Animal-assisted Placebo-induced Analgesia

Upon arrival, all participants will be asked to read the study information again and sign to confirm their informed consent. They will also be asked to complete the sociodemographic data (SDD) questionnaire.

During the experiment there will be three points of questionnaire-assessment. The following questionnaires will be used: expectancy will be assessed with the Expectancy of Relief Scale. Expectancy of Relief Scale is adapted to the scaling of the primary outcome. Expectancy has been measured in previous studies. It should detect if participants expectancy changes after the intervention phase. Further, it would also be interested to examine if the presence or absence of a dog has an impact on expectancy.

Furthermore, following each pain stimuli participants will be asked to complete two short questions on pain intensity and unpleasantness. Pain intensity and unpleasantness are adapted to the scaling of the primary outcome. Subjective pain intensity and unpleasantness are commonly assessed pain dimensions in heat pain paradigm studies. Intensity entails the cognitive dimensions of pain, whereas unpleasantness comprises the affective dimension of pain. Also, after each pain stimuli participants will complete the Counselor Rating Form-Short (CRF-S) to assess they perception of the experimenter.

After pain measurement, there will be a final assessment, using the credibility and effectiveness of the placebo analgesia expectation (CMQ; adapted Version of the Context Model Questionnaire), as well as the CRF-S and a short questionnaire on participants attitude towards dogs and pets (AAPL questionnaire). Study factors, dependent variables and schedule of the study are represented in Tables 1 and 2.

Before starting with the experimental procedures all participants will be introduced to the TSA-II de-vice and the study procedure. All participants will be assigned to a baseline assessment of heat tolerance and threshold. Participants will be randomized to the four experimental conditions (see below) followed by experimentally induced pain using an established and standardized heat pain paradigm: Heat stimuli will be administered to the right volar forearm using a 30x 30-mm Peltier device (Medoc, Ramatishai, Israel; TSA-II) placed at 2/3 of the distance from wrist to elbow. Heat pain threshold will be determined by the methods of limits. Temperature will be increased from the baseline (32°C) at a rate of 0.5°C /s. Participants are instructed to press the button to determine the turning point from perceiving warmth to the perception of pain. When the pain threshold has been reached, the device will resume from its baseline (32 °C) with a rise of 0.5 °C/s. This procedure will be repeated three times (Locher et al., 2017). Pain threshold will be defined as the average of the three measurements. Pain tolerance will also be determined by the method of limits: Participants will be asked to stop the increasing heat stimulus at the moment they cannot stand the heat any longer. Three measurements will start at 32 °C, with a rise of 0.5 °C/s. Heat tolerance will be defined as the average of the three measurements. Pain threshold will always be measured prior to pain tolerance in order to minimize interference between pain threshold and tolerance. After pain induction, participants will complete in the CMQ and the CRF-S questionnaires to detect how they perceive the experimenter. All instructions will be conveyed in a standardized manner to ensure that the participant-experimenter relationship is comparable in terms of friendliness and attention across all four conditions.

Experimental conditions:

• Placebo condition (PL): Participants will receive verbal information that they are receiving an analgesic cream (i.e. ""Antidolor, containing Lidocain "), which has been shown to produce significant pain reduction in previous clinical trials. However, they will receive an inert cream.
• Animal-assisted placebo condition (AAPL): Participants receive the same verbal information as in the PL condition. Additionally, they will be told that a dog will be present during the experiment to examine whether animals can be present during experimental studies or if they are too big of a distraction. Prior to the pain assessment, participants are allowed to greet the dog. The intensity of interaction will be documented and be rated on a scale from 1-5 (1=very low degree of interaction, 5=very high degree of interaction). During the experiment the dog will be lying in the room with some distance to participants to avoid further physical interaction. The dog will always be lying at the same spot. Therefore, the distance between participant and dog will always be the same. However, participants will still be able to see the dog.
• Dog only condition (DO): Participants will be told that a dog will be present during the experiment to examine whether animals can be present during experimental studies or if they are too big of a distraction. Prior to the pain assessment, participants are allowed to greet the dog. The intensity of interaction will be documented and be rated on a scale from 1-5 (1=very low degree of interaction, 5=very high degree of interaction). During the experiment the dog will be lying in the room with some distance to participants to avoid further physical interaction. During the experiment the dog will be lying in the room with some distance to participants to avoid further physical interaction. The dog will always be lying at the same spot. Therefore, the distance between participant and dog will always be the same. However, participants will still be able to see the dog. After the introduction of the dog, participant will have the verbal information that the applied cream only moisturizes the skin to allow accurate pain measurements.
• No Dog condition (ND): Participants will participant will have the verbal information that the applied cream only moisturizes the skin to allow accurate pain measurements.

After the intervention, pain induction will then be performed for a second time (test phase) and participants complete the CMQ, CRF-S and AAPL questionnaires. Finally, participants will be fully debriefed about the real aims of the experiment (delayed informed consent). The expected study duration will be 70 minutes.

Inclusion criteria

• Age ≥ 18 years
• Right-handedness

Exclusion criteria

• Being scared of dogs or dog hair allergy by self-report
• Any acute or chronic disease (chronic pain, hypertension, heart disease, renal disease, liver disease, diabetes) as well as skin pathologies, neuropathies or nerve entrapment symptoms, sensory abnormalities affecting the tactile or thermal modality
• Current medications (psychoactive medication, narcotics, intake of analgesics) or being currently in psychological or psychiatric treatment
• Insufficient German language skills to understand the instructions
• Previous participation in studies using pain assessment with Peltier Devices
• Current or regular drug consumption (THC, cocaine, heroin, etc.)
• pregnancy
• nursing women