An improved Horridge procedure for studying leg-position learning in cockroaches

The Horridge method for studying leg-position learning in insects was modified using an electronic device that eliminates stimulation of the trained leg and differences in positioning the experimental insect with respect to the yoked control. The device allows any conditioning stimulus to be applied to any part of the body contingent on either lifting or lowering a leg, and interfaces with a personal computer to store and analyze data on the percentage of stimulation during each minute, avoidance of stimulation by maintaining a leg position, and escape from stimulation by changing leg position. The device was used to train cockroaches with intact central nervous systems to keep a mesothoracic leg lifted to avoid shock to the prothorax. The performance of the experimental cockroaches was only marginally better than that of yoked controls during training and testing. The effect of leg-lift learning was much more apparent during reversal, however, when the experimental cockroaches kept their legs' lifted and therefore received many more shocks than did the formerly yoked controls.