How Breastfeeding Changes Your Brain


‘Motherhood changes you forever’ – the cliché your own mother forewarned you. And she was right. Motherhood, and specifically breastfeeding – the most central physiological act of mothering during infancy, changes you because it literally alters your brain – structurally, functionally, and in many ways, irreversibly. I am about to explain how the act of nursing sets apart mothers who breastfeed from those who don’t – on a neurological scale.
Breastfeeding mothers and their babies are attuned to each other on a deep biological level. In fact, a breastfeeding mother and her baby are sometimes referred to as a ‘dyad’ – two individuals so closely linked they are considered one unit. Her body nourishes him; his feeding determines her milk production. Scientists call this ‘limbic regulation’. It’s a remarkable natural phenomenon whereby the mother is neurologically and chemically in sync with her baby, and her baby to her. Michael Merzenich, the San Francisco University brain plasticity expert, has described breastfeeding as a kind of temporary breakdown of identity for both mother and child that powerfully affects both their brains. “At that point, the baby and the mother are unified” (Merzenich 1994). Glassy eyed, who, me?

New Pathways

When you breastfeed, you are relating to this little person in a way you have never related to anyone else in your life. The process of a baby suckling at the breast actually forges new neurochemical pathways in the mother’s brain that create and reinforce maternal behaviour. This process is aided by chemical imprinting and huge increases in oxytocin. These changes result in a motivated, highly attentive, and aggressively protective brain that compels the breastfeeding mother to alter her responses and priorities in life (Hahn-Holbrook 2011). This hormonal cascade makes mom want to respond to her baby and helps her to interpret his needs effectively (Rapley and Murkett 2012).

When a mother nurses, not only do her blood oxytocin levels increase, but her body makes more receptors, permanently increasing her feelings of love – and her ability to feel loved. Mom’s sensitivity to oxytocin’s power is one of the most fundamental ways she changes as a new mother. In humans, we have oxytocin receptors snuggled within our breast tissue. As Sweden’s Karolinska Institute, Kerstin Uvnas-Mobery, the global authority on oxytocin, found in a series of experiments, breastfeeding women tend to be less reactive to stress hormones, less physically tense, less suspicious, and less bored. They are also calmer and more sociable when tested for these traits than mothers of comparable ages who are not breastfeeding (Uvnäs-Moberg & Petersson 2005).

But the accolades don’t stop there! In another study, this time conducted by Margaret Altemus, a psychology professor at Cornell University, 10 lactating and 10 non-lactating women were stressed by being forced to engage in one of my favourite past times – pounding a treadmill for no particular reason. The research team found the lactating women released only HALF the amount of stress hormones, compared to those not nursing (Altemus 2010). Other studies back this up. It appears that oxytocin not only lowers blood pressure but also inhibits the release of the stress hormone glucocorticoid. Glucocorticoids are one reason why prolonged stress can damage the hippocampus. Meanwhile, prolactin, dubbed ‘the parenting hormone’, dampens fear and anxiety by inhibiting the amygdala (the part of the brain responsible for fear responses) (Kirsch 2005). Zen! The two hormones are elevated each time baby suckles at the breast reaching blood levels of eight times the norm (Ellison 2006). In other words: breastfeeding moms’ antistress systems are frequently activated and they are buffered. Oxytocin is Mother Nature’s weapon against stress, an innate mechanism that mammal mothers enjoy so that stress doesn’t interfere – and least not too much – with mental function. As Stanford biologist Robert Sapolsky, an international expert in stress (would you want his job?) has remarked: “Somehow mammals have worked this out, because cognition is a good thing to have when you have small dependents” (Sapolsky 2014).

Breastfeeding mothers respond to stress less with the banal ‘fight-or-flight’ model (commonly seen in men) and more with an alternative one that has been named ‘tend-and-befriend’ – with friendliness rather than anger. This ‘female model of the stress response’ is again, thanks to lactation’s triggering of oxytocin (Taylor 2000; McCarthy 1995). Throughout most of human history, women have had to watch out not just for themselves but for the sprogs they most likely had in tow. Their bodies knew they had little people to care for purely because of the signals produced through sustained lactation. A consequence of this biology is that each gender has evolved differently in the matter of psychological responses to stress. Formula feeding mothers respond to stress like men, in a more ‘fight or flight’ manner, due to their low exposure to oxytocin relative to lactating mothers. This in part explains why breastfeeding mothers are significantly less likely to abuse their babies (Strathearn 2009; On this touchy topic, see also: ‘Why the Way You Feed Your Baby is MY Business’).

Dr Kerstin Uvnas-Moberg, a world authority on oxytocin, has studied the changes between these two defence mechanisms, where she refers to the ‘tend and befriend’ approach as ‘calm and connection’. In her book ‘The Oxytocin Factor’ she compiled two striking lists:

For breastfeeding moms, it’s an upward spiral. The longer and more often their baby suckles, the more it triggers the prolactin-oxytocin response in the mother’s brain, forging more connections. Pretty soon, the mother forges enough receptors that she can feel her breasts tingling and leaking at the sight, sound, or merely passing thought of nursing her baby. As one Warwick University study discovered:
“Breastfeeding causes a massive increase in communication between the neurons, co-ordinating a ‘swarm’ of oxytocin factories producing intense bursts of the hormone”. To illustrate, take a gander at the virtuous circle depicted in the diagram below:

When a baby grasps its mother’s breast with tiny hands and sucks on her areola, it triggers explosive bursts of oxytocin and prolactin, prompting bursts of dopamine, in the mother’s brain. Prolactin is detected by a sensitive area on each milk-making cell and has the effect of priming them, or switching them on. Breast milk then begins to flow. These ‘receptors’ are much, MUCH stronger in lactating mammals than non-lactating mammals (Tzanou et al 2007). When these receptors are stimulated they make the mother want to protect her baby and hold him close.

These hormonal interactions create the notorious ‘breastfeeding bond’, switching off negative emotions and switching on pleasure circuits that produce feelings of exhilaration and attachment (Domes et al 2007; Hurlemann et al 2010). The hormonal exchange works as follows: The nursing response of the oxytoxin circuits is reinforced by the feeling of pleasure created by bursts of dopamine – the pleasure and reward chemical. Dopamine is jacked up in the mother’s brain by estrogen and oxytocin. The mother’s blood pressure drops, she feels peaceful and relaxed, and she basks in waves of oxytocin-inspired loving feelings for her baby. This neurological mechanism explains one of the ways that breastfeeding reduces the risk of a mom developing postpartum depression (Figueiredo et al 2013;  Figueiredo et al b 2013; Hahn-Holbrook et al 2013). Think of it like walking through a forest the same way again and again, each time making a clearer trail – this is what’s happening in mom’s brain. Circuits that activate as she breastfeeds, become stronger and respond more readily.

More Powerful Than Cocaine

Let’s explore this feel-good mechanism in even more detail. In one study, mother rats were given the opportunity to press a bar and get a squirt of cocaine or press a bar and get a rat pup to suck their nipples. Which do you think they preferred? Those oxytocin squirts in the brain outscored a snort of cocaine every time.

To give you another example of oxytocin’s potency, male prairie voles given a shot of the stuff are converted from roving-eyed bachelors into nurturing husbands and fathers (Ellison 2006).

Enhanced Empathy

In one Yale University study, a team of researchers examined new mothers – half who were breastfeeding, and half who were formula feeding. Two to four weeks after giving birth, the mothers had their brains scanned using a swanky ‘functional magnetic resonance’ (fMRI) machine while they listened to recordings of their babies’ cries. Why their cries? I can think of better stuff to put on my ipod. Why not their cute baby gurgles? Or their babbles? Well, the focus on crying was strategic: as I have discussed elsewhere, responding promptly and lovingly to a baby’s cry is an important part of helping that baby develop trust, a feeling of safety, of worthiness, and of mental well-being. The results of this Yale experiment revealed that the brains of the breastfeeding mothers showed a significantly stronger response to the sound of their babies’ cries than did the brains of the formula feeding mothers. Greater activity was revealed in several brain regions, including the superior frontal gyrus, striatum and amygdala. The researchers hypothesised that high activity in these regions contributes to breastfeeding mothers’ ability to understand how their babies are feeling and respond in an appropriate way (Kim et al 2011). In other words: breastfeeding mothers are more attentive than their formula feeding peers. Mammaries: 1. Man-Made Powder: 0.
The amazing hormonal cascade induced by lactation doesn’t end there. Lactation also facilitates learning and memory specifically for social information. Breastfeeding mothers show improved memory for human faces, in particular happy faces (Rimmele et al 2009; Guastella 2008). They also show improved recognition for positive social cues (Unkelbach 2008; Marsh 2010) and improved recognition of fear in others (Shofty 2010).
To examine how important this process is, let’s take a look at rats again. Female rats inhibited from producing oxytocin after giving birth do not exhibit typical maternal behaviour (Van-Leengoed 1987). They show a marked delay, and in some instances avoidance, of pup carrying, pup manipulation, nest building, autogrooming, and time spent on the nest with the pups. At the end of 1 hour, two out of the six mothers had not yet picked up a single infant. Consider that human mothers who formula feed are literally inhibiting their oxytocin production, lack of lactation is literally stunting their maternal brain circuits. Contrast this with mothers who breastfeed, they have been found to exhibit more behaviors that create a close relationship to their baby, such as singing a special song to them, bathing and feeding them in a special way, or thinking about them more (Odent 2011). Quite simply, the more oxytocin you have, the more loving and attentive you are to your baby. The reserve is equally true.
The breastfeeding mother has a brain that is literally marinating in oxytocin and dopamine making her feel loved, deeply bonded, and physically and emotionally satisfied. Just check out the smorgasboard of other psychological and physiological changes that oxytocin brings about in breastfeeding moms:

Enhanced Smarts

In the same way that lactation gives breastfeeding mothers the edge over formula feeding mothers on the attentiveness front, it also makes them smarter than their bottle wielding peers. By ‘smart’ I’m not talking about Hawkingesc quantum physics – nope – the smarts of a breastfeeding mother mean much more than that. I’m talking about the kinds of smarts that translate into enhanced perception, efficiency, resiliency, motivation and social skills. This is a topic I explore in depth in my book when I speak of breastfeeding mothers as ‘positive deviants’. Breastfeeding is nature’s academic plan for mothers. Harvard psychiatrist Dr John Ratey explains:
“When a mother gives birth, you want her to be really smart, as smart as she can be. You want her to know about the territory around her and remember things about her kids, and be in a prime state to function” (Ratey 2003).

When Dr Ratey examined the brains of mothers in late pregnancy, he found that their normal rate of cell replacement had slowed down and brain size had shrank – an event which may explain the oh-so-dopey ‘mommy brain’ fog of the third trimester. However, once mom has given birth and breastfeeding begins, cell replacement resumes and increases. Compared to those not breastfeeding, Dr Ratey found that lactating moms had more glial cells, which support the neurons by importing energy and exporting waste products.

Let me give you an example of these cells in action: breastfeeding mothers are more sensitive to the sounds of their own babies, and more skilled in interpreting what they mean. A breastfeeding mom’s pricked-up ears (as discussed in that crying experiment we spoke of earlier) make her more perceptive and aware – in a word, smarter – about her child. This perceptional ability becomes part of her general feeling of extraordinary attachment to this new being. Strong attachment itself can help make her smarter about the rest of the world, in part by keeping her brain elevated.

Then there’s the sensory aspect: a mother’s skin as she nurses her baby, is her most direct and loving means of communication, just as her suckling baby talks back with lips and hands, egging her on, before he knows a single word. Katherine Ellison, author of The Mommy Brain has extensively researched this area. She has noted that:
“Studies on animals strongly suggest that breastfeeding re-plots the map of the brain. When my baby son lay on my chest, he had direct impact on my sensory hormunculus. With repeated input from suckling and nestling, my chest, which used to be a purely aesthetic part of my personal repertoire, had acquired a leading role in the nurturing of another human being – and also in the way I was imagining myself, interpreting the world, and learning to behave”.
A decade ago, two neuroscientists, Judith Stern at Rutgers University and Michael Merzenich at the University of California, provided stunning evidence of this impact when they showed that in the cortex of a mother rat, the area devoted to the trunk, or chest, had actually doubled in size while that rat was breastfeeding. Both Stern and Merzenich have little doubt that the same kind of thing happens in humans:
“It is probable that human lactation results in substantial representational remodeling in most or all of more than 10 different somatosensory representational areas, as well as in a number of motor and
premotor zones” (Stern and Merzenich 1994).
Another boffin known for his scientific brilliance, anatomist Vincenzo Malacarne, has noted that breastfeeding is an especially powerful cognitive experience because it involves, in his words, “learning under high stakes conditions, which is just the sort of learning that drives changes in the brain”. In his work he discovered how lactation increases synapses in the part of the brain’s cortex that deals with attention and complex tasks. This however, he did not find surprising: “In breastfeeding, you are relating to another person like you never related to anyone before. In a sense, you are one person, and it’s pretty educational to have another human being extending into the makeup of your own self” (Ellison 2006). Indeed, breastfeeding forces moms to use certain talents up-close, constantly and repetitively. And, unlike the mental challenges of studying or working at a job, it’s much harder to check out for any length of time when you’re on the spot for nourishing. Add to this the fact that breastfeeding reduces stress via oxytocin, and opportunities for learning are improved even further. Have you ever tried to learn something new when you’re under stress? Breastfeeding strikes the perfect balance between keeping mom alert and yet also relaxed – an equalibrium which improves her overall comprehension skills.

Enhanced Efficiency

Does breastfeeding make a woman a more efficient mother? Formula apologetics would unsurprisingly argue – no. However suppose we did an experiment. Perhaps this experiment could involve depriving families of food and then watching to see which mothers were most efficient at obtaining it. Who would come up trumps, breastfeeders or formula feeders? This would, of course, be highly unethical, and so the hypothesis can never be tested on humans, but other mammals – bring it on. And that’s exactly what psychologist Dr Craig Kinsley did with our friends, the rats. He looked at the behaviour of age-matched rat moms, comparing those who were lactating and those who were not.  The rats were temporarily deprived of food and then given crickets. In order to feed, the rats had to capture and kill the crickets whilst Kinsley’s team observed.

In the animal world, a heightened ability to capture prey means a decreased amount of time the mother spends away from vulnerable offspring and this decreased window of vulnerability means a lower infant mortality rate. The results of Kinsley’s study showed that lactation gives mothers the edge, with the non-lactating rats taking around 290 seconds to catch the crickets, whilst the lactating group only took about 70 seconds. Speaking of his findings, Kinsley commented: “The lactating brain expresses a great deal of plasticity and creativity in service to, and in support of, reproduction. In other words, mothers are not born, they are made through breastfeeding” (Kinsley and Lambert 2006). And what’s more, the breastfeeding rats’ gains in learning and memory were lasting up to twenty-four months, a full eighteen months past their last litter, and the equivalent of about 80 years of age for a human! 80 years, people!

Another research team, this time from Okayama University in Japan, found more evidence to support the existence of permanent change. They discovered something called ‘long-lasting, long-term potentiation’, known as L-LTP, in the hippocampi part of the brain of lactating mammals. L-LTP is a psychological marker of long-term memory foundation, involving an actual increase in the efficiency of synapses – i.e. the structure that permits a neuron to pass a signal to another cell (Tomizawa et al 2003). Essentially: the changes to a mother’s brain do not subside once mom stops breastfeeding. Scientists have good evidence to believe that permanent changes occur. They base this partly on research showing that humans and other mammals respond more readily, and emotionally, to their second baby than to their first. This is much more than a matter of knowing what to expect: the differences appear to become hard-wired, even influencing mothers’ milk flow, which is generally freer second time around (Ellison 2006).
In short, breastfeeding mothers are more present, focused, and organized – changes which last for the entirety of a woman’s mothering AND grandmothering journey. Just as nursing rat mothers build a nest, protect their young from danger, and keep them clean, so nursing human mothers perform in comparable ways – and keep on performing.
Adoptive mothers and formulas feeders can also lap up these benefits. How? Well, it’s not easy. When virgin rats are injected with breastfeeding hormones (doing this to humans would be deemed ‘unethical’ so here we have the rats again), they go from their usual behaviour of rejecting rat pups, to nurturing them (Moberg 2011). Adoptive human mothers can induce lactation to produce the same effect. Formula feeders can relactate.
Wow. You’ve just sat through a neuroscience lecture. That’s a lot of learning, and being a badass breastfeeder, you probably soaked it all up. Let’s sum up this post: Breastfeeding is so much more than nutrition – it changes the architecture of the brain. The way neurons in a woman’s brain are restructured in response to lactation enables her to respond to her baby with a richer and more enhanced behavioural repertoire. In the blood, lactation hormones govern milk ejection, while in the brain they affect behaviour. And these changes are the most profound and permanent of a woman’s life. Mother Nature knows her stuff.
Now, of course, since breastfeeding is the biological norm for humans, an accurate conclusion from the science is not “Breastfeeding makes mothers more empathic, more intelligent and more efficient” but rather: “Formula feeding makes mothers less empathic, less intelligent, and less efficient”. Oh dear, sirens are going off at Formula Feeder HQ…
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