Effects of changing interstimulus interval during habituation in Caenorhabditis elegans.

The role of the interstimulus interval (ISI) in habituation in Caenorhabditis elegans was explored by examining the effect of changing the ISI on habituation and on spontaneous recovery from habituation. When habituation stimuli were delivered at variable ISIs with an average of 10 s, recovery was slower than when habituation stimuli were delivered at fixed 10-s intervals. There were no differences in recovery following either fixed or variable stimulation at a 60-s ISI. The effect of shifting to a different ISI during habituation training was also explored. A 60-s ISI affected habituation at a 10-s ISI, but a 10-s ISI did not influence habituation at a 60-s ISI. Therefore, habituation must be viewed as an ongoing equilibrium of a number of cellular processes--some decrementing some facilitating--that are differentially activated at different ISIs.