How the brain extracts information to from the environment and stores that information as a memory is a fundamental but unanswered question in behavioral neuroscience. The brain structure that is most intimately associated with memory in humans and other animals is the hippocampus. Damage to this brain area produces amnesia, or loss of memory, that shares many features in all mammals. This project focuses on two of these commonalties. One is that memories that were acquired shortly before hippocampal damage are lost but older memories remain. This pattern of memory loss is called temporally graded retrograde amnesia. Retrograde amnesia in rats will be examined by making very precise damage to the hippocampus after various times after rats are trained on a task that is not normally forgotten. The task is fear conditioning, where rats show an emotional reaction to stimuli that have previously predicted that they will receive a brief mild electric footshock. Another feature of the amnesia that stems from hippocampal damage is that certain types of memories are lost and others are completely spared. For example, if people with hippocampal damage are taught a new motor skill like tennis, their tennis playing ability will continual improve but they will have no memory of ever playing tennis. They remember how to play without being able to remember that they played. One form of this selective memory loss will be examined. If a tone predicts shock, hippocampal lesions may or may not cause amnesia for the relation between tone and the learned emotion. If the tone and shock overlap in time the hippocampus is not necessary. However, if a brief period of time is placed between tone termination and shock onset the hippocampus is necessary for memory. This type of conditioning is called trace conditioning and retrograde amnesia for trace conditioning following hippocampal damage will be examined. Amnesia for trace conditioning is unusual because it differs from other forms of memory for which the hippocampus is needed. Usually rats with hippocampal damage have problems with memory for spatial locations or for stimuli that are composed of several different components. In this project it will be determined whether retrograde amnesia for trace conditioning and complex configurations stem from the same or different functions of the hippocampus. It will also be determined if various manipulations that alter the ability of normal animals to learn trace conditioning can alleviate the amnesia for trace conditioning. By investigating and contrasting these forms of memory it is hoped to find exactly what the hippocampus is extracting from experience and more precisely define what is lost and preserved in amnesia.
