CHAPTER 2 MODULATION OF ELECTROPHYSIOLOGICAL ACTIVITY IN NEURAL NETWORKS: TOWARD A BIOARTIFICIAL LIVING SYSTEM Laura Bonzano, Alessandro Vato, Michela Chiappalone, and Sergio Martinoia 2.1 INTRODUCTION The unique property of the brain to learn and remember is what makes the nervous system different from any other. Its functional plasticity enables a large range of possible responses to stimuli, allowing the nervous system to integrate high-resolution, multimodal sensory information and to control extremely precise motor actions. These same properties can be studied in ex vivo cultured networks of neurons, where, at a simplified level of organization, the collective and functional electrophysiological properties emerge and can be experimentally characterized, so contributing to a better understanding of how the brain processes information [1, 2]. Consequently, cultured networks can be considered as simplified neurobiological systems leading to the theoretical analysis of neurodynamics. 2.2 MATERIALS AND METHODS Nowadays, networks of dissociated neurons can be cultured and kept in healthy conditions for a long time (from weeks up to months) as experimental preparations [3]. In such in vitro neurobiological systems, the neuronal physiology and the efficacy of synaptic connections between neurons can be quantitatively characterized, exploiting activity- dependent network modifications and investigating the time-dependent interactions among the nervous cells that might be used in the brain to represent information [4, 5]. In addition, such networks offer new assay and sensing systems that lie between biochem- istry and whole-animal experiments and provide rapid and quantitative information on neurophysiological responses to chemicals and toxins [6 –9] or specific electrical stimulating waveforms [10 – 12]. Handbook of Neural Engineering. Edited by Metin Akay Copyright # 2007 The Institute of Electrical and Electronics Engineers, Inc. 29