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Cognition and Behavior in Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disease that destroys memory as well as other cognitive functions. In Alzheimer’s, connections between brain cells as well as the cells themselves degenerate and eventually die which leads to the destruction of memory as well as other important mental functions. Additionally, in the brain, there is a protein called amyloid precursor protein which our brain is naturally able to get rid of. However, this does not happen in people with AD. Instead, the brain starts to form beta-amyloid deposits along with an abnormal amount of tau build-up causing our internal skeleton to fall apart. The abnormal form of tau clings to other proteins in the brain which form neurofibrillary tangles that affect the cognition of a person and slows down neuronal activity in the brain eventually leading to death. Factors such as diet, age, excessive drinking, smoking, and/or lack of exercise can contribute to a person developing Alzheimer’s.


In Alzheimer’s disease, the first part of the brain that gets affected is the hippocampus. Situated in the temporal lobe of the brain, the hippocampus is responsible for forming, and maintaining memories. Deterioration of the hippocampus causes people with Alzheimer’s to have trouble remembering important information such as the names of their family members, and having trouble recognizing objects. A cognitive deficit that may show up in someone with Alzheimer’s disease is anterograde amnesia. Anterograde amnesia is a type of memory loss that occurs when a person is unable to form new memories and can affect various subtypes of memories such as semantic memory, and episodic memory. Semantic memory is best defined as remembering something factually such as what a person did over the weekend, or what they did at work, while episodic memory is a type of long-term memory that involves conscious recollection of previous experiences together with their context in terms of time, place, associated emotions, etc. Furthermore, semantic memory also reflects but is not limited to the details of one’s life such as what hometown they’re from, what their favorite color is, and characteristics of that specific person. People with Alzheimer’s may have trouble remembering something they did last weekend because in Alzheimer's, short-term memory is usually affected first. Conversely, a person diagnosed with Alzheimer’s may still remember their wedding from 50 years ago since long-term memory is not significantly damaged in the early stages of Alzheimer’s disease. 


Agraphia, a reduction of the ability to write is also an effect of AD.  To be able to write, our brain has to be able to execute and integrate a lot of motor skills. Our brain has to be able to process language and we have to be able to convert our thoughts into words. Additionally, it is crucial that one can choose the right letters to spell the words correctly, know how to write each letter and have the ability to do this repeatedly. People with Alzheimer’s develop agraphia when any area in the brain involved in helping us write becomes damaged which is unfortunately irreversible and worsens over time. Because both spoken and written language are produced by neural networks in the brain that are interconnected, people who have agraphia can also have speech impediments as well as hardships with reading. Furthermore, there are several types of agraphia such as deep agraphia where there’s damage to the left part of the parietal lobe in the brain. The parietal lobe is the part of the brain that is responsible for spatial awareness, knowing how far two things are from each other, learning movements, sensory information, etc. When a person with Alzheimer’s has deep agraphia, they may not be able to remember how a word is spelled, and might also have issues with recalling how to “sound out” a word which is known as having a phonological inability. Moreover, people affected by this may confuse two words that are related to each other with an example being “restaurant” and “server.” 


Reading is a fundamental skill that we all learn how to do from a young age. Reading allows us to understand the world around us, and can even be a survival tool that can protect us from danger. However, when someone has Alzheimer’s they may slowly lose their ability to be able to read known as alexia. Alexia is associated with significant damage to the anterior part of the left hemisphere. The left hemisphere of the brain helps us with performing cognitive functions such as reading, doing mathematics, and analyzing details, on top of helping us be logical in our decision-making because of slow neuronal death throughout the brain, a person’s reading ability can be severely damaged to the point where they can’t read.

 

Additionally, it is said that the main brain area that’s affected in alexia is the left posterior cerebral artery resulting in the person knowing how to write but not being able to read (even what he has just written). However, because pure alexia affects visual input but not auditory input, patients with pure alexia may be able to recognize words spelled out loud to them which is due to the left visual cortex being damaged which leaves only the right visual cortex being able to process information but is unfortunately unable to send messages to the parts of the brain known as Broca’s area and Wernicke’s area because of damage to the corpus callosum.


Alzheimer’s affects a large amount of cognitive skills that a person has learned over time resulting in these abilities slowly diminishing over time. A large number of factors such as lack of exercise, excessive drinking, smoking, or even genetics can result in Alzheimer’s disease later in life. Simply leading a healthy lifestyle can significantly decrease the risk of developing this neurodegenerative disease.




Works Cited

 Knopman DS, Amieva H, Petersen RC, Chételat G, Holtzman DM, Hyman BT, et al. (May 2021). "Alzheimer's disease". Nature Reviews Disease Primers. 7 (1): 33. doi:10.1038/s41572-021-00269-y. PMC 8574196. PMID 33986301.



Farina N, Rusted J, Tabet N (January 2014). "The effect of exercise interventions on cognitive outcome in Alzheimer's disease: a systematic review". International Psychogeriatrics (Review). 26 (1): 9–18. doi:10.1017/S1041610213001385. PMID 23962667. S2CID 24936334.


Cherney LR. Aphasia, alexia, and oral reading. Top Stroke Rehabil. 2004 Winter;11(1):22-36. Alexia - StatPearls - NCBI Bookshelf (nih.gov)


Smith CN, Frascino JC, Hopkins RO, Squire LR. The nature of anterograde and retrograde memory impairment after damage to the medial temporal lobe. Neuropsychologia. 2013;51(13):2709-2714. doi:10.1016/j.neuropsychologia.2013.09.015

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