ABSTRACT
Bioelectricity has been studied since the days of Luigi Galvani (1737-1798) a nd A lessandro V olta ( 1745-1827).1 Be fore t he development of modern electronics, the sensitivity and limited speed o f ele ctromechanical re cording de vices h indered ac curate monitoring of bioelectrical signals. However, the basis for some of the nowadays widely used applications were laid over a century a go, w hen t he rst h uman ele ctrocardiogram w as published,2 and when spontaneous electrical activity of the brain wa s r eported i n so me a nimal speci es3 and i n humans.4 Hermann von Helmholtz measured the conduction velocity of a nerve impulse already in the nineteenth century,1 and the use of glass m icropipettes a s i ntracellular m icroelectrodes w as demonstrated in 1946.5 A major breakthrough in research at the cellular level was the development of the voltage clamp technique.6,7 is method allowed quantitative studies on time and voltagedependent io nic c urrents a nd c onductances o f e xcitable c ell membranes.8 M ore re cently, t he patc h c lamp me thod9,10 pr ovided a me ans for real-time monitoring of currents carried by single protein channels on cell membranes. Today, genuine bioelectrical signals can be faithfully acquired using di erent kinds of ele ctrodes, w hich p rovide t he i nterface b etween re cording devices and the live object. In what follows, the discussion will start w ith b ioelectrical sig nals, h ow t hey a rise at t he c ellular level, how larger scale signals are generated, what the properties of sig nals a re, a nd h ow t hey c an b e me asured. F inally, t his chapter will review in more detail some technical aspects of
recording and the properties of some electrode materials commonly used in commercial electrodes.
