Research has shown that patients with functional somatic symptoms continue to worry about having a serious disease despite medical reassurance from their doctors. This study aims to investigate whether cognitive immunization is a mechanism that underlies the sustained concern about having serious disease. To this end, the use of cognitive immunization strategies will be experimentally modulated after receipt of medical test results.

It is known from research on functional somatic symptoms that patients continue to worry about having a serious illness despite receiving medical reassurance and normal medical test results. However, the psychological mechanisms underlying this maintenance of concern are largely unknown. The planned study will therefore apply knowledge from depression research to this question: In the field of depression there is sound evidence that people with depressive symptoms maintain negative expectations despite positive experiences to the contrary, and in previous work it was shown that this is due to a cognitive re-appraisal of expectation-disconfirming experiences, referred to as cognitive immunization. The planned study seeks to investigate whether cognitive immunization is also a mechanism underlying sustained concerns about having a serious disease despite medical reassurance in patients with functional somatic symptoms. For this purpose, participants are presented with a vignette in which gastrointestinal complaints are reported; participants are instructed to imagine to suffer from these symptoms and to go a doctor to have their symptoms examined. Subsequently, participants watch a videotaped doctor's report in which a family doctor discusses the results of several medical tests that have been carried out to exclude the possibility of some serious diseases, such as colon cancer. In this report, the doctor states clearly that, based on the test results, a serious disease is very unlikely. Afterwards, participants of some experimental groups receive additional information on the accuracy of medical diagnostics, aimed at differentially varying the appraisal of the medical reassurance received.

The experimental conditions described above apply only to the sample of patients with functional somatic symptoms (inclusion and exclusion criteria see below). In addition, we will also recruit a clinical (patients with depression, n=30) and healthy control group (n=30). These control groups will not undergo the cognitive immunization manipulation, but will only pass through the basic procedure of the experimental paradigm, that is, the same procedure as the control group from the sample of patients with functional somatic symptoms. These two control groups (healthy and clinical) are recruited to replicate previous findings showing that patients with somatic symptoms report increased probabilities of suffering from a serious disease compared to patients with depression and healthy control participants. Below, we will only present the inclusion and exclusion criteria of the sample with functional somatic symptoms.

Inclusion Criteria:

• Primary diagnosis of a somatoform disorder (F45.x) (as assessed with the SKID interview)
• Age between 18 and 69
• Sufficient German language skills

Exclusion Criteria:

• acute life-threatening disease
• diagnosed mental disorder other than the somatoform disorder that is considered the primary diagnosis (people with other comorbid mental disorders are not excluded if the somatoform disorder is the primary diagnosis)

The investigator randomly assigns participants to one of the experimental conditions. Participants are not aware which experimental condition they are allocated to.