Cognitive health is a growing priority as populations age. Distinguishing normal aging from pathological cognitive decline is essential for appropriate management. Dementia is not inevitable — cognitive decline can be slowed through lifestyle and disease management.
Normal Cognitive Aging
Age-related cognitive changes are common and non-pathological. Processing speed slows (the most consistent change). Working memory declines — holding and manipulating information simultaneously becomes harder. Divided attention becomes more difficult. Episodic memory declines — recalling recent events, names, and where objects were placed takes longer. Language: word-finding difficulty increases (tip-of-the-tongue phenomenon), but vocabulary and knowledge are preserved and may improve. Executive function: planning and problem-solving slow. Cognitive reserve — built through education, cognitive engagement, bilingualism, and physical activity — helps compensate for age-related brain changes.
Normal aging does not cause functional impairment, progressive worsening, disorientation to time or place, personality changes, or loss of basic skills. These features suggest pathological cognitive decline.
Mild Cognitive Impairment (MCI)
MCI is an intermediate state between normal cognition and dementia. Cognitive decline is greater than expected for age but does not significantly interfere with daily activities. The amnestic subtype (memory-predominant) has a 10–15% annual conversion rate to Alzheimer disease. Non-amnestic MCI may progress to other dementias. MCI is diagnosed through clinical assessment and neuropsychological testing. Management: treat modifiable risk factors (vascular risk, depression, sleep apnea, vitamin B12 deficiency, hypothyroidism), provide cognitive stimulation, and monitor progression. No medications are FDA-approved for MCI. Aducanumab and lecanemab, anti-amyloid antibodies, may be appropriate for MCI due to Alzheimer disease with biomarker confirmation.
Dementia
Dementia is a syndrome of acquired, persistent cognitive impairment that interferes with daily functioning. It affects 55 million people worldwide.
Alzheimer Disease (AD)
The most common cause of dementia (60–80%). Progressive accumulation of beta-amyloid plaques and hyperphosphorylated tau neurofibrillary tangles. Clinical stages: preclinical (biomarker changes without symptoms), prodromal/MCI due to AD, mild AD (memory loss, difficulty with complex tasks), moderate AD (language impairment, visuospatial deficits, behavioral changes, assistance needed with daily activities), and severe AD (complete dependence, non-verbal, immobility). Diagnosis: clinical history, cognitive testing (MoCA, MMSE), exclusion of other causes, and biomarker testing (CSF amyloid/tau, amyloid PET, tau PET) when diagnosis is uncertain. Symptomatic treatment: cholinesterase inhibitors (donepezil, rivastigmine, galantamine) and memantine. Disease-modifying therapy: lecanemab and donanemab (anti-amyloid monoclonal antibodies) slow cognitive decline by approximately 30% in early AD.
Vascular Dementia
The second most common cause (15–20%). Caused by cerebrovascular disease — multi-infarct dementia, strategic single infarcts, or small vessel disease (cerebral microbleeds, white matter hyperintensities). Onset may be abrupt following a stroke. Stepwise progression. Cognitive domains affected depend on infarct location. Management: aggressive vascular risk factor control (blood pressure, diabetes, lipids, antiplatelets, smoking cessation). No FDA-approved treatments specifically for vascular dementia.
Lewy Body Dementia (LBD)
Characterized by alpha-synuclein aggregates (Lewy bodies) in the cortex and brainstem. Core features: fluctuating cognition, recurrent well-formed visual hallucinations, Parkinsonism (rigidity, bradykinesia, tremor), REM sleep behavior disorder (acting out dreams). Sensitivity to antipsychotics (neuroleptic sensitivity — severe reactions including death). Treatment: cholinesterase inhibitors (rivastigmine is particularly effective for hallucinations and cognition). Avoid typical antipsychotics (haloperidol). Carefully use atypical antipsychotics (quetiapine, low-dose) only for severe behavioral symptoms.
Frontotemporal Dementia (FTD)
Caused by tau or TDP-43 pathology in the frontal and temporal lobes. Behavioral variant: early personality changes, disinhibition, apathy, loss of empathy, compulsive behaviors, and hyperorality. Primary progressive aphasia variants: progressive language impairment. Onset is typically in the 50s or 60s. No disease-modifying treatments. Behavioral management is the mainstay.
Prevention of Cognitive Decline
Modifiable risk factors account for approximately 40% of dementia cases. The Lancet Commission identifies 12 key risk factors: less education, hypertension, hearing loss, smoking, obesity, depression, physical inactivity, diabetes, low social contact, excessive alcohol, traumatic brain injury, and air pollution. Preventive interventions: lifelong learning and cognitive stimulation, blood pressure control (especially midlife), hearing aid use for hearing loss, smoking cessation, maintaining healthy weight, treating depression, regular physical activity (150 minutes/week), managing diabetes, maintaining social connections, limiting alcohol, and protecting against head injury. The FINGER trial (Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability) showed that a multidomain intervention (diet, exercise, cognitive training, vascular risk management) improved or maintained cognitive function in at-risk older adults.
Summary
Cognitive aging varies widely. MCI is an intermediate state with elevated risk of progression to dementia. Alzheimer disease is the most common dementia, with emerging disease-modifying therapies for early stages. Vascular risk factor control prevents both vascular dementia and Alzheimer disease. Delirium is an acute, reversible condition that requires urgent medical evaluation. Prevention through management of 12 modifiable risk factors could prevent or delay up to 40% of dementia cases.