EFFECTS OF THE NOVELTY OR FAMILIARITY OF VISUAL-STIMULI ON THE EXPRESSION OF THE IMMEDIATE-EARLY GENE C-FOS IN RAT-BRAIN

To investigate substrates of recognition memory, the cellular expressi on of Fos protein in rat brain has been studied after groups of rats w ere either shown sets of novel or highly familiar objects, or were exp osed to the same pattern of illumination without objects being shown. Counts of stained nuclei were made in eight brain regions, where infor mation about novel or familiar visual stimuli is likely to be processe d or stored. The counts were relatively high in occipital visual assoc iation cortex and area TE of temporal cortex, intermediate in perirhin al cortex, entorhinal cortex, anterior cingulate cortex and the diagon al band of Broca, and low in the hippocampal formation and mediodorsal nucleus of the thalamus. The number of Fos-stained cells was signific antly higher for the rats shown novel objects than for those shown fam iliar objects in perirhinal cortex, area TE, occipital cortex and ante rior cingulate cortex. Arguments are advanced that these differences i n counts indicate areas involved in the processing and/or storage of i nformation about the novelty or familiarity of visual stimuli, informa tion important to recognition memory.