8. Multielectrode and Multitransistor Arrays for In Vivo Recording

In recent years the experimental toolkit at disposal of neuroscientists to investigate electrophysiologically the brain “in vivo” down to the level of neuronal microcircuits circuits and to elucidate their fundamental mechanisms for mapping and processing information has grown rapidly and even beyond expectations [1]. Driven by the compelling need of recording large numbers of neurons within the cortex and deeper structures, in a minimally invasive manner and over long time periods [2–4], the development of implantable brain probes based on microelectromechanical systems (MEMS) with arrays of microelectrodes has experienced a significant boost, leading to substantial optimization of pioneering approaches conceived in the 1970s [5] as well as to the development of novel technologies. Multielectrode arrays (MEAs) and multitransistor arrays (MTAs) integrated in silicon microchips constitute two major representatives from this class of brain implantable probes. Originally developed as “in vitro” prototypes for recording dissociated neurons or brain slices and other excitable cells [5–7], MEA and MTA reflect two different philosophies for transducing a neuronal electrical signal to a semiconductor chip, that is, either through a metal microelectrode or by means of an electrolyte–oxide–semiconductor field-effect transistor (EOSFET), a modified version of the metal–oxide–semiconductor field-effect transistor (MOSFET) that is widely used in integrated circuits [8] (Fig. 8.1).