Despite being fundamental to human interactions, the neural processes involved in affiliation remain underexplored in research.

A study published in the journal Neuroscience and Biobehavioral Reviews, led by researchers from the D’Or Institute for Research and Education (IDOR), tackled this gap by investigating the brain circuits underlying human bonding. This metanalysis reviewed a diverse range of functional MRI studies focused on the brain regions associated with affiliation, offering a more comprehensive view of the neural structures involved in social cognition. 

The Brain, Emotions, and Evolution 

Experts argue that what sets humans apart from other species lies in three key pillars: advanced cognition, social learning, and hypersociability. Our ability to form relationships is as significant to our evolution as our intellect. 

Between 14,000 and 50,000 years ago, during the Late Stone Age, our ancestors experienced the so-called Upper Paleolithic cultural explosion, which shaped our artistic, religious, and social manifestations, making them more akin to what we know today. These changes also transformed our species anatomically and neurologically. 

Although affiliation and sociability are central to human interactions—ranging from family ties to friendships and romantic relationships—research on these behaviors has been much more robust in animal models. Studies on human affiliation are still in their early stages. 

Most human studies have focused on a narrow set of affiliative stimuli, such as romantic partners or close family members, providing a fragmented understanding of the neural structures involved. Consequently, previous metanalyses have highlighted a limited number of brain regions, primarily those linked to the brain’s reward system, such as the nucleus accumbens. 

Key Brain Areas Related to Affiliation 

To expand upon this limited scope, researchers conducting the metanalysis examined 50 functional MRI studies that explored human affiliative stimuli. These included diverse relationships—parental, romantic, platonic—yielding a broader perspective on the spectrum of human emotional connections. The analysis involved activation maps from over 2,300 participants. 

The study employed rigorous methods, including advanced algorithms like Activation Likelihood Estimation (ALE) and Signed Differential Mapping (SDM), to ensure data precision and reliability. Key brain areas identified in affiliation processes include: 

• Medial Preoptic Area (mPOA): Critical for regulating social and parental behaviors. 

• Septal Region: Involved in modulating emotions and social behaviors. 

• Nucleus Accumbens (NAcc): Central to reward and motivation. 

• Amygdala: Processes emotional and social information. 

• Ventromedial Prefrontal Cortex (vmPFC): Contributes to decision-making and reward processing. 

• Anterior Insula (AI): Engaged in emotional awareness and interoceptive perception. 

• Dorsal Anterior Cingulate Cortex (dACC): Important for conflict evaluation and emotionally driven decision-making. 

New Insights from the Metanalysis 

In addition to previously noted regions like the nucleus accumbens, the study highlighted the medial preoptic area and septal region, both part of the basal forebrain, as crucial players in human affiliation and emotional bonding. These findings align with research on other mammals, underscoring shared mechanisms across species. 

The study also emphasized the role of the brain’s salience network, which includes the amygdala, anterior insula, and dorsal anterior cingulate cortex. These structures are associated with creativity, emotional perception, and social awareness, extending beyond traditional views of emotional processing. “The human brain uses regions that are evolutionarily similar to those of other mammals but appears to have a more extensive social circuitry, involving cortical areas related to social cognition,” says the study’s first author and IDOR researcher, Dr. Tiago Bortolini. 

Interestingly, cerebellar activation emerged during affiliative tasks. While traditionally linked to motor functions, this finding suggests potential roles in social interactions. However, researchers note that this activation might reflect tasks requiring mentalization, leaving its direct connection to social cognition inconclusive. 

The Importance of Social Neuroscience 

This study offers a more detailed and comprehensive view of the neural circuits underpinning human affiliation. By identifying new brain regions and confirming the importance of previously recognized areas, the researchers contribute significantly to understanding how the human brain orchestrates the complex social interactions central to our species. 

With a robust methodology and broad evidence base, the study establishes a solid foundation for future research in social neuroscience, human brain evolution, and the biological processes behind our social connections—the very essence of our humanity. 

Written by Maria Eduarda Ledo de Abreu.