Cyclical patterns of behaviour such as respiration and locomotion are generated by groups of neurones whose output depends not only upon their synaptic interconnections but also on the intrinsic membrane properties of individual cells. For example, the ionic conductances of some neurones in rhythm-generating circuits allow these cells to respond to non-patterned excitatory synaptic drive with ‘plateau’ or ‘driver’ potentials: prolonged, regenerative depolarizations which can drive bursts of impulses and, thereby, contribute to characteristics of the motor rhythm (Russell and Hartline, 1978, 1982; Tazaki and Cooke, 1979a-c, 1983a-c, 1986, 1990). Plateau potentials are not restricted to interneurones of the central pattern generator; they may also be recorded from motoneurones, which form the final output to muscles. Thus, plateau potentials have been recorded from locomotor motoneurones from the crayfish (Sillar and Elson, 1986), lamprey (Wallen and Grillner, 1987), cat (Hounsgaard et al. 1988) and turtle (Hounsgaard and Kiehn, 1989) (see also review by Kiehn, 1991).

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