ATTENTION AND STIMULUS-PROCESSING IN THE RAT

There is little doubt that rats are an essential species in laboratory testing. Given the substantial amount of anatomical and pharmacologic al information which is available for this species, rats are the anima l of choice for many initial neurobiological investigations of the bas ic mechanisms of learning and memory as well as for pharmacological sc reening. Indeed, the study of brain-behaviour interactions is greatly facilitated in the rat given the ease with which brain transmitter sys tems and structures can be selectively manipulated, in contrast to the technical difficulties involved in undertaking such techniques in non -human primates. However, when considering the processing of informati on that occurs during cognitive processes such as learning and memory it is important to remember that fundamental to such processes are mec hanisms of attention. When considering the concept of attentional func tioning, it is important to keep in mind that attention is not a unita ry construct but consists of several distinct mechanisms: vigilance, d ivided attention and selective attention, not all of which have been a dequately modelled in the rat. Furthermore, attentional processes are also involved in learning operant discrimination tasks and appear to b e quite different from those involved in maintaining high levels of tr ained performance. Consideration of discrimination learning is importa nt given that firstly, during such learning the animal must select fro m the environment those stimuli which are relevant and secondly, that this type of learning is obviously inherent in many other tests used t o assess cognitive function, such as delayed matching-to-sample proced ures. Such issues will therefore form the basis of the following discu ssion.