Principles of Neural Coding

Book Preface

At a glance we perceive a face or a scene and construct rich representations, emotions, and memories. In a split of a second we can evaluate complex information and make decisions seemingly effortlessly. Our brain manages this and many other incredible feats, yet we still do not fully understand exactly how it does it. This is the field that embraces many of us (the authors of this book), called neural coding; understanding how the firing of neurons in the brain leads to exquisite brain functions, from sensory processing to the execution of motor commands, emotions, memory, decision making, and so on.

The interesting fact is that neurons in our brain talk to each other, different areas exchange information and can interpret and understand their messages, but these areas are part of our brains, and we, the system as a whole, still struggle to understand how we manage to do so, still wonder what the code is in our own selves that makes us aware of our own existence and everything we do. We are still looking for the Rosetta Stone within us, the evidence that will make us understand our own neural code.

The main component of the neural code is the sequence of action potentials emitted by individual neurons, and since the 1950s we have been able to record the neurons’ firing using extracellular recordings in animals. The recording of individual neurons is probably the most central technique in neuroscience. Since the first single cell recordings, progress has been made at an incredible pace and correlations with behavior have given us good evidence of the function of different areas: neurons in primary visual cortex, for example, respond to local oriented lines giving the first steps in visual processing; neurons in area MT respond to movement, in the inferior temporal cortex to faces, cells in the posterior parietal cortex predict impending movements, in the rat hippocampus encode places, in the human hippocampus encode concepts, and so on. Nevertheless, despite all of this knowledge, we are still making the first steps to understanding how the system works. Simplifying things a bit, we know where some functions are located, but we do not know much about how these functions are implemented within neural circuits. For example, we know that infero-temporal cortex neurons fire to faces, but we do not know exactly how the neural responses in this area give rise to the recognition of a particular face in a crowd.