Exploratory behavior, reaction to novelty, and proactive memory in rats with temporo-entorhinal connections disrupted.

The parahippocampal cortex is ascribed a key function in mediating reciprocal connections between neocortical association areas and the hippocampal formation. Within this complex the lateral entorhinal cortex (LEC) seems to stand out as an important interface exerting modulating influence upon cognition and memory by way of its connections with the hippocampal formation and temporal cortex (TC), respectively. The purpose of the present study was to compare effects of TC/LEC disruptions in a novelty test with results previously obtained in the same test following lateral perforant path (LPP) disruptions. Further, effects of TC/LEC lesions on proactive memory were examined, since a profound impairment in retroactive memory has previously been found. Rats bearing TC/LEC lesions or LPP lesions behaved differently in the novelty test. It was also shown that the impairment in proactive memory was less severe than the one seen in retroactive memory following TC/LEC lesions. The results are discussed in terms of a highly integrative role of LEC.