Detour Experiments with Split-Brain Octopuses

Abstract

ABSTRACT Octopuses will move out of sight of their prey and make detours through a maze to get crabs that are initially visible but not directly accessible to them. Successful detours are made without training, and performance shows little change with practice. Longitudinal division of the vertical and subvertical lobes and/or of the superior and inferior frontal lobes does not affect performance. Extension of the cut downwards to include the optic commissures produces animals that sometimes perform quite normally, and at other times vacillate, apparently unable to prevent the onset of incompatible responses arising from visual inputs to the two sides of the body. If the optic nerves are cut on once side such animals perform normally. In the intact octopus conflict between the two sides must be avoided by exchange of information through the optic commissures, or though structures closely associated with these. This situation is compared with that found in training experiments involving visual discrimination. In detours the information acquired through one eye modifies the behaviour of both sides of the body for a few minutes. Its availability is not changed by prior removal of the superior frontal and/or vertical lobes. Following unilateral training involving visual discrimination, responses arising as a result of visual inputs to either side of the body are modified for many weeks, but only provided that the superior frontal-vertical lobe system remains intact. If this system is split the untrained side remains naive. It is concluded that the long and short-term storage of representations of objects seen must be different in kind and that the establishment of long-lasting bilateral traces involves structures that are not essential for the side-to-side distribution of information in the short-term situation. This state of affairs is compared with the situation in touch learning, where there seems to be no functional equivalent of the optic commissures. Long-term bilateral traces are established as a result of unilateral training but the effect takes an hour or more to spread to the untrained side.