Alzheimer's disease is a progressive brain disorder and a form of dementia that impacts memory, thinking and behavior. As symptoms grow more severe, the disease can seriously affect a person's ability to perform tasks that would otherwise be deemed routine. There is currently no cure for Alzheimer's, but there are medications available that can temporarily delay symptoms.

"Cognitive decline is the first clinical sign [of Alzheimer's]," said Elizabeth J. Coulson, a professor of neuroscience at the Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research at University of Queensland in Australia. "There are degenerative changes that cause cognitive impairment," she told Live Science. "One of the earliest degenerations occurs in the cholinergic neurons of the basal forebrain, which control attention and higher order cognition, and then the entorhinal cortex and hippocampus, which controls memory."

Around six million Americans are currently living with Alzheimer's, according to the Alzheimer's Association. By 2050, that figure is estimated to be closer to 13 million. Alzheimer's is a disease that prominently impacts older people, with 73% of patients age 75 or older. It is also more common in women, with two-thirds of Alzheimer's patients in the U.S. being women.

Brain changes and Alzheimer's disease

The first case of Alzheimer's was described in 1906 by Dr. Alois Alzheimer, a German neurologist. Alzheimer identified two of the disease's key physical traits when he examined a woman's brain tissue under a microscope after her death: He found abnormal protein clumps (now known as amyloid plaques) and tangled bundles of nerve fibers (now called neurofibrillary, or tau, tangles).

However, while many people argue that the amyloid plaques are the cause of the disease, others say they are just a biomarker for the disease showing that other physiological processes are wrong and they (the latter) cause the disease, Carson said.

"Recent FDA-approved drugs act to get rid of the beta-amyloid in the brain," she said. "They do this very well, but the cognitive processes are not improved — only a tiny bit less decline than someone without the drug."

Dr. Bradley Hyman, a neurologist and director of the Massachusetts Disease Research Center at Massachusetts General Hospital in Boston, also said that nerve bundles can build up inside nerve cells, and along with increased numbers of plaques, can block communication between nerve cells.