The Long Journey from Animal Electricity to the Discovery of Ion Channels

This retrospective begins with Galvani's experiments on frogs at the end of the 18th century and his discovery of animal electricity. It goes on to illustrate the numerous contributions in the fields of physical chemistry in the second half of the 19th century (Nernsts equilibrium potential, based on the work of Wilhelm Ostwald, Max Planck's ion electrodiffusion, Einstein's studies of Brownian motion), which led Bernstein to propose his membrane theory in the early 1900s as an explanation of Galvanis findings and cell excitability. These processes were fully elucidated by Hodgkin and Huxley in 1952, by detailing the ionic basis of resting and action potentials, but without addressing the question of where these ions passed. The emerging question of the existence of ion channels, widely debated over the next two decades, was finally accepted and, a decade later, many of them began to be cloned. This led to the possibility of modelling the activity of individual neurons in the brain and then of simple circuits. Taking advantage of the remarkable advances in computer science in the new millennium, together with a much deeper understanding of brain architecture, more ambitious scientific goals were dreamed of to understand the brain and how it works. The retrospective concludes by reviewing the main efforts in this direction, namely the construction of a digital brain, an in silico copy of the brain that would run on supercomputers and behave just like a real brain.