Closing the loop: Stimulation feedback systems for embodied MEA cultures

Abstract

In the vertebrate nervous system, all key functions are performed by many nerve cells working in concert. By contrast, single neurons are sometimes important for specific functions in invertebrates, such as the locusts giant motion detector neuron (LGMD), which integrates visual information and triggers jumping (Gabbiani et al., 1999). To understand more complex processing in vertebrates, we need to know how single-unit activity combines to form the network-level dynamics that take in sensory input, stores memories, and controls behavior. Cultured neuronal networks have provided us with much of our present understanding of ion channels, receptor molecules, and synaptic plasticity that may form the basis of learning and memory (Bi and Poo, 1998; Latham et al., 2000; Misgeld et al., 1998; Muller et al., 1992; Ramakers et al., 1991). To study the nervous system in vitro offers many advantages over in vivo approaches. In vitro systems are much more accessible to microscopic imaging and pharmacological manipulations than are intact animals. Recent developments in multi-electrode array (MEA) technology, including those described below, will enable researchers to answer questions not just at the single-neuron level, but at the network level. Most MEA research has involved recording activity that cultured networks produce spontaneously, via up to 64 extracellular electrodes. Although some studies also included electrical stimulation via the substrate electrodes, it was applied to only one or two of them at a time (Connolly et al., 1990; Fromherz and Stett, 1995; Gross et al., 1993; Jimbo and Kawana, 1992; Jimbo et al., 1998; Maeda et al., 1995; Oka et al., 1999; Regehr et al., 1989; Shahaf and Marom, 2001; Stoppini et al., 1997). We propose that in order to substantially advance our understanding of network dynamics, we need high-bandwidth (many neurons) communication in both directions, out of and into the network. This chapter describes technologies that allow recording and stimulation on every electrode of an MEA, and a new closed-loop paradigm that brings in vitro research into the behavioral realm.