Memory in mammals: Evidence for a system involving nuclear ribonucleic acid

Abstract

The learning of an avoidance response was confined to one hemisphere in rats by starting cortical spreading depression in the other. Removing the medial (but not anterior or posterior) cortex of the trained hemisphere impairs retention of the learning. If the medial tissue is intraperitoneally injected back into the donor animal, there is savings in relearning with the untrained hemisphere. This savings seems to be specific to the previously learned task and the effect occurs only when the tissue from the trained hemisphere is removed after consolidation of the learning has progressed for several hours. Ribonucleic acid molecules located in the nucleus of some group of cortical cells seem to mediate the savings effect. These results suggest that the effect of injecting the tissue from the trained cortex is to allow ribonucleic acid molecules which have coded the information about the learned response to migrate to the untrained hemisphere and function there as stored learning.