## 2 Materials and Methods
### Procedure  
The Ethical Review Board of the Terrassa Health Consortium (Consorci Sanitari de Terrassa) provided approval for all the procedures related to this study (reference number: 02-22-107-029). Informed consent was obtained from all participants, ensuring that any questions or concerns they had regarding the assessments or intervention were fully addressed prior to signing the consent form. Participants were informed about data confidentiality, and each participant was assigned a distinct identification code to protect their privacy. The study was conducted between January 2023 and September 2025. To complete the study, participants were required to attend at least 80% of the scheduled sessions. Those who failed to meet this attendance requirement were excluded. HRV measurements were taken at three stages: in the first session, mid-way through the intervention, and in the final session. Multimodal IVR Intervention  
The multimodal IVR program was conducted in two different time frames: 8 weeks for group 1 and 12 weeks for group 2. Participants attended two weekly 60 min sessions, resulting in 16 sessions for group 1 and 24 for group 2. The intervention was delivered using MK360 IVR hardware developed by Broomx Technologies, a lightweight, cost-effective solution designed for individual and small group sessions in small or medium-sized spaces, accommodating 1 to 10 participants. This headset-free IVR system employs a multiple-patented projection technology that displays 360\({}^{\circ}\) media and interactive virtual environments across three walls and the ceiling, creating an immersive group experience. The MK360 device integrates a projection module, CPU, GPU, speaker system, WiFi hotspot, and multiple connectivity options, ensuring seamless operation and adaptability to various settings. The study was conducted in a spacious clinical room at the hospital, optimized for group interaction, with all windows covered to prevent external light interference and furniture removed to eliminate obstructions, ensuring an unobstructed and fully immersive IVR experience. The sessions were conducted in groups of five and led by a neuropsychological. Each session began with a 10 min introduction given by the neuropsychological, who outlined the goals of the session and explained their importance. The briefing covered how PCC affects cognitive and emotional functions, and the neuropsychological encouraged participants to incorporate new skills into their everyday routines. Participants were also encouraged to evaluate their learning strategies and recognize their cognitive patterns. The 60 min sessions included three main components: mindfulness, cognitive training, and physical exercises. Although the specifics of each session varied, the structure and timing of the activities remained constant. Mindfulness (10 min): An adapted version of [PERSON]'s Mindfulness-Based Stress Reduction program [49] was followed, including body scanning, seated meditation, and gentle Hatha yoga to increase body awareness. The neuropsychologist highlighted thatthe objective of mindfulness was to help participants maintain functional stability under difficult conditions and to thereby enhance their ability to remain active and independent. Cognitive Training (30 min): Cognitive exercises were carried out in immersive virtual environments designed to replicate real-life settings (e.g., parks, tourist destinations) to strengthen cognitive abilities. The tasks were sequential and focused on different cognitive areas, including attention, memory, and executive function, with the degree of difficulty being adjusted to participant performance. The \"Parc Guell\" simulation involved recalling stimuli and details to boost attention, social cognition, and memory. The \"Crazy Lines\" activity promoted working memory and processing speed by asking participants to follow color-coded numerical sequences.