Teaching old dogs new tricks

Scientists have discovered a substance in the nervous system which, if removed or its actions are blocked, can make the mind learn things like it did when we were first born. But there might be a downside - you might forget things you already knew more easily too! Stanford University brain scientist Carla Shatz explained to Chris Smith how this discovery could help teach new tricks to old dogs, or even mice... 

Carla -   Why is it that kids have brains that seem to be able to learn like sponges?  In particular, I've always wondered why it is, it's so easy to learn several languages as a child.  But as I try to learn French as an adult, it is impossibly difficult for me.  And so, we have been studying what are known as early critical periods of development and trying to understand its mechanisms because the language problem is a great example of a critical period for learning language.  It's easy to learn in the child, but hard to learn in the adult.

Chris -   So, would you say then that it's not just language, that this is a phenomenon generalisable to the way the entire nervous system works?  It's not just language.  It could apply to how your visual system processes what you see, how your ears process what you hear and so on.

Carla -   Yes.  This is definitely a general problem and it's in fact known that for example, the visual system has a similar critical period because it turns out, we have two eyes and we only have one view of the world.  During a critical period of postnatal development, the brain learns how to combine the separate images from the two eyes into one single seamless binocular view of the world.  And this has to happen with normal vision through both eyes during this early developmental critical period which in kids is up until the age of around 6 or so.  If it doesn't then if an eye for example is weak, kind of a lazy eye or maybe it had a congenital cataract, and if that's not corrected during the critical period, then the vision through that eye is extremely diminished and possibly even, there's blindness.  On the other hand, you know perfectly well that if your grandmother gets a cataract as an adult, having normal vision throughout her life, even if the cataract isn't corrected for a number of years, once it is, she can see perfectly well again.

Chris -   Why do you think that the brain has evolved to be like a sponge when we're little, but extremely fixed and rigid as you get older?  Is that to stop me having to go to medical school again?

Carla -   The answer I think is really that when we're young, in terms of evolution, we almost certainly have to learn rapidly.  We have to learn a number of lessons extremely fast.  But on the other hand, if we have that same kind of rapid learning that allows for connections to kind of be loosened the way they are when we're young, if we have that when we're old we might lose things.  And as you say, wouldn't it be awful to have to go back to school again?  I couldn't imagine it.

Chris -   Do you have any insights into what is going on biochemically in the brain to mean that those connections are much more fluid when we're little and we learn very quickly, but as we get older then they do become more fixed and it's much harder to change behaviour?

Carla -   Well, this is part of the discovery that we've made because we've been trying to learn what are the underlying molecules that are mediating this kind of early flexibility, but later perhaps slightly more rigidity.  Obviously, we're not totally rigid because we can still learn as adults.  And we discovered molecules that appear to be really important for pruning away of connections in the brain.  And these molecules are present in the adult brain too.  So, there's some pruning going on even in the adult, but it is also known that for every connection that's pruned, there are connections that are added.  So, there's a kind of stable state.  What we discovered is that if we block the function of these molecules in the adult brain, then it becomes a more youthful brain in a sense that more connections can be made and fewer are removed.

Chris -   What are the molecules?

Carla -   In the mouse, there's a receptor which we call Pure B.  What's really surprising is that these molecules, these receptors were only thought to have roles in the immune system.  But a number of years ago, we discovered Pure B in the mouse nervous system in the brain and actually in neurons.

Chris -   Do you know what chemical it is that binds on to this receptor to activate it?

Carla -   Yes, we do and this is also surprising because these chemicals are the same ones that are known to bind on in the immune system.  So again, the whole system seems to be used both in the brain and in the immune system.

Chris -   Can we now go forward saying, "Right.  Now, we're going to be able to turn university of the third age subscribers into undergraduates again and learn like an 18-year-old"?

Carla -   I got really excited about this idea when we first made the discovery and then sort of reason took over and I realised that, "Gee!  Let's say we had a pill that you could take to do that which will be cool."  But would it be because maybe it would actually destabilise a lot of the learning that's happened.  And so, for every new thing we learn, maybe we would actually again, forget and have to go back to med school because it might be that the pill will not only allow us to make new connections and learn new things, but also, might lose some of our old connections.