History

The anatomist Giulio Cesare Aranzi (circa 1564) first used the term hippocampus to describe the cerebral organ because of its visual resemblance to a seahorse. This organ was initially connected with the sense of smell, rather than with its known function in memory acquisition. The Russian Vladimir Bekhterev noted the role of the hippocampus in memory around 1900, based on observations of a patient with profound memory disturbances. However, for many years, the conventional view of the hippocampus was that, like the rest of the limbic system, it was responsible for emotion.

The importance of the hippocampus in memory was brought to the attention of researchers by patient HM. HM suffered from a number of anterograde and temporally-graded retrograde memory impairments (such impairments are the subject of the movie Memento) following the bilateral removal of various medial-temporal lobe structures (including bilateral ablation of his hippocampi) to relieve frequent epileptic seizures. Of particular importance is that HM was still able to learn procedural tasks (which are associated with the Striatum) and had an above-average IQ. HM demonstrated a striking single-dissociation between intelligence and declarative memory. The relative size of the hippocampal formation in relation with the total volume of the brain is often conserved in most of the mammalian species. Nevertheless, it has been found that these areas are relatively hypotrophic in cetaceans.