Function of the hippocampus in memory formation: desperately seeking resolution.

Despite considerable efforts and successes investigating the function of the hippocampal formation in memory processes, there are still numerous elusive key issues. Some of them will be addressed in this review. We will argue that recent evidence supports hippocampal participation in several memory processes, such as encoding, short-term and long-term consolidation and retrieval. While some processes, for example encoding and short-term consolidation, have been the subject of detailed investigations, at least for specific and repeatedly used behavioural paradigms, there appears to be considerable lack of information with respect to other processes, for example long-term consolidation. Although the existence of long-term consolidation is not at debate here, there is only very fragmented information as to the cellular processes enabling long-term consolidation. Recent ample evidence now suggests a potential role in metabotropic glutamate receptors, and more specifically the phospholipase C-coupled receptor 5, in long-term consolidation. The hyperexpression of receptor protein was limited to CA1 indicating a specific role of this brain region in the consolidation of memories. Future work should further explore this important issue especially since long-term consolidation appears to be a necessity for permanent storage of information, and may thus engage memory mechanism that fail during ageing and dementia.