Object, Space, and Object-Space Representations in the Primate Hippocampus

Department of Experimental Psychology, University of Oxford, Oxford, United Kingdom Submitted 8 October 2004; accepted in final form 17 March 2005 A fundamental question about the function of the primate including human hippocampus is whether object as well as allocentric spatial information is represented. Recordings were made from single hippocampal formation neurons while macaques performed an object-place memory task that required the monkeys to learn associations between objects and where they were shown in a room. Some neurons (10%) responded differently to different objects independently of location; other neurons (13%) responded to the spatial view independently of which object was present at the location; and some neurons (12%) responded to a combination of a particular object and the place where it was shown in the room. These results show that there are separate as well as combined representations of objects and their locations in space in the primate hippocampus. This is a property required in an episodic memory system, for which associations between objects and the places where they are seen are prototypical. The results thus provide an important advance by showing that a requirement for a human episodic memory system, separate and combined neuronal representations of objects and where they are seen "out there" in the environment, is present in the primate hippocampus. Address for reprint requests and other correspondence: E. T. Rolls, Dept. of Experimental Psychology, Univ. of Oxford, Oxford OX1 3UD, UK (E-mail: Edmund.Rolls{at}psy.ox.ac.uk )