Recording neural activity from freely behaving animals has become extremely important for basic research in neuroscience. One of the major limitations in this domain arises from the need of a low-power, lightweight, wireless recording unit that can be used on small animals for at least a couple of hours. To conserve power, it is essential to reduce the large data volume from tens or even hundreds of recording sites. Since it is widely considered that the primary information in neural recording is limited to the infrequent action potentials (AP or spike), the data can be considerably reduced by using a system based on AP activity [1]. This paper presents a complete activity-dependent wireless system that utilizes an ASIC for recording simultaneous AP and local field potential (LFP) signals, improving the state of the art in terms of performance-to-weight ratio. In spite of large data compression, we demonstrate a method to accurately preserve the AP shape, essential for further processing and spike sorting. Finally, this is the first system (see Fig. 16.4.6 comparison table) particularly designed to take advantage of tetrode (four closely placed electrodes) based neural recording units (Fig. 16.4.1).
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