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Alzheimer’s disease is a progressive neurological disorder that gradually destroys memory and cognitive functions. 

As the disease progresses, it affects multiple areas of the brain that control not only thinking and memory but also basic bodily functions and senses. 

The five traditional senses – sight, smell, taste, touch, and hearing – play an important role in how we perceive and interact with the world. 

For Alzheimer’s patients, impairment or loss of senses adds another layer of difficulty as they navigate daily life. 

Some senses seem to be more susceptible to deterioration than others. Research has provided clues as to which sensory systems may be attacked most severely by the pathological changes of Alzheimer’s disease.

This article examines current evidence on how Alzheimer’s impacts each of the five senses, and which sense seems to be affected the most. 

Understanding how the different senses are impacted can help caregivers provide better support to patients as the disease advances. 

But first, let’s understand some basics about Alzheimer’s disease.

What is Alzheimer’s Disease?

Alzheimer’s disease, a progressive neurodegenerative disorder, is the most common cause of dementia among older adults. It gradually erodes cognitive function, impacting memory, thinking, and behavior. 

Named after Dr. Alois Alzheimer, who first described the condition in 1906, the disease primarily affects individuals aged 65 and older. 

However, early-onset Alzheimer’s can manifest in individuals in their 40s or 50s.

The disease involves an accumulation of abnormal deposits of beta-amyloid protein forming plaques and twisted strands of tau protein forming tangles inside brain cells. 

Over time, these deposits damage surrounding neurons and synapses in areas involved with learning, memory, and cognition, leading to the death of brain cells and the loss of brain tissue.

Loss of brain volume and neuronal death eventually lead to an inability to communicate and complete basic activities of daily living.

As Alzheimer’s progresses, symptoms will significantly worsen. 

In the final stages, individuals may be unaware of family/friends and need round-the-clock assistance with basic tasks.

While Alzheimer’s is widely believed to stem from a complex interplay of genetic, lifestyle, and environmental factors, the exact mechanisms through which it develops are still under research.

Common Signs and Symptoms of Alzheimer’s Disease

senses
Image Credit: anthemmemorycare.com
  • Memory loss that affects daily life
  • Challenges in planning or solving problems
  • Difficulty completing familiar tasks
  • Confusion with time or place
  • Trouble understanding visual images and spatial relationships
  • New problems with words in speaking or writing
  • Misplacing things and losing the ability to retrace steps
  • Decreased or poor judgment
  • Withdrawal from work or social activities
  • Changes in personality and mood, such as depression

In addition to the above cognitive symptoms, individuals with Alzheimer’s disease often experience changes in sensory perception. 

These can include the declining ability to recognize smells, tastes, and textures or to follow sound patterns like speech.

Let’s explore the science behind Alzheimer’s disease and sensory impairment.

The Science Behind Sensory Loss and Alzheimer’s Disease

Our five senses are not passive receptors, but rather complex systems that require extensive neural processing. 

Technically, it’s not the eyes that see, or the ears that hear; it is the brain that truly sees, hears, tastes, smells, and feels.

Our sensory organs simply collect stimuli from our environment. 

Sense impressions mean nothing until the brain processes them and turns inputs into perceptual experiences.

Alzheimer’s disease damages key brain regions involved in higher cognitive functions as well as sensory integration. 

As neurodegeneration progresses, it impacts the ability to perceive and comprehend sensory information.

For example, a familiar food may be tasted but not recognized as such, because the neurological pathways that associate flavors with memories have broken down.

Sensory loss can be associated with cognitive decline through different mechanisms for each sense. 

For example, for sight, research studies have shown evidence of increased retinal amyloid plaques and nerve cell degeneration in patients compared to cognitively healthy individuals.

For the sense of smell, research says that olfaction decline is linked to faster amyloid-β (Aβ) and tau deposition in olfaction-related regions of the brain. 

Greater olfactory dysfunction is associated with more extensive Alzheimer ‘s-related neuropathological changes in areas important for smell processing.

As sensory neural circuits get disrupted, it degrades the brain’s capacity to form new perceptions and retrieve associations from past experiences. 

This is what underlies the gradual loss of the ability to recognize faces, follow speech, or identify familiar scents and textures in advanced diseases.

How Alzheimer’s Disease Affects Our Five Senses

1. Alzheimer’s and Sense of Smell

One of the most prevalent signs of Alzheimer’s involves the sense of smell. 

Loss of smell sensitivity, or anosmia, can predate other cognitive deficits and serve as an early warning sign.

For those in the early stages of the disease, the ability to detect, identify, and differentiate odors can become impaired. 

Everyday scents that were once easily distinguished may all seem vaguely similar or ambiguous.

Numerous studies have found associations between declining olfactory test scores and a heightened risk of developing mild cognitive impairment or other forms of dementia. 

Poor performance on smell identification tests has also correlated with observable pathology in brain scans indicative of dementia-related changes.

How to help:

  • Regularly check and maintain smoke detectors to compensate for the reduced ability to detect the scent of smoke.
  • Keep the refrigerator and pantry organized, removing any outdated or spoiled foods. Regular checks help prevent individuals from accidentally consuming expired items.
  • Incorporate pleasant scents or aromatherapy in the living environment. This not only enhances the overall atmosphere but can also serve as a sensory stimulant.

2. Alzheimer’s and Sense of Taste

The sense of taste can also diminish as Alzheimer’s progresses. 

Individuals may complain that food lacks flavor even when it tastes normal to others. 

This is believed to result from a declining ability to detect the full spectrum of tastes like sweet, salty, sour, and bitter.

Similar to the temporary taste loss experienced by some with COVID-19, Alzheimer’s patients may find everything bland and unappetizing. 

Taste buds become less sensitive to the chemical signals triggered by different foods. 

As a result, the pleasure associated with eating can fade.

Food preferences of the individuals may also change, making it necessary for caregivers to adapt and be flexible in accommodating evolving tastes.

How to help:

  • Check date labels regularly and promptly remove spoiled items, as spoiled food may not register as foul-tasting.
  • Remain flexible about preferences and try preparing familiar foods in accustomed ways, focusing on past favorites that may still appeal through memory more than taste alone.
  • Enhance visual presentation and use flavorful garnishes/sauces to make meals more appetizing looking and smelling since these cues significantly influence our perception of taste.
  • Consider flavor-enhancing extras like seasoning salts, butter, gravy, etc. to boost bland foods. Moderate sweet flavors from fruits may also make meals more appealing.

3. Alzheimer’s and Sense of Hearing

Hearing impairment is another sensory change that is widely often associated with Alzheimer’s disease.

Previous research has demonstrated associations between hearing impairment and dementia, suggesting hearing loss may contribute to cognitive decline in older adults. 

Early case-control studies provided evidence of a link between hearing loss and cognitive decline in older adults. 

One such study of 100 cases demonstrated an association between hearing impairment and dementia, supporting the hypothesis that hearing problems contribute to cognitive dysfunction. 

Later studies also confirmed that hearing loss poses an independent risk factor for all-cause dementia.

In Alzheimer’s patients, changes in hearing can manifest in two main ways. 

Some individuals may start experiencing a clinical decline in their ability to hear certain sounds and volume levels. 

However, others may retain excellent hearing ability while still struggling to process and interpret sounds accurately. 

This reveals a key aspect of how Alzheimer’s impacts the sense of hearing – it is not just about the reception of sound inputs, but the brain’s capacity for sound processing and comprehension.

Even in the early stages, individuals may have difficulties following conversations, especially in noisy environments. 

As the disease progresses further, patients often lose the ability to recognize speech patterns, identify familiar voices, or discriminate between tones and pitches. 

This can significantly hinder communication and reduce quality of life if hearing aids or other assistive strategies are not provided.

Additionally, Alzheimer’s patients tend to get overstimulated easily by loud or numerous sounds. 

As author Mirian Green notes about her mother’s experience with dementia in her book, even normal background noises like passing vehicles or voices that others filter out easily could completely overwhelm her mother and cause her to withdraw.

How to help:

  • Create a calm living environment and reduce background noise to minimize auditory overstimulation. 
  • Speak slowly and calmly when communicating. Encourage clear communication from friends and family to facilitate better understanding and reduce confusion.
  • Avoid concurrent exposure to multiple sources of noise, such as having the television and radio on simultaneously.
  • Prioritize regular hearing checkups to promptly address emerging hearing issues. Early detection and intervention contribute to the effective management of hearing challenges.

4. Alzheimer’s and Sense of Sight

While the eyes themselves typically remain intact in Alzheimer’s disease, changes in the brain can disrupt how visual information is processed and perceived. 

Patients’ depth perception and sense of spatial relationships may become altered due to neurodegeneration. 

For example, rather than comprehending a set of black and white tiles as a patterned floor, it could incorrectly appear as dangerous holes. 

This impaired visual processing raises safety concerns as individuals may misjudge distances, levels, or sense of movement.

Other common sight-related difficulties include an inability to recognize familiar faces or objects. 

As the disease advances, a loved one may struggle to identify what or who is directly in front of them. 

Simple visual tasks like finding an object within their field of view or navigating spaces can become challenging without cues.

These visual cognitive deficits have meaningful implications for day-to-day activities and quality of life. 

Impairments in orientation and judging physical relationships in the environment increase risks for accidents, wandering, or other issues.

How to help:

  • Contrasting colors on doors, drawers, and fixtures like cabinets can aid navigation and identification of important rooms and items. 
  • Solid, differentiated wall and floor colors limit visual confusion compared to patterned designs. 
  • Picture cues on bathroom and bedroom doors also help orientation. 
  • Color-contrast safety strips running edge-to-edge on level changes are also a direct solution to issues with depth perception placing the person at risk for falls. 

5. Alzheimer’s and Sense of Touch

As Alzheimer’s pathology progresses throughout the body, the ability to perceive touch sensations typically deteriorates. 

Patients may lose sensitivity to heat, cold, discomfort, or pain – a profound change that impacts everyday experiences and safety.

Touch plays a key role in forming feelings of security, connectedness, and well-being. 

So declining tactile sensation can contribute to a sense of detachment and isolation for someone with advanced dementia.

How to help?:

  • Clearly label hot and cold on sinks to avoid accidental scalds. Use visual cues near appliances like ovens once hot. 
  • Check food temperatures yourself as the person may not feel if something is too hot/cold. 
  • Provide soft, textured comfort items that can still be appreciated through touch like blankets and stuffed toys. 
  • Gentle physical contact like holding hands, hugs, or shoulder rubs can be a meaningful way to communicate caring through the language of touch that is still relatable.

Which Sense Does Alzheimer’s Affect the Most?

human senses
Image Credit: verywellhealth.com

While sensory changes vary between individuals, the sense of smell (olfaction) may be most significantly impacted by Alzheimer’s disease pathology.

Several studies have found olfactory impairment, as measured by odor identification testing, can predict future cognitive decline. 

Individuals with normal cognition but low odor ID scores were more likely to later develop mild cognitive impairment compared to those with better smell function.

Among those with amnestic mild cognitive impairment, impaired olfaction predicted future conversion to full Alzheimer’s dementia. 

Odor identification has also correlated strongly with other objective biomarkers of Alzheimer’s disease.

Hearing loss is another sensory deficit common in Alzheimer’s. Previous research demonstrates associations between the degree of hearing impairment and the incidence of cognitive decline. 

Hearing problems independently increase the risk for all-cause dementia.

More research continues to enhance understanding of how specific sensory abilities deteriorate at different disease stages and which may serve as the most useful diagnostic and prognostic markers.

Why is the Treatment of Sensory Problems Important?

Sensory impairments are important to treat in Alzheimer’s patients as they can accelerate cognitive decline if left unaddressed. 

Problems with vision, hearing, and other senses have been identified as risk factors for dementia according to research. 

For example, one study estimated that nearly 100,000 dementia cases in the US could have been prevented if existing vision treatments were used, highlighting the role of visual impairment as a risk factor. 

When older adults experience untreated vision loss, they often stop driving, going out in the community, reading, and engaging in physical exercise due to fear of falling. 

This reduces social interaction, and emotional well-being, and leads to physical inactivity – factors that are themselves linked to a greater risk of cognitive decline.

Similarly, untreated hearing loss prompts social withdrawal as older adults try to avoid uncomfortable interactions where they struggle to engage in conversations during their daily activities. 

Sensory stimulation is important for maintaining functions like sound processing over time, and this social isolation and lack of stimulation may lead to shrinkage of sound processing areas of the brain.

Ongoing research, such as the Aging and Cognitive Health Evaluation in Elders (ACHIEVE) study, is actively exploring the impact of treating hearing loss on cognitive function. 

This five-year clinical trial is tracking nearly 1,000 older adults with hearing loss to compare cognitive outcomes between those treating their hearing loss and control groups who are not.

In essence, regardless of the specific sensory impairment one may be facing, prompt treatment is highly important.

Not treating impairments removes opportunities for sensory enrichment that may help preserve brain plasticity and function even in the face of disorders like Alzheimer’s.

Conclusion

In summary, Alzheimer’s disease impacts all senses in one way or another, however, the degree to which each is compromised varies significantly between individuals.

While vision, taste, and touch may also deteriorate to varying extents, olfactory dysfunction currently shows the greatest potential as a sensitive early biomarker for emerging Alzheimer’s pathology. 

Nonetheless, all sensory changes can reduce the quality of life for patients and increase safety risks if not addressed, which is why treatment is very important to slow cognitive changes and preserve brain functions.

Maximizing sensory enrichment through low-cost adaptations to the environment can also help optimize the independence of Alzheimer’s patients.

FAQ’s:

1. Can sensory problems be an early sign of Alzheimer’s disease?

Yes, sensory problems, particularly changes in vision, hearing, and smell, can serve as early indicators of Alzheimer’s disease.
These alterations may precede more overt cognitive symptoms and warrant attention for early detection and intervention.

2. How does sensory impairment impact the daily life of individuals with Alzheimer’s?

Sensory impairment in Alzheimer’s can lead to challenges in communication, safety concerns, and reduced engagement in daily activities.
For example, vision changes may affect navigation, while hearing loss can contribute to social isolation.

3. How can caregivers help individuals with Alzheimer’s cope with sensory challenges?

Caregivers can create a supportive environment by minimizing unnecessary stimuli, using visual cues, and encouraging the use of aids like hearing devices.
Additionally, understanding the individual’s specific sensory needs and preferences is vital for providing personalized care.

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