Placebo effects have so far been most extensively studied in relation to pain. However, the human affective system, comprising moods and feelings, also responds strongly to positive and negative expectations. For instance, placebo effects can account for up to 80 per cent of the effectiveness of antidepressant treatment.
Several research groups in our Collaborative Research Centre are therefore investigating how treatment expectations influence the affective system. This includes project A06, which is led by Prof. Stefanie Brassen at the University Medical Centre Hamburg-Eppendorf. Together with Prof. Winfried Rief and other researchers from our CRC, Prof. Brassen has now conducted an experiment to investigate how the cognitive resources of patients influence such placebo effects: What role do factors such as working memory, attention, and the ability to control emotions play?
In the experiment, the researchers evoked positive expectations in healthy volunteers by administering a special nasal spray and emphasizing its mood-enhancing effect during conversation. They then used behavioral observations and functional magnetic resonance imaging (fMRI) to measure how easily the volunteers were distracted by happy or anxious faces.
Better mood, less distracted by negative stimuli – when enough attention is available
The result: the placebo treatment improved the mood of the test subjects and reduced their distractibility by anxious faces. However, this was particularly true when the participants were more attentive during the experiment. Both the behavioral observations and the fMRI measurements confirmed this. Additionally, the greater the participants' individual control ability, the greater the placebo effects. (Here is the link to the original publication.)
Placebo effects in the affect system therefore depend to a large extent on the cognitive resources of those affected - at least when the positive expectations are only generated in conversation and without prior learning experience. This could be a disadvantage when treating depressed people, because they often react more strongly to negative stimuli, and their illness usually makes it harder for them to concentrate or control their emotions.
In the second funding phase of our Collaborative Research Centre, Project A06 is investigating how positive expectations can be generated in the affective system without verbal instructions or greater cognitive resources.
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