Pain is a highly subjective and variable phenomenon. Different persons perceive objectively identical nociceptive stimuli differently. Moreover, the same person may perceive objectively identical stimuli differently in different situations, or even from one moment to another. In the brain, the processing of pain is associated with different neuronal responses originating from an extended network of brain areas. These responses include evoked activity as well as neuronal oscillations at alpha (8-13 Hz), beta (14-30 Hz) and gamma (30-100 Hz) frequencies. All these responses covary with moment-to-moment variations of pain within subjects (intra-subject variability). However, only the gamma response correlates with variations of pain between subjects (inter-subject variability). To date, it has remained unknown whether these relationships remain stable and reproducible across longer periods of time (inter-session-variability). Thus, the current project aims to systematically characterize how different pain-associated brain responses encode intra-individual, inter-individual, and inter-session variations of pain perception. To this end, the investigators will record pain-associated brain responses of 155 healthy participants at two different points in time. Each time, short painful stimuli will be applied to the participants' hand and they will be asked to verbally rate the perceived pain intensity, while pain-associated brain responses will be recorded using electroencephalography (EEG). This will allow to investigate the relationships between pain-associated brain responses and intra-individual and inter-individual variations of pain and to compare these measures and their relationships between sessions. In order to quantify the influence of demographic and psychological factors, i.e. age, mood and sleep quality / quantity on pain variability, established questionnaires will be used. In order to compare the functional significance of brain responses to other pain-associated neuronal responses, pain-associated responses of the autonomic system will be recorded and related to pain variability. Results of the project promise to elucidate the neuronal mechanisms underlying intra-individual, inter-individual and inter-session variability of pain. Such knowledge provides the basis for the development of a biomarker for pain, which might reasonably complement the self-assessment of pain. Moreover, as pain perception and objective stimulation tend to dissociate in pathological pain, the current project promises insights into the neuronal mechanisms of chronic pain.

Inclusion Criteria:

• aged 18 years or above
• Right-handedness
• Written informed consent

Exclusion Criteria:

• Pregnancy
• Neurological or psychiatric diseases (e.g. epilepsy, stroke, depression, anxiety disorders)
• Severe general illnesses (e.g. tumors, diabetes)
• Skin diseases (e.g. dermatitis, psoriasis or eczema)
• Current or recurrent pain
• (Regular) intake of centrally acting, antibiotic or analgesic medication
• Surgical procedures involving the brain or spinal cord
• Head trauma followed by impairment of consciousness
• Past fainting spells or syncopes
• Side-effects following previous electrical or magnetic stimulation
• Side-effects following previous thermal stimulation

Pseudonymized individual participant data sets will be made available at the OSF online repository [https://osf.io/\] upon publication.

Participants will not be informed about the intensities of the nociceptive stimuli administered during the experimental paradigm.