Alzheimer’s disease is a progressive neurodegenerative disorder that affects memory, thinking, and behavior. It is the most common cause of dementia, accounting for 60-80% of dementia cases. Alzheimer’s disease typically follows a characteristic pattern of progression, with certain mental functions becoming impaired earlier than others. Identifying which mental functions are affected first in the course of Alzheimer’s provides insight into how the disease develops and spreads in the brain over time.
Memory Loss
One of the earliest and most prominent symptoms of Alzheimer’s disease is memory loss, particularly short-term or recent memory problems. This reflects the early degeneration of brain regions involved in forming new memories, like the entorhinal cortex and hippocampus.
In the initial stages of Alzheimer’s, the individual may have difficulty recalling recent events, conversations, or newly learned information. They may frequently repeat statements or questions, forget appointments, misplace items, or get lost in once familiar locations. Long-term memories from earlier life tend to be preserved longer into the disease. But as Alzheimer’s progresses, long-term recall also deteriorates.
Memory loss is one of the key criteria used in diagnosing Alzheimer’s dementia. If memory loss interferes significantly with daily functioning, it indicates progression from mild cognitive impairment to Alzheimer’s dementia. Virtually all individuals with Alzheimer’s experience worsening memory problems as an early prominent feature.
Stages of Memory Loss
There is a typical progression of memory loss in Alzheimer’s disease:
- Difficulty learning new information
- Forgetfulness about recent events or conversations
- Repeating statements and questions
- Misplacing valuables
- Forgetting appointments
- Getting lost in familiar places
- Trouble recalling personal history
- Confusion about current place and time
Language Difficulties
Another early feature of Alzheimer’s is increasing difficulty with language and communication. This reflects the degeneration of language-related brain areas like the temporal lobe.
Early on, the individual may struggle to find the right words in conversation. They may replace more specific words with generic terms, like saying “stuff” or “thing” instead of the proper word. Other early language difficulties include:
- Problems following conversations or long instructions
- Hesitant, vague language with filler words like “um”
- Unclear logic or disjointed sentences
- Trouble naming familiar objects
As Alzheimer’s advances, spoken and written language become more impaired. The individual eventually loses the ability to engage in meaningful conversation, read, and write. Communication becomes limited to simple words and phrases.
Aphasia
Progressive loss of language abilities in Alzheimer’s is known as aphasia. This reflects gradual deterioration of language areas in the brain’s left temporal lobe.
Types of aphasia in Alzheimer’s include:
- Receptive aphasia – difficulty understanding spoken or written language
- Expressive aphasia – difficulty producing speech or writing
Aphasia appears relatively early in Alzheimer’s and progressively worsens as neurodegeneration spreads through the temporal lobe.
Impaired Executive Function
Executive functions refer to cognitive skills that control and regulate other mental activities. This includes abilities like planning, organizing, decision-making, multi-tasking, and inhibitory control.
Impairment in executive function emerges in the early stages of Alzheimer’s disease. This reflects the early impact of Alzheimer’s pathology on brain regions like the prefrontal cortex, responsible for executive abilities.
Signs of executive dysfunction in early Alzheimer’s include:
- Difficulty planning and organizing tasks
- Problems with abstract thinking or logic
- Getting distracted easily
- Trouble holding information in mind
- Decreased ability to multitask
- Getting stuck on certain thoughts or behaviors
Declining executive function contributes to difficulties with complex tasks like managing finances, cooking, driving, and adherence to medication regimens. It also impairs judgment and decision-making.
Dysexecutive Syndrome
The pattern of executive deficits in Alzheimer’s is sometimes termed dysexecutive syndrome. Key features include problems with cognitive flexibility, abstract reasoning, inhibition, and short-term memory.
Dysexecutive syndrome interferes with the individual’s ability to initiate, plan, sequence, monitor, and inhibit their thoughts and behaviors. This progressively worsens through the course of Alzheimer’s disease.
Visual-Spatial Disturbances
Another mental faculty affected relatively early in Alzheimer’s is visual-spatial ability. This refers to skills in processing visual information and navigating physical spaces.
Early visual-spatial symptoms of Alzheimer’s include:
- Difficulty recognizing faces or common objects
- Problems perceiving depth and distances
- Issues with spatial orientation and getting lost
- Inability to process visual information as quickly
- Impaired ability to visualize images in the mind
These deficits reflect disturbed functioning of visual areas in the brain’s occipital and parietal lobes. Visual-spatial impairment contributes to many functional problems in Alzheimer’s, like getting lost, misinterpreting surroundings, and difficulty driving.
Simultanagnosia
A specific visual-spatial disorder called simultanagnosia is common in Alzheimer’s disease. This refers to difficulty perceiving multiple objects in a visual field at the same time.
For example, an individual with simultanagnosia may see a fork but miss the related plate and food items on a dinner table. Or they may see a dog but not process the surrounding yard or street.
Simultanagnosia worsens as Alzheimer’s progressively damages occipital and parietal lobe areas.
Impaired Reasoning and Judgment
Alzheimer’s disease also progressively impairs abilities like reasoning, problem-solving, and judgment. These skills rely heavily on executive functioning and memory.
Early in Alzheimer’s, the individual may show changes like:
- Poor judgment and illogical decision making
- Trouble following logical steps to complete tasks
- Difficulty recognizing a problem or crisis situation
- Problems grasping risk or consequences in decision making
- Rigid or inflexible thinking
Impaired reasoning and judgment reflects deficits in frontal lobe regions important for planning, foresight, and higher-order cognition. This worsens through the course of Alzheimer’s.
Anosognosia
Many individuals in the early stages of Alzheimer’s also experience anosognosia – reduced insight into their own cognitive deficits. For example, they may be unaware of or minimize their growing memory problems and functional impairments.
Anosognosia is due to damage to prefrontal cortex regions involved in self-appraisal and metacognition. It contributes to impaired judgment and safety risks in early stage Alzheimer’s.
Changes in Mood and Personality
Alzheimer’s disease also commonly causes changes in mood and personality in the early stages. The person may become increasingly moody, withdrawn, irritable, anxious, or depressed.
Specific signs can include:
- Apathy and loss of interest in usual activities
- Social withdrawal or loss of interest in relationships
- Mood swings between calmness and agitation
- Anxiety or feelings of sadness
- Irritability and frustration
Mood changes occur partly as a response to the Alzheimer’s diagnosis and progressive decline in function. But they also reflect pathological changes in brain regions that regulate mood and behavior, like the hippocampus, amygdala, and frontal lobes.
Frontotemporal Dementia vs. Alzheimer’s
While mood changes can happen in Alzheimer’s, dramatic changes in personality, emotions, and behavior are more characteristic of frontotemporal dementia. This is another common cause of dementia producing distinct patterns of neurodegeneration.
Motor Impairments
Though not as prominent as cognitive changes, Alzheimer’s disease can also lead to progressive issues with motor function and coordination. This reflects the growing impact of Alzheimer’s pathology on motor regions of the brain cortex.
Motor symptoms in early stage Alzheimer’s can include:
- Subtle clumsiness or coordination issues
- Slower gait and reduced stability
- Shuffling walk rather than fluid strides
- Difficulty initiating voluntary movements
- Tremors or shaking of limbs
- Reduced facial expressions or gesturing
Severe motor impairment emerges in later stage Alzheimer’s, with symptoms like immobility, rigidity, and loss of swallowing ability.
Parkinson’s vs. Alzheimer’s
Parkinson’s disease also involves motor impairment, but from degeneration of subcortical motor pathways. Tremors and rigidity are hallmark initial symptoms of Parkinson’s, contrasting with Alzheimer’s.
Sleep Disturbances
Sleep-wake disturbances frequently occur in early stage Alzheimer’s as well. This reflects degeneration of brainstem nuclei that regulate sleep-wake timing.
Common sleep disorder symptoms include:
- Excessive daytime drowsiness
- Frequent nighttime awakenings
- Altered night-day sleep patterns
- Sundowning with confusion/agitation at night
- REM sleep behavior disorder
Sleep problems worsen as Alzheimer’s progresses, further disrupting the circadian rhythm. Maintaining a consistent sleep schedule can help manage some of these disturbances.
REM Sleep Behavior Disorder
REM sleep behavior disorder involves acting out vivid dreams during REM sleep. It stems from dysfunction in brainstem regions that induce muscle paralysis during REM sleep.
REM disorder can appear early in Alzheimer’s. It can cause injury to patients or bed partners from uncontrolled, sometimes violent limb movements while dreaming.
Attention and Concentration
Impairments in attention and concentration also emerge early in Alzheimer’s disease. These skills rely heavily on intact executive functions and alertness mechanisms mediated by frontal and parietal brain networks.
Signs of early impairment include:
- Shortened attention span
- Distractibility and difficulty staying on task
- Wandering or loss of goal-directed behavior
- Difficulty filtering out excess stimuli
- Problems sustaining focus for reading or conversations
Attention deficits worsen through Alzheimer’s progression, severely limiting meaningful interaction with the environment.
ADD vs. Alzheimer’s
Attention deficits can also occur in conditions like ADD/ADHD. But in Alzheimer’s, attention difficulties reflect progressive neurodegeneration, often accompanying other cognitive impairments.
Conclusion
In summary, while Alzheimer’s disease eventually affects all aspects of mental function, certain faculties are impacted earliest in the disease course. Memory loss and language deficits are typically among the first manifestations. Executive dysfunction, visual-spatial impairment, decreased reasoning abilities, and mood/personality changes also emerge relatively early. Recognizing this typical profile of cognitive decline facilitates prompt diagnosis and management of Alzheimer’s dementia.