Alzheimer's disease (AD) is a progressive neurodegenerative disorder that accounts for 60-80% of dementia cases. It is characterized by the accumulation of amyloid-beta plaques between neurons and neurofibrillary tangles of tau protein within neurons, beginning in the medial temporal lobe (especially the entorhinal cortex and hippocampus) and spreading progressively to other cortical regions. These pathological changes cause synaptic dysfunction and neuronal death, producing the characteristic pattern of cognitive decline.
Cognitive Profile
The earliest cognitive symptom is typically episodic memory impairment — difficulty forming new memories of personal experiences — reflecting hippocampal involvement. As the disease progresses, it affects semantic memory (word-finding difficulties), visuospatial function (getting lost in familiar places), executive function (poor judgment, difficulty planning), and eventually language, praxis, and basic self-care. The pattern of cognitive decline reflects the anatomical progression of pathology from medial temporal structures to association cortex.
Cognitive psychology research has developed sensitive measures for early detection. Tests of delayed recall (story recall, word list learning) are the most sensitive behavioral indicators. Subtle deficits in spatial navigation, olfactory identification, and metamemory (awareness of one's own memory failures) may precede clinical diagnosis by years. Biomarker research (amyloid PET, CSF markers, blood tests) aims to identify disease before significant cognitive decline, opening a window for early intervention.
Cognitive Reserve
Cognitive reserve theory explains why individuals with more education, occupational complexity, and cognitive engagement show later onset and slower progression of symptoms despite similar levels of brain pathology. Reserve may reflect more efficient neural networks, greater capacity for compensatory processing, or more robust synaptic connections that buffer against pathological damage, highlighting the importance of lifelong cognitive engagement.