The role of conditioning and verbal expectancy in the placebo response.

Both conditioning and expectancy models have been offered in recent years as explanations for the placebo response. Following our earlier work on conditioning placebo responses in human subjects the current study examined the relative contribution made by conditioning and verbal expectancy. Group 1 received a Combined Expectancy and Conditioning Manipulation; group 2 received Expectancy Alone; group 3, Conditioning Alone; and group 4 was the control group. Subjects' responses were compared with and without a placebo cream, using iontophoretic pain stimulation. The results suggest that conditioning was more powerful than verbal expectancy in creating a placebo response.

Conditioned response models of placebo phenomena: further support.

Following our earlier research, we further investigated a model that conceptualizes placebo phenomena as the result of conditioning and attempted to extend and replicate the finding that placebo responses can be conditioned in human subjects. Two groups of 10 subjects were told that they were receiving an analgesic which was in fact a placebo. During the conditioning, placebo administration was surreptitiously paired with an increase in the painful stimulus for half of the subjects and with a decrease for the other half. Subjects were tested pre and post conditioning for a placebo response. A second type of experimental pain was also used to determine stimulus generalization. The results confirmed a previous finding that placebo responses can be conditioned in human subjects. The implications for clinical practice of a learning model of placebo behavior are discussed.

The MMPI and psychological factors in chronic low back pain: a review.

The Minnesota Multiphasic Personality Inventory (MMPI) is widely used in the psychological assessment of patients with chronic low back pain (LBP). Patients' profiles have been used in a number of ways: in attempts to discriminate between cases; as predictors of both medical treatment and pain management program outcomes; and in attempts to assess degree of disability. Studies reviewed here indicate that the concept of psychological etiology of chronic LBP, despite widespread use, has failed to differentiate patients and to reliably predict response to specific treatment. A promising alternative approach has emerged in recent years: profile distinctions between different types of psychological response to chronic LBP. These subgroups are associated with different pain-related behaviors and may show differential response to various treatments, although further work remains to be done to specify the relationships more precisely. Methodological difficulties that continue to appear in the literature are addressed and recommendations for further developments in the use of the MMPI with this patient population are made.