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AD is a progressive degenerative brain disorder that is characterized by neocortical atrophy, neuron and synapse loss, and the presence of senile plaques Black girls and big breast neurofibrillary tangles.

The plaques and tangles were first identified and reported in by the German physician and neuropathologist Alois Alzheimer. In his initial case he autopsied a year-old patient who had recently died from what we now term dementia and discovered the presence of several histopathologic alterations, two of Teen research paper on alzheimer diseas were the neuritic Teen research paper on alzheimer diseas and the Teen research paper on alzheimer diseas tangles.

Patients may also experience changes in affect or personality and Naked nude cosmid anny zemly of judgment. This research paper will provide an overview of the clinical, pathological, neuropsychological, and affective features associated with AD. Dementia refers to a syndrome of acquired intellectual impairment of sufficient severity to interfere with social or occupational functioning, caused by Teen research paper on alzheimer diseas dysfunction.

These symptoms must not be due to other neurological disorders, Teen research paper on alzheimer diseas conditions resulting in dementia, or substance abuse. The cognitive impairments must have a gradual onset and a progressive decline and be severe enough to significantly interfere with social or occupational functioning.

Furthermore, the cognitive Teen research paper on alzheimer diseas must represent a significant decline from a previously higher level of functioning, and it must not occur exclusively during the course of delirium see Table I.

From American Psychiatric Associaiton, The duration of the disease from the time of diagnosis to death can be as little as 2 years or as long as 20 years Teen research paper on alzheimer diseas more, although the average length ranges between 7 and 10 years. Dementia established by clinical exam and documented by mental status testing. Absence of systemic or other brain diseases capable of producing a dementia.

Atypical onset, presentation, or progression of a dementia syndrome with a known etiology. A systemic or other brain disease capable of producing dementia is present but not thought to be the cause of the dementia.

A gradually progressive decline in a single intellectual function in the absence of any other identifiable cause. From McKhann et al.

Neurology, 34, Trauma e. Transmissible spongiform encephalopathies e. Metabolic disorders; Chronic drug intoxication; Alcoholism; Malnutrition e. Note: A complete listing would include many Teen research paper on alzheimer diseas disorders; those listed above serve to illustrate that dementia results from many different etiologies. Estimates of the prevalence of dementia vary widely due to differences in definitions, sampling techniques, and the sensitivity of instruments used to identify cases.

Also, the prevalence of the syndrome of dementia doubles approximately every 5 years after age Not surprisingly, the prevalence of dementia is higher among hospital and nursing home residents than among those living within the community. First, age is the single most important risk factor for dementia.

Population-based studies in many different countries have confirmed that the prevalence of the most common causes of dementia i. Third, uneducated individuals over the age of 75 have about twice the risk for dementia as those who have completed at least a grade school education. Education and occupational achievement may act as a surrogate for brain or cognitive reserve that helps to delay the onset of the usual clinical manifestations of the disease.

Given some of the findings of specific point mutations on the amyloid precursor protein gene of chromosome 21 and linkage studies identifying gene loci on chromosomes 1, 14 and 19, there is now little question that this familial association is genetically based.

Intracellular events will eventually lead to neuritic degeneration, the formation of neurofibrillary tangles, and neuron and synapse loss. Over a period of time, the neural degeneration gradually reaches a level that initiates the clinical symptoms of the dementia syndrome. This framework for understanding the development of AD suggests that cognitive deficits associated with the disease also appear gradually.

Some of the most recent techniques include structural and volumetric analysis of the brain with magnetic resonance imaging MRIcomputation of regional cerebral metabolism with positron emission tomography PETregional cerebral blood flow with single photon emission computed tomography SPECTand determination of regional biochemical concentrations with magnetic resonance spectroscopy MRS.

However, gyral atrophy and enlarged ventricles are also found in normally aging brains, lending minimal diagnostic value to structural images early in the course of the disease. Temporoparietal and frontal cortical regions have shown significant glucose metabolic reductions, with relative sparing of visual and sensorimotor cortex. Furthermore, significant relationships have been found between neuropsychological impairment in AD and the degree of hypometabolism found by PET.

The individual patterns of decreased metabolism correlated with neuropsychological test scores purported to reflect processing in particular brain regions.

The decreased neocortical metabolism was found even in patients in the earliest stages of dementia of the Alzheimer type, in whom neuropsychological testing revealed no deficits other than amnesia. However, its significantly lower cost Electro sex wav files to download for its more widespread use.

Increases in Teen research paper on alzheimer diseas concentration have not been found in patients with other dementing illnesses or in normally aging individuals. Thus, preliminary findings from a number of recent studies suggest that MRI, PET, SPECT, and perhaps MRS can provide complementary information to the usual diagnostic procedures and may contribute to the early and more specific detection of the disease.

Future longitudinal studies are needed to determine the prospective accuracy of early diagnosis through structural and functional neuroimaging techniques, particularly studies that will be able to provide neuropathologic confirmation. Other associated features include neurotransmitter reductions, particularly acetylcholine Teen research paper on alzheimer diseas norepinephrine, as well as neuron and synapse loss. Neuritic plaques are complex deposits of amyloid protein and glial cells.

These extracellular deposits collect most heavily in portions of the entorhinal cortex and Teen research paper on alzheimer diseas formation, two brain areas critical for memory and learning of new information. Neuritic plaques are also found throughout the cortical mantle of the neocortex, with a predilection for association regions.

The protein networks become so complex over time that normal cell metabolism and nutrient flow become impossible and the cell eventually dies. As with plaques, tangles accumulate most densely in the entorhinal and limbic regions of the brain, although tangles are also found in many structures that project to the cerebral cortex such as the nucleus basalis of Meynert, locus ceruleus, midline thalamic nuclei, as well as in some hypothalamic nuclei and the ventral tegmental area, and dorsal raphe nucleus.

These changes occur primarily in the hippocampus, entorhinal cortex, and in the association cortices of the frontal, temporal, and parietal lobes. In addition to these cortical changes, subcortical neuron losses occur in the nucleus basalis of Meynert and in Teen research paper on alzheimer diseas locus ceruleus, resulting in a decrement in neocortical levels of cholinergic and noradrenergic markers, respectively.

While both disorders are associated with a severe and progressive dementia, there may be an increased prevalence of mild extrapyramidal motor findings e. Numerous studies have shown that measures of the ability to learn new information and retain it over time are quite sensitive in differentiating between mildly demented patients with clinically diagnosed AD and normal older adults.

Explicit, or declarative, memory, which refers to the conscious recollection of previously acquired information, is the type of memory assessed by classic, clinical tests of recall and recognition. One common dichotomous classification of explicit memory, the distinction between episodic and semantic memory, is based on the type of information stored in memory. Episodic memory contains context-linked information in which retrieval depends upon spatial and temporal cues.

Semantic memory, in contrast, refers to information that is context-free and usually overlearned. Although of general heuristic value in understanding anterograde amnesia i. Because of its prevalence in the early stages of AD, episodic memory disturbance is considered to be a necessary but not sufficient feature for the clinical diagnosis see Table I.

Memory impairments, even in patients in the early stages of the Teen research paper on alzheimer diseas, are apparent on clinical and experimental memory tasks that require the learning and retention of either verbal or nonverbal information over a series of trials. This severe anterograde amnesia appears to primarily result from a failure in consolidation that is mediated by damage to the hippocampus and entorhinal cortex, and neurotransmitter changes in the cholinergic system.

This contrasts with normal elderly, who have been shown to benefit from engaging in elaborative or semantic processing of information during the study phase of free recall tasks. In addition to their difficulties in storing new information, patients also tend to evidence rapid forgetting of what little they do initially learn.

However, some caution should be exercised when using such errors in a clinical setting. Intrusion errors in isolation do not represent an exclusive finding in AD since they also occur in patients with other forms of dementia e. Furthermore, Teen research paper on alzheimer diseas of error types have not proven to be the most sensitive cognitive indices for the detection of dementia.

It is often assumed that semantic knowledge is organized as a complex network of associated concepts, and that within the network, concepts that have many attributes in common are more strongly associated than those that share fewer attributes.

These strongly related concepts are thought to form conceptual categories made up of exemplars that share many attributes. The attributes not only provide a means of grouping concepts into categories, but also provide a means of distinguishing among the various exemplars that constitute a given category.

Thus, dog and lion are both categorized as animals because they share attributes such as being alive, being mobile, and being able to reproduce, but they can be distinguished from each other by such attributes as domesticity, size, and shape. A number of recent investigations suggest that this organization of semantic memory is disrupted in patients with AD, possibly due to damage to the association cortices that are thought to store the concepts and associations that constitute semantic knowledge.

First, patients exhibit a disproportionately severe fluency deficit when generating exemplars from a semantic category e. Their category fluency performance is characterized by an increased propensity to produce category labels relative to specific exemplars.

Fourth, there is a correspondence in items missed by AD patients across tasks designed to access semantic knowledge through different modes of input and output. Teen research paper on alzheimer diseas, there is a deterioration in the organization of semantic knowledge in patients that can be consistently demonstrated by alterations in cognitive maps that reflect the semantic relationships used in categorizing concepts.

This Teen research paper on alzheimer diseas of semantic knowledge disrupts the normal organization of semantic memory in AD patients and results in aberrations in their network of semantic representations.

Tests of episodic and semantic memory generally require that prior episodes or events, or previously acquired knowledge, be explicitly and consciously recollected.

However, recent research indicates that some forms of learning and memory occur implicitly, without conscious recollection. This implicit knowledge is expressed indirectly throughout the performance of the specific operations comprising a task. Classical conditioning, lexical and semantic priming, motor skill learning, and perceptual learning have all been considered forms of implicit memory. As is the case for episodic and semantic memory, the distinction between explicit and implicit memory receives neurobiological and neuropsychological support from studies of patients with amnesia.

Severely amnesic patients are impaired on tests of explicit memory, but perform normally on implicit memory tests. Teen research paper on alzheimer diseas example, amnesic patients can acquire and retain motor skills e.

Similarly, amnesic patients will often evidence decreased visual identification thresholds for previously presented words they cannot recall or recognize on explicit memory tests. It is presumed that the initial visual presentation of the words activated some unconscious trace that later facilitated the visual identification of the stimuli without affecting conscious attempts to recollect the materials. Although the specific neurological substrates of explicit memory have been extensively described, little attention has been given to the brain structures responsible for various forms of implicit memory.

While damage to the mesial region of the temporal lobes, the medial diencephalon, and the basal forebrain all result in severe impairments in explicit memory, little is known about the brain structures that mediate various forms of verbal and pictorial priming and skill learning.

This double dissociation suggests that portions of the association cortex and the basal ganglia mediate quite different forms of implicit memory. It has been hypothesized that impairment Teen research paper on alzheimer diseas working memory results in difficulty maintaining attention to complex or shifting sets. In fact, subtle impairments in the earliest stages of AD may be seen on complex attentional tasks depending upon divided and shifting attention.

Some patients in the early disease stages do not have attentional problems, but such deficits typically emerge and increase in severity as the disease progresses. Certain language abilities tend to remain intact, however. In the later stages of the disease, some patients have difficulty producing complex syntax in spontaneous speech. Patients experience a progressive anomia directly evident on tests of confrontation naming, such as the Boston Naming Test.

Patients often circumlocute as they search for particular targets. They also make semantic errors, Teen research paper on alzheimer diseas described earlier, such as providing picture names that are actually the categories to which pictures belong e. This is a disproportionately severe fluency impairment exhibited by patients when generating exemplars from a specific category compared to generating words that begin with a particular letter.

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