Memory and Learning – Animal Models

Many treatments, including hormones, drugs that alter neurotransmitter functions, electroshock, and localized direct electrical stimulation of the brain, can modify retention. If a treatment affects retention, the effectiveness of the treatment decreases as the time after training is increased. Depending on the treatment and on the specific experimental procedures, the effect on retention is either impairment or enhancement of the memory. The time after training during retention loses its susceptibility to modify by a particular treatment is called the retrograde amnesia gradient. A post-trial injection of vasopressin enhances the retention of inhibitory avoidance training and impairs extinction of the avoidance training. The major difference between the effects of adrenocorticotropic hormone (ACTH) and vasopressin on learning and memory is that ACTH is administered throughout training or extinction trials to enhance acquisition or retard the development of extinction. Vasopressin effects on learning and memory seem to be of much longer duration than those of ACTH. Peripheral catecholamines have received less attention than pituitary hormones in terms of involvement in learning and memory. Epinephrine injections administer, shortly after inhibitory avoidance training enhance later retention performance and delayed injections are ineffective.