Biopsychosocial Predictors of Cognitive Functioning: A Focus on Stress, Loneliness, and Physiological Regulation in Young Adults

This Doctoral Thesis examines cognitive functioning in young adults from an integrative biopsychosocial perspective, analyzing the interaction between psychosocial stress, loneliness, dispositional vulnerability traits, and physiological regulation markers, particularly the hypothalamic–pituitary–adrenal axis and the autonomic nervous system. The research is framed within contexts of social transformation, including the post-pandemic period and international academic mobility. Both subjective cognitive functioning, assessed through self-reported memory complaints and perceived executive difficulties, and objective cognitive performance across domains were evaluated. Findings show that subjective cognitive functioning is mainly influenced by psychological and dispositional factors. Higher perceived stress and neuroticism were associated with greater memory complaints. Chronic HPA-axis biomarkers were not directly linked to these complaints but moderated the association between psychological vulnerability and cognitive self-perception. High harm avoidance and low self-directedness were related to increased perceived prefrontal symptomatology. These associations were partially mediated by psychological inflexibility, indicating that rigid emotional and cognitive regulation intensifies perceptions of executive inefficiency. Objective cognitive performance revealed domain-specific effects shaped by social context. Greater loneliness and residence abroad were associated with poorer working memory and prospective memory. Loneliness also strengthened the association between cortisol levels and prospective memory, suggesting that social context modulates the cognitive impact of physiological stress. During academic mobility, students in advanced stages reported lower perceived stress and showed better performance in delayed declarative memory and time-based prospective memory, reflecting adaptive processes. Physiological indicators played a modulatory role. Higher cortisol levels were associated with better working memory and delayed recall, while greater vagally mediated heart rate variability was linked to improved event-based prospective memory. Among international students with low heart rate variability, loneliness combined with subjective cognitive complaints predicted poorer prospective memory, highlighting autonomic flexibility as a protective factor. Overall, two complementary pathways emerge: a psychological pathway, in which stress, neuroticism, loneliness, and psychological inflexibility increase negative self-monitoring of cognition; and a physiological pathway, which does not directly determine performance but influences when psychological vulnerability translates into objective cognitive inefficiency. Cognitive variations in young adulthood may be understood as dynamic expressions of emotional, social, and physiological adaptation to prolonged change.