It would probably be quicker to answer with what we DO know about the way the brain works, because it’s just fewer things. But there’s a few key things that are real unexplored territory.
For example, we can look at the brain on the level of the individual braincells – neurons – and how they connect, but there’s this whole other dimension to that which is neurotransmitters: chemicals that flow around your brain. The brain is electrical in that it’s transmitting signals from one neuron to the next using electricity, but there’s also this chemical system, which varies throughout the brain: different neurons have different neurotransmitters.
Most people have heard of serotonin or maybe dopamine, but there’s quite a few of different ones. Sometimes that pans out into clearly distinct networks, but sometimes it’s much more mixed up across the brain. On the stuff I do, where I’m looking at the activation of the brain, I’ve actually got no idea of what neurotransmitters are involved, none whatsoever.
"Nobody’s ever found an end-point to long-term memory. Maybe it’s because of our lifespan, maybe if we lived for 500 years we’d fill it up, but we’ve never found a way of doing that"
It’s this whole other level of neuroanatomy, which even taken on its own is quite baffling. Take dopamine, for example. We know it’s important in rewards, and in things like enjoyment of music, but it’s also what goes wrong when you have Parkinson’s disease. It’s very important in the motor system, in coordinating your movements. So neurotransmitters don’t have simple functions, generally. They tend to be very complex in how they interact, so the brain – which is already very, very complex in terms of its wiring – has got this whole other set of dimensions of complexity, and at the moment we can only measure one or the other. You can look at the signals between the cells, or you can look at the chemistry. It’s very hard to look at things all as one.
I think that’ll be one of the next big developments, being able to look at the whole picture of which part of the brain is activated and which neurotransmitters are involved at the same time.
Another thing – which we know happens, but we can’t really see it happening – is learning. Something that’s staggering is there’s literally no known capacity to human learning or memory. There’s no computer out there in the world that has unlimited storage capacity, but as far as we know our brains are unlimited. Nobody’s ever found an end-point to long-term memory. Maybe it’s because of our lifespan, maybe if we lived for 500 years we’d fill it up, but we’ve never found a way of doing that.
"Even in an inconsequential conversation where you’ll barely remember anything you’ve talked about, there’ll have been a huge amount of reorganisation in your brain"
What gets more difficult as you get older is accessing the memories. But storing them in the first place seems to be continuous. You don’t reach a point where to get more in other stuff starts getting pushed out. Change and learning obviously happens faster as a child, but it is going on throughout your entire life and that means constant rewiring of your brain, generally new connections being made between neutrons. We can get glimpses of this, but we don’t really properly understand what’s driving it. It’s very rapid. Even in an inconsequential conversation where you’ll barely remember anything you’ve talked about, there’ll have been a huge amount of reorganisation in your brain.
Related to that, we don’t really understand why we have dementia – why in adult life we become prone to onset of progressive diseases that winnow away particular brain areas, some global, some local. Sometimes we know there’s a strong genetic component, but much more often we’ve got no real idea what’s driving it. We may be able to name a disease, but we don’t know if it’s an infectious agent, if it’s something toxic in the environment, if it’s inflammation, if it’s the cardiovascular system or what. Hopefully in ten years time we’ll have a better answer. But the big picture of dementia is that we have next to no idea why it happens.