small two-point thresholds). An experimental session consisted of a stimulus-application period (200 s), and a post-application period (600 s) during which the itching increases markedly. (After wiping off the grated yam, itching is increased because of the needle-crystals of calcium oxalate contained in the yam peel which penetrate slightly into the skin in the process of wiping.) Self-ratings on itching and the volume of dermal blood flow were recorded during two periods. The results support our hypothesis and suggest that tactile sensation has some interaction with itching.