The biology of love

Perhaps an aid for character development. Or not.

In any case, PG found this fascinating.

From Aeon:

An infant is born. The radiant mother holds the baby in her arms and immediately begins to scan the infant’s face, softly caressing the little fingers while uttering repetitive sing-song vocalisations, her face lighting up in an affectionate smile. She has never had a baby before but intuitively knows what to do. Proud and oblivious, she feels no one has ever cared for such a gorgeous child; yet she stands along a great line of mammalian mothers who lick, groom, sniff, smell, touch, poke, nurse and handle. Rats do it, sheep do it, even educated chimps do it … let’s fall in love.

Behind our loving mother, evolution works with its quick-and-dirty tools to ensure the bond is cemented, the infant finds the nipple, the mother engages; brain meets the world. The synchronous dance of mother and child begins and, upon its unique rhythms, a relationship is formed. This relationship will incorporate, like expanding ripples, the child’s emerging abilities across development and into dialogue: babbling, creating imaginary scenarios, the capacity to collaborate, feel the pain of others, comprehend emotions, discuss conflicting positions, argue convictions, until the child grows and can meet the mother in a full adult-to-adult relationship of empathy, intimacy and perspective-taking. Like the 12-bar-blues, synchrony gains in range, repertoire, complexity and timbre, but its basic rhythms stay safe and secure.

The synchronous mother-infant dance will set the stage for the child’s affiliative bonds throughout life: with father and siblings at home, with close friends in school, through adolescence and first love and, finally, as parents to children of their own. Those affiliations, and the terms of endearment they set, will guide the child’s conduct within society-at-large, shaping the empathy, responsibility, collaboration and self-restraint by which he or she will meet fellow-humans: co-workers, neighbours and strangers.

Evolution is thrifty, and once a trick works, it will be repurposed endlessly. A new mother and infant enter the world tapping the social patterns, habits, beliefs, customs, fears, hopes, joys and rituals of the old ones. The family, the group, the tribe lives on from one generation to the next. Resilience, endurance and the durability of the group can be achieved only by coordinating action among kin, first genetically and then symbolically. Infants acquire the capacity for coordinated action in the context of the mother’s body and its unique provisions: a mother’s smell, touch, heart rhythms, eye-gaze, smile. Then it expands across time, place and person. But such massive expansion does not come without its risks.

What tricks of the trade does evolution utilise to ensure that bonding, so critical for survival and continuity of life on Earth, happens as planned and all pieces of the puzzle fall safely into their place? After decades following thousands of mother-infant dyads, hundreds from birth to young adulthood, my lab has mapped the ‘neurobiology of affiliation’ – the emerging scientific field that describes the neural, endocrine and behavioural systems sustaining our capacity to love. The foci of our research – the oxytocin system (based on the neurohormone of bonding); the affiliative, or social, brain; and biological synchrony between mother and child – are all marked by great plasticity, and sculpted throughout animal evolution to reach their exquisite complexity in humans. And they all lean on automatic and ancient machinery that runs the risk of turning love on its head into fear.

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Oxytocin, the first element in the neurobiology of bonding, is an important driver of both care and prejudice. A large molecule produced mainly by neurons in a small region of the brain called the hypothalamus, oxytocin is known for coordinating bonding, sociality, and group living. From the hypothalamus, oxytocin targets receptors in the body and the brain, primarily the amygdala, a centre for fear and vigilance; the hippocampus, where memory resides; and the striatum, a locus of motivation and reward. Through these pathways, the bonding hormone, oxytocin, functions with the precision of a neurotransmitter and the longevity of a hormone, reaching faraway locations and broadly influencing behaviour. Importantly, oxytocin is released not only through the central part of the neuron, but also its extensions, called dendrites. The dendrites are primed to increase oxytocin release whenever attachment memories are invoked.

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Memory of these early attachments helps us re-enact the unique state that Sue Carter, a neurobiologist at the University of Indiana, calls ‘immobility without fear’. These same memories enable what the English psychoanalyst Donald Winnicott in 1958 described as ‘the capacity to be alone’ in the presence of someone in a state of peace, serenity and transcendence, where aloneness is not loneliness. In our studies, we found that, throughout life, during periods of bond-formation – for instance, when we fall in love or form a close friendship – oxytocin production increases to cement the new bond, as it does at birth. During birth, a surge of oxytocin triggers uterine contractions, and oxytocin release initiates milk letdown. Maternal oxytocin is then transferred to the infant through the mother’s milk, touch and caregiving behaviour. It bonds mother and child forever but it also reorganises the infant’s brain to what it means to be in love and what it takes to feel safe.

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Still, oxytocin is an ancient system that functions in a quick-and-dirty way; no time for complexities when the lion is at your door. The oxytocin molecule presumably evolved approximately 600 million years ago, and is found in all vertebrate and some invertebrate species. Its role across animal evolution was to help organisms manage life in harsh ecologies. Hence the system supports regulation of basic life-sustaining functions: water conservation, thermoregulation or energy balance in species such as nematodes, frogs or reptiles.

With the evolution of mammals, oxytocin became integrally involved in controlling birth and lactation; as a result, the young acquired life sustaining functions and skills not in the context of the group but within the intimacy of the mother-infant bond. This created the main schism I wish to underline, the core conflict of the human condition: mammals learn to manage hardship through relationships, and bonding is their key mechanism for stress reduction. Being born a mammal, then, implies that oxytocin, the very system that sustains parental care, pair-bonds, group sharing, and consoling behaviour, also became intensely sensitive to danger. Oxytocin protects against danger by immediately differentiating “friend” from “foe” based on nuances of social behaviour.

When mammals perceive slight alterations in social behaviour, they identify the approach of ‘others’, activating the alarm systems of the fight-or-flight response and their bodies prepare to attack. Those ‘others’ may indeed intend to eat us up for supper, or they could just as readily be going about their daily social life in ways that seem to us odd, unfamiliar, or even disrespectful. 

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The second element in the neurobiology of bonding is the affiliative brain. Research into its role in maternal care began in the 1950s with the work of Jay Rosenblatt at Rutgers University-Newark in New Jersey and colleagues, who wished to chart the brain structures that enable rodent mothers to care for their offspring. Following decades of careful work by several research groups, the scientists were able to describe the ‘mammalian maternal brain’ both in terms of its neural networks and, more recently, their molecular composition. Primed by oxytocin’s increase during pregnancy, the hypothalamus (specifically, the medial preoptic area of the hypothalamus) sends projections to the amygdala, and this sensitises an oxytocin-amygdala ‘line’ that makes mothers extremely attuned to signs of infant safety and danger. This line of constant vigilance and worry is implanted into the maternal brain as soon as an infant is born and, without it, our fragile offspring might not survive.

In human mothers, the amygdala activates four times more than in fathers: from the moment of birth and, I believe, forever thereafter, mothers sleep with their amygdala open. Imagine this: a 15-year-old goes to a party. You trust her, have arranged for your best friend to pick her up, and know who she’s with. You go to sleep, but your amygdala is open. It is 3am and you hear the door open and her footsteps tiptoeing in. You turn to the other side and finally sleep in earnest. The ‘care’ and the ‘scare’ become inseparable the minute you love someone for real. It is precisely this entanglement that defines, in my mind, the ancient curse: ‘In sorrow thou shalt bring forth children’ – not the birth itself, which we soon forget due to the analgesic properties of oxytocin.

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The evolutionary role of the oxytocin-dopamine line is to ‘glue’ the mother to her baby so she can tolerate the sleepless nights, physical pain and endless mess. This oxytocin-dopamine line is even engraved into the neurons. The nucleus accumbens, a node in the striatum, contains neurons that encode both oxytocin and dopamine, enabling the brain to combine the motivation and vigour of dopamine with the social focus of oxytocin in order to set the parent’s – and, via the cross-generational cycle, the infant’s – reward system for a lifetime of longterm attachments. When the connection between oxytocin and dopamine breaks, results are devastating. When dopamine is directed to neural targets unrelated to sociality, a risk is addiction; when dopamine and oxytocin are produced out of synch, depression can result.

Link to the rest at Aeon

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