Recognition memory in rats--II. Neuroanatomical substrates.

A discussion of the neuroanatomical systems thought to be of importance for the mediation of recognition memory in the rat warrants consideration of different, but not necessarily exclusive concepts. An important concept is the hypothesis that a dichotomy in the neural systems mediating spatial and non-spatial (item) memory exists in the rat. We have adopted a model of recognition memory suggesting that information about previously encountered items is stored in a dynamic pattern of neural activity and not in a localized representation. These patterns are features of distributed neuronal networks and different networks may process different forms of recognition memory. Two parallel-distributed neuronal networks are proposed in the rat. Network 1 is essential for the processing of non-spatial/item recognition memory processes and incorporates the cortical association areas such as TE1, TE2 and TE3, the rhinal cortices, the mediodorsal thalamic nucleus and prefrontal cortical areas. Network 2 comprises the hippocampus, mamillary bodies, anterior thalamic nuclei and medial prefrontal areas, especially the prelimbic cortex, and is suggested to be pivotal for the processing of spatial recognition memory.