A Touch-Learning Centre in Octopus

Abstract

Octopuses were trained to reject objects touched, after section of the optic nerves and removal of parts from the supraoesophageal brain mass. Removal of the vertical lobe has effects, described in full elsewhere, that may be broadly described as reducing the efficiency of the learning process—the animals require more trials to attain the same standards of accuracy of response as controls. Additional removal of the basal lobes produces no further decline in learning performance, although such animals show postural defects and cannot make movements that entail integration of the activities of the individual arms. Extension of the lesion to remove the inferior frontal and subfrontal lobes produces animals that cannot be taught to change their reactions towards objects touched, although the movements concerned in taking or rejecting objects by single arms remain unimpaired. The latter are integrated within the axial cords of the arms concerned, and can be demonstrated in isolated arms. Evidence is given that the organizational changes constituting learning are limited to the lateral inferior frontal and subfrontal lobes, and that the median inferior frontal is a distributive region. Animals with only a few tens of thousands of cells left in the lateral inferior frontal/subfrontal system can learn to reject an object repeatedly presented, but rather more tissue must remain before a satisfactory performance is obtained in discrimination experiments.