All people experience stress at certain times, as it is a natural response to threats. However, a complex interaction of social, technological, work-related, and environmental factors has contributed to a prolonged stress response, leading to a rise in chronic anxiety problems throughout the 21st century. According to the National Health Survey, 6.7% of adults report chronic anxiety. Furthermore, there is a significant gender gap, with prevalence being twice as high in women as in men (9.1% in women and 4.3% in men). Members of the university community are not immune to this issue. Several recent studies have highlighted that, for example, university students are exposed to alarmingly high levels of stress. According to various surveys, 35% of higher education students suffer from anxiety, and 30% suffer from depression. Moreover, this is a global phenomenon. In the United States, a survey by the American College Health Association shows that stress has become the most serious obstacle to studying among American students; in the United Kingdom, another study shows that 45% of students report feeling stressed by their courses. Gender, as a demographic factor, also seems to play a significant role, as female students are the most affected, not only by stress but also by other aspects of mental health. In fact, this represents another problem: most university students report, in addition to stress, a large number of symptoms associated with mental health problems, such as sadness, lack of energy or motivation, anxiety, depression, hopelessness, insomnia, irritability, mood swings, panic, or self-harm ideations. Another aspect that has negatively impacted not only stress but also the mental health of the student population worldwide has been the COVID-19 pandemic. Several studies have shown an increase in stress among university students from various countries, both European and non-European, following the start of the pandemic. Regarding the working members of the university community, such as teaching and research staff (PDI) or administrative and service staff (PTGAS), chronic work-related stress and associated pathologies, such as burnout syndrome, are among the leading emerging psychosocial risks. In this population, sociodemographic factors such as age and gender play a fundamental role, with younger staff and, within this group, women, scoring the highest in areas related to emotional exhaustion and stress. In particular, among the PDI, younger women in the social sciences, in the early stages of their professional development, with lower contractual figures and high teaching loads, experience higher levels of stress. Both stress and other mental health issues decrease quality of life, increase absenteeism among workers and students, and reduce professional and academic performance within the university community. Therefore, the development of preventive and palliative strategies, within the university itself, to reduce the impact of stress and protect the health and well-being of its members is highly recommended. By implementing these measures and promoting a culture of well-being, universities can help mitigate the negative impact of stress and improve the quality of life of their community members. In this context, it is a priority to develop new, cost-effective, and accessible stress reduction programs within the university space. Three approaches that meet these criteria are Heart Rate Variability Biofeedback (HRV-BF), Mindfulness-based programs (MBPs), and Interoception Training programs (ITPs). Heart Rate Variability (HRV) is the temporal variation between successive heartbeats (RR intervals) and serves as a quantitative biomarker of the autonomic nervous system (ANS) balance and physiological stress. Dysregulation of the ANS, mainly increased sympathetic activity and decreased parasympathetic activity (vagal hypofunction), is a common feature of chronic stress, anxiety, and mood disorders and appears to be a central biological substrate linking these disorders to a range of physical dysfunctions. Alterations in the functioning of the autonomic nervous system that promote a decrease in vagal (parasympathetic) activity are reflected in reductions in HRV indices, which in turn are associated with emotional dysregulation, decreased psychological flexibility, and faulty social engagement-disorders linked to hypoactivity in the prefrontal cortex. Similarly, work-related stress has been shown to reduce HRV. On the other hand, high HRV indicates greater parasympathetic activity and better self-regulation, which is associated with a lower cardiovascular risk and better cognitive performance. Together, these findings support the idea that HRV could represent a useful endophenotype for psychological/physical comorbidities, and its measurement and routine application should be recommended to assess the effectiveness of training based on these measures for emotional regulation dysfunctions. Indeed, HRV is currently considered a biomarker of the ANS function associated with both physical and mental health and well-being. Biofeedback is a way of helping individuals develop greater awareness and the ability to regulate their physiological functioning using signals from their own bodies to improve their well-being, health, and performance. Specifically, HRV biofeedback is a well-established and empirically supported technique to improve emotional self-regulation and alleviate symptoms of stress, anxiety, and other psychophysiological disorders. Quantitative studies suggest that HRV-BF training reduces anxiety by 26%, fatigue by 15%, blood pressure by 10%, cholesterol by 14%, and increases fitness levels by 40%. During HRV-BF training, individuals learn to breathe slowly, gradually reaching the optimal breathing frequency that maximizes HRV. Additionally, it has recently been shown that this training induces plastic changes in brain activity and connectivity in regions related to emotion regulation and executive functions. Although there are numerous studies highlighting the effectiveness of HRV-BF in reducing stress, most of them rely on subjective measures obtained through self-reports, so there is a need for research that includes both neuropsychological and physiological parameters when analyzing the effectiveness of biofeedback training in preventing and reducing stress in high-demand work or academic environments. Mindfulness has been defined as "paying attention in a particular way, on purpose, in the present moment, and without judgment". The first mindfulness-based stress reduction (MBSR) program was developed over 50 years ago by Jon Kabat-Zinn, and since then, countless scientific studies have demonstrated the effectiveness of MBPs in reducing stress, as well as their efficacy in treating anxiety and depression disorders. In fact, a recent randomized clinical trial has shown that MBPs are as effective as escitalopram (first-choice medication) in treating anxiety disorders. Various formats of MBPs for stress reduction among university community members have been used in several studies, varying primarily in the focus of attention, duration, or the traditional in-person nature of the training versus those guided by new technologies (apps). Despite this variability, all these studies show a positive effect of these programs on perceived stress in this population. Also, like HRV-BF, all reviewed studies rely on self-reports of stress without measuring or evaluating any psychophysiological or neurophysiological parameters (objective). In conclusion, the success of MBPs in reducing or mitigating stress in university community members makes these techniques a useful tool for preventing psychosocial risks, such as stress, in university settings. In recent years, our understanding of the physiological changes associated with mindfulness practice, as well as the potential mechanisms underlying its efficacy and effectiveness as a treatment for various mental disorders, has significantly advanced. For example, it is widely accepted that the implementation of an MBP in non-clinical samples leads to an increase in HRV. On the other hand, similarly to the case of HRV-BF, mindfulness practice can modulate prefrontal cortex activity, promoting emotional regulation, cognitive control, attentional stability, and resilience to stress. These changes may underlie many of the cognitive and emotional benefits associated with mindfulness training. However, individual responses to mindfulness practices can vary, and further research is needed to fully understand the underlying mechanisms of these effects. Interoception is the process by which the nervous system perceives, interprets, and integrates signals from within the body, including sensations from internal organs and physiological states. This encompasses sensory signaling (neural and humoral), perceptual processing, and the psychological representation of such sensations. In simpler terms, interoception is the ability to feel and understand what is happening inside the body, such as heartbeat, breathing, hunger or fullness, thirst, and body temperature. Interoception plays a key role in emotion regulation, decision-making, self-awareness, and health regulation. Some authors suggest that interoception plays a key role in emotional experience, as it allows individuals to recognize their emotional states and regulate them. It has also been shown that emotional dysregulation can result in distorted perceptions of interoceptive information, and vice versa, that training interoception improves emotional regulation and helps reduce anxiet. In fact, recent studies have shown that interoception training can improve mental health outcomes, including emotional regulation and stress management, and it is considered a promising intervention for those suffering from high levels of stress and anxiety. Recent research into interoception has led to the development of interoceptive training programs, which have proven effective in reducing stress, improving emotion regulation, and increasing mindfulness. A growing body of evidence suggests that ITPs can enhance emotional awareness and regulation and improve autonomic nervous system regulation, potentially contributing to reduced anxiety and stress. To summarize, interoception-based interventions provide promising strategies for reducing stress and improving well-being by fostering greater body awareness and self-regulation. Like HRV-BF and MBPs, ITPs can be easily implemented in university settings and may represent a cost-effective alternative for managing stress. However, like mindfulness, it would benefit from more research into the neurophysiological and cognitive effects of such training, especially in terms of potential changes in brain activity related to emotional regulation and stress reduction.

Although the scientific evidence on the benefits of HRV-BF (Heart Rate Variability Biofeedback), MBPs (Mindfulness-Based Programs), and ITPs (Interoception Training Programs) in relation to stress reduction is more than notable, to the best of our knowledge, there are no randomized experimental studies analyzing the effectiveness of HRV-BF, MBPs, and ITPs in the prevention and/or reduction of stress that rely on the evaluation of variables of different natures: psychological, neuropsychological, psychophysiological, and neurophysiological. Furthermore, it would be of great interest to conduct a long-term evaluation of the effects of these training programs.

The aim of this project is to analyze the impact of a HRV-BF training program, an MBP, and an ITP among members of the University of Seville community, evaluating their effects on stress in both women and men through neuropsychological, psychophysiological, and brain activity measures.