All recent memory theories of hippocampal function have incorporated the idea that the hippocampus is required to process items only of some qualitatively specifiahle kind, and is not required to process items of some complementary set. In contrast, it is now proposed that the hippocampus is needed to process stimuli of all kinds, but only when there is a need to associate those stimuli with other events that are temporally discontiguous. In order to form or use temporally discontiguous associations, it (...) is essential to maintain some memory of the first component until the second component has occurred. When the temporal gap to he spanned is small, and the number of items to be temporarily retained is low, a limited-capacity, short-term store is sufficient to allow associations to be formed. Such a store is presumed to operate in parallel with the hippocampus in normal animals. Hippocampal damage disrupts a much higher-capacity store that has a slower decay rate, and so leaves animals with only a very limited ability to form temporally discontiguous associations. Hippocampal damage, however, is not held to affect the long-term storage of associations of any kind, if they can be formed. Analyses of both new and existing data are presented to show that by classifying tasks in terms of the need to use a temporary memory store to retain temporally discontiguous information one can cut right across existing classifications as well as achieve a better fit to the data. The hippocampus thus seems best described as a high-capacity, intermediate-term memory store. (shrink)

Two experiments were run to demonstrate the presence of a partial reinforcement extinction effect (PREE) and a partial punishment effect (PPE) 4 weeks after training in a 1-trial/day procedure. In the PREE paradigm, two groups of animals were trained to run a straight alley for food reward; one group was rewarded on every trial (CRF), whereas the other was rewarded on only 50% of the trials (PRF). In the test phase, extinction, no reward was present on any trial. Four weeks (...) after the end of acquisition, and subsequent to 7 days of CRF retraining, PRF animals showed greater resistance to extinction than did their CRF controls. The PPE paradigm resembled the PREE paradigm in all aspects, except that mild electric foot shock, together with the food reward, was used instead of nonreward on 50% of the acquisition trials. In the test phase, all animals were shocked and given a food reward on every trial. Four weeks after the end of acquisition and retraining, the animals with previous experience of shock in acquisition showed greater resistance to punishment than did their controls. (shrink)