Alzheimer's disease is a brain disorder that slowly destroys memory and thinking skills. Over time, it affects the ability to carry out even the simplest tasks. It's the most common cause of dementia, a general term for a decline in mental ability severe enough to interfere with daily life.

The disease is progressive, meaning symptoms develop gradually and become more severe. It's not a normal part of aging, though the greatest known risk factor is increasing age.

To understand Alzheimer's, we need to look at what's happening on a microscopic level. The disease is characterized by two main culprits: amyloid plaques and neurofibrillary tangles. These two abnormal protein structures disrupt the work of neurons, the specialized cells that process and transmit information.

Beta-amyloid is a protein fragment that, in a healthy brain, is broken down and eliminated. In Alzheimer's, these fragments clump together to form hard, insoluble plaques between the neurons. These plaques can block cell-to-cell signaling at synapses, and they may also trigger inflammation.

The other culprit is neurofibrillary tangles. These are abnormal accumulations of a protein called tau that collect inside neurons. In a healthy brain, tau helps stabilize microtubules, which are like tiny railway tracks that transport nutrients and other essential materials throughout the cell.

In Alzheimer's, tau proteins change shape and organize themselves into twisted strands, or tangles. These tangles disrupt the transport system and are toxic to the cells, eventually leading to neuron death. As neurons die, the brain begins to shrink, a process called brain atrophy.

Alzheimer's primarily affects older adults. In the United States, about 6.9 million people aged 65 and older are living with Alzheimer's dementia. The prevalence increases significantly with age; more than 70% of those with the disease are 75 years old or older.

The initial symptoms of Alzheimer's can be subtle. One of the most common early signs is difficulty remembering new information. This is because the disease often begins by damaging the parts of the brain involved in learning and memory.

As the disease progresses, other symptoms appear. These can include:

• Challenges in planning or solving problems: Some people may experience changes in their ability to develop and follow a plan or work with numbers. They might have trouble following a familiar recipe or keeping track of monthly bills.
• Difficulty with familiar tasks: Everyday tasks can become challenging. A person might have trouble driving to a familiar location or remembering the rules of a favorite game.
• Confusion with time or place: People with Alzheimer's can lose track of dates, seasons, and the passage of time. They may sometimes forget where they are or how they got there.

Now, let's test your understanding of these fundamental concepts.

Recognizing the biological basis and early signs of Alzheimer's is the first step in understanding this complex condition.