The Impact of Alzheimer's disease on Cognitive Function: A Neuropsychological Perspective

Yavuz Guan^*
*Correspondence: Yavuz Guan, Department of Psychology, Northeast Normal University, Changchun, China, Email:

Introduction

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder that primarily affects cognitive function, leading to a gradual decline in memory, attention, executive function, and other cognitive abilities. As the most common cause of dementia in older adults, Alzheimer's disease poses significant challenges not only to those diagnosed but also to their families, caregivers, and healthcare systems. The hallmark symptoms of AD, such as memory loss, confusion, and difficulty with daily tasks, are the result of complex and progressive changes in the brain, particularly the accumulation of amyloid plaques and tau tangles that disrupt neural communication and function. From a neuropsychological perspective, Alzheimer's disease is understood as a disorder that primarily targets areas of the brain involved in memory and learning, such as the hippocampus and the entorhinal cortex. As the disease progresses, it extends to other regions responsible for higher-order cognitive functions, including language, problem-solving, and spatial awareness. Understanding the cognitive impact of AD involves not only identifying the specific deficits in brain function but also examining how these deficits manifest in real-life behavior and day-to-day functioning. This paper will explore the impact of Alzheimer's disease on cognitive function from a neuropsychological standpoint, focusing on the cognitive domains most affected by the disease, such as memory, executive function, language, and visuospatial abilities. We will also review neuroimaging and neuropsychological assessment tools used to detect and monitor cognitive decline in AD, along with current theories on the pathophysiology of the disease. By examining the cognitive and neural changes associated with Alzheimer's disease, we can gain a deeper understanding of the disease's progression and the challenges it presents to both diagnosis and treatment, while also exploring potential interventions aimed at preserving cognitive function and quality of life for those affected [1].

Description

Alzheimer's disease is a devastating neurodegenerative disorder that primarily affects memory and cognitive function, gradually impairing an individual’s ability to perform everyday tasks and diminishing their quality of life. As the most common cause of dementia, AD accounts for 60-80% of dementia cases worldwide and affects millions of older adults, typically beginning after the age of 65. Despite significant advancements in understanding the disease, Alzheimer's remains a progressive and irreversible condition, with no known cure. The cognitive decline associated with AD is not merely a consequence of aging, but the result of pathological processes in the brain that lead to neuronal death, synaptic loss, and changes in brain structure and function. Understanding the cognitive impact of Alzheimer's disease requires a neuropsychological perspective one that considers the relationship between brain function and behavior, as well as the specific cognitive domains that are most vulnerable to impairment in AD. This neuropsychological approach provides a framework for diagnosing the disease, tracking its progression, and developing interventions aimed at mitigating its effects. The cognitive decline in Alzheimer's disease typically begins with mild memory impairment and can extend to profound deficits in attention, executive function, language, and visuospatial skills as the disease progresses [2].

At the heart of Alzheimer’s disease are pathological changes in the brain, which include the accumulation of amyloid-beta plaques and the formation of neurofibrillary tangles. Amyloid plaques are deposits of the amyloid-beta protein that accumulate in the spaces between nerve cells, disrupting communication between neurons. Tau tangles, formed from an abnormal accumulation of the tau protein inside neurons, interfere with the neuron’s internal transport system, impairing its function and eventually leading to cell death. These pathological changes primarily affect regions of the brain involved in memory and learning, particularly the hippocampus and entorhinal cortex, which are among the earliest areas to experience damage in Alzheimer's disease. As the disease progresses, it spreads to other areas of the brain, including the frontal cortex (responsible for executive function), parietal lobe (involved in spatial awareness), and temporal lobes (which house language centers). This widespread brain degeneration explains the diverse cognitive deficits observed in Alzheimer's patients as the disease advances. The cognitive impact of Alzheimer's disease can be broadly categorized into several domains that are progressively affected as the disease advances; Memory loss is the most prominent and earliest symptom of Alzheimer's disease. Initially, individuals may experience episodic memory deficits, which affect the ability to recall specific events or experiences. They may forget recent conversations, appointments, or where they placed items. As the disease progresses, semantic memory (the recall of facts and general knowledge) and working memory (the ability to hold and manipulate information in the short term) are also compromised. The hippocampus, which plays a central role in forming new memories, is one of the first areas of the brain to be affected in AD, leading to the characteristic early memory problems seen in the disorder.

As Alzheimer's disease progresses, individuals experience significant impairments in executive function, which involves higher-order cognitive skills such as planning, decision-making, problem-solving, and the ability to switch between tasks. Damage to the prefrontal cortex contributes to difficulties in organizing thoughts, managing daily tasks, and adapting to new situations. People with Alzheimer's may become less able to manage finances, plan events, or keep track of personal care routines. They may also struggle with abstract thinking, such as understanding cause-and-effect relationships or making decisions in unfamiliar situations. Language deficits are also a prominent feature of Alzheimer's disease, particularly in the later stages. Initially, individuals may have difficulty finding the right words or may repeat themselves frequently. As the disease advances, expressive language (speaking or writing) becomes increasingly impaired, and individuals may have trouble forming coherent sentences. Receptive language (understanding spoken or written language) is also affected, making it difficult for individuals to follow conversations or understand instructions. The temporal lobes, especially areas involved in language processing like Broca's area and Wernicke’s area, are significantly impacted in AD, which explains the gradual decline in both comprehension and production of speech [3].

Impairments in visuospatial skills are common in Alzheimer's disease, particularly as the disease progresses. The parietal lobe, which is involved in spatial awareness, is often affected, leading to difficulties in tasks such as navigating familiar environments, recognizing faces, and judging distances. Individuals may become disoriented in familiar places or have difficulty judging the spatial relationships between objects. Apraxia, a condition in which individuals have trouble performing coordinated movements, may also develop, further hindering tasks like dressing or feeding oneself. In addition to memory and executive function, Alzheimer's disease can cause impairments in attention and processing speed. Individuals with AD may become easily distracted and may have difficulty focusing on tasks for prolonged periods. Cognitive processing slows down, making it more challenging to complete tasks quickly and accurately. These deficits can contribute to feelings of frustration and confusion, particularly when the person is required to shift attention between tasks or respond rapidly to changing information. While social cognition (the ability to recognize and interpret social cues and emotions) is often overlooked in clinical descriptions of Alzheimer's, it can also be significantly affected. Damage to the brain regions involved in processing emotions and understanding social interactions can lead to inappropriate behavior, social withdrawal, and a diminished capacity for empathy. As cognitive decline progresses, individuals may have trouble recognizing faces, understanding emotional cues, or maintaining appropriate social interactions. This, in turn, can lead to isolation and difficulty maintaining relationships. The diagnosis and monitoring of Alzheimer's disease often rely on neuropsychological assessments that evaluate the various cognitive domains affected by the disease. Standardized tests are used to measure specific cognitive functions, including memory, attention, language, and executive function. These assessments can help clinicians establish a baseline of cognitive abilities, monitor changes over time, and differentiate Alzheimer's disease from other forms of dementia.

Some commonly used neuropsychological tests for AD include; The Mini-Mental State Examination (MMSE), which evaluates general cognitive function. A wider variety of cognitive skills, such as memory, attention, language, and executive function, are evaluated by the Montreal Cognitive Assessment (MoCA). The Wechsler Memory Scale, which focuses on memory function in particular. The Wisconsin Card Sorting Test and the Trail Making Test evaluate executive function, processing speed, and attention. In addition to traditional neuropsychological assessments, neuroimaging techniques such as MRI (magnetic resonance imaging) and PET (positron emission tomography) scans are increasingly used to observe brain changes associated with AD. Imaging allows clinicians to visualize atrophy (shrinkage) in the hippocampus and other brain areas involved in cognition, providing crucial insights into the structural changes that occur as Alzheimer's disease progresses [4].

Alzheimer's disease is typically categorized into three stages: early, middle, and late stages. In the early stages, cognitive changes are often subtle, with mild memory problems and some difficulty with attention and executive function. In the middle stages, cognitive deficits become more pronounced, and individuals may require assistance with Activities of Daily Living (ADLs) such as dressing, bathing, or managing medications. In the late stages, individuals may become fully dependent on caregivers, experiencing severe memory loss, language impairment, and physical symptoms, such as difficulty walking or swallowing. The ability to communicate is often lost, and individuals may not recognize loved ones or remember basic facts about their lives. While Alzheimer's disease currently has no cure, there is ongoing research into treatments that may help slow the progression of cognitive decline or alleviate symptoms. Current treatments, such as acetylcholinesterase inhibitors (donepezil, rivastigmine) and glutamate regulators (memantine), provide modest benefits by improving communication between nerve cells or regulating neurotransmitter activity, but they do not halt the underlying disease process. Neuropsychological interventions, including cognitive training and cognitive rehabilitation, are also being explored as means to improve or preserve cognitive function in Alzheimer's patients. These therapies aim to help individuals compensate for cognitive deficits and maintain functional independence for as long as possible. Looking to the future, biomarker research and advances in genetic and neuroimaging techniques offer hope for earlier diagnosis and more targeted interventions. Additionally, neuroprotective treatments aimed at preventing or slowing the neurodegenerative process may provide new avenues for managing Alzheimer's disease [5].

Conclusion

Alzheimer's disease profoundly impacts cognitive function, with early and severe disruptions in memory, executive function, language, and visuospatial abilities. A neuropsychological perspective provides valuable insight into the specific cognitive deficits associated with AD, offering critical tools for diagnosis and monitoring. Although no cure currently exists, ongoing research into the pathophysiology of Alzheimer's disease holds promise for future breakthroughs in treatment. By understanding the cognitive and neural changes that characterize Alzheimer's disease, clinicians and researchers can continue to develop effective interventions that improve the quality of life for individuals living with this challenging disorder.

Acknowledgement

None.

Conflict of Interest

None.

References

1. Bai, Wei, Pan Chen, Hong Cai and Qinge Zhang, et al. "Worldwide prevalence of mild cognitive impairment among community dwellers aged 50 years and older: a meta-analysis and systematic review of epidemiology studies." Age Ageing 51 (2022): afac173.

Google Scholar, Crossref, Indexed at

2. Ganguli, Mary, Yichen Jia, Tiffany F. Hughes and Beth E. Snitz, et al. "Mild cognitive impairment that does not progress to dementia: A population‐based study." J Am Geriatr Soc 67 (2019): 232-238.

Google Scholar, Crossref, Indexed at

3. Bekris, Lynn M., Chang-En Yu, Thomas D. Bird and Debby W. Tsuang. "Genetics of Alzheimer disease." J Geriatr Psychiatry Neurol 23 (2010): 213-227.

Google Scholar, Crossref, Indexed at

4. Jun, Gyungah, Adam C. Naj, Gary W. Beecham and Li-San Wang, et al. "Meta-analysis confirms CR1, CLU, and PICALM as Alzheimer disease risk loci and reveals interactions with APOE genotypes." Arch Neurol 67 (2010): 1473-1484.

Google Scholar, Crossref, Indexed at

5. Apostolova, Liana G., Lisa Mosconi, Paul M. Thompson and Amity E. Green, et al. "Subregional hippocampal atrophy predicts Alzheimer's dementia in the cognitively normal." Neurobiol Aging 31 (2010): 1077-1088.

Google Scholar, Crossref, Indexed at