TO investigate the functional organisation and information processing in Lymnaea neuronal networks, artificial spike trains were elicited in one of the main respiratory interneurons (RPeD1) and the modulation of the firing patterns of postsynaptic cells was examined. This was performed by precisely timing the action potential generation of the presynaptic cell using a computer-controlled voltage clamp amplifier (pattern clamp technique). Induced oscillation (0.1-0.4 Hz) in the firing pattern of RPeD1 spread to a large number of post-synaptic cells, as clearly demonstrated by Fourier power spectra. At the same time, no signs of precise (millisecond) spike timing was observed in the cells studied. The results confirm that the neurons used in our experiments process information as pure rate-coders.