The location of the hippocampus in the human brain.

The hippocampus is a part of the brain located inside the temporal lobe (humans have two hippocampi, one in each side of the brain). It forms a part of the limbic system and plays a part in memory and navigation. The name derives from its curved shape, which supposedly resembles that of a seahorse (Greek: hippocampus). Wikipedia does not have an article with this exact name. ... Wikipedia does not have an article with this exact name. ... Comparative brain sizes In the anatomy of animals, the brain, or encephalon (Greek for in the head), is the higher, supervisory center of the nervous system. ... The temporal lobes are part of the cerebrum. ... The limbic system is a group of brain structures that are involved in various emotions such as aggression, fear, pleasure and also in the formation of memory. ... Memory is the ability to retain information, a faculty of the brain. ... There are several traditions of navigation. ...

In Alzheimer's disease, the hippocampus becomes one of the first regions of the brain to suffer attack; memory problems and disorientation appear amongst the first symptoms. Damage to the hippocampus can also result from oxygen starvation (anoxia) and encephalitis. Asphyxia is a condition of severely deficient supply of oxygen to the body. ... Encephalitis is an acute inflammation of the brain, commonly caused by a viral infection. ...

In the anatomy of animals, the hippocampus is among the phylogenetically oldest parts of the brain. The hippocampal emergence from the archipallium is most pronounced in primates and Cetacean sea mammals. Nonetheless, in primates, the hippocampus occupies less of the telencephalon in proportion to cerebral cortex among the youngest species, especially humans. The significant development of hippocampal volume in primates correlates more with overall increase of brain mass than with neocortical development. Anatomical drawing of the human muscles from the Encyclopédie. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anenomes) Placozoa (trichoplax) Subregnum Bilateria (bilateral symmetry) Acoelomorpha (basal) Orthonectida (flatworms, echinoderms, etc. ... In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ... In anatomy of animals, the archipallium the oldest region of the brains pallium. ... [[{{{diversity_link}}}|Diversity]] {{{diversity}}} Binomial name {{{binomial}}} Trinomial name {{{trinomial}}} Type Species {{{type_species}}} Families * 15, See classification [[Image:{{{range_map}}}|{{{range_map_width}}}|]] Synonyms {{{synonyms}}} A primate is any member of the biological order Primates, the group that contains all lemurs, monkeys, apes, and humans. ... Suborders Mysticeti Odontoceti (see text for families) The order Cetacea includes whales, dolphins and porpoises. ... [[{{{diversity_link}}}|Diversity]] {{{diversity}}} Binomial name {{{binomial}}} Trinomial name {{{trinomial}}} Type Species {{{type_species}}} Families * 15, See classification [[Image:{{{range_map}}}|{{{range_map_width}}}|]] Synonyms {{{synonyms}}} A primate is any member of the biological order Primates, the group that contains all lemurs, monkeys, apes, and humans. ... The telencephalon (te-len-seff-a-lon) is the technical name for a large region within the brain which is attributed many functions, which some groups would class as unique features which make humans stand out from other species. ... Location of the Cerebral cortex Slice of the Cerebral cortex, ca. ... In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ... [[{{{diversity_link}}}|Diversity]] {{{diversity}}} Binomial name Homo sapiens Linnaeus, 1758 Trinomial name {{{trinomial}}} Type Species {{{type_species}}} Subspecies Homo sapiens idaltu (extinct) Homo sapiens sapiens [[Image:{{{range_map}}}|{{{range_map_width}}}|]] Synonyms {{{synonyms}}} Homo (genus). ... In the anatomy of animals, the neopallium or neocortex is a part of the telencephalon in the brain. ...

Anatomy

Diagram of hippocampal regions. DG: Dentate gyrus.

Although there is a lack of consensus relating to terms describing the hippocampus and the adjacent cortex, the term hippocampal formation generally applies to the dentate gyrus, fields CA1-CA3 (or CA4, frequently called the hilus and considered part of the dentate gyrus), and the subiculum (see also Cornu ammonis). The CA1 and CA3 fields make up the hippocampus proper. Image File history File links Diagram of hippocampal regions. ... Image File history File links Diagram of hippocampal regions. ... The dentate gyrus is part of the hippocampal formation. ... The dentate gyrus is part of the hippocampal formation. ... The subiculum (Latin: support) forms the most inferior portion of the hippocampus. ... Daigram of hippocampal regions. ...

Information flow through the hippocampus proceeds from dentate gyrus to CA3 to CA1 to the subiculum, with additional input information at each stage and outputs at each of the two final stages. CA2 represents only a very small portion of the hippocampus and its presence is often ignored in accounts of hippocampal function, though it is notable that this small region seems unusually resistant to situations that usually cause large amounts of cellular damage, such as epilepsy. Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, and are sometimes called the building blocks of life. ...

The perforant path, which brings information primarily from entorhinal cortex (but also perirhinal cortex, among others), is generally considered the main source of input to the hippocampus. Layer II of entorhinal cortex (EC) brings input to the dentate gyrus and field CA3, while EC layer III brings input to field CA1 and the subiculum. The main output pathways of the hippocampus are the perforant path, the cingulum bundle, and the fimbria/fornix, which all arise from field CA1 and the subiculum. The entorhinal cortex (EC) is an important memory center in the brain. ... The cingulum is a collection of white matter fibers projecting from the cingulate gyrus to the entorhinal cortex in the brain. ... Categories: Medicine stubs | Central nervous system ...

Perforant path input from EC layer II enters the dentate gyrus and is relayed to region CA3 (and to mossy cells, located in the hilus of the dentate gyrus, which then send information to distant portions of the dentate gyrus where the cycle is repeated). Region CA3 combines this input with signals from EC layer II and sends extensive connections within the region and also sends connections to region CA1 though a set of fibers called the Schaffer collaterals. Region CA1 receives input from region CA3 as well as EC layer III and then projects to the subiculum as well as sending information along the aforementioned output paths of the hippocampus. The subiculum is the final stage in the pathway, combining information from the CA1 projection and EC layer III to also send information along the output pathways of the hippocampus. Schaffer collaterals are axon collaterals given off by CA3 pyramidal cells in the hippocampus. ...

It is widely accepted that each of these regions has a unique functional role in the information processing of the hippocampus, but to date the specific contribution of each region is poorly understood.

Role in general memory

Drawing of the neural circuitry of the rodent hippocampus. S. Ramón y Cajal, 1911.

Psychologists and neuroscientists dispute the precise role of the hippocampus, but generally agree that it has an essential role in the formation of new memories about personally experienced events (episodic or autobiographical memory). Some researchers prefer to consider the hippocampus as part of a larger medial temporal lobe memory system responsible for general declarative memory (memories which can be explicitly verbalized—these would include, for example, memory for facts in addition to episodic memory). Image File history File links Download high resolution version (687x1280, 347 KB)Drawing of the neural circuitry of the rodent hippocampus. ... Image File history File links Download high resolution version (687x1280, 347 KB)Drawing of the neural circuitry of the rodent hippocampus. ... Santiago Ramón y Cajal Santiago Ramón y Cajal (May 1, 1852–October 17/18, 1934), Nobel laureate, 1906, was a Spanish histologist and is considered to be the father of modern neuroscience. ... Psychology (ancient Greek: psyche = soul or mind, logos/-ology = study of) is an academic and applied field involving the study of mind and behavior. ... Neuroscience is a field of study that deals with the structure, function, development, genetics, biochemistry, physiology, pharmacology, and pathology of the nervous system, divided into the central nervous system (the brain and spinal cord), and the peripheral nervous system, consisting of the myriad nerve pathways running throughout the body. ... Episodic memory, or autobiographical memory, is the explicit memory of events. ... This article needs to be wikified. ... Declarative memory is the aspect of memory that stores facts and events. ... Semantic memory refers to the memory of meanings, understandings, and other factual knowledge; in contrast to episodic memory. ... Episodic memory, or autobiographical memory, is the explicit memory of events. ...

Some evidence exists that, although these forms of memory often last a lifetime, the hippocampus ceases to play a crucial role in the retention of the memory after a period of consolidation. Damage to the hippocampus usually results in profound difficulties in forming new memories (anterograde amnesia), and normally also affects access to memories prior to the damage (retrograde amnesia). Although the retrograde effect normally extends some years prior to the brain damage, in some cases older memories remain - this sparing of older memories leads to the idea that consolidation over time involves the transfer of memories out of the hippocampus to other parts of the brain. However, experimentation has difficulties in testing the sparing of older memories, and in some cases of retrograde amnesia the sparing apparently affects memories formed decades before the damage to the hippocampus occurred, so its role in maintaining these older memories remains controversial. The broad definition of memory consolidation is the process by which recent memories are crystallised into long-term memory. ... Anterograde amnesia is a form of amnesia, or memory loss, where new events are not transferred to long-term memory. ... Retrograde amnesia is a form of amnesia where someone will be unable to recall events that occurred before the onset of amnesia. ...

Damage to the hippocampus does not affect some aspects of memory such as the ability to learn new skills (playing a musical instrument, for example), suggesting that such abilities depend on a different type of memory (procedural memory) and different brain regions. And there is evidence (e.g. O'Kane et al 2004) that patient HM (who had his medial temporal lobes removed bilaterally as a treatment for epilepsy) can form new semantic memories. Procedural memory, also known as implicit memory, is the long-term memory of skills and procedures, or how to knowledge. ... A memory impaired patient known as HM (an acronym used to keep his identity confidential) has been widely studied since the late 1950s and has been very important in the development of theories that explain the link between brain function and memory, and in the development of cognitive neuropsychology, a... Semantic memory refers to the memory of meanings, understandings, and other factual knowledge; in contrast to episodic memory. ...

Role in spatial memory and navigation

Some evidence implicates the hippocampus in storing and processing spatial information. Studies in rats have shown that neurons in the hippocampus have spatial firing fields. These cells are called place cells. Some cells fire when the animal finds itself in a particular location, regardless of direction of travel, while most are at least partially sensitive to head direction and direction of travel. In rats some cells, termed splitter cells, may alter their firing depending on the animal's recent past (retrospective) or expected future (prospective). Different cells fire at different locations, so that by looking at the firing of the cells alone, it becomes possible to tell where the animal is. Place cells have now been seen in humans involved in finding their way around in a virtual reality town. The findings resulted from research with individuals who had electrodes implanted in their brains as a diagnostic part of surgical treatment for serious epilepsy. Neurons (also called nerve cells) are the primary cells of the nervous system. ... A place cell is a type of neuron in the hippocampus which shows activity in response to an animals being in a certain area in space. ... Virtual Reality (VR) is an environment that is simulated by a computer. ...

The discovery of place cells led to the idea that the hippocampus might act as a cognitive map — a neural representation of the layout of the environment. Studies with animals have shown that an intact hippocampus is required for simple spatial memory tasks (for instance finding the way back to a hidden goal).

Without a fully functional hippocampus humans may not successfully remember the places they have been to and how to get where they are going. Researchers believe that the hippocampus plays a particularly important role in finding shortcuts and new routes between familiar places. Some people exhibit more skill at this sort of navigation than do others, and brain imaging shows that these individuals have more active hippocampi when navigating.

London's taxi drivers must learn a large number of places — and know the most direct routes between them (they have to pass a strict test, The Knowledge, before being licensed to drive the famous black cabs). A study at University College London showed that part of the hippocampus is larger in taxi drivers than in the general public, and that more experienced drivers have bigger hippocampi. It may be that having a bigger hippocampus helps you to become a cab driver. It also seems that finding shortcuts for a living may make your hippocampus grow. Part of the London skyline viewed from the South Bank London is the most populous city in the European Union, with an estimated population on 1 January 2005 of 7. ... A taxicab (sometimes called taxi, cab, or hack) is a vehicle for hire which conveys passengers between locations of their choice. ... THE KNOWLEDGE, BOOKS BY SCHOLASTIC. CLICK HERE The Knowledge is the study of London that a prospective taxi driver must complete in order to obtain a license to operate a black cab in London, the purpose of which is for them to demonstrate that they know the roads, routes and...

A study on rats at Indiana University suggested that the sexual dimorphism in the hippocampus morphology is tied to a sexual dimorphism in repeated maze performance. Males seem to be better at contexualizing their whereabouts because they have more hippocampus to work with.

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. Vladimir Bekhterev (January 20, 1857 – December 24, 1927) was a Russian neurophysiologist and psychiatrist who noted the role of the hippocampus in memory around 1900. ... The limbic system is a group of brain structures that are involved in various emotions such as aggression, fear, pleasure and also in the formation of memory. ... Emotions are essentially impulses that move an organism to action, originating automatic reaction behavior which has been adapted through evolution as a survival need. ...

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 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. A memory impaired patient known as HM (an acronym used to keep his identity confidential) has been widely studied since the late 1950s and has been very important in the development of theories that explain the link between brain function and memory, and in the development of cognitive neuropsychology, a... Epilepsy (often referred to as a seizure disorder) is a chronic neurological condition characterized by recurrent unprovoked seizures. ... The striatum is a subcortical part of the brain consisting of the caudate nucleus and the putamen. ... A memory impaired patient known as HM (an acronym used to keep his identity confidential) has been widely studied since the late 1950s and has been very important in the development of theories that explain the link between brain function and memory, and in the development of cognitive neuropsychology, a... Suborders Mysticeti Odontoceti (see text) The order Cetacea includes whales, dolphins and porpoises. ...

External links

• Brain Atlas, Brain Maps, Neuroinformatics
• Artificial Hippocampus
• For more information about this structure visit BrainInfo