Learning of leg position by the ventral nerve cord in headless insects

Abstract

When a suspended headless large insect (cockroach or locust) is arranged so that the leg receives a regularly repeated electric shock for all the time that the foot falls below a particular position, there is a progressive change in the animal’s behaviour over a period of about half an hour. The animal at first receives many shocks but progressively raises its leg for longer and longer intervals, with the result that fewer shocks are received. A second animal is arranged in series with the first, and receives the same shocks but in this animal they are not related to a particular position of the foot. Therefore, the second animal cannot associate the shocks with the position of the foot at the moment when they are received, in the way that the first has an opportunity to do. After an initial training period of 40 to 45 min the two animals are disconnected and reconnected in parallel to the stimulator so that each now separately receives a shock when its leg falls below a critical position. When retested in this way the first animals of each pair receive less shocks than do the second animals, especially at the start of the retest before the second animal of the pair has had an opportunity to make an association in the course of the retest. Similar results are obtained when the animals are trained on one leg and retested on another leg on a different segment. The conclusion is that in the absence of a brain the ventral ganglia are able to associate a position of the leg with a repeated punishment by electric shock.