What do experimental pain models tell us about aging and clinical pain?

During presentations about aging and clinical pain, almost invariably, someone will ask, " Does pain threshold change with age? Wouldn't that explain your results? " These are complicated questions, and there is rarely time in the few minutes usually allotted for " Q and A " to give an adequate response. Instead, more than once I've replied, " What would age differences in pain threshold tell you about clinical pain? " This is not intended to challenge the audience member but rather to reflect the pain research commu-nity's long struggle to understand the relevance of data from experimental pain models to clinical pain. Most experimental, or laboratory, pain models involve the application of carefully controlled stimulation. Experimental participants are asked to indicate when they first feel the sensation (detection threshold), when it first becomes painful (pain threshold), and if stimulation is continued or its intensity increased, when they would like it to be terminated (pain tolerance) [1]. In these studies, participants are informed that they will suffer no permanent damage from the stimulation and may terminate it whenever they choose. Critics have suggested that the experimental situation cannot adequately mirror the clinical situation, especially in regard to the affective and evaluative dimensions of pain [2]. For instance, while a healthy older person may experience some transient anxiety about an upcoming shock which they have been assured will cause no permanent damage and can be easily terminated, this is far from the anxiety an older person with cancer might experience in the face of an exacerbation of pain. This person may fear disease progression, uncontrollable pain, physical disability that may necessitate institutionalization, and the impact of the pain on their quality of life and death. Proponents of experimental pain models do not deny this limitation. Instead, they point out that there are important questions that can only be answered, whether for methodological or ethical reasons, using experimentally applied noxious stimulation [3]. In addition , there is evidence that some experimental pain parameters may have important predictive value in the clinical situation (e.g., [4]). Therefore, it is evident that both experimental and clinical studies are necessary to further our understanding of pain mechanisms [3]. There is a long history of studies comparing pain sensitivity in younger and older volunteers, with reports that sensitivity increases, decreases, and does not change with age (see Gagliese and Melzack [5] for a review). The findings may …