RECOGNITION MEMORY IN RATS - I - CONCEPTS AND CLASSIFICATION

Recognition is the process by which a subject is aware that a stimulus has been previously experienced. It requires that the characteristics of events are perceived. discriminated, identified and then compared (matched) against a memory of the characteristics of previously experi enced events, Understanding recognition memory, its underlying neurona l mechanisms, its dysfunction and alleviation of the latter by putativ e cognition enhancing drugs is a major research target and has trigger ed a wealth of animal studies. One of the most widely used animals for this purpose is the rat, and it is the rat's recognition memory which is the focus of this review. In this first part, concepts of recognit ion memory, stages of mnemonic processing and paradigms for the measur ement of the rat's recognition memory will be discussed. In two subseq uent articles (parts II and III) we will focus on the neuronal mechani sms underlying recognition memory in rats. Three major points arise fr om the comparison of paradigms that have in the past been used to asse ss recognition memory in rats. First, it should be realized that some tasks which, at face value, can all be considered to measure recogniti on memory in rats, may not assess recognition memory at all but may, f or example, be based on recall rather than recognition. Second, it is evident that different types of recognition memory can be distinguishe d and that tasks differ in the type of recognition memory taxed. Some paradigms, for example, measure familiarity, whereas others assess rec ency. Furthermore, paradigms differ as to whether spatial stimuli or i tems are employed. Third, different processes, ranging from stimulus-r esponse learning to the formation of concepts, may be involved to vary ing extent in different tasks. These are important considerations and question the predictive validity of the results obtained from studies examining, for example, the effects of putative cognition enhancing dr ugs. (C) 1998 Elsevier Science Ltd.