On Micro-Electrode Array Revival: Its Development, Sophistication of Recording, and Stimulation

Network activity of electrically active cells such as neurons and heart cells underlies fundamental physiological and pathophysiological functions. Despite the well-known properties of single neurons, synapses, and ion channels to exhibit long-term changes upon electrical or chemical stimulation, it is believed that only a concerted effort of many cells make up what it is commonly experienced in humans as self-awareness. In particular, higher brain functions such as associative learning, memory acquisition and retrieval, and pattern and speech recognition depend on many neurons acting synchronically in space and time. Moreover, pathophysiological conditions such as epilepsy, Alzheimer’s disease, or other psychological mental impairments have been shown to rely on many neurons to form one of the latter states. Thus many researchers have been seeking a multi-channel approach to bridge the gap in understanding single-cell properties and population coding in cellular networks. Despite the pioneering work by Thomas et al. (1972), Wise and Angell (1975), and Gross (1979) a remarkable step forward in Micro-Electrode Array (MEA) applications has been achieved only over the last ten years or so, particularly due to the lack of affordable computing power and commercial MEA systems. In this chapter we describe the technology of the most common MEA chips manufactured by the NMI (Natural and Medical Sciences Institute, Reutlingen, Germany), its various design approaches, and current developments. Furthermore, the multi-channel recording and analysis system around the MEA chip developed by and available from Multi Channel Systems (MCS, Reutlingen, Germany) together with new developments for multi-site stimulation are described. Additionally, emphasis is given towards an in-depth understanding of the physical prerequisites for adequate extracellular stimulation and recording using MEA. This in turn has led to new approaches in MEA electrode and insulation material as well as new developments in artifact suppression by using digital electronic feedback circuits implemented in a 60-channel MEA amplifier.