Learning about learning – what mouse babies can tell us about the brain

Today I had the opportunity to speak to Jennifer Shiavo, a third-year PhD student and one of the many, many scientists collectively working to piece together one of the biggest puzzles of neuroscience: How the brain learns. It’s easy to take for granted what our brain does for us – constantly taking in everything we see, feel or hear, somehow making sense of it all and ultimately deciding on which bits we remember, which ones we forget, and which ones we learn for life. But what exactly the 100 billion nerve cells in our brain are doing to allow this, is something that we don’t quite yet understand.

Shiavo works in a lab led by Dr. Robert Froemke, which has been looking at mice to understand this. More specifically, she’s looking at how mother mice pick up a particular habit common to all mothers in the animal kingdom. Dutiful mouse mothers tend to change nests from time to time, carrying their pups along the way. Occasionally, one will become lost, and it’s up to the mother to respond to her pup’s distress cries and bring it safely to the nest. This is not an ingrained instinct that the mothers do naturally – it’s something they have to learn. What’s more, some females can pick up this behavior too, after being around the pups for a few days – without having gone through the hormonal and other bodily changes needed to become a real mother.

These virgin mice have become the focus of the lab’s work on learning. The team started by comparing the brains with the virgin mice that had learned to respond to the pup calls and rescue them, and those that hadn’t – and found that they actually have very different responses to hearing the pup calls. When playing recordings of the pup calls to the mice, there is always some electrical activity in the area of the brain that processes sounds, the auditory cortex. In the auditory cortices of those mice that knew to respond to the pup calls, activity spiked in a very precise way upon hearing the pup calls – looking a lot like the cortical responses of the mother mice themselves. In comparison, in the naïve mice that had not developed this rescue behavior, the spikes of activity appeared erratic, and had little correlation with the hearing of the pup calls.

But what actually transforms a naïve brain into a brain that has effectively ‘learned’ to react properly to pup calls? Knowing that a particular hormone, oxytocin, is involved in maternal and social behavior in general, the team investigated its effects on this process – with some remarkable findings. They found that they could prompt the brains of naïve mice to learn to react to pup calls a lot faster if they injected them with oxytocin whilst playing them the recordings. Shortly after this, the naïve mothers would run to the rescue of pups in distress. Blocking the activity of the left auditory cortex, which is particularly dense in receptors for the hormone, causes them to ignore crying pups.

Along with other experiments, this supports the idea that oxytocin is pretty important for mice to learn how to respond to pup calls. The complete picture, though, is likely to be more complicated, Shiavo explains: It’s probably not just oxytocin alone that facilitates this process, and there will be other brain regions involved, too.

But it’s a start, and for now, Shiavo’s goal is to track the changes in the brains of naïve virgin mice as they become experienced virgins, step, for step: Nailing down exactly when and how oxytocin acts will lay the groundwork for understanding how this learning occurs. In the grand scheme of things, this will shine a light on how we humans, too, learn from social experience and grow as social creatures.

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