EFFECTS OF TAP WITHDRAWAL RESPONSE HABITUATION ON OTHER WITHDRAWAL BEHAVIORS - THE LOCALIZATION OF HABITUATION IN THE NEMATODE CAENORHABDITIS-ELEGANS

Four experiments were conducted to identify the possible loci of habit uation of the nematode tap withdrawal response (TWR) by characterizing the effects of TWR habituation on other nonmechanosensory withdrawal behaviors that are mediated by overlapping sets of neurons. Experiment s 1-2 established behavioral and anatomical relationships between spon taneous and tap-induced backward locomotion in the worm. Experiment 3 demonstrated that habituation of the TWR affected neither the magnitud e nor frequency of spontaneous reversal activity. Experiment 4 extende d this result to an evoked response: Habituation of the TWR had no eff ect on reversals evoked by a thermal stimulus. These studies, which sh ow that the loci of change associated with habituation of the TWR are presynaptic to the interneurons and motor neurons that control locomot ion, probably distributed among the mechanosensory neurons, illustrate that a complete understanding of plasticity requires a knowledge of b oth the anatomical and molecular substrates of change.