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Memory In The Brain

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Last Updated: 02 July 2021

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General | Latest Info

When now - famous neurological patient Henry Molaison had his brain hippocampus surgically section to treat seizures in 1953, Sciences understanding of Memory inadvertently received perhaps its biggest boost ever. Molaison lost the ability to form new memories of events, and his recollection of anything that had happened during the preceding year was severely impaired. Other types of memory, such as learning physical skills, were unaffected, suggesting the hippocampus specifically handles recall of eventsknown as episodic memories. Further research on other patients with hippocampal damage confirms recent memories are more impaired than distant ones. It appears the hippocampus provides temporary storage for new information whereas other areas may handle long - term memory. Events that we are later able to remember appear to be channels for more permanent storage in the cortex. In the cortex, these memories form gradually, becoming integrated with related information to build lasting knowledge about ourselves and the world. Episodic memories that are intended for long - term storage accumulate to form an autobiographical memory that is so essential for our sense of identity. Neuroscientists know a lot about how short - term memories form in the brain, but the process underlying long - term storage is still not well understood. A new study published this month in Science, by neuroscientist Susumu Tonegawa and a group of colleagues at RIKEN - MIT Center for Neural Circuit Genetics, provides insight into what happens in the brain when long - term memory is form, highlighting the critical role of the forward part of the cortex. It most detailed circuit analysis of the contribution of the prefrontal cortex to memory retrieval we have to date, said neuroscientist Stephen Maren of Texas & M University in College Station, who was not involved in the work. The new study from Tonegawa's group builds on previous research demonstrating that episodic memories are physically represented in populations of cells in parts of the hippocampus. In those studies, researchers genetically engineered mice so that certain neurons produce light - sensitive proteins. Electrical and chemical activities in neurons could then be activated or switched off by pulses of light delivered via fiber - optic cable implanted in each mouse skull, technique know as optogenetics. Wired mice were given drug that blocked production of light - sensitive proteins. Taking mice off drug allows cells to fire while they explore new environment to make proteins, effectively tagging memory for that environment. These groups of cells, know as memory engrams, could then be controlled with fiber - optic beams. With these tools in hand, investigators give mice electric shocks to their feet in some of their enclosures, but not others. Mice freeze when put back into environment in which they were previously shock, indicating fear memory. When researchers activate engrams, this invokes the same fearful reaction. Emotional aspects of memories are stored separately, in a region called amygdalabut activating engram in hippocampus activates all link components, bringing back full memory.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

THE AMYGDALA

First, let's look at the role of the amygdala in memory formation. The main job of the amygdala is to regulate emotions, such as fear and aggression. The amygdala plays a part in how memories are stored because storage is influenced by stress hormones. For example, one researcher experimented with rats and fear response. Using Pavlovian conditioning, neutral tone was paired with foot shock to rats. This produces fear memory in rats. After being condition, each time they hear tone, they would freeze, indicating memory of the impending shock. Then researchers induced cell death in neurons in the lateral amygdala, which is a specific area of brain responsible for fear memories. They find fear memory fade. Because of its role in processing emotional information, amygdala is also involved in memory consolidation: process of transferring new learning into long - term memory. The amygdala seems to facilitate encoding memories at a deeper level when an event is emotionally arousing.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

THE HIPPOCAMPUS

Interest in the critical role of Hippocampus in Memory dates from classic studies of patients HM. In 1978, Mishkin published the first primate lesion study that appeared to mimic HMs syndrome, using delay nonmatching to sample. In intervening years, large number of studies on humans, monkeys, rabbits, rats, and mice have focused on animal models of human amnesia and on the presumed role of Hippocampus and related structures in memory. The Memory deficit following hippocampal lesions is not global but rather much more specific for one kind of memory, term declarative. Declarative Memory is sometimes associated with consciousness or awareness, in contrast to many other forms of Memory, including implicit Memory in humans and a range of associative Memory phenomena in humans and other mammals: motor and perceptual skills, classical conditioning, operant conditioning, habit formation, etc. Lesions in Mishkins ' original study were designed to reproduce HMs lesions and include the Hippocampus, amygdala, and adjacent cortical regions bilaterally. It now seems relatively clear that the amygdala, per se, is not critical, at least for declarative Memory, but the hippocampus and related cortical structures are G, perirhinal, parahippocampal, and entorhinal Cortex. Lesions including all these structures produce the most profound amnesia and lesions including subsets produce substantial but less profound amnesia. Currently, there are some questions about the role of Hippocampus proper in this medial temporal lobe Memory system. Number of tasks in infraprimate mammals are sensitive to hippocampal damagee. G, water maze, odor discrimination event timing, cue relationships, spatial Memory, spatial alternation, radial arm maze, conditional learning, discrimination reversal, trace classical conditioning, and contextual conditioning. Although it is difficult to generalize, common threads in many of these tasks include relational memoriesi. E, memories for relations among stimuli and events, and memories that utilize spatial - contextual information, both of which would seem reasonable analogs of primate declarative Memory in lower mammals. For neurobiological analysis, one would ideally wish to utilize preparations where much of the essential neuronal circuitry generating behavior is know. Only a few animal models meet this modest requirement to some degree.


Functions

The Hippocampus helps humans process and retrieve two kinds of memory, declarative memories and spatial relationships. Declarative memories are those related to facts and events. Examples include learning how to memorize speeches or lines in play. Spatial relationship memories involve pathways or routes. For example, when cab drivers learn route through the city, they use spatial memory. Spatial relationship memories appear to be stored in the right hippocampus. The Hippocampus is also where short - term memories turn into long - term memories. These are then stored elsewhere in the brain. Research has shown that nerve cells continue to develop throughout adulthood. The hippocampus is one of few places in the brain where new nerve cells are generate.

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* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

THE CEREBELLUM AND PREFRONTAL CORTEX

My recent reports on brain training for older adults converge on the idea that cognitive training can indeed be beneficial for older adults ' cognition, but there is little wider transfer beyond skills being practice. That in itself can be valuable, but it does reinforce the idea that best cognitive training covers a number of different domains or skill - sets. New Study add little to this evidence, but do perhaps emphasize the importance of persistence and regularity in training. The study involved 59 older adults, of whom 33 use brain fitness program 5 days a week for 30 minutes a day for at least 8 weeks, while another group of 26 were put on a waiting list for the program. After two months, both groups were given access to the program, and both were encouraged to use it as much or as little as they want. Cognitive testing occurs before the program start, at two months, and at six months. The first group to use program use program on average for 80 sessions, compared to an average 44 sessions for the wait - list group. The Higher Use group showed significantly higher cognitive scores at both two and six months, while the lower use group showed improvement at the end of the six month period, but not as much as the higher use group. I am afraid I do have any more details because it was a conference presentation, so I only have access to the press release and abstract. Because we dont know exactly what training entail, we do know the extent to which It practice same skills that were test. But we may at least add it to evidence that you can improve cognitive skills by regular training, and that length / amount of training matters. Another interesting presentation at the conference was an investigation into mental stimulating activities and brain activity in older adults. In this study, 151 older adults from Rush Memory and Aging Project answered questions about present and past cognitive activities, before undergoing brain scans. Questions concern how frequently they engage in mentally stimulating activities and the availability of cognitive resources in their home, during their lifetime. Higher levels of Cognitive activity and Cognitive resources were also associated with better Cognitive performance. Moreover, after controlling for education and total brain size, it was found that frequent cognitive activity in late life was associated with greater functional connectivity between the posterior cingulate cortex and several other regions. More cognitive resources throughout life was associated with greater functional connectivity between the posterior cingulate cortex and several other regions. Previous research has implicated decline in connectivity with posterior cingulate cortex in mild Cognitive Impairment and Alzheimers disease. Cognitive activity earlier in life was not associated with differences in connectivity. Findings provide further support for the idea of Use It or lose It!, And suggest that mental activity protects against cognitive decline by maintaining functional connectivity in important neural networks.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

NEUROTRANSMITTERS

Your ability to recall the color of your childhood home depends on long - lasting changes in your brain. Forming new memory requires rerouting nerve fibers and altering synapses, tiny gaps across which neurons relay chemical messages. The ability of synapses to change, or remodel, themselves is called synaptic plasticity. Encoding new long - term memory involves persistent changes in the number and shape of synapses, as well as the number of chemical messages sent and molecular docking stations, or RECEPTORS, available to receive messages. Neurons communicate in a stepwise sequence of events. First, electrical signal in the neuron triggers release of chemical messengers called neurotransmitters from its axon terminals. Those neurotransmitters from sending, or presynaptic, neuron diffuse across synaptic gap to receiving, or postsynaptic, neuron. There, they interact with RECEPTORS embed in the membrane of the postsynaptic neuron. The interaction is bite like lock and key right neurotransmitter can unlock and activate receptor. Upon binding neurotransmitters, RECEPTORS unleash a cascade of molecular events that convert messages back into electrical signal. Receptors then release neurotransmitters, which are recycled back into the presynaptic terminal or broken down enzymatically, allowing postsynaptic RECEPTORS to receive new signals from presynaptic neuron. Two opposing but equal processes are key for synaptic plasticity: long - term potentiation and long - term depression. Ltp is a long - lasting increase in synaptic strength, which occurs in many brain regions but especially in the hippocampus. Ltd, conversely, decreases synapse effectiveness. Without LTD, you would not be able to learn anything new or form new memories because synapses would reach maximum level of strength, after which theyd no longer be plastic. Experience physically changes our brains through both LTP and LTD, shown in numerous animal and human studies to be essential for long - term memory consolidation. Ltp occurs throughout the brain, but it has been studied most extensively in the hippocampus, brain region associated with encoding new memories. How this is accomplished depends upon the type of neuron. In general, LTP involves an increase in the number of GLUTAMATE RECEPTORS on postsynaptic neuron. Glutamate is the most prevalent neurotransmitter in the mammalian nervous system, and it bind to several different kinds of RECEPTORS. Nmda and AMPA classes of GLUTAMATE RECEPTORS are ion channels. Upon binding GLUTAMATE, they permit calcium and sodium ions, respectively, to flow into the cell. Increasing number of RECEPTORS on postsynaptic cell strengthens synapses by allowing more electrically conductive ions to enter. Calcium ions also function as second messengers signaling molecules that set off a chain of molecular events within cells. Ltp boosts concentration of calcium ions inside postsynaptic cell, while LTD increases it to a lesser degree. Differing concentrations of calcium activate different enzymes: kinase proteins in the case of LTP, or phosphatases for LTD. These enzymes modify synapse, making them more or less efficient at relaying nerve impulses.

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* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Summary

Models are one of the main essences of biology. Models within the scope of this essay are worth mentioning, as they have tried their best to explain the complex human memory system. This is a very simple model describing how information finds its home in long - term memory storage. According to the Atkinson - Shiffrin Memory Model, only possible gateway piece of information has to reach planes of long - term memory is by its rigorous repetition. However, this idea of reaching long - term memory through rehearsals was denied as there are scenarios when a person remembers an event, which happens only once, in his whole life. This model is rather complex which claims to have several components and each component plays a different role in the processing of information and preservation of memories. The Working Memory Model was proposed by Baddeley and Hitch. It is an actively working model that is more focused on short - term memory storage and recalling information stored in short - term memory storage. This model has three integral components that act as stores, One is called central executive, second one is known as phonological loop and the third most is considered visuospatial sketchpad. Central executive is related to processing information. The other two manage visual and auditory information. This model proves the fact that it is hard to hear or visualize two different things at same time, rather than using the ability to hear and see each other on two different subjects.


Types of Memory

Unlike short - term memory, long - term memory has a very large span of storage. Moreover, storage capacity for the amount of information which can be stored is almost unlimited. Information sometimes reaches long - term memory storage and it gets stored there for a whole lifetime. Some particular pieces of information make their way into long - term storage very easily. You do not need to consciously or forcefully put your attention on it, but they reach into planes of long - term memory storage without even bothering you. And sometimes you need to repeat piece of information to make it reach your long - term memory. Let us take a simple example, You will always remember your first date, your wedding day, or your last day at school / college. Memories are so deep and clear that most people can even recall minute details of a particular day or event. Contrary to this scenario, you have to cram, repeat, and do multiple rehearsals of your course to pass your exams. This lay the foundation for two particular types of long - term memory types.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Explicit memory

Explicit Memory is one of two major subdivisions of long - term Memory. Explicit Memory requires conscious thoughtsuch as recalling who came to dinner last night or naming animals that live in the rainforest. It is what most people have in mind when they think of memories and whether theirs are good or bad. Explicit Memory is often associative; your brain links memories together. For example, when you think of a word or occasion, such as automobile, your memory can bring up a whole host of associated memoriesfrom, carburetors to your commute to family road trips to a thousand other things.


Mechanism

Recent studies of implicit and explicit memory suggest that modulation of synaptic strength and structure is fundamental mechanism by which these memories are encode, process, and stored within the brain. Two model systems have been extensively studied as examples of these two forms of memory: sensitization in marine snail Aplysia californica as an example of implicit memory, and spatial memory formation in rodents as an example of explicit memory. In this review, we discuss and compare critical synaptic sites and underlying cellular and molecular mechanisms of short - term, intermediate - term, and long - term memory and consider how conservation of common elements in each form may contribute to different temporal phases of both implicit and explicit memory storage.


I.A Definition

Explicit memory can be thought of as intentional retrieval. That is, explicit memory is a willful process of thinking back in time for the purpose of retrieving previously encountered events. It is also sometimes referred to as episodic memory because explicit memory involves memory of prior episodes in one's life. In psychology experiments, explicit memory is usually defined operationally in terms of test instructions. That is, if participants are asked to retrieve previous event, then the experiment is one that taps explicit memory.


A Types of Memory

Few people know that ancient Greeks, together with other arts, invented the art of memory, usually associated with mnemotechnics. In ages before the invention of the printing technique, this art was vitally important. Although nowadays we rely on memory stored in books, computers, and the Internet, importance of our own memory is difficult to overestimate. In general, explicit memory involves awareness of memory, whereas implicit memory does not necessarily involve being aware of memory. Procedural memory as a type of implicit memory is based on learning and recalling motor and cognitive skills. The distinction between implicit and explicit learning can be exemplified in language 1. When an organism learns any information, number of brain systems are engage. However, in most cases, there is one critical brain system, which when damaged causes permanent impairment in particular forms of learning and memory. Many readers will recall Lashleys pessimistic conclusion from his series of experiments and state in his famous article, in Search of Engram. In all respect to Lashleys genius research, existence of several different forms of memory with differing neuronal substrates was not recognized at his time, nor were modern analytic techniques available then. A major achievement of recent research on brain mechanisms of learning and memory is the recognition that there are several different types of memory involving different brain systems. One distinction can be made on the basis of temporal dynamics of memory traces such as ultra - short, short - term, and long - term memories. Long - term memories, in turn, can be divided into two broad categories depending on type of stored information and neuronal mechanisms. They are explicit and implicit memories.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Implicit memory

Implicit Memory is sometimes referred to as unconscious Memory or automatic Memory. Implicit Memory uses past experiences to remember things without thinking about them. Performance of implicit Memory is enabled by previous experiences, no matter how long ago those experiences occur. The subset of implicit Memory, Procedural Memory, enables us to perform many everyday physical activities, such as walking and riding bike, without having to give it think. The large majority of implicit memories are procedural in nature. Procedural Memory primarily involves learning new motor skills and depends on cerebellum and basal ganglia. Priming is another, smaller subset of implicit memory. It involves using pictures, words or other stimuli to help someone recognize another word or phrase in future. Examples include using green to remember grass and red to remember apple.Ss


What is Explicit Memory?

Like implicit memory, explicit memory also is not unitary. Psychologists distinguish between two main types: semantic memory, which refers to general knowledge such as vocabulary and facts about the world, and even facts about oneself, and episodic memory, which refers to memory of past events associated with particular autobiographical experience, such as a memorable day on vacation or an embarrassing episode. According to Tulving, each type of memory is also associated with, or dependent on, distinct type of awareness or consciousness. Semantic memory is associated with noetic awareness, which occurs when one thinks of something one know, whereas episodic memory is associated with autonoetic consciousness, which occurs when one remembers a particular experience, autobiographical event. At the core of autonoetic awareness is subjective, personal experience associated with self, which confers a phenomenal flavor that distinguishes remembering from other kinds of awareness. The distinction between autonoetic and noetic awareness is crucial to understanding different aspects of recognition memory. Basing himself on research conducted in the late 1970s and early 1980s, Tulving proposed a distinction between two aspects of recognition memory, remembering and knowing. Remembering involves reexperiencing or reliving past event in mind, what he and others have term mental time travel. Characterize by recovering and recreating the context in which a stimulus or event occur, is the hallmark of true episodic memory. Knowing, on other hand, is associated with a sense of recognizing or experiencing stimulus or event as old but with little or no information about the context in which it was encounter. Though knowing refers to recognition of memory associated with episode, it has much in common with semantic memory. Because remembering and knowing are not pure processes, investigators refer to recollection and familiarity, respectively, as processes that underlie them.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Neural Correlates of Memory Storage

Behavioral evidence suggests that episodic memory develops from childhood through adulthood, with substantial qualitative changes in episodic memory happening during infancy and younger childhood. In study of memory development between middle childhood and adulthood, much of behavioral literature focuses on how encoding, storage, and retrieval of information are influenced by children's use of memory strategies, children's knowledge base, and by manners in which these components interact. Below is a brief consideration of these developmental effects. Children tend to under - perform compared with adults, under conditions that directly test the effect of deliberate use of memory strategies. For example, adults are more accurate than children when old and new pictures are similar and thus memory distinction is difficult. When minimal use of memory strategies is needed, children can recognize old from new pictures as efficiently as adults, and are as accurate as adults, although slower, on verbal encoding tasks. The effect of knowledge on ability to memorize is well documented by findings that experts out - perform novices in memorizing material within their domain of expertise. The basic notion is that with age, increases in knowledge result in improvements in ability to memorize. As stated by Flavel: what the head knows changes enormously in the course of development, and these changes consequently make for changes in memory behavior. Furthermore, when the amount of knowledge between children and adults is control, age effects on memory ability are minimize, and under some conditions, younger children can even out - perform older children and adults. Finally, interaction between strategy and knowledge is illustrated by finding that growth of knowledge may allow older children and adults to use additional task - relevant processing of to - be - learn material that are not available to younger children. Although this Review is not intended to present a comprehensive survey of behavioral evidence about development of memory, it is important to note a few influences that, due to space limitations, are largely missing from this Review. First, development of memory is considered to reflect age - related improvements in more basic Cognitive functions such as speed of processing, attention, and capacity in working memory. Second, there is mounting evidence that metamemory, knowledge about memory, plays a critical role in memory development. It is important to recognize that the relation between memory and other cognitive functions, and the relation between memory and metamemory are inextricably intertwine. When considering the net effects of factors contributing to changes in memory from middle childhood into adulthood, one consistent finding is that developmental effects can be specific to certain aspects of memory, whereas other aspects show little change with age. For example, with age, quality of memories changes as memories become richer in details. Testing the quality of memory is currently accomplished with a variety of paradigms adapted from adult studies of memory. These include asking participants to reflect on their own memory, using Remember / Know judgment, or using confidence scale.


1. Introduction

Autobiographical memory - memory of events or facts retrieved from individuals ' own lives be context - specific with rich episodic details, or acontextual with only the gist of self - relevant events or personal knowledge 1 2 3. Former is often associated with retrieval of specific events that can be measured by amount of recollected event details 4 5 or subjective vividness of memories 4 5 6 7; and later reflects experience of recognition without recalling details 8 9. Another related concept is temporal specificity that indicates whether event memory is specific to one point in time or repeat over time 4 10. The ability to recollect event details is indicative of psychological and cognitive functioning, and is influenced by aging 10 11 12. For example, older adults tend to remember fewer episodic details than young adults 5 13, which in turn contributes to other types of cognitive problems, such as, susceptibility to AM conjunction errors 14 and difficulties in imagination 15. Therefore, it is beneficial to maintain a higher level of autobiographical event memory. Many researchers investigate neurocognitive mechanisms of AM, such as, brain network that is selectively activated by personal episodic memory versus other non - personal memory 16 17 18 19 20. Characteristics of AM have also been studied according to dissociable neural structures and processes related to recall of personal specific events versus general autobiographical events or personal semantic knowledge 2 21 22. Some studies investigate further brain regions that track the amount and fidelity of recollected information 23 24 25. It shows that the amount of recollected event details modulates activation in some cortical areas, such as, ventromedial prefrontal cortex 26 27, hippocampus, posterior parahippocampal gyrus 28, and left angular gyrus 27. Some studies examine the effect of aging on the neural process of AM retrieval, and find few possible neural markers related to reduced episodic richness among older adults, such as, reduced engagement of hippocampus 29, reduced involvement of dorsal anterior cingulate cortex 12, and reduced ability to perform strategic control over recovery of specific details 30. Despite progress in neurocognitive studies on AM, extant work is inadequate in few aspects. First, although many studies have used photo cues taken in the real world by participants 7 17 20 27 28 31 32 33 34, experimental paradigms of these studies were notably different in terms of sample sizes, encoding strategies, methods to select visual stimuli, and metrics used to characterize recollective memory, leading to inconsistent findings 17 32. Second, in view of the importance of AM in mental health and aging, there is limited neuroimaging evidence on how subjects ' performance in recall of autobiographical events is affected by cognitive intervention. Recent studies show that more episodic details could be retrieved through retrieval practice as compared to the re - study process, Know as testing effect 36 37.


Discussion

Within MTL, more anterior regions show greater ESA than RSA, whereas more posterior regions show greater RSA than ESA. This double dissociation is consistent with meta - analysis of functional neuroimaging studies, which conclude that encoding tends to activate anterior, and retrieval tends to activate posterior MTL. However, Schacter and Wagner note that encoding activations in anterior MTL were sometimes found in RM studies, whereas encoding activations in posterior MTL were sometimes observed in non - RM studies. Thus, they suggest that, rather than encoding - retrieval differences, anteroposterior MTL gradient might reflect relational - nonrelational differences. In the present study, RM demands were high during both phases, and hence, this alternative hypothesis cannot easily account for the present dissociation. As for left parahippocampal / hippocampal activation, IT is consistent with the notion that the hippocampus is involved in RM and additionally suggests the role of the parahippocampal cortex in RM. Although consistent with the HIPER model, three caveats should be noted about anterior MTL activation. First, this activation could reflect novelty rather than encoding per se. Encoding and novelty interpretations are difficult to distinguish, because novelty promotes encoding, and both tend to engage similar brain regions. Second, although anterior MTL activation does not show significant phase content interaction, IT tends to be larger for perceptual than for semantic RM. Greater hippocampal activity in perceptual condition may reflect use of unusual fonts or cross - domain binding between words and fonts. Third, several fMRI studies of episodic encoding have found activations in posterior parahippocampal regions. Present results are not inconsistent with these studies, because we are not claiming that only anterior MTL regions are involved in encoding processes. What we find is that, in direct within - subject comparison, anterior MTL regions show greater ESA than RSA. Within PFC, ESA - RSA contrast yields double dissociation within left PFC, whereas left ventrolateral regions show greater ESA, and leave dorsolateral and anterior regions show greater RSA. The finding of ESA in left ventrolateral PFC is consistent with fMRI studies using subsequent memory paradigm. The finding of RSA in left PFC is generally consistent with functional neuroimaging evidence linking leave PFC to source memory but not with studies that do not find difference in this region between successful and unsuccessful source memory trials. The present study provides first clear evidence that different leave PFC subregions are differentially involved in successful encoding versus successful retrieval. The speculative explanation for the dissociation between ventrolateral PFC and dorsolateral PFC is that these two areas are differentially involved in working memory maintenance versus manipulation. Successful RM encoding may be more dependent on continuous maintenance of incoming information, whereas successful RM retrieval may be more dependent on reorganization of retrieve output within working memory. Involvement of anterior PFC in RSA is consistent with evidence that this region is typically activated during retrieval.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Of cats and bicycles

In this section, we review evidence from behavioral studies in support of the notion that sleep benefits memory consolidation. Key experiments for different theoretical accounts and concepts will be described in more or less chronological order, thus complementing previous reviews of studies on sleep and memory. In 1885, Ebbinghaus, father of experimental memory research, published a series of studies, on himself, about forgetting of lists of nonsense - word pairs that established the Well - know forgetting curve, indicating that forgetting occurs rapidly in the first hours after learning and levels out after several days. He noticed already in this work that forgetting is reduced when sleep occurs in retention interval, phenomenon similarly observed in follow - up studies examining forgetting curve. Others report that depriving participant of night of sleep impairs his ability to remember. Rosa Heine was first to show in a more systematic study that learning in the evening before sleep results in less forgetting 24 h later than learning before daytime retention interval of wakefulness. This work provides first clues as to the importance of sleep for memory. Memory research in the first half of the 20th century was preoccupied with the causes of forgetting. Two concepts were propose, ie, decay account, assuming that memory traces decay over time resulting in Time - dependent forgetting, and interference account, assuming that forgetting results from learning of new information which interferes and overwrites old memory traces. In classic study, Jenkins and Dallenbach compare retention of nonsense syllables across 1 -, 2 -, 4 -, and 8 - h retention periods that were filled either with sleep or wakefulness. Sleep after learning reduces the amount of forgetting. Because the time retention interval was identical to sleep and awake conditions, authors conclude that results of our study as a whole indicate that forgetting is not so much a matter of decay of old impressions and associations as it is a matter of interference, inhibition, or obliteration of old by new. Because sleep represents time in which new encoding of external and, perhaps, also internal information is strongly reduce, reduction of interference by sleep appears to be crucial. However, findings by Jenkins and Dallenbach also pose challenge to interference theory, because learning of highly similar material does not occur during waking periods in these studies. Interference is considered to depend on similarity between learning and interference materials with stronger interference for highly similar tasks. Regardless of this issue, findings were interpreted as evidence that any waking mental activity increases forgetting by kind of nonspecific interference. Many studies have subsequently confirmed the positive effect of sleep on memory, examining longer retention intervals of from 24 h up to 6 days. The underlying concept was that sleep acts as temporary shelter that simply postpones the effect of interference and, thereby, passively maintains memory traces.


I. INTRODUCTION

Sleep is defined as a natural and reversible state of reduced responsiveness to external stimuli and relative inactivity, accompanied by loss of consciousness. Sleep occurs at regular intervals and is homeostatically regulate, ie, loss or delay of sleep results in subsequently prolonged sleep. Sleep deprivation and sleep disruptions cause severe cognitive and emotional problems, and animals deprived of sleep for several weeks show temperature and weight dysregulation and ultimately die of infections and tissue lesions. Sleep probably occurs in all vertebrates, including birds, fishes, and reptiles, and sleeplike states are similarly observed in invertebrates like flies, bees, and cockroaches. Sleep in mammals consists of two core sleep stages: slow - wave sleep and rapid - eye - movement sleep, which alternate in a cyclic manner. In human nocturnal sleep, SWS is predominant during the early part and decreases in intensity and duration across sleep period, whereas REM sleep becomes more intense and extensive towards the end of the sleep period. Sws is hallmarked by slow high - amplitude EEG oscillations, whereas REM sleep is characterized by wakelike fast and low - amplitude oscillatory brain activity. In addition, REM sleep is characterized by phasic REMs and by muscle atonia. Almost 50% of sleep in adult humans is marked by a lighter form of non - REM sleep that is characterized by occurrence of distinct sleep spindles and K - complexes in EEG, but minor SWA. Sleep stage N2 is not discriminate from SWS in rodents. Is sleep essential? From an evolutionary perspective, reduced responsiveness to potentially threatening stimuli during sleep represents significant danger to survival. The fact that almost all animals sleep strongly argues in favor of the adaptive role of sleep in increasing the overall fitness of organism, although its exact functions are still a matter of debate. Sleep has been proposed as serving energy - saving function, restoration of energy resources and repairing of cell tissue, thermoregulation, metabolic regulation, and adaptive immune functions. However, these functions could be likewise achieved in a state of quiet wakefulness and would not explain loss of consciousness and responsiveness to external threats during sleep. These prominent features of sleep strongly speak to the notion that sleep is mainly for the brain. Here, different functions have been propose, ranging from detoxication of the brain from free radicals, glycogen replacement to involvement of sleep in memory and synaptic plasticity. In this review we discuss this latter function, ie, critical role sleep serves in the formation of memory.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

The Cerebellar Cortex and LTD

Simplify views of olivocorticonuclear circuitry involved in motor memory formation, with cortical interneurons, multiple mossy fiber inputs, and some brainstem circuits omitted for clarity. Each panel shows how information transmission and excitabilities within system may change after different interventions. Excitability increases and decreases are indicate. Asterisks denote synapses at which muscimol may be acting. Post - training muscimol infusions to the cerebellar Cortex prevent consolidation, but it is uncertain whether consolidation processes are disrupted directly by targeted structure or indirectly through disturbance of the OCN loop. In particular, excitability of cerebellar nuclear neurons will increase as a consequence of cortical inactivation. However, post - training muscimol infusions to cerebellar nuclei do not affect consolidation. Nucleo - olivary inhibition is depress, so olivary excitability will increase. At Purkinje cells, increased climbing fiber activity increases complex spike activity with corollary reduction in simple spike activity, indicated by, but this does not impair the consolidation process. It remains possible that consolidation occur entirely in cerebellar nuclei only if these processes are disrupted by excitability increases, but insensitive deep neuronal inhibition with muscimol. Hence, in the present investigation, post - training muscimol infusions to both cortex and nuclei cause deep inhibition of cortical neurons, whilst protecting cerebellar nuclei from disinhibition. Key to panels - C and Model of cerebellar pathways engage in NMR conditioning. Cs - and US - relate information converges within the cerebellar Cortex and within cerebellar nuclei through mossy fiber and climbing fiber inputs, respectively. Inhibitory olivo - cortico - nuclear loop is indicated by dashed arrows. Conventions: excitatory neurons and synapses are shown in white; inhibitory neurons and synapses in black. Abbreviations: Ba, basket cell; cf, climbing fiber; Go, Golgi cell; Grc, granule cell; mf, mossy fibers; NV, trigeminal Nucleus; Pc, Purkinje cell; pf, parallel fibers; RN, red Nucleus;, Stellate cell. Experimental design: each daily session is shown as an open rectangle. Solid vertical lines indicate 3 day rest periods. Post - training cortical and nuclear infusions of muscimol or vehicle are indicate. Behavioral data: daily, mean session% CRs for Control and Cortex + Nucleus groups. Control subjects acquire asymptotic CRs during Phase 1, but Cortex + Nucleus subjects do not. Cortex + Nucleus subjects developed robust CRs during Phase 2, when muscimol was not give. Post - training infusions of muscimol given to Control subjects during Phase 3 had no consequences for maintained expression of CRs during Phases 3 and 4. Expand view of CR acquisition in Phase 1. Rate of acquisition is related to depth of cortical inactivation with muscimol: Cortex + Nucleus subjects fail to acquire robust CRs during Phase 1, whilst Incomplete subjects do acquire CRs, but not as rapidly as Nucleus Only and Off - Target subjects, which acquire CRs at a similar rate to Controls. Cannula tip locations are shown for all subjects in each group on series of 8 standard transverse sections at levels from 1. 0 mm to 4. 5 mm relative to skull lambda. For each subject in five groups, two matching symbols indicate the location of cortical and nuclear cannula tips.


Long-Term Depression

Ltd is a phenomenon by which synapses become less efficient in transmitting neuronal signals. As a counterpart to LTP, it is also important for adapting neural networks to physiological activity requirements. Ltd has been characterized in various systems and brain areas, including the cerebellum, hippocampus, cerebral cortex, and striatum. Experimentally, LTD induction requires low - frequency stimulation over prolonged time period. In cerebellum, LTD plays an important role in trial - and - error motor learning processes, and it has been most thoroughly characterized by synapses formed between parallel fibers and Purkinje cells. In hippocampus, LTD has been primarily investigated at CA3 to CA1 connections, in association with spatial learning in rodents. Similar to differences in polarity of synaptic strength changes between LTP and LTD, actin cytoskeletal dynamics behave in opposite direction during LTD, compared to LTP. In FRET experiments using fluorescently labelled actin, low - frequency stimulation to induce LTD shifts balance between G - actin and F - actin toward G - actin in dendritic spines, leading to net loss of postsynaptic F - actin. These changes were accompanied by shrinkage of spine and, sometimes, by spine disappearance. Long - term depression is the opposite of LTP, and is characterized by a decrease in postsynaptic strength. This happens by dephosphorylation of AMPA receptors and facilitation of their movement away from synaptic junction. Ltd is prominently seen in the hippocampus and cere - bellum, though current research shows LTD in other areas of the cortex involved in memory and learning. This mechanism is chiefly responsible for the removal of old memory traces. However, LTD also sharpens the image by enhancing contrast. It also has a major role in executing motor memory.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Sources

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

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