Memory consolidation of weak training experiences by hormonal treatments

Day-old chicks trained on a single-trial passive discrimination avoidance task using a concentrated chemical aversant, methyl anthranilate (MeA), have been shown to exhibit three stages of memory processing; short-, intermediate- and long-term. A similar learning task with the aversant diluted to 20% in ethanol leads to short-and intermediate-term memory, but no long-term memory. Subcutaneous administration of selected doses of the stress-related hormones, noradrenaline, ACTH and vasopressin in close temporal proximity to the training trial, produced long-term memory in chicks trained on the weakly reinforced task, mimicking the outcome of strongly reinforced learning and of retraining with the weakly reinforced task reported previously. These effects are shown to be associated with the production of a nonenergy-dependent phase of the intermediate memory stage, postulated to be necessary for long-term memory consolidation.