Cold Water and Decision-Making

The behavioral within-subject cross-over design study "CoVa" aims to investigate the effect of a short-term full-body cold-water immersion vs. warm-water immersion control on value-based choice, psychological well-being, and peripheral physiology.

This randomized within-subject cross-over design behavioral study in cognitive neuroscience will employ an acute peripheral physiological intervention, i.e., a 10-minute full-body cold-water (10-16°C) immersion vs. a control condition (10 min @ 30- 36°C water) on two visits separated by approx. 30 days. Forty eligible female and male participants will be subject to a head-out full-body cold-water immersion or a warm-water condition (control) on two visits. Participants will perform resting-state and task-based non-invasive electrophysiological recordings of the heart, pulse, respiration, skin conductance, and pupil, will undergo thermographic imaging, pre- and post-immersion blood sampling (4 time points), engage in two computer-based decision-making tasks (reinforcement learning task, risk decision-making task), a brief food choice task, and receive a battery of psychometric questionnaires. The visits are separated by approximately 30 days and do not differ in their timeline except for the primary intervention, i.e., cold vs warm-water immersion, and the medical screening on visit 1.

Inclusion Criteria: * 18-40 years of age * Consent to participate * Fluency in German * Physically and mentally healthy * BMI 18-30 kg/m2 * Normal day-night rhythm Exclusion Criteria: * Raynaud syndrome * Cold urticaria * High resting heart rate (\>160 beats per minute) * Acute infection * Diagnosed current or former illnesses of * Brain and mind * Heart and blood circulation * Gastrointestinal system * Endocrine system * Other serious past or present medical conditions * Wearing of medical devices (e.g., pacemaker) * Fear of blood, needles, or phlebotomy * Allergies to plasters, gels, and other medical equipment * Allergies to commercially available liquid meals (e.g., shakes, yfood Labs GmbH) * Recurrent intake of medication which affect metabolism * Regular nicotine consumption (e.g., vaping, cigarettes) * Excessive alcohol consumption (\>14 servings/week) * Recent illegal drug consumption (within 2 weeks prior) * Strong mental or physical stress * Excessive exercise (\>2 h high-intensity exercise/day) * Pregnancy or breastfeeding * Inability to wear skin-exposing swimwear, e.g., for religious reasons * Affinity for winter swimming, cryotherapy, breathwork (\>3 times/year)