In many central neurons, including motoneurons, accommodation of the spike threshold is slow, partial, or absent (Bradley and Somjen, 1961; Koike et al., 1968; Schlue et al., 1974). This means that these cells possess a subthreshold slowly-or noninactivating inward current (Gutman, 1971). Noninactivating sodium currents (Magee and Johnston, 1995; Lipowsky et al., 1996; Schwindt and Crill, 1996) and calcium currents (Hounsgaard and Kiehn, 1993; Avery and Johnston, 1996; Magee et al., 1996; Hsiao et al., 1998; Morisset and Nagy, 1999) have been found in many nerve cells. These currents mediate slow dendritic spikes in many CNS neurons (Hounsgaard and Kiehn, 1993; Kim and Connors, 1993; Andreasen and Lambert, 1995; Schwindt and Crill, 1999), and plateau potentials in motoneurons (Hounsgaard and Kiehn, 1989; Hsiao et al., 1998; Lee and Heckman, 1998), Purkinje cells (Llinás and Sugimori, 1980a, 1980b), nociceptive deep dorsal horn neurons (Russo and Hounsgaard, 1994; Morisset and Nagy, 1998), neocortex pyramidal neurons (Schwindt and Crill, 1999), and striatal neurons (Dunia et al., 1996). In neurons bistability means that there is a net slow inward current that can cause a prolonged plateau potential without stimulation or active synaptic input. In bistable neurons the input current-voltage characteristic (I-Vin) is N-shaped and has two stable points of zero current.