Why does Alzheimer disease cause memory loss and a decline in thinking skills?

Alzheimer disease causes memory loss and cognitive decline through several interconnected pathological processes in the brain:

• Neuronal Loss: As the disease progresses, there is a significant loss of neurons, leading to a decrease in overall brain size and weight. This loss is particularly severe in the hippocampus, a region essential for forming new memories.12
• Tissue Lesions: The cerebral cortex develops neuritic plaques—deposits of amyloid beta protein—and neurofibrillary tangles, which are twisted fibers of the protein tau inside nerve cells. These lesions are believed to interfere with normal cellular functioning and communication.31
• Neurotransmitter Deficiency: Nerve cells rely on neurotransmitters to communicate. Alzheimer disease is associated with diminished levels of these chemical messengers, most notably acetylcholine, which plays a critical role in memory processes.31

Together, these structural and chemical changes disrupt the brain's ability to process information, retain new memories, and maintain cognitive function.12