Perceived social isolation, or loneliness, is a significant risk factor for cognitive decline and is associated with various negative cognitive and emotional outcomes. Research indicates that loneliness affects attention, cognition, and behavior, contributing to poorer executive functioning, increased negativity, and depressive cognition. It also heightens sensitivity to social threats and leads to a confirmatory bias in social cognition, which can be self-protective but paradoxically self-defeating. Loneliness is linked to heightened anthropomorphism and social contagion, which may threaten social cohesion. Studies show that loneliness is associated with reduced cognitive performance, faster cognitive decline, and an increased risk of Alzheimer's disease. Longitudinal studies, such as those by Tilvis and Wilson, found that loneliness independently predicts cognitive decline and is linked to a higher risk of clinical Alzheimer's disease. These findings suggest that loneliness may be a causal factor in cognitive decline rather than just a consequence. Additionally, loneliness is associated with increased cortisol levels, reduced lymphocyte proliferation, and altered gene expression related to glucocorticoid response. Loneliness also impairs executive functioning, particularly in attentional control and self-regulation. Experimental studies show that lonely individuals perform worse on cognitive tasks and exhibit poorer self-regulation when they feel isolated. Loneliness is also linked to increased negative mood, anxiety, and depressive symptoms, and it affects social interactions, leading to more negative social experiences. Lonely individuals tend to form more negative social impressions and have less charitable expectations and actions toward others. This can lead to a cycle of social isolation and negative social interactions. Loneliness can also promote social connections through various means, such as nostalgic reminiscences, parasocial relationships, and anthropomorphism of pets, technology, and celestial bodies. Loneliness is contagious and can spread through social networks, affecting individuals' social connections and increasing their sense of isolation. This contagion is not secondary to depression but is a separate phenomenon. The mechanisms underlying the association between loneliness and cognitive decline are not fully understood, but research suggests that loneliness may affect neurophysiological processes, including reduced prefrontal-cortico-striatal functioning and increased inflammation. The study highlights the complex relationship between perceived social isolation and cognition, emphasizing the need for further research into the biological and cognitive bases of loneliness and its effects on cognitive functioning. Understanding these mechanisms is crucial for developing interventions to reduce perceived social isolation and promote healthy social connections.Perceived social isolation, or loneliness, is a significant risk factor for cognitive decline and is associated with various negative cognitive and emotional outcomes. Research indicates that loneliness affects attention, cognition, and behavior, contributing to poorer executive functioning, increased negativity, and depressive cognition. It also heightens sensitivity to social threats and leads to a confirmatory bias in social cognition, which can be self-protective but paradoxically self-defeating. Loneliness is linked to heightened anthropomorphism and social contagion, which may threaten social cohesion. Studies show that loneliness is associated with reduced cognitive performance, faster cognitive decline, and an increased risk of Alzheimer's disease. Longitudinal studies, such as those by Tilvis and Wilson, found that loneliness independently predicts cognitive decline and is linked to a higher risk of clinical Alzheimer's disease. These findings suggest that loneliness may be a causal factor in cognitive decline rather than just a consequence. Additionally, loneliness is associated with increased cortisol levels, reduced lymphocyte proliferation, and altered gene expression related to glucocorticoid response. Loneliness also impairs executive functioning, particularly in attentional control and self-regulation. Experimental studies show that lonely individuals perform worse on cognitive tasks and exhibit poorer self-regulation when they feel isolated. Loneliness is also linked to increased negative mood, anxiety, and depressive symptoms, and it affects social interactions, leading to more negative social experiences. Lonely individuals tend to form more negative social impressions and have less charitable expectations and actions toward others. This can lead to a cycle of social isolation and negative social interactions. Loneliness can also promote social connections through various means, such as nostalgic reminiscences, parasocial relationships, and anthropomorphism of pets, technology, and celestial bodies. Loneliness is contagious and can spread through social networks, affecting individuals' social connections and increasing their sense of isolation. This contagion is not secondary to depression but is a separate phenomenon. The mechanisms underlying the association between loneliness and cognitive decline are not fully understood, but research suggests that loneliness may affect neurophysiological processes, including reduced prefrontal-cortico-striatal functioning and increased inflammation. The study highlights the complex relationship between perceived social isolation and cognition, emphasizing the need for further research into the biological and cognitive bases of loneliness and its effects on cognitive functioning. Understanding these mechanisms is crucial for developing interventions to reduce perceived social isolation and promote healthy social connections.