Single perturbations cause sustained changes in searching behavior in stick insects

Abstract

Summary Stick insects (Cuniculina impigra) possessing only a single front leg that cannot contact the ground perform untargeted stereotypical cyclic searching movements with that leg. When encountering an object animals grasp it. Here we removed the object immediately after contact with the leg's tibia. We hypothesized a change in searching strategy, i.e. searching movements confined to the former location of the object to regain contact. In our set-up, searching movements were restricted to up- and downward movements. After removal of the object searching movements were continued. However, in post-contact searching two movement parameters were usually changed. (1) Average positions of searching movements were shifted towards the former position of the object. (2) Movement amplitudes were considerably smaller and accompanied by a decrease in cycle period. This confinement of searching movements to the location of contact was interpreted as targeting behavior. All parameters regained initial values after about 6 seconds. Changes in position and amplitudes were independently controlled. Both changes were not under visual control but depended on the presence of the trochanteral hairplate, a sensory organ that measures the coxa-trochanter joint position. Changes in average leg position were linked to changes in the ratio of electrical activity in the levator and depressor trochanteris muscle that were based on altered activity in both or either one of the muscles. Our data demonstrate a switch in a simple behavior that is under local sensory control and may utilize a form of short term memory.