Hippocampus | Define Hippocampus at Dictionary.com hippocampus [hip-uh-kam-puh s] /ˌhɪp əˈkæm pəs/ Spell [hip-uh-kam-pahy, -pee] /ˌhɪp əˈkæm paɪ, -pi/ (Show IPA) 1. Classical Mythology. a sea horse with two forefeet, and a body ending in the tail of a dolphin or fish. 2. Anatomy. an enfolding of cerebral cortex into the lateral fissure of a cerebral hemisphere, having the shape in cross section of a sea horse. Origin of hippocampus 1600-10; < Latin < Greek hippókampos, equivalent to hippo- hippo- + kámpos sea monster Dictionary.com Unabridged Examples from the Web for hippocampus Expand How Sad Moms Change a Child’s Brain Sharon Begley August 21, 2011 Historical Examples There are two denizens of the deep which bear the name of sea-horse—one the tiny hippocampus, the other the mighty walrus. Museum of Antiquity L. W.

Yaggy Eventually it ends in the substance of the hippocampus and in the uncus of the temporal lobe. British Dictionary definitions for hippocampus Expand noun (pl) -pi (-paɪ) 1. a mythological sea creature with the forelegs of a horse and the tail of a fish 2. any marine teleost fish of the genus Hippocampus, having a horselike head See sea horse 3. an area of cerebral cortex that forms a ridge in the floor of the lateral ventricle of the brain, which in cross section has the shape of a sea horse. It functions as part of the limbic system Derived Forms C16: from Latin, from Greek hippos horse + kampos a sea monster Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Word Origin and History for hippocampus Expand n.

c.1600, a kind of sea monster, part horse and part dolphin or fish (they are often pictured pulling Neptune's chariot), from Late Latin hippocampus, from Greek hippokampos, from hippos "horse" + kampos "a sea monster," perhaps related to kampe "caterpillar." Used from 1570s as a name of a type of fish; of a part of the brain from 1706, on supposed resemblance to the fish. Online Etymology Dictionary, © 2010 Douglas Harper Hippocampus - definition of hippocampus by The Free Dictionary Hippocampus - definition of hippocampus by The Free Dictionary (hĭp′ə-kăm′pəs) n. pl. hip·po·cam·pi (-pī′) 1. A ridge in the floor of each lateral ventricle of the brain that consists mainly of gray matter and has a central role in memory processes. 2. Variant of hippocamp . [New Latin, from Late Latin, hippocamp (from the shape of the structure in cross section ); see hippocamp.] hip′po·cam′pal (-pəl) adj.

hippocampus (ˌhɪpəʊˈkæmpəs) n, pl -pi (-paɪ) 1. (Classical Myth & Legend) a mythological sea creature with the forelegs of a horse and the tail of a fish 2. (Zoology) any marine teleost fish of the genus Hippocampus, having a horselike head. See seahorse 1 3. (Anatomy) an area of cerebral cortex that forms a ridge in the floor of the lateral ventricle of the brain, which in cross section has the shape of a sea horse. It functions as part of the limbic system [C16: from Latin, from Greek hippos horse + kampos a sea monster] ˌhippoˈcampal adj (ˌhɪp əˈkæm pəs) n., pl. -pi (-paɪ, -pi) a curved ridge in the lateral ventricles of the mammalian brain: part of the limbic system. [1600–10; < Latin < Greek hippókampos=hippo- hippo - + kámpos sea monster] hip`po•cam′pal, adj.

ThesaurusAntonymsRelated WordsSynonymsLegend: Seahorse (Hippocampus) - Animals - A-Z Animals Characteristics unique to the animal Long snout and brooding pouch on the male Seahorse Location Seahorse The seahorse is a small species of vertebrate that is found in the tropical shallows and temperate waters around the world. The sea horse is also commonly found around coral reefs where there is plenty of food and places for the seahorse to hide. The seahorse is most closely related to a pipe fish although, the seahorse does not have scales like most fish and instead the seahorse has a bone structure that is made up of little plates and covered with a thin layer of skin. There are 32 recognised species of seahorse found in all water types worldwide, with the exception of the polar regions . Seahorses are generally small animals averaging around 10cm in height although this is dependent on the species . Seahorses can also be found in many different colours but the exact colour of the seahorse is down to the particular species of seahorse and the area in which it lives.

Seahorses spend their time bobbing in the sea grasses and coral reefs and due to their colourings, seahorses are able to camouflage themselves pretty effectively into the aquatic plants and larger coral so as to hide from their predators. The seahorse has a number of distinctive features which help the seahorse to survive in it's marine environment . The seahorse has a long snout for sucking in food and a long tail which the seahorse uses both for moving through the water and also for clinging onto coral and aquatic plants, which the seahorse does by curling this long tail around things in order to anchor itself down. The seahorse is an omnivorous animal and the seahorse therefore eats a mixture of plant and animal matter which the seahorse does by sucking the food into it's body through it's elongated snout. The seahorse primarily feeds on brine shrimp . plankton , tiny species of fish and algae. Due to the small size and vulnerability of the seahorse , the seahorse has numerous predators within it's natural environment .

Crustaceans such as crabs , fish and rays are all common predators of the seahorse along with humans who harvest the seahorse for use in medicine. The seahorse is also vulnerable to bad weather as in storms, seahorses are often thrown from the place that they were clinging onto and onto the shore. The sea horse is best known for the remarkable fact that the male seahorse is the one that actually carries the eggs before they hatch. In most other animal species the female of the species if the one to protect the offspring until birth. Instead the female seahorse lays her eggs (anywhere between 8 and 600 eggs are laid depending on the species of seahorse), into the male's brooding pouch where they remain until they hatch within around 3 weeks. The seahorse is a highly endangered animal mainly due to habitat loss and over-hunting. The seahorse is a popular ingredient in medicine (mainly in the far east), and hundreds to thousands of seahorse are harvested every year for this purpose.

Share This Article Seahorse Facts | The Seahorse Trust The Latin name for seahorse is Hippocampus which means "Horse Caterpillar" What is a Seahorse Seahorses are fish. They live in water, breath through gills and have a swim bladder. However they do not have caudal fins and have a long snake-like tail. They also have a neck and a snout that points down. British Seahorses There are two species around British Coastline, the Spiny Seahorse (Hippocampus Guttulatus and the Short Snouted Seahorse (Hippocampus Hippocampus). Both British Seahorses can be found from the Shetland Isles down the west coast of the UK (and all around Ireland) and along the south coast of England; we also have sightings of Seahorses on the east coast and a few years ago they were found in the North Sea. Eyesight Seahorses have excellent eyesight and their eyes are able to work independently on either side of their head. This means they can look forwards and backwards at the same time! This is particulartly useful as they hunt for food by sight.

Snout Seahorses have long thin snouts enabling them to probe into nooks and crannies for food. When they find food they suck it up through their snouts like a vacuum cleaner. Their snouts can expand if their prey os larger than the snout. They are not able to chew and have to disintergrate the food as they eat it. Diet Seahorses eat small crustacea such as Mysis Shrimp. An adult eats 30-50 itmes a day. Seahorse fry (baby seahorses) eat a staggering 3000 pieces of food per day. Territory Females have a territory of about 1.4 sq metres and males have a territory of about 0.5 sq metres. Their territories overlap. Courtship Seahorses pair for life. They meet first thing in the morning to reinforce their pair bonding with an elaborate courtship display. The female meets the male in his territory and as they approach each other, they change colour. The male circles around the female and the pair often spiral around an object. This display can last for upto an hour. Once over the female goes back to her territory.

Pregnancy The male is the only creature where the male has a true reversed pregnancy. The female transfers her eggs to the male which he self fertilises in his pouch. The number of eggs can vary from 50-150 for smaller species to 1500 for larger species. They receive everything they need in the pouch from oxygen to food. Gestation time varies from 14 days to 4 weeks. Giving birth can be a long process with contractions lasting upto 12 hours. Baby Seahorses Baby seahorses are known as fry and when they are born they are totally on their own. They spend the first two to three weeks of their lives drifting along in the plankton layer of the ocean. Less than one in a thousand will survive long enough to become an adult due to predators. Tail Seahorses have a prehensile tail. This allows them to grip onto eel grass and other weeds and prevents them from being washed away by strong currents and waves. Colour Seahorses can change colour very quickly and match any surroundings in which it finds itself. They have even been known to turn bright red to match floating debris. Both males and females also change colour during their courtship display.

Body Unlike most other fish, seahorses have an exo-skeleton. Their bodies are made up of hard, external, bony plates that are fused together with a fleshy covering. They do not have scales. Movement Seahorses are poor swimmers. They rely on their dorsal fin beating at 30-70 times per second to propel it along. Pectoral fins either side of the head help with stability and steering. Appendages The Hippocampus The Hippocampus A page from: Eric Hargreaves'Page O'Neuroplasticity The hippocampus is one of the brain structures making up the limbic system. Although the hippocampus lies beneath the cerebral cortex it is not truly a subcortical structure in that it is really a cortical infolding itself, albeit much older and more primitive than the surrounding neocortex. Hence, it is also referred to as archicortex, or paleocortex. Further, the older and therefore also simpler paleocortex of the hippocampus is composed of only three layers, which can be contrasted to the much more entangled six layers of the neocortex, but more on that later.

The hippocampus is so named since early on its appearance was likened to a "seahorse", and thus was dubbed the latin equivalent. Personally, I think the early neuroanatomists spent too much time dissecting brains and not enough time on the beach looking at seahorses among the other flora and fauna of beach life worth looking at. Regardless, Jim Ranck Jr. of the Downstate SUNY group, once gave me the article outlining the historical delineation of the structure's name (ref). Jim also used to greet anyone new to the hippocampal group at SUNY within the first couple of weeks, and present them with a real honest to God dried seahorse, of which I still have mine. Hmm... ...maybe a little too much digression here, so back to the topic at hand. The importance of the hippocampus to the neuroplasticity phenomena discussed in the articles presented here is that most of the phenomena were originally discovered in the hippocampus. The hippocampus still remains the structure of choice in which to study many of these same pheomena.

As such, an oft neglected but important step to understanding hippocampal neuroplasticity is to understand hippocampal anatomy and that of the surrounding cortices and other structures providing the major aferents/efferents (inout/output) of the system. Basic Anatomy At left is a depiction of a rat brain with the hippocampus, fornix, and mammillary bodies highlighted in mauve tones, which is based upon figure 1 of Amaral and Witter (1989) . The hippocampal formation is a bi-lateral limbic structure which, in overall shape resembles two "Cs" leaning together at the top and spread apart at the base. The top portion of the formation is known as the "dorsal hippocampus" and because of its proximity to the septum, a structure at the midline of the brain, the dorsal tip of the hippocampus is called the "septal pole" ( Amaral and Witter, 1989 ; Witter, 1989 ). The course of each hippocampus follows the medial aspects of the ventral floor of the lateral ventricle, ending at the bottom tip or "temporal pole".

The internal structure of the hippocampus is the same throughout its length, and consists of an infolded convolution of the evolutionarily older and more simple (fewer cell layers), archicortex or allocortex, as contrasted above to the six-layered neocortex. A cross-section taken perpendicular to the long axis (septal-temporal) will reveal the internal structure as two interlocking "Cs", one reversed in relation to the other, each with its own principle cell layer. One "C" makes up Ammon's Horn or Cornu Ammonis (CA1-CA3), also known as the "Hippocampus proper". The principle cell layer of Ammon's Horn is the stratum pyramidale, or the pyramidal cell layer. The other "C" is made up of the Dentate Gyrus, of which the stratum granulosm, or granule cell layer is the principle cell layer.

Although the dentate gyrus is commonly included as part of the Hippocampus, it is cytoarchitectonically distinct from the hippocampus proper (the structure of the cells, or their architecture is different; Amaral 1978 ; Bayer, 1985 ; Amaral and Witter, 1989 ; Witter, 1989 ). However, sometimes the hilus of the dentate gyrus, the area inside the C created by the granule cells is referred to as CA4, as though it belonged to the hippocampus proper. The hilar region is referred to as CA4 because the pyramidal cell layer of the CA1-CA3 regions begins to breakdown as a tightly packed cell layer and becomes more spread out and sparse, or more of a polymorph layer, in this region. Consequently, early neuroanatomists did not distinguish between these areas. Since the dentate gyrus is not truly part of the hippocampus, terms like "Hippocampal formation" are used to discuss Ammon's Horn and the dentate gyrus together. The intrinsic connections between the principle cell layers of the dentate gyrus and CA regions of the hippocampus are very clear.

The intrinsic connections were so clear, in fact, that Ramon y Cajal was able to determine the major direction of afferent connections or synaptic flow of the "trisynaptic circuit" through the examination of Golgi stained normal material by itself, as early as 1911 ( Andersen, 1975 ). Trisynaptic Circuit The hippocampus, when cut transverse to its longitudinal (septal-temporal) axis, exibits a strong afferent set of three connected pathways known as the "trisynaptic" circuit or loop ( Andersen, Holmqvist, and Voorhoeve, 1966 ; Swanson 1978 ; 1982 ; Witter, 1989 ). First, layers II and III or the "surface layers" of the entorhinal cortex project to the granule cells of the dentate-gyrus, via the perforant-path. Second, the granule cells of the dentate gyrus project to the large pyramidal cells of Cornu Amonnis or Ammon's horn, subfield 3 (CA3), via the mossy fibres system.

Third and finally, the CA3 pyramidal cells project to the pyramidal cells of the CA1 subfield, via the Schaffer collateral system ( Lorente de No, 1934 ; Blackstad, 1956; 1958 ; Amaral 1978 Bayer, 1985 Amaral and Witter, 1989 Witter, 1989 ). However, in the last decade, more emphasis has been placed on the associational fibres that connect the transverse circuitry (septal-temporal axis), and thus, more emphasis on the integrated three-dimensional functioning of the hippocampus as a whole ( Amaral and Witter, 1989 Witter, 1989 ). As more is understood about the overall functioning of the hippocampus, terms like "hippocampal system" come into play, based on the hippocampus, the dentate gyrus, and the adjacent subicular, entorhinal and perirhinal cortices that form the major afferents and efferents to the system.

The idea of the hippocampal system being that the adjacent cortices provide a number of diverse and/or related signals, upon which the hippocampus, at the core of the system, performs some unique set of computations transforming, binding or synthesizing the signals into something new that is then returned to different aspects of the same adjacent cortices. Hippocampal Anatomy: An Historical Overview From the above discussion it can be seen that delineating the boundaries of what is, and what is not the hippocampus plays only a small part of anatomy research and that much of the work deals with the mapping of the pathways like Ramon Y Cajal's description of the afferent flow a century ago. As such, the bulk of anatomical research identifies what projects to what, and what the projections use to get there. As elegant as Ramon Y Cajal's description of the afferent flow of the hippocampus was 100 years ago, the hippocampal system in its entirety is far more complex, subtle, and differentially distributed than the much simplified "connect-the-dots" of the tri-synaptic circuit.

To understand all the work that has been done, it is helpful to see the anatomical results through a historical framework founded on the development and advances in histological staining. These advances in techniques have tended to develop along two directions; first, revealing greater isolation of individual and later specific neurons and second, revealing greater distances along pathways between neural connections. Knowing the techniques that came into play at what time and what each revealed, better enables us to understand hippocampal anatomy, and thus the hippocampus itself. Although this section focuses on staining techniques, it must also be noted that advances in the technology of light microscopy had also just barely been completed in the first half of the nineteenth century, with great improvements in the optics of compound microscopes, such as the condenser system (Zeiss and Abbe, 1873) and thin slice microtome (Willhem His, 1866) and its refinement (Minot, 1886). The histological stains of the times, much like today, dyed different cell organelles and not entire cells.

Also the stains were often literally dyes for clothes, like Carl Weigert's borrowing of hematoxylin (1885), which stained the nuclei of cell bodies a deep blue-violet. Lifted from the textile industry, Hematoxylin came from the logwood tree of Central America and was originally brought over by the conquistatdors as a clothing dye ( Titford, 2005 ). Similarly, Carmine, another clothes and cosmetics dye, derived from the ground up bodies of cochineal insects also brought over from Central America, produces a vibrantly enduring crimson stain (think of flaming red lipstick). Although stains such as these give an indication of the size and packing density of the cells and cell layers, they could not distinguish between the various "protoplasmic processes" identified earlier, or trace their full extent ( Cimino, 2000 ). Silver Nitrate Impregnation, Camillo Golgi (1843-1926) The histological technique to provide the first big advance in hippocampal anatomy was the Golgi method.

Initially developed by the Italian physician Camillo Golgi, who published his first work in 1873 using "la reazione nera" or "the black reaction" ( Jones, 1999 ). The Golgi method was not so much a staining technique as it was a means of impregnating a limited number of neurons, possibly as low as 1/100 with silver nitrate, such that the entire extent of the cell was rendered opaque and highly visble in all its exsquisite detail. This was very different from the staining of the time, which as mentioned above could not penetrate the full protoplasmic extent of the cells, thereby typically only revealing the cell bodies, and their immediate projections. In contrast, the Golgi impregnation, could outline in beautiful detail all of the "protoplasmic processes" later to become Wilhelm His' dendrites (1881) and Kolliker's axon (1896). Additionally, from the Golgi impregnation one could identify the shape of the cell, and therefore its orientation, and of course the full extent of the dentritic arborization.

Golgi's lone work on the hippocampus in 1883 was the first to use the silver nitrate impregnation revealing such great detail. At right is one Golgi's schematic drawings summarizing the structure of the hippocampus taken from his collected works or "Opera Omnia" of 1903, which included the original pes Hippocampi major of 1883 ( Swanson, 1999 ). Although a fairly accurate representation of what we think of the hippocampus today, one can note that while the apical dendrites of the pyramidal system end freely, the basal dendrites in the stratum oriens fuse together into a tightly woven web. Golgi, from his observations, incorrectly assigned the apical dendrites a nutritive role, taking sustenance from the glia and vasculature, he presumed they encapsulated. As a reticularist, Golgi further incorrectly argued that the basal dentrites formed part of the continuously connected neural reticulum or finely wrought web.

Yet, by functionally differentiating between the apical and basal dentritic systems, Golgi had begun to set himself apart from the earlier reticularists, and had begun to lay the groundwork for the Neuron Doctrine. Along with settling on a standard terminology for the hippocampus' lamination, Golgi's other lasting contribution to the hippocampus was at the gross level, where he was the first to argue that Ammon's horn was separate from the fascia dentata or dentate gyrus ( Swanson, 1999 ). Despite the errors stemming from his theoretical viewpoint, Golgi was awarded the Nobel prize for medicine in 1906, along with Cajal. Santiago Ram�n y Cajal (1852-1934) Although developed by Camillo Golgi, it was in the hands of Santiago Ram�n y Cajal that "la reazione nera" flourished. Cajal, similar to the small number of his contemporaries, who were beginning to employ the black reaction, modified the technique to his advantage, by re-impregnating the samples a second time, a double-dipping so to speak.

The next two figs are why I remain amazed at what can be found on the web. First up is an actual slide of Cajal's, complete with his handwritten labels, identifying the slide as "bueno, bueno, bueno", for its good quality. This is followed by an even more amazing pic, a modern photomicrograph taken of a small segment of one of Cajal's original Golgi slides. How cool is that? Here, one is literally peering in at a small segment of history that has had major implications for where Neuroscience is today. Even though the slide is over a century old, for its clarity, the photomicrograph may have been taken of a specimen stained and coverslipped within less than a week. The segment itself depicts a single, but well outlined (as though in Chinese ink), pyramidal cell from the cerebral cortex. In the latter half of the 19th century, although cells were accepted as the basic unit for the rest of the body ( Virchow, 1855 ), the nervous system was considered by many to be a finely wrought mesh of continuously connected fibres or "reticulum", the proponents of which included Camillo Golgi.

Cajal and the likes of Kolliker and His, began publishing evidence to the contrary, culminating in the Neuron Doctrine and establishing modern Neuroscience. Cajal and the handful of his contemporaries were successful due in part to the fact that they studied not just mature human tissue, but ontologically earlier specimens from immature or embryological samples, where neurons could be examined at different stages of development. Cajal and his contemporaries also tended to study simple and clearly laminated (layered) structures , such as the retina, cerebellum, and hippocampus. These approaches combined with the new and sparsely staining Golgi technique allowed the previously complex web of interconnected reticulum to be reduced to its constituent components. Where before a tangled forest stood blocking the view, now stood, but a few well-defined trees. In 1906 Cajal, along with Golgi were awarded the Nobel Prize in Medicine for their contributions to the advancement of "Neurology"; Golgi for his silver impregnation technique, and Cajal for his tremendous use of the technique.

Of course still on opposite sides of the Neuron/Reticulum debate, Golgi's acceptance speech was an attack on the Neuron Doctrine, while the next evening's acceptance speech by Cajal was summary of evidence in favour of the Neuron Doctrine. Cajal turned to the hippocampus, as one of several subjects, during the course of the early 1890s, as the Neuron Doctrine was first becoming established. Initially presented in individual papers, the hippocampal work was best summarized in Cajal's opus magnum "Textura del Sistema Nervioso del Hombre y los Vertebrados" the first volume of which was published in 1899, with the second being published in 1904. Unfortunately much of this remained inaccessible to the scientific community at large until translated into French as "Histologie du Syst�me Nerveux de l'Homme et des Vert�br�s" in 1909 and re-published as a 2nd edition in 1911, with some additional figures from Cajal.

Of course I had to wait for Neely and Larry Swanson's 1995 english translation before I could actually read the chapters, insterad of merely gazing at the pretty drawings. Since then, I've come to appreciate a more literal translation, and beautiful reproduction of the figures in Pedro and Tauba Pasiks 1999 (for Volumes I & II) and 2001 (for Volume III) translation . From these chapters Cajal described in detail the cytoarchitecture or cells and cellular components that populated the lamina defined earlier by Golgi and others (alveus, oriens, pyramidale, rediatum, lacunosum moleculare). He also provided an ontological framework for the development of the various laminar components, with a cross species comparison. Finally, Cajal introduced two divisions for Ammon's horn or hippocampus proper based on the presence or absence of recurrent circuitry of the pyramidal cell layer ( Cajal, 1904 ), which eventually was surpassed by the nomenclature of Cajal's final and most influental student: Rafael Lorente de N�.

Rafael Lorente de N� (1902-1990) A precocious medical student in Zaragoza, first published at age 15, Raphael Lorente de N� became fascinated with the nervous system. Lorente de N� quickly exhausted the knowledge of his immediate mentor Professor Pedro Ramon, who had in turn learned from his older brother Santiago. As such, in 1920, Pedro passed his eager 18 year old student on to the great Cajal then 68 years old himself in Madrid ( Kruger and Woolsey, 1990 ). There, already proficient in the Golgi technique Lorente de N� set about intentionally disproving an early Cajal idea. Previously Cajal had suggested in passing that the strength of human intellect over other animals, may lie in the number and complexity of morphological cell types in the nervous system. Lorente de N� using the Golgi technique examined the mouse cortex, considered at the time, to be the lowest animal with a neocortex. The neuronal patterns that Lorente de N� found and described in the primary auditory cortex were at least as complex as those observed in humans.

Subsequently, in a move that says as much about master, as it does about the pupil, Cajal had the work published in his own journal. Although proofed, Cajal left the manuscript largely unaltered and untouched by his own hand, published, written as it was, by Lorente de N�, ( Lorente de N�, 1922 ). more to come... To quickly list succession of techniques would be to start with the Golgi techniqe of silver imgregnation, later to become Golgi-Cox gold impregnation, followed by Fink Heimer silver degeneration for tracing, followed by fluorescing aldehydes under ultra violet light, to identify the amine transmitter systems (indole amines and xx amines noradrenaline (epinephrine if you're a Brit), dopamine and serotonin) and immuno-fluorescing essentially the same, but generating sizeable antibody reactions that fluoresced, followed by autoradiographic lighting, followed by specific and unique stains such as lucifer yellow diamon blue. etc. More Anatomy than you ever wanted to know Coming soon...

Finally, there have been a number of attempts to produce encompassing theories of hippocampal function that take into account the human lesion literature, the experimental lesion literature, and hippocampal electrophysiology ( Cohen and Eichenbaum, 1993 ). Hippocampus Sensitive Tasks Although animal models of learning deficits using hippocampal lesions have been unable to generate the global learning impairment exhibited by H.M., hippocampally lesioned animals have shown consistent impairment in a number of tasks. Often these tasks are also impaired by lesions to areas other than the hippocampus, but it is worth noting that these areas typically either feed into the hippocampus or feed from the hippocampus. Initial acquisition has been found to be sensitive to hippocampal lesions ( Morris et al., 1982 ; Sutherland, Whishaw and Kolb, 1982 ), and selective lesions of the dentate gyrus ( Sutherland, Whishaw and Kolb, 1983 ).

Acquisition is also disrupted by lesions downstream of the hippocampus, in the subicular complex ( Morris, Schenck, Tweedie and Jarrard, 1990 ) and medial frontal cortical region ( Sutherland, Whishaw and Kolb, 1982 ). Lesions upstream of the hippocampus such as the perforant path, the main entorhinal input to the hippocampus ( Skelton and McNamara, 1992 ) and lesions to the medial septum, the other major input to the hippocampus ( Hagan et al., 1988 ) also disrupt acquisition. Additionally, as indicated above, the hippocampal system may also interact or run in parallel with other forebrain learning systems to solve certain aspects or variants of the water maze ( McDonald and White, 1994 ; Devan, Goad, and Petri, inpress ). Finally, somewhat like DNMS, the hippocampus' role in the traditional aspects of the water maze has also come into question. Whishaw et al.

( 1995 ) have shown that with extensive visible platform training, in which the distance to the platform was gradually increased, rats with fimbria/fornix lesions (disconnected hippocampi) exhibited a degree of spatial learning by heading for the hidden platform from distal sites. Yet subsequently, when the platform was switched to a new location, the fimbria/fornix lesioned animals could not learn its new position, even after many trials. Whishaw et al. ( 1995 ) use these data to argue that a further distinction may be required in the water maze between discovering the appropriate strategy "getting there" in addition to the more traditional "knowing where", and that hippocamnpally lesioned animals are impaired on the former, but not the latter. However, Devan et al. ( inpress ) suggest that other forebrain learning systems, particularly in the striatum, may be allowing the hippocampally lesioned animals to solve the first platform location in a non-spatial manner, albeit, not as successfully as had the hippocampus been intact. It is more than likely that traditional water maze protocols will give way to more advanced protocols that can tease apart the specific aspects currently being debated.

Similarly, simple escape latency measures will more than likely give way to more advanced pattern detection measures. Hippocampus References... Amaral, D.G. (1978). A golgi study of cell types in the hilar region of the hippocampus in the rat. Journal of Comparative Neurology, 182, 851-914. Amaral, D.G. & Witter, M.P. (1989). The three-dimensional organization of the hippocampal formation: a review of anatomical data. Neuroscience, 31, 571-591. Andersen, P. (1975). Organization of hippocampal neurons and their interconnections. In R.L. Isaacson & K.H. Pribram (Eds.) The Hippocampus Vol. I (pp. 155-175), New York, Plenum Press. Bayer, S. (1985). Hippocampal region. In G. Paxinos (Ed.) The Rat Nervous System Vol1; Forebrain and Midbrain (pp. 335-352), New York, Academic Press.

Blackstad, T.W. (1956). Commissural connections of the hippocampal region in the rat, with special reference to their mode of termination. Journal of Comparative Neurology, 105, 417-528. Blackstad, T.W. (1958). On the termination of some afferents to the hippocampus and fascia dentata. Acta Anatomica, 35 202-214. Cajal, SRY (1888a). Estructura de los centros nerviosos de las aves. Revista Trimestral de Histologia Normol y Patologica, 1, 1-10. Cajal, SRY (1888b). Sobre las fibras nerviosas de la capa molecular del cerebelo. Revista Trimestral de Histologia Normol y Patologica, 1, 33-49. Cajal, SRY (1889a). Conexion general de los elementos nerviosos. Medical Practica, 2, 341-346.

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Question: What is another name for a hippocampus?
Answer: Sea horse