The sequential-interval state space: a means of displaying temporal information in neuron firing

Variability in neuronal firing exhibits sufficient uncertainty so that a simple average firing frequency code is probably inadequate for most nervous system signalling. Temporal patterns certainly play an important role in neuronal coding. We have used interval histogram and 3-dimensional sequential interval state space plots to investigate various common patterns of firing in neurons of the land snail, Helix aspersa. Typical firing patterns included random, highly regular, doublet, and burst firing. Individual neurons could be made to change their temporal firing pattern in response to changes in transmembrane currents, or temperature, or the application of convulsant drugs. In every instance, the sequential interval state space plot provided a more distinctive display of temporal pattern than did the more common interval histogram. State space plots were also investigated for evidence of a predicted chaotic attractor. In no instance was this type of state space plot observed.