Jianzhong Xiang | PubMed Health

PubMed2005

Object, space, and object-space representations in the primate hippocampus.

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.

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PubMed2003

Perirhinal cortex neuronal activity related to long-term familiarity memory in the macaque.

Lesion studies suggest that the perirhinal cortex plays a role in object recognition memory. To analyse its role, the activity of single neurons in the perirhinal cortex was recorded in three rhesus monkeys (Macaca mulatta) performing a delayed matching-to-sample task with up to three intervening stimuli. A set of familiar visual stimuli was used. Some neurons had activity related to working memory, in that they responded more to the sample than to the match image within a trial, as shown previously. However, when a novel set of stimuli was introduced, the neuronal responses were on average only 47% of the magnitude of the responses to the familiar set of stimuli. Moreover, it was shown in eight different replications in three monkeys that the responses of the perirhinal cortex neurons gradually increased over hundreds of presentations of the new set of (initially novel) stimuli to become as large as with the already familiar stimuli. The mean number of 1.3-s presentations to induce this effect was 400 occurring over 7-13 days. These results show that perirhinal cortex neurons represent the very long-term familiarity of visual stimuli. A representation of the long-term familiarity of visual stimuli may be important for many aspects of social behaviour, and part of the impairment in temporal lobe amnesia may be related to the difficulty of building representations of the degree of familiarity of stimuli.

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