by PARTTYLI RINNE, JUHA M. LAHNAKOSKI, HEINI SAARIMAKI, MIKKE TAVAST, MIKKO SAMS, & LINDA HENRIKSSON
Abstract
Feelings of love are among the most significant human phenomena. Love informs the formation and maintenance of pair bonds, parent-offspring attachments, and influences relationships with others and even nature. However, little is known about the neural mechanisms of love beyond romantic and maternal types. Here, we characterize the brain areas involved in love for six different objects: romantic partner, one’s children, friends, strangers, pets, and nature. We used functional magnetic resonance imaging (fMRI) to measure brain activity, while we induced feelings of love using short stories. Our results show that neural activity during a feeling of love depends on its object. Interpersonal love recruited social cognition brain areas in the temporoparietal junction and midline structures significantly more than love for pets or nature. In pet owners, love for pets activated these same regions significantly more than in participants without pets. Love in closer affiliative bonds was associated with significantly stronger and more widespread activation in the brain’s reward system than love for strangers, pets, or nature. We suggest that the experience of love is shaped by both biological and cultural factors, originating from fundamental neurobiological mechanisms of attachment.
Introduction
Feelings of love are among the most salient in human life: they may provide intense pleasure while promoting pair bonding and parental investment (Bartels and Zeki 2000; Bartels and Zeki 2004; Nummenmaa et al. 2014; Nummenmaa et al. 2018; Rinne et al. 2023). Previous studies suggest that feelings of romantic and maternal love are associated with activation of attachment and reward networks in the brain (Bartels and Zeki 2000; Bartels and Zeki 2004; Aron et al. 2005; Fisher et al. 2005; Noriuchi et al. 2008; Acevedo et al. 2012; Shih et al. 2022). These evolutionarily old brain regions have been shown to be involved in both long-term bonding and parental care behaviors also in other mammals (Winslow et al. 1993; Bartels and Zeki 2004; McGraw and Young 2010; Tabbaa et al. 2016). But when we love, is it neurally the same thing to love, for instance, our child as to love nature?
Even though romantic and parental love form the prototypical and biological core of love, the human phenomenon of love is much more. Psychological, philosophical, and theological conceptualizations of love abound with various taxonomies, often offering rich vocabularies that permit love to be felt for people beyond one’s immediate family—think of love for one’s friends and love for strangers (or “neighbors,” as strangers are often called in Christian parlance). Complex, historically resilient social and cultural institutions concerning billions of people are built on notions involving transcendent entities that allegedly feel love for the whole of humankind—or at least for a particular ethnic or sociocultural subgroup. Human love may transcend boundaries between species, as pet owners feel and express love for their pets, and mutual gazing between dogs and their owners has been found to engage oxytocin pathways similarly to mother–infant bonding (Nagasawa et al. 2015, see also Applebaum et al. 2021). Feelings of love may not even require individual organisms or beings as their counterparts, as a recent study found that love of nature is among the most often experienced types of love (Rinne et al. 2023). Objects of love are socially, culturally, and subjectively variable (see Fehr and Russell 1991; Fehr 1994; Shpall 2016; cf. Rinne et al. 2023). Subjective feelings of love for various objects form a continuum from strongly to weakly felt loves (Rinne et al. 2023).
Love is closely linked to feelings and behaviors related to attachment. Even though the concept of attachment is often associated mainly with pair bonding and/or parental care, the human phenomenon of attachment covers a wider array of relations and objects. In her recent theorization of the neurobiology of human attachments, Feldman treats the neurobiology of attachment bonds as synonymous with that of love (Feldman 2017). With respect to mammals, she classifies these bonds into parent–infant, pair bond, peer (friend), and conspecific (unknown member of the same species) relations according to degrees of social proximity and biobehavioral intimacy. In this conceptualization, the term “attachment” cannot be reduced to pair bonding or parent-offspring relations but is a generic term informing various gradients of affiliation such that affiliations with conspecifics (strangers) represent the weakest degree of affiliation. In their state-of-the-art meta-analysis of neuroscientific research on human affiliation, Bortolini et al. (2024, 2) adopt the view that the terms “affiliation,” “bonding,” and “attachment” may be treated synonymously because of conceptual overlap. These authors define “affiliation” as “one’s disposition to enjoy, seek, and sustain close interpersonal bonds. On a subjective level, it involves feelings of warmth and affection for significant others.” Here, we adopt the gradient typology of Feldman (2017), according to which affiliation comes in degrees according to social closeness.
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