The age-old nature versus nurture debate is alive and kicking in the world of pregnancy and parenting.

Is the intuitive ability to nurture infants written into the female genome?

Is maternal instinct a patriarchal myth designed to keep women locked in the home?

Is oxytocin (literally, the hormone which allows swift childbirth) an absolute requirement for parental empathy? Or can fathers and non-birth mothers learn by doing?

Do women forget because pregnancy shrunk their brain? Or are they so frazzled by the demands of trying to do it all that their attention is torn and they’re too tired to notice?

Is parenting hardwired or learned? Instinctive or experiential? Biological or cultural? Guided by Mother Nature or the patriarchy?

The real story of matrescence probably lies in the glorious mess in the middle.

The Bottom-Up, Outside-In, Top-Down Model

There’s never a straightforward answer or way of ‘ranking’ nature versus nurture or what matters more or less. So, I’ve created a framework to conceptualise how biology, culture and psychology interact to sculpt our brains.

The Bottom-Up, Outside-In, Top-Down model is loosely inspired by the well-known biopsychosocial model, which considers the interactions of biological, psychological and social factors on our health over the lifespan. My framework puts the brain in the middle.

Bottom-Up elements are the biological or physiological determinants of brain health, development and ageing. Our brains receive constant streams of data about what’s happening inside our body, some of which we’re conscious of (like a full bladder, sore back or kicking baby), other factors we’re unaware of (like hormone levels or gut pH). Bottom-Up elements include genes, hormones, the immune system, nutrition, exercise, sleep and other lifestyle choices we make.

Outside-In elements are outside us and make their way
in via our senses (what we see, hear, smell, touch and taste). Outside includes our social circle, the culture we’ve grown up in, the built and natural environment, current circumstances and external stressors.

Top-Down elements include what we think of as our mind – our conscious thoughts, emotions, personality, language, expectations and belief systems.

Not only do these many elements regulate the brain’s development, performance and health, but each element interacts with and influences others in dynamic ways. For example:

Our Top-Down thoughts can influence our Bottom-Up biology, which is why simply thinking about your baby triggers the breastmilk letdown reflex.

Outside-In social connections can directly impact Top- Down mood, which is why mothers who lack social support are vulnerable to postnatal depression.

Bottom-Up pregnancy hormones alter auditory brain networks, which is why birth mothers respond rapidly to the Outside-In sound of a baby’s cries (sometimes waking before they cry, or so it seems).

Lessons from the Animal Kingdom

In the animal kingdom, mammalian mothers (who don’t read books on what to expect when they’re expecting) are more efficient at problem-solving, learn quickly, have better memories, are less stressed, show less fear, and, when compared to their childless sisters, live healthier, more resilient lives. Human mothers, it turns out, are not that different.

Neuroscience Insights on Motherhood

Neuroscience research published over the past two decades shows that during pregnancy women’s brains undergo remarkable reorganisation in neural networks devoted to social cognition – thinking about what other people are thinking, feeling and what they might need. The extreme hormonal changes of pregnancy trigger dramatic brain rewiring, propelling our brains into a state of heightened sensitivity and readiness to respond to infant cues, cries and cuteness.

Pregnancy, science has shown, prepares our minds for impending parenthood.

Despite the common complaints about forgetfulness, colloquially known as ‘baby brain’, mothers’ brains are primed to learn, by experience and by example, to be empathetic, attentive, socially savvy and to remember what really matters.

And our perceptive plastic maternal minds don’t tune out once our offspring grow up – we stay uniquely synchronised with our children, even when they’re adults. The traces of pregnancy and children’s cells endure within our brains into midlife and old age. Indeed, elderly mothers’ brains show resilience to ageing.

Human Parenting in the Context of Mammalian Biology

Biologically, we’re mammals. Our closest relations are chimpanzees and bonobos. However, in the neuroscience research lab, rats and mice dominate the data. Although we tend to shy away from one another, rodent and human endocrinology, physiology, neurobiology and behaviour have remarkable similarities.

The reproductive processes female rodents go through – conception, pregnancy, labour and delivery, lactation, care of offspring, even menopause and ageing – give scientists insights on mammalian biology without the added complications of human psychology or culture.

The Complexity of Parental Brain Networks

Biologically, we’re also Homo sapiens. We read (and write) books and raise our children in culturally diverse families and geographically diverse settings. Our varied pregnancy and parenting experiences are an intricate blend of mammalian biology and human culture.

Pregnancy prepares mothers’ minds for the tasks of parenthood, but the art and act of raising babies (and children and teens) also change the brains of fathers, grandmothers and other mother helpers.

The Ongoing Impact of Social and Cultural Influences

The examples of our rodent and primate cousins’ behaviour often help us disentangle mammalian biology from the social and cultural experience of being human. But not always. Neuroscientists have found it challenging to establish causal links between hormones, the brain and behaviour. They struggle to make links in carefully controlled laboratory studies of rodent brain biology, let alone in humans.

The struggle to draw simple conclusions can be attributed to the fact that extensive networks of neurons control who we are and how we behave. One role of those neural networks is to integrate and make meaning of multiple streams of information.

There’s never one brain region, one hormone, one gene, one childhood experience, one social message or one mechanism of evolution that explains everything.

And so it is, for example, that the same exquisite maternal brain plasticity that ensures we’re vigilant to our newborn’s needs leaves us vulnerable to anxiety and depression, which can affect our infants as well as us in the process.

Throughout our lifespan, social, cultural and psychological influences collide with our biology in complex and sometimes unpredictable ways to determine how we think, feel and behave.

This is an edited excerpt from: Baby Brain: The surprising neuroscience of how pregnancy and motherhood sculpt our brains and change our minds (for the better).

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