Winnie Lim

Full-grown, these monkeys are living proof of limbic regulation’s enduring power: they are timid, clingy, subordinate, and clumsy in their efforts to establish ties to other monkeys. The brains of these animals evidence permanent alterations in neurochemistry. Just because their mothers once lived under a pall of uncertainty, these adult animals show lifelong changes in levels of neurotransmitters like serotonin and dopamine. With their vulnerability to anxiety and depression, their social awkwardness and failures to attach as adults, these monkeys exhibit a close animal counterpart to the multifaceted misery that in human beings is labeled neurotic.

Children aren’t the only ones whose bodies respond to the intricacies of loss: cardiovascular function, hormone levels, and immune processes are disturbed in adults subjected to prolonged separation.

all of the infants died before uttering a single word. The emperor had stumbled upon something remarkable: that “children could not live without clap-pings of the hands, and gestures, and gladness of countenance, and blandishments.”

Lengthy parental absence deprives a child of limbic regulation. If he is very young, losing his parents upends his physiology. Prolonged separations even can be fatal to an immature nervous system, as vital rhythms of heart rate and respiration devolve into chaos. Sudden infant death is increased fourfold in the babies of mothers who are depressed—because without emotional shelter, infants die. The heart rhythms of securely attached babies are steadier than those with insecure relationships, just as the breathing teddy bear regularizes the respiration of premature infants. Synchronicity with parents (or, in a pinch, with another reliable rhythmic source) becomes the baby’s developing physiologic strength.

Cortisol levels rise sixfold in some mammals after just thirty minutes of isolation.

Adults remain social animals: they continue to require a source of stabilization outside themselves. That open-loop design means that in some important ways, people cannot be stable on their own—not should or shouldn’t be, but can’t be. This prospect is disconcerting to many, especially in a society that prizes individuality as ours does. Total self-sufficiency turns out to be a daydream whose bubble is burst by the sharp edge of the limbic brain. Stability means finding people who regulate you well and staying near them.

A second person transmits regulatory information that can alter hormone levels, cardiovascular function, sleep rhythms, immune function, and more—inside the body of the first. The reciprocal process occurs simultaneously: the first person regulates the physiology of the second, even as he himself is regulated. Neither is a functioning whole on his own; each has open loops that only somebody else can complete. Together they create a stable, properly balanced pair of organisms.

We call this mutually synchronizing exchange limbic regulation. The human body constantly fine-tunes many thousands of physiologic parameters—heart rate and blood pressure, body temperature, immune function, oxygen saturation, levels of sugars, hormones, salts, ions, metabolites. In a closed-loop design, each body would self-monitor levels and self-administer correctives, keeping its solitary system in continuous harmonious balance.

Remove a mother hamster’s whole neocortex and she can still raise her pups, but even slight limbic damage devastates her maternal abilities. Limbic lesions in monkeys can obliterate the entire awareness of others.

Because people are most aware of the verbal, rational part of their brains, they assume that every part of their mind should be amenable to the pressure of argument and will. Not so. Words, good ideas, and logic mean nothing to at least two brains out of three.