ICA Applied to VSD Imaging of Invertebrate Neuronal Networks

Invertebrate preparations have proven to be valuable models for studies addressing fundamental mechanisms of nervous system function (Clarac and Pearlstein 2007). In general the nervous systems of invertebrates contain fewer neurons than those of vertebrates, with many of them being re-identifiable in the sense that they can be recognized and studied in any individual of the species. The large diameter of many invertebrate neurons makes them amenable for study with intracellular recording techniques, allowing for characterization of synaptic properties and connections, leading to circuit diagrams of neuronal networks. Further, there is often a rather straight-forward connection between neuronal networks and the relatively simple behaviors that they produce. For example, years of experimentation on the nervous systems of leeches, sea-slugs and crabs/lobsters have led to significant advances in the understanding of how small neuronal networks produce a variety of different behaviors (Harris-Warrick and Marder 1991; Hawkins et al. 1993; Katz 1998; Kristan et al. 2005). For the most part, these investigations have been carried out using sharp electrode recordings from about three to four neurons at a time (although see (Briggman and Kristan 2006)). Intracellular recording has been a very productive and fruitful technique for revealing details of neuronal connectivity and for studying synaptic changes caused by modulators or by simple forms of learning. However, since even simple behaviors are produced by the activity of populations of dozens to hundreds of neurons, the limited view offered by recording from only four neurons at a time makes it an inadequate technique for understanding larger-scale, network level phenomena that underlie behavior.