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Introduction R O M a I N B R E T T E a N D a L a I N

Most of what we know about the biology of the brain has been obtained using a large variety of measurement techniques, from the intracellular electrode recordings used by Hodgkin and Huxley to understand the initiation of action potentials in squid axons to functional magnetic resonance imaging (fMRI), used to explore higher cognitive functions. To extract meaningful information from these measurements, one needs to relate them to neural activity, but this relationship is usually not trivial. For example, electroencephalograms (EEG) measure the summed electrical activity of many neurons, and relating the electrical signals of the electrodes to neural activity in specific brain areas requires a deep understanding of how these signals are formed. Therefore, the interpretation of measurements relies not only on an understanding of the physical measurement devices (what physical quantity is measured), but also on our current understanding of the brain (the relationship between the measured quantity and neural activity). The biophysics of neurons is explained in great detail in a number of books. This book deals with the biophysical and mathematical principles of neural activity measurement, and provides models of experimental measures. We believe this should be useful for at least three broad categories of scientists: (1) neuroscientists who use these techniques in their own experimental protocols and need to interpret the results precisely, (2) computational neuroscientists who use the experimental results for their models, (3) scientists who want to develop new techniques or enhance existing techniques. Chapters in this book cover an exhaustive range of techniques used to measure neuronal activity, from intracellular recording to imaging techniques. Each chapter explains precisely what physical quantity the technique actually measures and how it relates quantitatively to neural activity. In the remainder of this introduction, we will give a brief overview of neuronal biophysics, in relation with the different measurement techniques that are covered in this book. More detailed accounts can be found in several books (Tuckwell, 1988; Koch, 1999; Dayan and Abbott, 2001; Hille, 2001; Gerstner and Kistler, 2002).