Development of a planar microelectrode array offering long-term, high-resolution neuronal recordings P. Wijdenes 1,3 *, C. Dalton 2,3 *, R. Armstrong 1 *, W. Zaidi 1 , N.I. Syed 1 1 Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Alberta, Canada 2 Department of Electrical and Computer Engineering, University of Calgary, Alberta, Canada 3 Biomedical Engineering, University of Calgary, Calgary, Canada * These authors contributed equally to this study Abstract — All nervous system functions, ranging from sim- ple reflexes to learning and memory, rely on networks of inter- connected brain cells called neurons, which initiate and convey electrical information. Monitoring neuronal activities of a large neuronal ensemble, non-invasively and over an extended time period, is pivotal for understanding all brain functions. A variety of neuro-electronic interfaces now allow monitoring of neuronal and ion channel activities. These neuronal monitor- ing devices are however limited vis-à-vis their efficacy, fidelity and longer-term recording capabilities. Here we report on a novel microelectrode array technology that allows for the detection and characterization of neural activity from individ- ual cells and networks, over long periods of time and with a higher signal-to-noise ratio than commercially available devic- es. Our in-house development of planar microelectrode arrays has focused on modifying design parameters and fabrication techniques to improve their performance. One such device, the Soma-Soma Chip (SS-Chip), allows us to record activity from single and paired cells (pre- and post-synaptic neurons) con- tinuously over extended periods of time with a signal-to-noise ratio higher than similar standard devices. This allows for the analysis of neural activity, which can help to characterize firing patterns of neurons at various developmental-stages. Of particular importance is the precise “signatures” of neuronal firing pattern that offers a unique opportunity to decipher how neuronal activity influences brain network connectivity. Our data also underscore the importance of further development of novel microelectrode array technologies. These developments will provide novel tools and open new research opportunities critical for understanding the fundamental cellular and net- work properties underlying network activity under both nor- mal and disease conditions. Keywords — Microelectrode array, long-term recording, single cell activity, signal amplitude I. INTRODUCTION The sophistication and complexity of micro- and nano- fabrication processes have considerably impacted the devel- opment of biomedical devices, such as neuro-electronic hybrids and microelectrode arrays (MEAs). The neurosci- ence and computational fields have used these techniques to explore fundamental biological and electrophysiological principles of cellular excitability. Several trans-disciplinary research groups have since established themselves by pro- posing new technological advances offering the ability to study neural connectivity, network activity, sub-threshold potentials, or brain plasticity. There have been a wide range of innovative designs to improve MEAs, from non- penetrating nanopillar electrodes, mushroom-shaped pro- truding microelectrodes, to planar patch-clamp MEAs [1]. These efforts have focused on improving the electrical sig- nal that can be recorded. The strength of this signal is typi- cally defined as the electrical coupling coefficient, which is the ratio of the signal amplitude recorded with extracellular techniques compared to intracellular recording with sharp electrodes. Ideally, these extracellular recording MEAs will allow the detection of action potentials (APs) as well as sub- threshold currents with a resolution equivalent (coupling coefficient of ~1) to standard intracellular methods over long-term periods up to several months. The main advantage of MEAs is their ability to record and stimulate neural activity in-vivo or in-vitro over extend- ed periods of time without damaging the cell membranes [2]. However, three-dimensional microelectrode arrays that penetrate or are engulfed by the cell’s membrane have all but eliminated this essential benefit. By partially protruding into the cell membrane, thereby limiting the slight move- ments of the cell in its environment, three-dimensional electrodes tend to damage the cell, which significantly af- fects their viability and thus the potential for long-term recordings. While these new configurations are validated in their ability to record activity with a high resolution, they do so while neglecting the long-term recording capabilities of MEAs – the original purpose of extracellular recordings. This in turn severely limits their usefulness. For example, long-term recording on fully biocompatible MEAs is critical to study the long-term effects of drugs on neural network formation [3] and synaptic plasticity [4]. The need to record neuronal activity over an extended time period with high fidelity while also monitoring synap- tic activity led us to develop an in-house novel planar MEA. The goal was not only to investigate activity changes from © Springer International Publishing Switzerland 2015 D.A. Jaffray (ed.), World Congress on Medical Physics and Biomedical Engineering, June 7-12, 2015, Toronto, Canada, IFMBE Proceedings 51, DOI: 10.1007/978-3-319-19387-8_284 1173