Why do we Parent? Ancient Brain Circuits for Parental Care

Matt Higgs | 03 MAR 2021

I for one predicted that all the extra time that couples have spent inside last year would result in a 2021 baby boom. In fact, PwC predicts that we might actually be facing a baby bust, since couples are postponing their pregnancy plans to later dates. While the factors causing couples to delay or pushforward pregnancy are interesting, the question that interests me as a neuroscientist is perhaps more fundamental – I want to understand what happens in our brain to motivate us to care for our children. Essentially – what is parenting and why do we do it?

Now this may seem a silly question but bear with me. It is currently estimated that a human child will cost £152,747 – £185,413 (Hirsch, 2020), consume an estimated 13 million calories, require a lot of attention, and cost you many hours of sleep over an 18-year period (Kohl, 2018). By the numbers, parenting is tough. However, parenting is obviously not without upsides, since – quite predictably – sociological research shows that being a parent “has a substantial and enduring positive effect on life satisfaction” (Pollmann‐Schult, 2014). But for many other people, the work of being a parent tends to outweigh the positives and, on average, parents tend to be similarly or less happy than their childless peers (Glass et al., 2016). Yet many still willingly choose the burden of parenthood. What in our brain motivates us to do this?

When we look across the animal kingdom, we see that many animals have a set of behaviours directed at their offspring to support their survival. This is particularly true for the class of animals that humans belong to – mammals. Mammalian offspring are particularly helpless and mammals are the only animals that feed their young directly from the teat. This means that both the parent and the offspring become tied into an intimate relationship from birth and to further see their offspring to adulthood requires a lot of parental motivation. Since this intensive parenting behaviour is crucial to the continuation of a species, yet is poorly rewarding and distinctly sacrificial for the caregiver, parenting is seen as an innate behaviour in most mammals (i.e. a neurally hardwired behaviour that an animal is able to perform, at least partially, in advance of experience). This is particularly telling since most mammals are able to take up parenting with little training or experience. They suddenly become motivated to care for their young and know how to feed and protect them. This combination of motivation for and instinctual knowledge of parenting suggests to neuroscientists that the basis of this behaviour across mammals is likely evolutionary shaped neural circuits ready to motivate us when we first become parents.

And this is exactly what has been found.

By focusing on mice and rats, and utilising the abundance of behavioural neuroscience technology available to them, scientists have been able to identify what is happening in rodent brains while performing parenting behaviour. Like humans and most other mammals, mice are heavily motivated to care for their offspring post-birth. This involves a more modest 3-5 weeks of feeding, grooming and protection but they perform these behaviours diligently in spite of the costs. So, what exactly is happening in their brains?

Several decades of research on rodents has shown that a structure within the hypothalamus of the brain (a region commonly associated with regulating core function such as body temperature, sleep and appetite – see image below for location of hypothalamus in the human brain) called the medial preoptic area (MPOA) is of central importance for some of the most fundamental motivated behaviours such as mating and parenting (Numan & Insel, 2003). When researchers specifically destroy this area of the brain, parenting behaviour is abolished, whilst other behaviours are left intact (Lee et al., 2000). This is all well and good, but scientists Johannes Kohl and Catherine Dulac recently went one step further and identified the specific neuronal populations within the MPOA in mice that are active during parenting behaviour – aka the parenting neurons.

These neurons were found to express the protein Galanin, which has become a useful marker to identify these cells. They make up a comparatively small population (10,000 neurons), especially when compared to the 100 million neurons in the whole mouse brain (Wu et al., 2014). Are these neurons really the hub of such a crucial behaviour? Specifically inactivating these neurons in mice caused disruption in parenting behaviour similar to destroying the whole MPOA, which was a good start. Taking it further, Kohl et al. (2018) used viruses to infect the Galanin neurons in the MPOA which can then infect, and allow us to visualise, the input neurons and the output neurons to the MPOA. This revealed the brain regions connected to the MPOA which formed the basis of a parenting circuit in the brain. The Galanin neurons were the hub of this circuit and, when tested, were active during all forms of parenting behaviour, while other parts of the circuit were only active for distinct parts of the parenting repertoire. For example, MPOA neurons projecting to the Ventral Tegmental Area and Nucleus Accumbens (key dopamine regions of the brain) are responsible for ‘motivating’ the parent to care for their offspring, while others projecting to the Periaqueductal gray (a region associated with motor control) are involved in mechanical behaviours such as grooming pups.

This parenting circuit appears to be present in both males and females, but in females the MPOA is heavily influenced by the rising concentrations of hormones of late pregnancy (e.g. estrogen, prolactin). These hormones travel through the maternal bloodstream and are detected by receptors in the MPOA. This hormonal signal primes the MPOA, and the mother, for caregiving behaviour just prior to birth (Rilling & Young, 2014). Life experience and physiological state also go a long way to changing these behaviours/circuits despite their evolutionary origin (Kohl, 2018). Yet this core motivational circuit is a powerful driver and likely does a lot of the heavy lifting to convince a mouse to negate its own wellbeing in favour of its offspring.

One of the core goals for behavioural neuroscientists is to understand the neural mechanisms and the evolution of complex social behaviours. The discovery of this neural network orchestrating parenting behaviour,  with a central coordinating hub (the MPOA) and pools of neurons responsible for producing distinct aspects of this complex behaviour, gives an insight into how neural circuits for complex behaviours can be organized. Hence, this finding can be utilised when it comes to investigating other motivated behaviours such as mating and feeding (Kohl, 2020).

However, to return to our question – why do we parent? Humans are not mice, and the existence of this parenting hub in the human hypothalamus is not confirmed. But since the hypothalamus is deeply conserved across mammals, and it is of central importance to all non-human mammals studied (Numan, 2017), it is highly likely this circuit exists in humans and is performing a similar function.

This combination of motivation for and instinctual knowledge of parenting suggests to neuroscientists that the basis of this behaviour across mammals is likely evolutionary shaped neural circuits ready to motivate us when we first become parents.

For humans, parenting behaviour was never going to be as simple as the output of a highly conserved hypothalamic behaviour circuit. For example, we know there is a strong sense of intentional and chosen effort to rise to the task of parenting. We also know from brain imaging studies that parenting behaviour in humans additionally relies on the cortical areas of the brain, likely infusing our parenting behaviour with feelings of love, devotion and care (Numan 2017; Rilling, 2013). However, this work suggests that an instinctual urge to care for children is driven by an evolutionarily conserved brain structure and not only is it fundamental to most mammals but perhaps to humans as well.  

This research is still a way off having clinical applications but considering the impact that aberrant parenting can have on the parent and offspring (Joseph & John, 2008; Letourneau et al., 2012), understanding this behaviour is a crucial step in the right direction. As to why we parent, naturally we have the capability to decide whether to be a parent or not, and many people chose to skip the ordeal completely, but it is highly likely that deep in your brain lies the ancient circuit that will contribute to the great reward and meaning that being a parent will likely bring you if you choose that path in life.

Editors: Ian Fox and Uroosa Chughtai


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