Nelson – brain and memory development

Now in memory the goal here was to understand what are the areas of the brain that develop over the first one to two years of life that facilitate the development of memory and then to be more specific in the type of memory we look at so we no longer think that there’s a type of memory, there’s probably different types of memory so memory for what you had for breakfast this morning or the name of the teacher you had in Grade 10 English is quite different than memory for riding a bicycle or playing an instrument. And so our goal is to understand the different types of memory, their development on a trajectory and what parts of the brain are facilitating that development over the first two years of life.  

And what we find there is that we see a very early form of memory that depends primarily on a single structure in the brain called the hippocampus which lies deep in the brain and it’s hard to show you but this is the outside surface and this is the inside. It’s a structure that lies in here. Basically in the mid-point between your two ears almost. And that’s called the hippocampus. We know that that matures a little bit early. We know that that matures in the first month or two to the point where young infants have some evidence of, can show evidence of memory. But over the next several months that area of the brain and areas in the other portions of the temporal lobe which is the part of the brain right above your ear, right through here, start to mature more, making possible more sophisticated forms of memory and the ability to remember things for longer periods of time.  

And then the last event probably is long-term memory. So most of us are familiar with the following phenomenon. I say to you: What’s your earliest memory? How old were you? And what most people report is that they were usually not younger than two; on average three or four for those early memories. Every now and then you’ll find somebody who was twenty or twenty-two months but the accuracy is a little bit questionable. So that leaves open the possibility of, that leads to the question of so why is it we don’t remember the events of our lives before the age of two. And one possibility, in our view, is that the areas of the brain that store memories for the long term are not in the temporal lobe or in the hippocampus but they’re outside. And those areas develop slowly. And so as kids get beyond the age of two those storage sites for long-term memories develop. 

And then the last event is that we all know, some of us more than others, that as we get older, our memory starts to not be as good and we need the little tricks for learning how to remember things. Those are mnemonics. So you repeat something over and over again and you remember to write it down. Things like that. The frontal lobes play an important role in our use of strategies, the little tricks we use to help us remember. And the frontal lobes mature slowly and very late. They don’t really start to mature in a big way until four, five or six. And it’s not until really adolescence that they’re much more mature. And so the last change in memory would then be the facilitation of memory based on development of the frontal lobe. And that’s why children, when they’re four, would do the following: If I say to you: I’m going to say some numbers. How many can you remember? You might say six or seven. If I say to a four-year old: I’m going to say some numbers out loud, how many can you remember? They might say 25. So you’d give them some numbers and they’d remember on average, four. So then you say, Ok, let’s do it again. How many do you think you can remember this time? And they’d say 30. They have no perspective that things can be forgotten, in part because they haven’t developed the strategies to help them remember because the areas of the frontal lobe are immature.    

So those are sort of our studies of memory. Again, in babies we focus on recording the neural correlates, or the electrical activities we associate with memory and as kids get to be five or six we can actually look at the anatomy of their brain by doing functional magnetic resonance imagery. The last thing I’ll add about memory is that a big focus of our work, particularly the applied side, is that we’re not only interested in how memory develops in typically developing children but what happens in children at risk for problems with their memory or other cognitive functions?  

So we spend a lot of time looking at infants and children, particularly infants who suffered various pre or perinatal brain injuries, that may predispose them to having problems in cognitive development, particularly memory development. And the goal there is not only to track their development but as well to develop the tools that will allow us to identify those babies much earlier than we were ever able to before. Typically a learning disability isn’t diagnosed until kids are school age. And if we can, in a sense, flag children at risk for a learning disability when they’re a month old, or six months old, then we can intervene much sooner. And the last part is that the tools we use to study these things and event-related potentials, can be used to evaluate any intervention. So an example would be if we know what a normative brain response looks like in a memory task and what an abnormal brain response looks like, if we do an intervention, can we see that abnormal response becoming a normal response? So then we have an outcome measure in our intervention. So that’s the application part to the work on memory.