Hierarchy of habituation induced by mechanical stimuli in Caenorhabditis elegans

C. elegans becomes habituated to repetitive mechanical stimuli. We compared the habituated states induced by three types of mechanical stimuli: touch on the head (head-touch), touch on the anterior body (body-touch), and mech anical tapping of the Petri dish, all of which evoke backward movement. The habituation patterns were similar, but differed in retention period and/or the rate of recovery. We found a hierarchy between the habituated states i nduced by the three types of mechanical stimuli in the decreasing order of head-touch, body-touch, and tap stimulus. Evidence is presented that the hi erarchy is brought out by the magnitude of stimuli rather than by independe nt neural pathways.