Sample stimulation pulses. (A) Pulses can have arbitrary waveforms, such as biphasic pulses (A1), sine waves (A2), or even playing back previously recorded local field potentials (A3). The data from (A3) was obtained from an epileptic animal and shows several large-amplitude interictal spikes (de Curtis and Avanzini, 2001). How such low-voltage fields influence neuronal networks is an open question; for example, see McCormick and Contreras (2001), where ephaptic interactions are discussed, and Gluckman et al. (2001), where low-voltage fields are used to control epileptic activity. (B) Diagnostics allow monitoring of the voltage and current simultaneously, whether the pulse is current-controlled (B1) or voltage-controlled (B2). To generate the traces in (B1) and (B2), a 33-mm diameter tungsten microelectrode (Tucker-Davis Technologies, Inc.; Alachua, FL, USA) was stimulated in artificial cerebrospinal fluid (Rolston et al., 2009c) using a stainless steel wire as the counter (ground) electrode.