Healthy participants
Conditions
Interventions
Participants will receive a verbal suggestion that an ‘itch solution’ will increase the itch sensation evoked by cowhage spicules and that a ‘control solution’ will not affect their itch sensation. In
Sponsors
Leiden University, Leiden, the Netherlands
Eligibility
Inclusion criteria
Inclusion criteria: 1. Healthy participants between 18 and 35 years old; 2. Fluency and regular use of English
Exclusion criteria
Exclusion criteria: 1. Refusal to give written informed consent 2. Have received a diagnosis from a doctor of severe physical illness (e.g., multiple sclerosis, heart or lung disease, diabetes, hypothyroidism) 3. Have a psychiatric diagnosis (e.g., depression, autism, ADHD) 4. Are suffering or have suffered from itch lasting for = 6 weeks (e.g., due to allergy or hay fever) 5. Experience itch = 3 on a 0 (not itch at all) to 10 (worst itch imaginable) scale at the start of the testing session 6. Current use of medication 7. Use of drugs (e.g., cannabis, XTC) more than 3 times a month 8. Use of alcohol, any medication or any other form of drugs in the 24 hours prior to participating in the study. 9. Pregnancy or lactation 10. Insensitivity to cowhage, i.e., inability of cowhage spicules to evoke itch (participation will be stopped right after baseline stimuli)
Design outcomes
Primary
| Measure | Time frame |
|---|---|
| Nocebo effects on cowhage-evoked itch. After receiving the verbal suggestion, the participants will receive two trials with 25 cowhage spicules each, once after application of the ‘itch solution’ and once after application of the ‘control solution’. Our primary outcome is the comparison of the difference in average itch scores between the ‘itch solution’ and the ‘control solution’ trials. | — |
Secondary
| Measure | Time frame |
|---|---|
| Generalization of nocebo effects to mechanical itch and to mechanical touch. Following the cowhage test phase, the participants will receive mechanical itch stimuli and mechanical touch stimuli by using six different von Frey filaments twice, once after application of the ‘itch solution’ and once after application of the ‘control solution’. Our outcomes are the comparison of the difference in average itch scores between the ‘itch solution’ and the ‘control solution’ for the mechanical itch and the mechanical touch stimuli separately. Additionally, peak itch, peak and average urge to scratch scores, as well as the awareness of a sensation will be compared between the ‘itch solution’ and the ‘control solution’ trials for both cowhage and mechanical itch and mechanical touch stimuli. Nocebo effects on the alloknesis area surrounding the cowhage sites. The average alloknesis areas surrounding the cowhage application sites will be assessed using a brush and will be compared between the ‘itch solution’ and the ‘control solution’ trials to test possible nocebo effects on alloknesis area as an exploratory analysis. Psychological factors. The individual characteristics (i.e., state anxiety, depression, anxiety, stress, itch-related attention, itch-related magnification, rumination, helplessness) will be used to test possible moderators of the induction and generalization of nocebo effects within and across sensory modalities (i.e., itch and touch) as an exploratory analysis. | — |
Contacts
Public ContactAndrea Evers
Leiden University
Outcome results
None listed