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THE BASICS
Parenting changes everything. There’s no getting around it. Becoming a mother or father is hard and demanding, And when you become a parent for the first time, your life alters dramatically. Yet for the most part, we take to the job naturally and immediately when babies arrive. And it’s not just us. Mammals of all sorts, from mice to monkeys, must do the same because mammalian babies are born particularly vulnerable. That suggests that parenting behavior is hard-wired.
Neuroscientists have long wondered how the brain manages such a complex and important feat. They’ve known for decades some of the brain areas involved, but they didn’t know much about how they were connected--how they worked together in other words. Now, a report just published in Nature gives us the first ever look at the inner workings of a brain-wide circuit orchestrating parenting behavior.
The circuit that’s been identified is in mice, but there’s reason to think it might be similar in humans. In this circuit, a relatively small set of neurons coordinate all the necessary behaviors, sending signals to subsets of neurons, which handle the specifics. For instance, in mice, grooming pups is very important. The new paper identifies a subset of neurons that trigger that grooming behavior. The whole system works like a mayor’s office managing a large city, with a staff of several hundred running different departments that serve a population of millions.
The study comes from the laboratory of neuroscientist Catherine Dulac of Harvard University, who is also a Howard Hughes Medical Institute investigator. I spoke with Dulac about the significance of the new findings.
First, how do neuroscientists think about parenting?
We would like to understand how the brain controls social behavior. Parenting behavior is particularly attractive as a social behavior because it’s very counterintuitive. For us, parenting is obvious. We understand that young have to be protected and parents have a unique role in this. If they don’t do it, obviously this is bad news for the young and also for the species. But if you think what parental behavior entails, this is where it becomes quite surprising.
For an adult, there’s really no immediate benefit of taking care of that helpless individual. What that means is that somewhere, the genetic program embedded in the brain of an individual drives the development of neuronal circuits that in turn control that behavior. There is this instinctive aspect. This is fascinating. What is the drive to take care of a pup or young offspring? How does it work?
How does a mouse’s behavior change when it becomes a parent?
The parent has to build a nest, groom or take care of offspring, retrieve them to the nest. The motivation of the animal in the interaction with young is completely modified. A parent is absolutely attracted to all the needs of their offspring. Before that, if young [animals] are screaming, [the adults] don’t care. Parents will also now engage in interaction with other adults very differently. Animals are no longer interested in mating because they have to take care of their offspring, or in fighting with other animals except as it relates to the protection of the young.
As a metaphor, you have kids at home. You’re going to stay at home and watch videos with them instead of going to the pub like you used to do when didn’t have any offspring. The entire life of being a parent is changed.
Your description of the parenting circuit focuses on a certain type of neuron. Can you explain?
THE BASICS
In 2014, we made the first breakthrough to crack this problem by identifying a particular population of neurons in [a part of the hypothalamus] that express this neuropeptide galanin. The identification of this population really gives us a handle on trying to see how these neurons work. In the 2014 paper, we showed that if you get rid of these galanin neurons, the animals, whether they are moms or dads, no longer parent. These galanin neurons are the control hub to regulate parenting behavior.
What does the new study tell us about how the parenting circuit works?
What we were able to do was first better understand the wiring of these neurons—what type of signal they receive from the rest of the brain, and what type of signal they send to the rest of the brain. That’s an understanding of the connectivity. We found about 20 brain areas that send signals to these neurons and about 20 brain areas that receive signals from these neurons. There are recurrent loops of information.
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A second step was to look mechanistically at what these different brain areas were doing. Our hypothesis was that different brain areas are in charge of particular aspects of parenting. We tested these experimentally by both activating [the neurons] as well as inactivating them. Guess what? Our hypothesis was confirmed. [One area] affects the grooming behavior and nothing else. When we manipulate [another area] motivation is increased. And then there was another area, which is known to be involved in social interaction between adults such as mating or aggression. What we see is that it modifies the level of interaction of the parent with the other adults.
Is human parenting behavior likely to be organized the same way?
it’s entirely hypothetical since nobody has looked. But each time a neuron has been found in the hypothalamus that controls one of these instinctive behaviors such as reproduction, hunger, sleep or feeding, they are found to be conserved throughout the brain of vertebrates and mammals in particular. They play exactly the same role throughout the evolution of the mammalian brain. [And] parenting is a very conserved behavior across mammals. It makes sense because in mammals the mother dedicates a lot of resources through pregnancy and lactation to have the offspring to thrive. The parents really have an enormous investment in the survival of their offspring.
Obviously, humans have a larger brain. There are a lot of other parts of the brain that will be involved in parenting. But this seat of the control of parenting is very likely to be conserved.
This tells us more about how the brain works. How might we use that knowledge?
Once you try to understand the normal functions of this subset of neurons then maybe you can understand sometimes why this goes wrong as in post-partum depression.
Copyright: Lydia Denworth 2018.
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