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What Part Of The Brain Is The Hippocampus Located

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Involvement Of The Hippocampus In Eyeblink Classical Conditioning

The Brain’s Hippocampus – its location and function explained by Psychology Professor Bruce Hinrichs

The hippocampus and septohippocampal acetylcholine system are involved in basic associative learning of the sort represented by eyeblink conditioning. In a series of studies using delay eyeblink classical conditioning in rabbits, it was observed that activity recorded in the CA1 pyramidal cell region of the hippocampus forms a predictive model of the amplitudetime course of the learned behavioral response, but only under conditions in which behavioral learning occurs. This response is generated largely by pyramidal neurons. The role of the hippocampus in classical conditioning of the eyeblink response is called modulatory because manipulations of the hippocampus can impair or enhance the rate of acquisition. The memory trace itself is not in the hippocampus, but the hippocampus can markedly influence the storage process.

Although the hippocampus is not necessary for normal acquisition in the delay procedure, it is necessary for trace conditioning. A long-lasting neuronal plasticity is formed in the hippocampus following eyeblink conditioning. This change is essential for learning to occur in the trace eyeblink conditioning procedure, at least until the learning is consolidated. Age-related electrophysiological changes in the hippocampus have been associated with age-related impairment in trace eyeblink conditioning.

A.K.Martig, S.J.Y. Mizumori, in, 2010

Communication Bridge Between Other Parts Of The Brain

It should not be forgotten that beyond the mental processes carried out by the amygdala, it also acts as an intermediate stop between different regions of the brain.

Specifically, each amygdala communicates through neurons with the diencephalon , the nucleus accumbens, the locus coerulus, and many others.

Where Are The Hippocampus And Amygdala Located

The hippocampus and the amygdala are located in the temporal lobe.

To locate the temporal lobe we must visualize that area contained at the level of the ears. It is separated from the parietal lobe by the Silvio fissure and is for many biologists one of the newest parts of the brain in fact, it only appears in vertebrates.

Likewise and like all other regions of the brain, it is not an anatomically isolated structure. It works in conjunction with the other regions of the brain but, yes, we could say that it is a very dynamic, sensitive structure in constant interaction with the senses and our environment.

In fact, and this data is interesting, we are dealing with the brain lobe that has the most connections with the limbic system. Therefore, it has a great responsibility in a large number of processes related to our emotions and memory. That is why there are two fundamental structures here: the amygdala and the hippocampus.

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The Hippocampus: What Is It

When learning about the human brain, its helpful to remember that even the most powerful computer in the world is no match for this part of the human body. With its billions of nerve cells, and the thousands and thousands of connections each nerve cell makes, the brain gives new meaning to the word complex. There is much that scientists have come to learn and understand about the human brain. A small structure within the brain called the hippocampus played a big part in how that knowledge was obtained.

What is the hippocampus?

Thanks to the sacrifice of his memory and his willingness to participate in ongoing studies, researchers were able to greatly expand their understanding of memory, the brain, and brain disease. Molaison made a great contribution to science and was reportedly happy to know he was helping others.

Related areas of the brain

The hippocampus is part of the limbic system, which includes parts of the brain associated less with conscious thought and more with feeling and reacting.Situated on the edge of the cortex, the limbic system includes the hypothalamus and the amygdala. These structures help control different bodily functions, such as the endocrine system and what is commonly known as the fight or flight reaction.

Functions of the hippocampus

What happens if the hippocampus is affected by illness or injury?

Diseases that affect the hippocampus

  • Alzheimers disease
  • Epilepsy
  • Depression

Last reviewed: Thu 6 October 2016

Modulation Of Hippocampal Activities

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Modulation of activities in the hippocampus and in the neural chain that begins at the entorhinal cortex and runs through the CA areas to the subiculum may occur through influences mediated by the diffusely projecting biogenic amine systems, afferent cholinergic influences, and both localized and systemic neuropeptide and hormonal systems. There are vast numbers of potential modifying influences. Norepinephrine, serotonin, histamine, VIP, cholecystokinin, substance P, somatostatin, the enkephalins, and the hypocretins influence neuronal activity in the hippocampus. In addition, a significant dopaminergic input arising primarily from the ventral tegmental area reaches the hippocampus and the entorhinal cortex.

The substantial norepinephrine projections received by the hippocampus come from cells in the anterior part of the locus coeruleus. These cells are the sole source of the noradrenergic input to the hippocampus, but collaterals of these locus coeruleus cells reach other areas, including the neocortex, thalamus, and spinal cord. Some cells in this nucleus project bilaterally to the hippocampus. The serotonergic fibers that reach the hippocampus arise in large part from the median raphe cell group of the brain stem. Some fibers also reach the hippocampus from the dorsal raphe. These fibers terminate in the dentate gyrus and reach the molecular layers of the CA1 and CA3 to a greater extent than do noradrenergic fibers.

L.M. Hilt, … S.D. Pollak, in, 2011

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What Is The Hippocampus

The hippocampus is located in the internal zone of the temporal lobe of the brain and according to the anatomy it is related to the hypothalamus and the amygdala, therefore they work together in the composition of the limbic system.

The hippocampal formation is a curved and recurve sheet of cortex, located on the medial surface of the temporal lobe.

Cross sections show that the hippocampal formation is made up of three distinct areas: the dentate gyrus, the hippocampus, and the subiculum.

In these types of sections, the dentate gyrus and hippocampus are shaped like two interlocking Cs. The subiculum is a transition zone that continues with the hippocampus at one end and the parahippocampal cortex at the other.

The three components are organized as anterior to posterior bands within the temporal lobe, which together form a cylinder.

The hippocampus is an important part of the brain since, thanks to research, we know that it has functions related to declarative, non-declarative and long-term memory and to maintain memories depending on what the person experiences emotionally at the moment it is created, what which indicates that it is related to the ability to learn.

Likewise, it is a brain structure capable of intervening in spatial visual processes, which is why it is considered a necessary area to remember, locate ourselves in space and memorize.

History Of The Hippocampus

The term hippocampus is derived from the Greek word hippokampus because the structure resembles the shape of a sea horse. The structure was first described by the anatomist Julius Caesar Aranzi. Because the hippocampus has been known of and observed for centuries, it is one of the most studied areas of the brain.

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The Hippocampus And Memory

The term hippocampus originates from the Greek word hippokampus as the shape of the hippocampus resembles that of a sea horse.

About 1.5 to 2 inches in length, the hippocampus is embedded deep within the temporal lobe of your brain. It plays a vital role in regulating learning, memory encoding, memory consolidation, and spatial navigation.

In basic terms, the hippocampus is where your short-term memories and new learning are turned into long-term memories that are then stored elsewhere in the brain. The hippocampus helps us to process and retrieve two kinds of memory: declarative memories and spatial relationships. Declarative memories are both episodic and semantic .

Spatial relationship memories involve pathways or routes. It appears that neurons in the hippocampus encode information about our environment in such a way that they create a mind map of our surroundings. Interestingly, brain scans have shown that some taxi drivers have an enlarged hippocampus compared to non-taxi drivers, due to the spatial memories required to do their job!

How The Hippocampus Directs Behavior And Emotion

Memory and the Hippocampus

The hippocampus is not only implicated in memory, navigation and learning, but can also affect mood and behavior.

Stress itself can impact the hippocampus, and in turn, our demeanor, Reichelt said. “If we’re getting any sort of oxidative stress build up that can start to damage the function of the neurons in the hippocampus, and then lead to forgetting things,” she said. And that can lead to frustration or other changes in mood, she added.

Because part of the hippocampus is connected to the amygdala an almond-shaped region of the brain central to processing fear and other emotions it, too, is believed to be involved in emotion processing.

Animal data suggest that the hippocampus is one of the few areas of the brain where new nerve cells are generated, even in adulthood, according to a 2011 review published in the journal Neuron. Animal research has also shown that promoting the proliferation of neurons within the hippocampus can improve mood, and these effects might also be reflected in humans, Reichelt said.

Although research suggests that antidepressants act on the serotonin system, they might also be increasing the ability of the brain to modify its connections or rewire itself in areas, such as in the hippocampus. Antidepressants take roughly four weeks to kick in, which coincides with the approximate period of how long it takes for new neurons to integrate into the hippocampus properly, Reichelt said.

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Blood Supply And Lymphatics

The anterior choroidal artery runs medially and superiorly to the uncus, between the ambient and semilunar gyrus. It then sends perforating arteries to reach deeper structures. The uncus is closely related to the M1 segment of the middle cerebral arteries and its lenticulostriate arteries.

The P2 segment of the posterior cerebral artery and the basal vein supply and drain the caudal part of the head of the hippocampus that faces the crus cerebri and crural cistern.

Internal cerebral veins drain into thalamostriatal basal ganglia, thalamus, internal capsule, tela choroidea of 3 ventricles, and hippocampus. The veins on each side unite to form the internal cerebral vein.

Anatomy Of The Hippocampus

The anatomy of the hippocampus is of chief importance to its function. The hippocampus receives input from and sends output to the rest of the brain via a structure known as the entorhinal cortex, which is located beneath the anterior region of the hippocampus. The hippocampal formation itself is composed of several subregions, which include the cornu ammonis , the dentate gyrus, and the subiculum.

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Input To The Hippocampus

The entorhinalcortex is an important source of two different groups of afferent fibers delivering information to the hippocampal formation. The lateralperforantpathway arises from the lateral entorhinal cortex and extends into the molecular layer of the hippocampus. The medialperforantpathway arises from the medial entorhinal cortex, extends through the white matter from the subicular cortex, and enters the alveus of the hippocampus. Many of these fibers carry olfactory, visual, and auditory information to the hippocampus.

The diagonalbandofBroca originates from the septal area, and acts as part of a feedback circuit to the hippocampus from the septal area. The other part of this feedback circuit is the precommissural fornix, which allows the septal area to receive feedback from the hippocampus.

Key facts about the hippocampus

Layers
Learning, memory, aggression, rage, hormone regulation
ClinicalTemporal lobe epilepsy, rabies encephalitis, global cerebral ischemia, Alzheimers dementia, Korsakoff syndrome,

The hippocampus also receives afferent input from the prefrontal cortex, anterior cingulate gyrus, and premammillary region of the brain, as well as from monoamine neuronal projections from the reticular formation in the brainstem . The monoamine pathway in particular plays an essential role in regulating mood.

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How To Promote A Healthy Hippocampus

The best way to stimulate the hippocampus and improve our memory is exercise.

Physical aerobic exercise increases blood flow to the brain but it also stimulates the birth of new neurons, as does stimulating the brain by engaging crossword puzzles or games such as chess or sudoku.

Reichelt’s research suggests that high fat and high sugar foods also have a rapid, detrimental inflammatory impact on the hippocampus. Eating a healthy diet is key, she said a diet that is high in anti-inflammatory and antioxidant rich foods, including blueberries, leafy green vegetables, fatty fish, and spices, such as turmeric.

“I think that it’s critical that we eat well, and stay active,” she said, adding that while memory declines with age, a healthy lifestyle can help mitigate that decline, although it cannot completely neutralize it.

Theories Of Hippocampal Functions

Over the years, three main ideas of hippocampal function have dominated the literature: response inhibition, episodic memory, and spatial cognition. The behavioral inhibition theory ” rel=”nofollow”> John O’Keefe and Lynn Nadel as “slam on the brakes!”) was very popular up to the 1960s. It derived much of its justification from two observations: first, that animals with hippocampal damage tend to be hyperactive second, that animals with hippocampal damage often have difficulty learning to inhibit responses that they have previously been taught, especially if the response requires remaining quiet as in a passive avoidance test. British psychologist Jeffrey Gray developed this line of thought into a full-fledged theory of the role of the hippocampus in anxiety. The inhibition theory is currently the least popular of the three.

It has also been proposed that the spiking activity of hippocampal neurons is associated spatially, and it was suggested that the mechanisms of memory and planning both evolved from mechanisms of navigation and that their neuronal algorithms were basically the same.

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Lesions Of The Hippocampus Associated With Diseases Of The Brain

The hippocampus is a sensitive part of the brain. A range of illnesses can negatively affect it, including long-term exposure to high levels of stress.

Several diseases and factors are known to interfere with the ability of the hippocampus to function normally.

Alzheimers disease

The atrophy of the hippocampus region of the brain is one of the features most consistent with Alzheimers disease. It is the most severely affected region of the brain.

One hypothesis has proposed that early lesions of the hippocampus cause « dissociation » between the hippocampus and the cerebral cortex, leading to failure to record information from the hippocampus. Hippocampal atrophy is used as both a diagnostic and prognostic marker in clinical trials for Alzheimers disease. It has been observed that patients with mild cognitive impairment have 10-15% loss of hippocampal volume while in those with early-onset Alzheimers disease this loss is approximately 15-30%. In those with moderate Alzheimers disease, it can reach 50%.

Depression

Schizophrenia

Reduction in hippocampal volume is one of the findings observed by MRI in schizophrenic patients. It is less marked than that observed in Alzheimers disease.

Epilepsy

The hippocampus is believed to have an inhibitory effect on the seizure threshold . Once it is damaged, the seizures become more uncontrollable.

Cushings disease

Ongoing research

Functions Of The Hippocampus

Hippocampus, amygdala, and the hypothalamus relation to mental health

The two most-influential theories for hippocampal function are related to space and memory. The spatial hypothesis was supported by the seminal discovery in 1971 of cells in the hippocampus that fired bursts of action potentials when a rattraversed specific locations in space, or place fields. That suggested that the hippocampus was a sort of device used by the brain for mapping layouts of the environment. Data supporting that idea came from later virtual navigation studies in humans, which suggested a strong association between the hippocampus and spatial navigation. The memory hypothesis originated in 1957 and was supported by studies and observations in which hippocampal removal resulted in a loss of the ability to form new memories, particularly fact- and event-related memories.

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Medieval Renaissance And Modern

The mythic hippocampus has been used as a heraldic charge, particularly since the Renaissance, most often in the armorial bearings of people and places with maritime associations. However, in a blazon, the terms hippocamp and hippocampus now refer to the real animal called a seahorse, and the terms seahorse and sea-horse refer to the mythological creature. The above-mentioned fish hybrids are seen less frequently. In appearance, the heraldic sea-horse is depicted as having the head and neck of a horse, the tail of a fish and webbed paws replacing its front hooves. Its mane may be that of a horse or it may be replaced with an additional fin. Sea-horses may be depicted with wings, and winged sea-horses with a horn were part of the armorial bearings granted to Sir Sean Connery in 2018 by the Lord Lyon King of Arms, the head of Scotland’s heraldic authority.

The sea-horse is also a common image in Renaissance and Baroque art, for example, in the Trevi fountain, dating to 1732.

A winged hippocampus has been used as a symbol for Air France since its establishment in 1933 it appears today on the engine nacelles of Air France sea craft

Bronze hippocampi appear in Dublin, Leinster, Ireland on lampposts next to a statue of Henry Grattan and on Grattan Bridge.

The English football club Newcastle United has two hippocampi depicted on its crest. They appear to the left and right of the shield in the middle.

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