By Kate Jeffery, University College London
Let’s say Martians land on the Earth and wish to understand more about humans. Someone hands them a copy of the Complete Works of Shakespeare and says: “When you understand what’s in there, you will understand everything important about us.”
The Martians set to work – they allocate vast resources to recording every detail of this great tome until eventually they know where every “e”, every “a”, every “t” is on every page. They remain puzzled, and return to Earth. “We have completely characterised this book,” they say, “but we still aren’t sure we really understand you people at all.”
The problem is that characterising a language is not the same as understanding it, and this is the problem faced by brain researchers too. Neurons (brain cells) use language of a kind, a “code”, to communicate with each other, and we can tap into that code by listening to their “chatter” as they fire off tiny bursts of electricity (nerve impulses). We can record this chatter and document all its properties.
We can also determine the location of every single neuron and all of its connections and its chemical messengers. Having done this, though, we still will not understand how the brain works. To understand a code we need to anchor that code to the real world.
Place, memory and administration
We easily anchor Shakespeare’s code (we find out that “Juliet” refers to a specific young woman, “Romeo” to a specific young man) but can we do this for the brain? It seems we can. By recording the chatter of neurons while animals (and sometimes humans) perform the tasks of daily life, researchers have discovered that there are regions where the neural code relates to the real world in remarkably straightforward ways.
The best known of these is the code for “place”, discovered in a small and deeply buried part of the brain called the hippocampus. A given hippocampal neuron starts chattering furiously whenever its owner (rat, mouse, bat, human) goes to a particular place. Each neuron tends to be most excited at a particular place (near the door, halfway along a wall) and so a large collection of neurons can, between them, be ready to “speak up” for any place in the environment. It is as if these neurons encode space, to form something akin to a mental map.
To determine where you are, you simply consult your hippocampus and see which neuron is active. (In practice, of course, many neurons will be active in that place and not just one – otherwise every time a neuron died you would lose a small piece of your map.) These neurons in the hippocampus are called “place neurons”, and are remarkable entities that form the foundation not only for our mental map of the space around us, but also for memories of the events that occur in that space – a kind of biographical record. Their importance is evident in the terrible disorientation and amnesia that result from their degeneration in Alzheimer’s disease. When the brain loses its link to its place in the world, and to its past, its owner loses all sense of self.
There are many other neurons in the brain whose code seems decipherable. Neurons that activate when facing a particular direction, or near a wall, or when you see your grandmother … Gradually we are piecing together the network of nodes in the brain that connect the inner code to the world outside.
This is not all that neurons do, of course. Much of the brain is involved with internal “administration”. For example, a large part of the frontal lobe (the brain behind the forehead) is involved in making decisions – how to prioritise activities, what to do next, and so on. Many neurons, scattered throughout the brain, have housekeeping duties to do with maintaining the code, improving and refining it, preserving the relevant parts as memory and discarding the rest.
Some of the most numerous neurons seem simply to have the job of suppressing their neighbours, so that the neural conversation, as it were, does not degenerate into the equivalent of uncontrollable shouting (which, in technical terms, we recognise as epilepsy).
Still room for psychology
It is clear that to understand the brain we need to investigate all aspects of its functioning, not just those that relate to internal administration but also those that connect to the outside world.
We need to determine how brain activity relates to what the brain’s owner is thinking, feeling and doing with respect to the world outside that brain – that is, we need to anchor the code to the real world.
For this, we need scientists who study thoughts, feelings and behaviour – psychologists – as much as we need those who study anatomy and physiology. Study of the brain requires investigation at all levels – otherwise, we will have a complete characterisation, but no understanding, of this remarkable organ.
Decoding the brain, a special report produced in collaboration with the Dana Centre, looks at how technology and person-to-person analysis will shape the future of brain research.
I receive, or have received, funding for my work from the BBSRC, MRC, Wellcome trust and European Commission FP7
I am non-shareholding director of the biomedical instrumentation company Axona Ltd, which makes data acquisition systems for in vivo electrophysiological recording