Friday, May 13, 2022

What Does The Hippocampus Do In The Brain

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Translating Advances In Basic Cognitive Neuroscience Into Clinical Applications

Converging evidence shows that varying degrees of hippocampal dysfunction have been implicated in a wide variety of patients with neurological conditions, such as traumatic brain injury and Alzheimers disease, as well as psychiatric conditions, such as schizophrenia, post-traumatic stress disorder , depression, anxiety, and autism . For example, in schizophrenia patients we found the same kind of impairment on a hippocampal-dependent relational memory paradigm , though to a lesser degree, than amnesic patients with profound hippocampal damage . In depressed patients, structural neuroimaging studies revealed reduced hippocampal volumes relative to control groups . In patients with PTSD, a meta-analysis of functional neuroimaging studies found hypoactivations during fear-conditioning in a network of structures, including the anterior hippocampus, relative to a control group . The hippocampus also plays a role in regulating the hypothalamic-pituitary-adrenal axis , which is perturbed in both PTSD and depression . Thus, the evidence that hippocampal dysfunction can be found in clinical cases more broadly than only those discussed in the amnesia literature raises an interesting question as to whether clinicians may be more aware of the larger reach of the hippocampus, beyond its impact on traditional memory test performance, than we get from the amnesia literature alone.

Hippocampus Function: What Does It Do

Daniel Nelson

The is a central structure within the brain of vertebrates, responsible for handling the storage of memories and the linking of memories to sensations. Another function of the hippocampus is aiding in navigation by enabling spatial memory.

There are two hippocampi in the brain, one in each cerebral hemisphere. The hippocampus is vaguely shaped like a horseshoe, and what bridges the two halves of the hippocampus is a long arch made out of nerve fibers and referred to as fornix.

The hippocampus is located in the temporal lobes of the brain. Without the hippocampus, people wouldnt be able to link sounds and smells to memories or retrieve the right memories from long-term storage when they are needed.

The Network Of Brain Structures Supporting Flexible Cognition And The Hippocampus

Flexible cognition is often discussed in the context of executive function, supporting the ability to switch between competing goals, as well as contributing to high-level human behavior, such as planning, organizing, and decision-making . On neuropsychological assessments that rely on executive functions, patients with damage to frontal areas demonstrate impairments, exhibiting various forms of behavioral inflexibility that include perseveration of behavior, rigid rule structure, and social inappropriateness . Thus, the frontal lobes are properly emphasized as making a critical contribution to flexible cognition and social behavior.

The frontal lobes, however, are part of a large and distributed network of brain structures that support the flexible use of information. For example, complex social interactions that rely on the flexible use of information involve various parts of the frontal lobes , as well as structures located in temporal, parietal, and limbic circuits . Thus, there is consensus that complex information processing draws upon a variety of brain networks in order to respond to varying task demands; however, the usual description of the network for flexible cognition rarely, if ever, includes the hippocampus.

What Happens If The Hippocampus Is Small

Alzheimers disease, depression, and stress appear to be linked to a smaller-sized hippocampus.

In Alzheimers, the size of the hippocampus can be used to diagnose the progress of the disease.

In people with depression, the hippocampus can shrink by up to 20 percent , according to some researchers.

Reviews of studies have suggested that the hippocampus in people with severe depression may be an average of 10 percent smaller than in those without depression.

Cushings disease features a number of symptoms that are linked to high levels of cortisol, a hormone produced when people are under stress. One of these symptoms is a reduction in the size of the hippocampus.

A study in monkeys has shown that the size of the hippocampus is 54 percent heritable. However, since the hippocampus continues to produce neurons throughout adult life, the link remains unclear.

It is also unclear whether a small hippocampus is an underlying cause of certain conditions, or whether it is a result.

Functions Of The Hippocampus

Hippocampus

The two most-influential theories for hippocampal function are related to space and memory. The spatial was supported by the discovery in 1971 of cells in the hippocampus that fired bursts of action potentials when a 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 . 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.

Hippocampus Brain Injury: Key Points

The hippocampus is one of the most crucial structures of thebrain. Not only does it play a pivotal role in the formation of new memories,but it also helps the brain produce new nerve cells.

An injury to the hippocampus can cause serious memory problems. But fortunately, physical and cognitive exercises can help reverse some of the worst effects of hippocampal damage and improve your memory skills.  

Featured image: ©iStock/monkeybusinessimages

What Happens When The Hippocampus Is Disturbed

An injury to the hippocampus can mean problems generating new memories. An brain injury can cause anterograde amnesia, affecting specific memories but leaving intact learning skills or abilities.

Lesions can cause anterograde or retrograde amnesia. Non-declarative memory would remain intact and uninjured. For example, a person with a hippocampal injury may learn to ride a bicycle after the injury, but he would not remember ever seeing a bicycle. That is, a person with the damaged hippocampus can continue to learn skills but not remember the process.

Anterograde amnesia is memory loss that affects events occurring after the injury. Retrograde amnesia, on the other hand, affects the forgetfulness generated before the injury.

At this point, you will wonder why the hippocampus is damaged when there are cases of amnesia. It is simple, this part of the brain acts as a gateway to brain patterns that sporadically retain events until they pass to the frontal lobe. One could say that the hippocampus is key to memory consolidation, transforming short-term memory into long-term memory. If this access door is damaged and you cant save the information, it wont be possible to produce longer-term memories. In addition to losing the ability to remember, when injuries or damage to the hippocampus occurs, you may lose the ability to feel the emotions associated with such memories, since you would not be able to relate the memories to the emotions that evoke it.

Spatial Navigation And Spatial Memory:

The Hippocampus plays an important role in spatial navigation and spatial memory. It is helpful in learning and storing information. The Involvement of the Hippocampus in memory function and learning behaviors have been studied by Neuroscientis John O Keefe and Professor of Psychology, Lynn Nadel, during 1960s and 1970s. Together, they wrote a book in 1978, The Hippocampus as a Cognitive Map, which outlines the role of the hippocampus in learning and storing information referring to portions of space, in the form of Cognitive maps.

What Is Your Hippocampus

The hippocampi are two arched organs based in the medial temporal lobe. They form an integral part of the limbic system. This plays an important role in emotion regulation.

Theyre awesome for two reasons: a) They store your memory, and, b) They look like a pair of seahorses!

Every time you learn something new, a unique neural pathway is created. Revisiting this new discovery makes the pathway stronger. Its then easier for the hippocampus function to recall the information. In other words, when you revise for an exam or test, you are in fact making your neural pathways stronger.

 

Signs And Symptoms Of Hippocampus Atrophy

Because the hippocampus is involved in so many brain functions, hippocampus atrophy can produce multiple different symptoms, some of which are closely associated with particular conditions.

Symptoms that are particularly related to Alzheimers disease or other forms of include:

  • Memory loss that disrupts daily life such as appointments or events
  • Difficulty solving problems or planning
  • about place or time
  • Difficulty completing familiar tasks
  • Difficulty with images and spatial relationships
  • Problems with words, either speaking or writing
  • Misplacing things and not being able to retrace steps
  • Decreased judgment
  • Social or professional withdrawal
  • Changes in mood or personality

It can often be difficult to judge whether these symptoms are related to or to typical age-related changes. However, early detection matters, so schedule a doctors visit if youre concerned.

Study Shows How The Hippocampus Provides Information To Other Brain Areas During Learning

Date:
Arizona State University
Summary:
Without an intact hippocampus, forming new memories is impossible. Researchers have found an equally important role for the hippocampus: feeding information to brain areas responsible for learning. Using fMRI, the research team found it was the hippocampus that encoded associations between relevant features of the environment during learning and that the associations encoded in the hippocampus were used by brain systems responsible for learning.

Avid hikers know to be cautious of plants with leaves made up of three leaflets if they are red in the spring or fall. Parents worldwide know the precarious relationship between proximity to bedtime and roughhousing with their children.

How do hikers know to link the color of a leaf with the season to determine if it is poison ivy? How do parents know to link the time of day with a child’s excitement level to determine the success of a bedtime routine? Just like Pavlov’s dogs salivated when a bell rang, people learn to recognize poisonous plants or prevent tears of exhaustion in a toddler by forming associations among details in their surroundings and what happens.

Researchers from Arizona State University and Stanford University analyzed patterns of brain activity in humans and discovered a previously unknown role for the hippocampus, a brain area important to memory, in forming associations during learning. The study will be published on March 6 in Nature Communications.

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Damage Of The Hippocampus

Public Domain via Wikimedia Commons

Damage to the hippocampus can result in various memory and cognitive disorders. The primary symptom of damage to the hippocampus is difficulty retrieving memories, being unable to recall memories from storage. Diseases can impact the hippocampus in different ways. For example, Alzheimers disease causes tissue loss of the hippocampus, and research into the state of the hippocampus within Alzheimers patients has found that Alzheimers patients who still have good cognitive abilities have larger hippocampi than those who have developed dementia.

However, while the hippocampus is related to disorders of memory recall, it is also linked with other disorders like epilepsy and Posttraumatic Stress Disorder. Individuals with epilepsy who experienced chronic seizures are also frequently victims of retrograde amnesia and other memory issues. As for the relation of the hippocampus to Posttraumatic Stress Disorder, it is thought that sustained emotional stress can lead to the degradation of neurons within the hippocampus, brought about by the continued release of cortisol by the body in reaction to stress.

The Hippocampus And Flexible Memory Representations Are Critical In Many Cognitive Abilities And Complex Social Behaviors

Function of Hippocampus

We suggest that the flexibility afforded by hippocampal representations permits various pieces of information to be called upon promiscuously to support diverse and complex cognitive and social abilities. The importance of flexible representations in many cognitive and social behaviors has recently been explored in a number of experimental paradigms in patients with hippocampal amnesia. These paradigms assess the ability of humans with hippocampal damage to perform tasks that approximate real-world interactions in which there is a high demand on flexible representations for adaptive and successful performance. The performance of humans with hippocampal damage on these tasks provides useful insight into the specific role that the hippocampus performs in supporting the flexible use of information. Indeed, we highlight a variety of findings from patients with hippocampal amnesia on both tasks in the cognitive and social domains, in which the basic processing mechanisms are not impaired , but the nature of the task places significant processing demands on the flexible use of information , resulting in abnormal or impaired performance. Thus, while the PFC may be important for switching between or integrating abstracted representations, the hippocampus is required to form and deploy those representations flexibly for use by other neural systems.

The Role Of The Hippocampus In Flexible Cognition And Social Behavior

  • 1Department of Psychology and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, USA
  • 2Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA
  • 3Department of Neurology, Division of Behavioral Neurology and Cognitive Neuroscience, University of Iowa, Iowa City, IA, USA

Reconciling Accounts Of The Functional Role Of The Hippocampus

The critical claim here is that representations supported by the hippocampus contribute not only to performance on memory tasks but also to a diverse set of cognitive abilities, which are engaged in accomplishing a variety of complex cognitive and social behaviors. The evidence reviewed above documents the striking deficits following disruption of the hippocampus or of its interconnections within a broad network of structures, impairing a broad array of abilities across multiple domains and paradigms. This leads to some hard questions: what is in common between the memory tasks typically associated with the hippocampus and the much broader range of abilities we now see as also dependent on the integrity of the hippocampus? And, what does this apparent expansion of the purview of the hippocampus mean with regard to accounts of the nature of the critical processing performed by the hippocampus?

Magnetic Resonance Imaging Findings In Conflict

Vythilingam et al.,87 for example, report that of 14 studies of hippocampal volume in MDD, 8 were unable to find significant between-group differences, whereas 6 found significantly smaller left or left and right hippocampus. Reduced hippocampal volume was correlated with total duration of depression in some but not all studies. Differences in hippocampal volume in bipolar disorder have also been mixed, with reports of increased, decreased, and unchanged hippocampal volumes.87 Indeed, Ladouceur et al.94 reported increased hippocampal and parahippocampal volume in individuals with high risk of BPD. Sheline,95 on the basis of a literature review, concluded that volumetric brain studies exhibit inconsistency in measurements from study to study. These inconsistencies were attributed to clinical and methodological sources of variability.60

To date, studies examining the hippocampus in MDD have been mostly cross-sectional.100 Longitudinal prospective studies that track patients over disease onset are required. In this respect, Chen et al.101 appear to be the first to report smaller hippocampal volume in healthy girls at high familial risk of depression. A recent longitudinal study of adolescents found that smaller hippocampal volumes preceded clinical symptoms of depression in at-risk adolescents, particularly in those who experienced high levels of adversity during childhood.98

Donna L. Algase, in, 1998

Content: Alcohol Memory And The Hippocampus

Learning and memory are crucial events during adolescence, when the brain is maturing both physically and functionally. Thus, it is not surprising that cognitive processes are exquisitely sensitive to the effects of chemicals such as alcohol. Among the most serious problems is the disruption of memory, or the ability to recall information that was previously learned. When a person drinks alcohol, he can have a blackout. A blackout can involve a small memory disruption, like forgetting someones name, or it can be more seriousthe person might not be able to remember key details of an event that happened while drinking. An inability to remember the entire event is common when a person drinks 5 or more drinks in a single sitting .

Learn more about the formation of memory.

In order to affect cognitive functions such as learning and memory alcohol must first enter the brain. Due to its small size alcohol in the blood can passively diffuse into the brain. The ability of alcohol to cause short term memory problems and blackouts is due to its effects on an area of the brain called the hippocampus. The hippocampus is a structure that is vital to learning and the formation of memory.

Learn more about the passive diffusion of alcohol through the blood brain barrier.

 the basics of neuron structure.

Figure 3.2 Originally named for its resemblance to a seahorse the hippocampus is a small curved structure located within the temporal lobes of the brain

 the basics of neurotransmission

Dig Deeper: Inaccurate And False Memories

Even flashbulb memories can have decreased accuracy with the passage of time, even with very important events. For example, on at least three occasions, when asked how he heard about the terrorist attacks of 9/11, President George W. Bush responded inaccurately. In January 2002, less than 4 months after the attacks, the then sitting President Bush was asked how he heard about the attacks. He responded:

I was sitting there, and my Chief of Staffwell, first of all, when we walked into the classroom, I had seen this plane fly into the first building. There was a TV set on. And you know, I thought it was pilot error and I was amazed that anybody could make such a terrible mistake.

Contrary to what President Bush recalled, no one saw the first plane hit, except people on the ground near the twin towers. The first plane was not videotaped because it was a normal Tuesday morning in New York City, until the first plane hit.

Can Hippocampal Volume Differentiate Between Different Types Of Dementia

Several research studies have measured the hippocampal volume and looked at how it relates to other types of dementia. One possibility was that physicians could use the extent of in the hippocampal area to clearly identify what type of dementia was present.

For example, if Alzheimer’s disease was the only type of dementia that significantly affected the size of the hippocampus, this could be used to positively diagnose Alzheimer’s. However, multiple studies have shown that this measure is often not helpful in distinguishing most types of dementia.

One study published in the journal Neurodegenerative Diseases noted that a decreased size of the hippocampus occurred in vascular dementia.

A second study found that decreased hippocampal size was also correlated with frontotemporal dementia.

Scientists did discover a significant difference, however, when comparing Lewy body dementia with Alzheimer’s disease. Lewy body dementia shows far less atrophy of the hippocampal areas in the brain, which also coincides with less significant effects on memory, especially in the earlier stages of Lewy body dementia.

Shrinking Hippocampus Signals Early Alzheimers

May 4, 2009

People who have lost brain cells in the hippocampus area of the brain are more likely to develop dementia, researchers report. The findings add to a growing body of evidence that shrinkage of the brain, particularly in the hippocampal area, may be an early sign of Alzheimers disease, occurring years before obvious memory loss and other symptoms appear.

The study, from researchers in the Netherlands, appeared in Neurology, the medical journal of the American Academy of Neurology. It involved 64 people with Alzheimers disease, 44 people with mild cognitive impairment, a less severe form of memory loss that sometimes precedes Alzheimers disease, and 34 people with no memory or thinking problems.

The researchers performed MRI brain scans on all of the participants at the beginning of the study, and again an average of a year and a half later. During that time, 23 of the people with mild cognitive impairment had developed Alzheimers disease, along with three of the healthy participants.

Researchers measured the volume of the whole brain as well as the hippocampus area, which is affected by Alzheimers disease, at the beginning and end of the study, and calculated the rate of shrinkage in the brain over that time.

The seahorse-shaped hippocampus, from the Greek for seahorse, is widely recognized as a seat of memory. Researchers have been focusing on this part of the brain in the search for clues to Alzheimers disease.

How To Promote A Healthy Hippocampus

Hippocampus Part of the Limbic system, in each temporal ...

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 suggests that high fat and high sugar foods also have a rapid, detrimental 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. 

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.

Social Discourse And Language Use

The hippocampus also contributes to social discourse, which often requires highly creative and flexible uses of language. Two examples of creative and flexible uses of language ubiquitous in social discourse include reported speech, in which speakers represent or reenact words or thoughts from other times and/or places and verbal play, in which speakers play with the sounds and meanings of words through the use of puns, voices, teasing and telling funny stories . Both of these discourse features require flexible access to previous knowledge as well as the ability to flexibly and creatively generate unique combinations of the reconstructed elements . We have suggested that these processes are hippocampal dependent and we find deficits in the use of both reported speech and verbal play in individuals with hippocampal amnesia . That is, patients with hippocampal damage use significantly less reported speech and verbal play in their social interactions with either a clinician or familiar communication partner and when they do use reported speech or verbal play it is qualitatively different from healthy comparison participants . Furthermore there is some degree of hippocampal specificity; damage to vmPFC does not disrupt verbal play or reported speech .

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 ; 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 Graydeveloped 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.

Role In Spatial Memory And Navigation

Place cellaction potential

In humans, cells with location-specific firing patterns have been reported during a study of patients with drug-resistant epilepsy. They were undergoing an invasive procedure to localize the source of their , 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. Similar brain imaging studies in navigation have shown the hippocampus to be active. A study was carried out on taxi drivers. Londons black cab drivers need to learn the locations of a large number of places and the fastest routes between them in order to pass a strict test known as The Knowledge in order to gain a license to operate. A study showed that the posterior part of the hippocampus is larger in these drivers than in the general public, and that a positive correlation exists between the length of time served as a driver and the increase in the volume of this part. It was also found the total volume of the hippocampus was unchanged, as the increase seen in the posterior part was made at the expense of the anterior part, which showed a relative decrease in size. There have been no reported adverse effects from this disparity in hippocampal proportions. Another study showed opposite findings in blind individuals. The anterior part of the right hippocampus was larger and the posterior part was smaller, compared with sighted individuals.

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