The medial temporal lobe: memory and beyond

The structures of the medial temporal lobe, e.g., the hippocampus, entorhinal cortex, perirhinal cortex, and parahippocampal cortex, are known to be essential for long-term memory processing and hence are labeled the medial temporal lobe memory system. Nevertheless, the exact contributions of each structure and the involvement in different cognitive processes remain controversial. This article discusses recent findings dealing with recognition memory and a long lasting involvement of the hippocampus and perirhinal cortex in episodic memory, based on functional imaging and lesion studies. Furthermore, a new paradigm employing objective manipulations of recollection and familiarity is presented, showing no anatomical distinction for these two processes, as opposed to studies using subjective ratings. Additionally, results regarding an involvement of the medial temporal lobe in visual processing are presented, in general supporting the visual-mnemonic theory. The discussed findings show that many questions regarding the functional organization remain unsolved, and that we are in need of further research to create a comprehensive model of the medial temporal lobe. For this, we might need to give up the distinctions into different cognitive processes and start to investigate the different types of representations that are processed by the medial temporal lobe.