Further investigations on the effect of electroconvulsive shock (ECS) on memory in Octopus vulgaris

Summary

• 1. The shuttle-box method was used to train octopuses in an avoidance response. Unlike previous experiments, animals received now only 10 learning trials on Day 1 and 10 retention trials 3 days later. Time records were made of the animals movements in the box. No improvement in the performance occurred concerning anticipatory runs to the light compartment (ARs) neither was a decrease in the anticipatory run time (ART). But a significant decrease in the number of returns to the dark compartment (incorrect crossings, ICs) was recorded and the error time (ET) during which octopuses were receiving shocks was less on Day 4 than on Day 1. Thus, octopuses can learn with the shuttle-box method: a) to hold back spontaneous movements into darkness, b) to flee towards light quickly when a shock is received. On the other hand, it seems impossible to achieve a linkage between a change of illumination and a subsequent punishment.

• 2. When an ECS was given immediately after the last trial on Day 1, results of Day 4 showed neither a fall in the number of ICs nor a reduction in the error time. But when ECS was given 6 hours afterwards changes similar to those of the control group occurred.