In 1906, Dr. Alzheimer noticed changes in the brain tissue of a woman who had died of an unusual mental illness. Her symptoms included memory loss, language problems, and unpredictable behavior. After she died, he examined her brain and found many abnormal clumps (now called amyloid plaques) and tangled bundles of fibers (now called neurofibrillary, or tau, tangles).
These plaques and tangles in the brain are still considered some of the main features of Alzheimer’s disease. Another feature is the loss of connections between neurons in the brain. Neurons transmit messages between different parts of the brain, and from the brain to muscles and organs in the body.
During the very early stage of Alzheimer’s, toxic changes are taking place in the brain, including abnormal buildups of proteins that form amyloid plaques and tau tangles. Previously healthy neurons stop functioning, lose connections with other neurons, and die. Many other complex brain changes are thought to play a role in Alzheimer’s as well.
The damage initially appears to take place in the hippocampus and the entorhinal cortex, which are parts of the brain that are essential in forming memories. As more neurons die, additional parts of the brain are affected and begin to shrink. By the final stage of Alzheimer’s, damage is widespread and brain tissue has shrunk significantly.
Memory problems are typically one of the first signs of cognitive impairment related to Alzheimer’s. Some people with memory problems have a condition called mild cognitive impairment (MCI). With MCI, people have more memory problems than normal for their age, but their symptoms do not interfere with their everyday lives. Movement difficulties and problems with the sense of smell have also been linked to MCI. Older people with MCI are at greater risk for developing Alzheimer’s, but not all of them do so. Some may even revert to normal cognition.
The first symptoms of Alzheimer’s vary from person to person. For many, decline in nonmemory aspects of cognition, such as word-finding, vision/spatial issues, and impaired reasoning or judgment may signal the very early stages of the disease. Researchers are studying biomarkers (biological signs of disease found in brain images, cerebrospinal fluid, and blood) to detect early changes in the brains of people with MCI and in cognitively normal people who may be at greater risk for Alzheimer’s. More research is needed before these techniques can be used broadly and routinely to diagnose Alzheimer’s in a health care provider’s office.
As Alzheimer’s worsens, people experience greater memory loss and other cognitive difficulties. Problems can include wandering and getting lost, trouble handling money and paying bills, repeating questions, taking longer to complete normal daily tasks, and personality and behavior changes. People are often diagnosed in this stage.
In recent years, scientists have made tremendous progress in better understanding Alzheimer’s and the momentum continues to grow. Still, scientists don’t yet fully understand what causes Alzheimer’s disease in most people. In people with early-onset Alzheimer’s, a genetic mutation may be the cause. Late-onset Alzheimer’s arises from a complex series of brain changes that may occur over decades. The causes probably include a combination of genetic, environmental, and lifestyle factors. The importance of any one of these factors in increasing or decreasing the risk of developing Alzheimer’s may differ from person to person.
For more information about Alzheimer’s disease
NIA Alzheimer’s and related Dementias Education and Referral (ADEAR) Center
The NIA ADEAR Center offers information and free print publications about Alzheimer’s and related dementias.
Explore the Alzheimers.gov portal for information and resources on Alzheimer’s and related dementias from across the federal government.
This content is provided by the NIH National Institute on Aging (NIA). NIA scientists and other experts review this content to ensure it is accurate and up to date.