On familiarity and recall of events by rats

Memory for a previously experienced event such as seeing a particular object can involve either a sense of familiarity for the object or of recall for seeing the object on a particular occasion. In humans, it has been claimed that recall and familiarity can be selectively impaired as they are based on dissociable neural systems. However, most tasks used to test memory in nonhuman animals use recognition memory tasks, in which successful performance can be based entirely on familiarity cues. Without the means to selectively investigate recall and familiarity in nonhuman animals, it has until recently proved difficult to dissociate the neural basis of these processes, and their very existence as separable entities has been questioned. Here we discuss a number of studies from our laboratory in which we have developed tasks that require recall and contrast these with recognition memory tasks that can be performed using familiarity alone. We use these tasks to begin to unravel familiarity and recall in the rat and the underlying neural bases of these processes.