Methodologic factors which contribute to variations in experimental pain threshold reported for older people.

Using the same study groups and psychophysical methods, we have tested the hypothesis that variations in pain threshold with advancing age are best explained by variations in stimulus duration. Fifteen young adults and 15 older people without clinical evidence of neurologic disease or psychologic dysfunction had pain thresholds determined with heat and electrical stimuli using the method of limits; for electrical stimulation a double random staircase design was used. The stimulus duration was 1-100 s for heat and 50-5000 ms for electrical stimulation. It was found that older people have an increased threshold for thermal and electrically induced pain if the stimulus duration is kept short. This result explains much of the variability in age associated pain threshold in the literature.