Dementia & Cognitive Decline Quiz

Dementia Overview

• Dementia is a decline in cognitive ability over time, impacting daily activities, primarily affecting memory.
• Significant cognitive impairment hinders routine tasks.
• Dementia involves cellular inclusions and extracellular protein accumulation, with varying glial and microglial activation.

Learning Outcomes

• Review the pathophysiology and risk factors of dementia types
  • Alzheimer's Disease
  • Vascular Dementia
  • Lewy Body dementia
  • Frontotemporal Dementia
  • Parkinson's Dementia
• Critique the modifiable risk for dementia: hearing impairment.
• Hypothesize the pathophysiology of traumatic brain injury and its relation to dementia etiology.
• Critique the connection between gut microbiome and the pathophysiology of dementia.

Risk Factors

• Early Life (Under 45 years): Lower education levels impact cognitive reserve.
• Midlife (45-65 years) & Later Life (Over 65 years): Risk factors further impact cognitive reserve and initiate neuropathological processes.
• Less Education: Cognitive ability typically improves with education, but plateaus in late adolescence, beyond 20 years, gains in cognitive ability is limited with additional education.
• Cognitive Decline: Individuals in cognitively challenging occupations experience less cognitive decline, both before and after retirement.
• Hearing Loss: Hearing impairment in midlife is linked to a more pronounced decline in temporal lobe volume (hippocampus and entorhinal cortex).
• Traumatic Brain Injury (TBI): Solitary and severe TBI is correlated with extensive hyperphosphorylated tau pathology.
• Hypertension: Hypertension (starting age 40) is associated with diminished brain volumes and heightened white matter hyperintensity, with no observed association with amyloid deposition.
• Alcohol Consumption: Consuming over 21 units per week and prolonged abstinence are linked to a 17% rise in dementia risk compared to consuming less than 14 units. Overconsumption of alcohol is linked to right-sided hippocampal atrophy in MRI scans.
• Obesity: Higher BMI is linked to the development of dementia.
• Smoking: Ceasing smoking reduces the risk, with exposure to secondhand smoke associated with greater memory decline. Duration of exposure intensifies the risk.
• Depression: A component of prodrome and initial phases of dementia. Can lead to reverse causation where depressive symptoms may precede dementia.
• Social Isolation: Reduces the cognitive reserve, which is a protective factor for promoting positive behaviors. Reduced social contact raises dementia risk.
• Physical Inactivity: Individuals may discontinue exercise due to dementia's early signs, and this is a risk factor for individuals with cardiovascular morbidity.
• Air Pollution: Airborne particulate pollutants expedite neurodegenerative processes, influencing cerebrovascular and cardiovascular diseases, Aβ deposition, and amyloid precursor protein processing.
• Diabetes: Type 2 diabetes poses a distinct risk for dementia onset.

Dementia - Pathophysiology

• Degenerative Types: Pathological anatomy is widespread, making it challenging to pinpoint specific areas. Memory impairment is a central feature, occurring with extensive disease in parts of the cerebrum, while the diencephalon's and medial temporal lobe's integrity is fundamental for memory. Language function impairment is closely associated with disease in the dominant hemisphere (frontal, temporal, and parietal lobes). Also, reading and calculation capacity loss relates to posterior lesions of the dominant cerebral hemisphere. Damage to tools, gestures (apraxias), and drawing or constructing simple and complex figures (more frequently right-sided lesions) is related to parietal lobe degeneration. Behavior and personality stability issues are often from frontal lobe degeneration.
• Cerebral Disease: Clinical manifestation varies based on lesion location and extent. Diencephalon and basal ganglia implication are also implicated.
• Biochemistry of Proteins: Intracellular and intracytoplasmic inclusions are deeply intertwined with neurodegenerative disorders. Protein homeostasis disruption plays a central role. In neurodegenerative disorders, inclusions compromise native cellular proteins and their stress response conjugates. Cells activate stress responses in presence of damage.
• Accumulations of Proteins: These aggregations obstruct axons, dendrites, hampering cellular protein recycling, and disrupting homeostasis. They create toxic fibrils that perpetuate and intensify cellular stress. Fundamental neurodegenerative diseases revolve around proteostasis.
• Arteriosclerotic Cerebrovascular Disease: Follow a distinct trajectory from neurodegenerative diseases. Involves multiple infarctions, affecting motor, sensory, visual, and association areas. Recurring strokes impair intellectual function, resulting in multi-infarct or vascular dementia.
• Severe Cerebral Trauma: Located in cerebral convolutions (frontal and temporal poles, corpus callosum, and thalamus). Also, there are cases where deep white matter mechanical disruption occurs leading to axonal shearing or diffuse axonal injury. Some dementia cases don't involve brain tissue destruction, but chronic hydrocephalus is frequently linked to cognitive decline due to compression of cerebral white matter.
• Diffuse Inflammatory Process: Inflammatory processes (syphilis, cryptococcosis, chronic meningitides, and viral infections like HIV encephalitis) disrupt neuron function, both due to a reduction in neurons and inflammatory response in remaining neurons.
• Prion Diseases: Are associated with widespread loss of cortical neurons, with spongiform changes leading to distinct cognitive dysfunction patterns. Adult forms of leukodystrophy typically exhibit subcortical dementia with prominent frontal lobe features. Extensive white matter lesions result from advanced multiple sclerosis, progressive multifocal leukoencephalitis, or certain vascular dementias.

Dementia Types

• Alzheimer's Disease (AD): Most common neurodegenerative dementia type. Characterized by abnormal accumulation of ẞ-amyloid and tau proteins. Results in gradual, progressive memory loss, cognitive impairment, and dementia. More prevalent in older people (over 65), but incidence is low under the age of 65 and is highest over 85. Women are affected twice as often as men.
• Pathology of AD: Cortical atrophy is evident with widened sulci and narrowed gyri. Parahippocampal regions are particularly affected. Atrophy intensifies across temporal, frontal, and parietal cortex. Neuritic plaques(senile plaques) are ẞ-amyloid extracellular deposits. They occupy substantial volumes of affected cerebral grey matter. These plaques exhibit reactive astrocytes and microglia, with swollen and distorted neuronal processes (dystrophic neurites). Neurofibrillary tangles are collections of polymerized tau filaments found intracytoplasmically. These filament distributions are associated with the clinical severity of Alzheimer's disease. Tangles in the entorhinal cortex and parahippocampal gyrus can be observed in asymptomatic individuals years before typical AD onset; this suggests early disease stages. Cytopathologic features involve hyperphosphorylated tau protein binding to microtubules. Extracellular amyloid plaques have a ẞ-amyloid core and reactive glial cells. ẞ-amyloid peptides are derived from APP(amyloid precursor protein) through a series of hydrolytic steps by different enzymes. Toxic peptides from the breakdown of this protein aggregate, adhere to receptors causing influx, and causes a triggering of an inflammatory response, resulting in intracellular tangles and eventual cell death.
• Pick Disease (Frontotemporal Lobe Dementia - FTLD): Characterized by abnormal tau accumulation without ẞ-amyloid. It typically starts in the fifth to seventh decades, being nearly as prevalent as AD in this age group. It is initially characterized by disruptive and inappropriate behaviors, in contrast to AD, which starts with memory difficulties. Often hereditary, with up to 40% of cases having a family history of dementia.
• Pathology of Pick Disease: Cortical atrophy is the main feature, primarily in the frontotemporal regions; atrophy can reach sever levels. Affected gyri are reduced to thin slivers—a knife-edge atrophy. Cytopathologic features involve the presence of neuronal cytoplasmic inclusions, known as Pick bodies, which results from the dense aggregation of straight tau filaments.
• Lewy Body Disease (LBD): Presents as either Parkinson's disease and dementia or dementia with Lewy bodies (DLB). The second most common cause of neurodegenerative dementia. Characterized by the widespread involvement of cortical neurons with Lewy body inclusions, but typically having a lack of, or minimal, neurofibrillary tangles or amyloid plaques.
• Pathology of LBD: Lewy bodies are intraneuronal cytoplasmic inclusions, consisting of straight neurofilaments. The inclusions show the presence of epitopes recognized by antibodies against phosphorylated and non-phosphorylated neurofilament proteins, ubiquitin, and a-synuclein. Lewy bodies and Lewy neurites are found in the substantia nigra, amygdala, cingulate gyrus and the neocortex.
• Vascular Dementia: Subset of dementia cases primarily results from one or more symptomatic strokes. Involves multiple infarctions throughout thalami, basal ganglia, brainstem, and cerebrum, affecting multiple areas. Results in strokes, vascular lesions, contribute to impaired intellectual function, resulting in multi-infarct or vascular dementia. This is more commonly prevalent with limited access to medical care.

Hearing Impairment and Dementia

• Sensorineural hearing loss (SNHL) in the elderly is related to age, with varying mechanisms affecting the auditory pathways.
• Brain atrophy is a common factor connecting cognitive decline, Mild Cognitive Impairment, Alzheimer's Disease, and hearing loss.
• A cross-sectional study indicated a decline in cognition with each 10 dB reduction in hearing level, persisting even below clinical thresholds (below 25 dB).
• The theories propose that hearing loss elevates the cognitive load leading to an increase in brain effort to process speech, causing structural changes in the brain and impacting neurodegeneration in working memory. This is connected to a decrease in overall brain volume and primary auditory cortex in the temporal lobe. Impaired activation of auditory-limbic pathway, and atrophy to frontal lobes and hippocampi result from hearing loss.
• Both hearing loss and cognitive impairment likely stem from a shared neurodegenerative aging process in the brain, affecting stria vascularis, hair cells, and primary afferent neurons, and impacting neurotransmitter release.
• Social disengagement arises from issues in communication, from hearing loss, resulting in social isolation, reduced cognitive stimulation, apathy, depression, and potentially increased pro-inflammatory gene expression and impacting brain functions.

Traumatic Brain Injury (TBI) and Dementia

• Severe TBI, particularly recurrent mild TBIs, can trigger prolonged neurodegenerative processes, resulting in pathological features similar to Alzheimer's.
• Determining specific types of post-traumatic dementia remains challenging, though cerebrovascular dysfunction (CVD) plays a crucial role in the onset of dementia.

Gut Microbiome and Dementia

• Accumulating evidence indicates a significant role of intestinal microbiota in initiating and progressing neurodegenerative diseases, with reports highlighting a connection between intestinal microbiota dysfunctions and dementia.
• Mounting data suggests gut microbiota's involvement in various conditions, including obesity, diabetes, cancers, aging, autoimmune diseases, and neuropsychiatric disorders like depression and AD.
• Gut microbiota's impact on AD pathogenesis is recognized through several pathways, which involves abnormalities in Aβ, tau phosphorylation, inflammation, neurotransmitter dysregulation, and oxidative stress.

Post-Assessment MCQs

• MCQ 1: Alzheimer’s disease (AD) is characterized by the accumulation of amyloid plaques and neurofibrillary tangles.
• MCQ 2: Parkinson's dementia is associated with motor symptoms like tremors, rigidity, and bradykinesia.
• MCQ 3: Vascular dementia results from impaired blood flow to the brain (multiple small strokes), resulting in gradual cognitive decline.

References

• Include the provided references in your study notes.

Test your knowledge on the cognitive functions affected by dementia and the factors influencing cognitive health. This quiz covers various types of dementia, risk factors, and the relationship between hearing impairment and cognitive decline. Perfect for students and enthusiasts of neuroscience and psychology.