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Hippocampus, Hippocampus

Damage to the hippocampus can also result from oxygen starvation (hypoxia), encephalitis, or medial temporal lobe epilepsy.

Finger, p. 183 There continues to be some interest in hippocampal olfactory responses, particularly the role of the hippocampus in memory for odors, but few people believe today that olfaction is its primary function. Eichenbaum et al ., 1991 Vanderwolf, 2001 Over the years, three main ideas of hippocampal function have dominated the literature: inhibition, memory, and space.

Best & White, 1999 The second major line of thought relates the hippocampus to memory.

Squire, 1992 Eichenbaum and Cohen, 1993 The third important theory of hippocampal function relates the hippocampus to space.

Rolls and Xiang, 2006 In humans, place cells have been reported in a study of patients with drug-resistant epilepsy who were undergoing an invasive procedure to localize the source of their seizures, with a view to surgical resection. The patients had diagnostic electrodes implanted in their hippocampus and then used a computer to move around in a virtual reality town. Ekstrom et al ., 2003 Place responses in rats and mice have been studied in hundreds of experiments over four decades, yielding a large quantity of information.

Smith and Mizumori, 2006 The discovery of place cells in the 1970s led to a theory that the hippocampus might act as a cognitive mapa neural representation of the layout of the environment. O'Keefe and Nadel Several lines of evidence support the hypothesis.

Chiu et al ., 2004 Studies with animals have shown that an intact hippocampus is required for some spatial memory tasks, particularly ones that require finding the way to a hidden goal. Morris et al ., 1982 The "cognitive map hypothesis" has been further advanced by recent discoveries of head direction cells, grid cells, and border cells in several parts of the rodent brain that are strongly connected to the hippocampus.

Whether having a bigger hippocampus helps an individual to become a cab driver, or if finding shortcuts for a living makes an individual's hippocampus grow is yet to be elucidated.

Ktter & Stephan, 1997 The hippocampus as a whole has the shape of a curved tube, which has been analogized variously to a seahorse, a ram's horn ( Cornu Ammonis , hence the subdivisions CA1 through CA4), or a banana.

Prull et al ., 2000, p. 105 Some early studies reported substantial loss of neurons in the hippocampus of elderly people, but later studies using more precise techniques found only minimal differences.

Chang and Lowenstein, 2003 It is not yet clear, though, whether the epilepsy is usually caused by hippocampal abnormalities, or the hippocampus is damaged by cumulative effects of seizures. Sloviter, 2005 In experimental settings where repetitive seizures are artificially induced in animals, hippocampal damage is a frequent result: this may be a consequence of the hippocampus being one of the most electrically excitable parts of the brain.

Suzuki et al , 2005 There is also a general relationship between the size of the hippocampus and spatial memory.

Jacobs, 2003 This relationship also extends to sex differences: in species where males and females show strong differences in spatial memory ability, they also tend to show corresponding differences in hippocampal volume. Jacobs et al ., 1990 Non-mammalian species do not have a brain structure that looks like the mammalian hippocampus, but they have one that is considered homologous to it. The hippocampus, as pointed out above, is essentially the medial edge of the cortex.

Aboitiz et al ., 2003 The pallium is usually divided into three zones: medial, lateral, and dorsal. The medial pallium forms the precursor of the hippocampus.

There is now evidence that these hippocampal-like structures are involved in spatial cognition in birds, reptiles, and fish. Rodrguez et al ., 2002 In birds, the correspondence is sufficiently well established that most anatomists refer to the medial pallial zone as the "avian hippocampus". Colombo and Broadbent, 2000 Numerous species of birds have strong spatial skills, particularly those that cache food. There is evidence that food-caching birds have a larger hippocampus than other types of birds, and that damage to the hippocampus causes impairments in spatial memory. Shettleworth, 2003 The story for fish is more complex. In teleost fish (which make up the great majority of existing species), the forebrain is distorted in comparison to other types of vertebrates: most neuroanatomists believe that the teleost forebrain is essentially everted, like a sock turned inside-out, so that structures that lie in the interior, next to the ventricles, for most vertebrates, are found on the outside in teleost fish, and vice versa. Nieuwenhuys, 1982 One of the consequences of this is that the medial pallium ("hippocampal" zone) of a typical vertebrate is thought to correspond to the lateral pallium of a typical fish. Several types of fish (particularly goldfish) have been shown experimentally to have strong spatial memory abilities, even forming "cognitive maps" of the areas they inhabit.

Source: Wikipedia > Hippocampus