Parental Brain 101 : Ready, Set, Go
Welcome to the start of my Parental Brain 101 Series where I'll be using The Parental Brain: Mechanisms, Development, and Evolution by M. Numan (Oxford) as a guide from which to write. Let's do this!
Building the Parental Brain
The Parental Brain - that ominous thing we’ve been hearing more and more about. The brain transformation that seems inevitable when you birth a child. The basis of all prosocial behavior? The foundation of empathy? The source of memory loss?
How does the brain become maternal or paternal? And why? Before we get into what happens in the brain, we need to understand some basics.
First things first - the Parental Brain is not a *new* brain. It’s essentially a modification of existing neurocircuitry to enhance caregiving of the young. It is probably more appropriate to say ‘the brain of a parent’, but for ease, we’ll be talking about the parental brain.
Second thing - parenting behaviours, which are governed by the brain, differ in different species based on the needs of the offspring, the environment, the experiences of the parent, to name a few. Although many conserved neural circuits govern aspects of parenting, there are also differences between species for various reasons (ie, evolution).
We will be focusing on mammals throughout this series, as this is the focus of much of the parental brain research to date, and humans are mammals, so if we want to learn about what is happening in our brains, it makes sense to focus on this research.
However, I must tell you that parenting is fascinating in mammals and many other species. What is ‘natural’ comes in many forms. If you’d like to learn more about mothers in the wild, I highly recommend Wild Moms by Dr Carin Bondar.
What is Parenting?
Parental behaviour can be defined as any behavior displayed by one member of a species toward an immature and developing organism of the same species that increases the likelihood that the immature organism will survive. (Numan, 2020)
Parenting occurs to some degree in many species, but in mammals and birds it is often more complex than in fish, amphibians, and reptiles. For example, birds and mammals usually have more direct contact with their young and are directly responsible for the survival of their young compared to fish, amphibians, and reptiles. There are, of course, exceptions to the rule, such as the Cuckoo, which never parents but lays its eggs in the nest of another bird species).
I also want to point out that many fish guard their nest of eggs, which is often essential for their offspring to survive (I think other reptiles and amphibians do too). I’m not an expert on anything non-mammal, but here’s a fun fact, there are sex changing fish that change sex to guard their nest. Wild! Oh, and it’s the male who does the guarding. Apparently, paternal behaviour occurred first during evolution. Interesting!
Back to the book. Birds, which 90% of the time have a social monogamous system (ie, stay together but have sex with others), are often biparental. This means that both the mother and the father show parental care. This biparental care is much rarer in mammals.
Mammals, which are rarely monogamous, generally have a uniparental care system where the mother, who lactates, is the primary or sole parent, caring for the young alone. Of course, there are exceptions to this, such as in California Mice or Prairie Voles or Humans, but, in general, lactating is a defining feature of who becomes the primary parent.
It should be noted that there are shared nursing situations in rodents, humans, and likely other species, which can take the pressure off the mother to be the primary source of food. We also can’t forget that the development of formula has provided a wealth of different opportunities for human parents and has definitely been easier than hiring a wet nurse (which was common practice for many who could afford it in Europe a couple of hundred years ago). For a fascinating history lesson on motherhood in humans, I highly recommend Mother Love by Elisabeth Badinter and The History of the Breast by Marilyn Yalom (Elisabeth and Marilyn were also close friends, coincidentally or perhaps not surprisingly, once you read their books).
Maternal Care and Offspring Needs
As we walk through the development of the parental brain, it’s important to know a few key things about parents and offspring.
To begin with, it needs to be empasized that for most mammalian mothers, the hormonal and other physiological events associated with pregnancy and parturition act on the brain to trigger or turn on maternal responsiveness. (Numan, 2020)
This is not the same as an instinct - an automatic response to something. These physiological changes of pregnancy and birth are priming the brain to respond to the young, which makes sense; A mother needs to be prepared to figure out how to care for the young she has devoted her life to creating. (More on hormones to come.)
We also know that maternal care is affected by the maturity of the young at birth, which dictates what they need from her (ie, food, temperature regulation, protection, grooming…).
Let’s briefly look at the maturity of the young of the four species we will focus on: rodents, rabbits, sheep, and primates. (See the figure below for a nice summary of the types of young at birth.)
Rodents have pups that are immature and immobile (altricial) at birth. The mother (dam) typically has several offspring within a nest site (the most I’ve seen birthed in the lab is 24!) and spends a significant amount of time during the first postpartum week on the nest, caring for her young. Within 4 weeks, the offspring are rather self-sufficient and usually weaned. Rodents can form communal nests and share in caring for offspring (this is something the author of The Parental Brain doesn’t talk about, but there is a growing body of research on this, as well as how older siblings help care for young).
Rabbits give birth to a few altricial young (kits) within a burrow. The mother (doe) enters the burrow and cares for her kits for only 3-4 minutes per day! She doesn’t form a selective bond with her young and will mother any young that is in her burrow. On a side note, I started my maternal brain career, so to speak, raising mini-lop rabbits (the cute ones with the floppy ears) while growing up on a small farm in the Okanagan Valley. I even had Grand Champion Rabbit at the local County Fair! Not surprisingly, I never saw my rabbits nurse, probably because the bouts are so short.
Sheep give birth to young (typically 1 or 2, depending on the breed) that are relatively mature and mobile at birth (precocial). The mother (ewe) forms a selective bond to her young, as it is more advantageous, in terms of individual reproductive success (from an evolutionary perspective) for her to invest in the young she produced.
The selective bond between ewes and lambs develops rapidly through an olfactory learning process in the hours after parturition. It’s quite fascinating watching sheep form the mother-infant bond! I’ve had the opportunity to see it first-hand (I have sheep). There is a coordination of senses - vocalizations, smells, touch - that happens rapidly between the ewe and lamb during birth, which sets up the selective bond. Of note, human parents can also recognize their infants by smell and touch within a few hours of birth.
Primates give birth to young that are semi-altricial - not mobile but not fully altricial. Usually, the mother births one offspring and is in constant contact with her infant, whom she nurses, grooms, and protects (ie, in the case of Rhesus monkeys). Selective maternal bonds develop in most primates, but the development of this bond can take time.
Mother-Infant Bonding
It’s important to note that there is a two-stage process to the development of the mother-infant bond (I’ll be referring to bond, and not attachment, as the current definition of attachment has changed and refers to forming an attachment to a figure who is a source of safety).
Recognition process - in which certain infant stimuli gain access to the parental brain's motivational mechanisms. This is most often caused by hormonal and physiological events of late pregnancy and birth, and can differ in different species.
Attraction process - persistent attraction to infants across the postpartum period. This stage is similar in all mammalian mothers. All mothers usually form an enduring attraction to their infants that persists at least until the offspring are weaned and independent.
In brief, hormones prime the brain to respond to the young, and somehow this response and attraction are maintained, even in the absence of these hormones (or at least the absence of the high levels of these hormones at the time of birth). We’ll see how this is done further on in the book.
By breaking down the neural mechanisms that regulate the mother-infant bond into a recognition stage and an attraction phase, one can explore conserved neural mechanisms across species even though the specific materal behaviours shown by different species may difffer. (Numan, 2020)
Fathers and Others
I’ll be talking a lot about birthing mothers throughout this series, as that is where the research has focused, but we know fathers and other members of social groups care for young, particularly in species that are cooperative breeders, where other group members act as parents or ‘helpers’.
Not surprisingly, it is rare to have fathers and helpers care for the young. Of the 2,545 mammalian species, only 5% have fathers that actively care for their young. It is thought that in this 5%, paternal care evolved in situations where, in addition to maternal care, it increased the reproductive success of both sexes - a key driver of evolution. Of course, mammalian fathers don’t lactate (or at least rarely), but they can do all the other ‘maternal’ behaviors essential for offspring survival.
Cooperative breeding systems occur in only 3% of mammalian species. It’s even rarer than biparental mammalian species, but it is something that we, humans, also do. Cooperative breeding systems have alloparents - individuals who provide care towards young that are not their direct offspring. Alloparental care can be provided by aunts, uncles, grandparents, older siblings, friends, neighbours…the list goes on. In humans, alloparenting is in our biology.
Bringing It Back To the Brain
The big questions then are how does the brain change to become ‘parental’ in mothers, fathers, and alloparents? What activates this change and responsiveness to the young? What are the similarities and the differences within parents of the same species and between parents of different species? What changes? What stays the same?
We’ll gradually tackle these questions within the series.
Next up: How do hormones control maternal behavior?
Chapter 1: Introduction (brief takeaways)
Parental Brain neural circuitry is a neural foundation for all other types of prosocial bonds
Research on the human parental brain is primarily correlational
Research in animals is primarily experimental or mechanistic
The book is divided into 3 major themes
Mechanisms - neural regulation of parental behaviour
Development - intergenerational continuity of parental behaviour styles
Evolution - how the parental brain acted ended up creating broader forms of caregiving and prosocial behaviors
Chapter 2: Parental Behaviour (brief takeaways)
This book will focus on mammals - primarily rodents, rabbits, sheep, and humans - as these are the species most studied in terms of the hormonal and neural mechanisms of parenting.
There are similarities and differences between them, but there is a core neural circuitry for parental behaviour that is evident in all mammalian species.
The development of the mother-infant bond can be broken down into two stages: 1) Recognition Stage and 2) Attraction Stage. By doing this, we can explore the conserved neural mechanisms behind each stage.
It is not always the birthing parent who plays an important role in raising young. Fathers and alloparents are essential in some species (cooperative breeders and biparental species) to ensure offspring survival. Their brains change, too. More to come.