Caregiver guide
How does Alzheimer's disease affect the brain?
Alzheimer's disease damages the brain by letting two kinds of protein clumps, plaques and tangles, build up and cut the connections between brain cells. The cells stop working and die, the damage spreads outward from the brain's memory center, and over years the brain shrinks, which is why memory goes first and other abilities follow.
Why it helps to understand the brain
When your person asks the same question for the fifth time, accuses you of taking their wallet, or can't figure out how to button a shirt, it's easy to take it personally. Knowing what's happening inside the brain changes that.
These aren't choices. They're symptoms of real, physical damage. Understanding where the damage is can help you respond with more patience, and give yourself a little grace, too.
How a healthy brain works
Your brain has billions of nerve cells, called neurons. Each one connects to many others at tiny gaps called synapses. Neurons send messages across those gaps using chemical messengers. Every memory, thought and movement depends on this network.
Other cells, called glial cells, support the neurons. They feed them, protect them and clear away waste. A huge web of tiny blood vessels brings the oxygen and fuel the brain needs.
Some changes are normal with age, like being a bit slower to learn something new or recall a name. But in a healthy older brain, the network keeps working. In Alzheimer's, it breaks down.
Plaques, tangles and lost connections
Alzheimer's has three main hallmarks:
- Amyloid plaques. A protein called beta-amyloid clumps together between brain cells. These sticky clumps can block messages between cells.
- Tau tangles. Inside healthy neurons, a protein called tau helps hold up the cell's internal "tracks" that carry food and supplies. In Alzheimer's, tau twists into tangles, the tracks fall apart, and the cell starves.
- Lost connections and cell death. As plaques and tangles spread, neurons lose their links to one another, stop working and die.
The brain's clean-up cells also go into overdrive, causing inflammation that may add to the damage. Changes in the brain's blood vessels can make things worse, too.
What part of the brain does Alzheimer's affect first?
Alzheimer's usually starts deep in the brain, in an area called the entorhinal cortex. From there it spreads to the hippocampus, the brain's memory center. The hippocampus is where new experiences get turned into lasting memories.
That's why the first sign is often trouble remembering recent things, like a conversation from this morning or where the keys went, while memories from decades ago stay clear.
These changes can begin 10 to 20 years before anyone notices a symptom. So the brain is the first organ Alzheimer's affects, long before a family sees anything wrong.
How Alzheimer's spreads through the brain, stage by stage
As the disease moves outward, it reaches new brain areas, and you see new changes at home.
Before symptoms (preclinical). Plaques and tangles are forming, but the person seems fine. This can last for years.
Mild Alzheimer's. Damage spreads into the outer layer of the brain (the cerebral cortex). You may notice getting lost, trouble paying bills, repeating questions, poor judgment, taking longer to do daily tasks, and mood changes like anxiety. This is when most people are diagnosed.
Moderate Alzheimer's. Damage reaches the areas that control language, reasoning, the senses and conscious thought. Your person may struggle to recognize family, follow multistep tasks like dressing, or cope with anything new. Restlessness in the late afternoon, wandering, outbursts, and seeing or believing things that aren't real can appear.
Severe Alzheimer's. Plaques and tangles are throughout the brain, and the brain has shrunk a great deal. Your person can't communicate in words and needs full care. The body is affected too: walking, swallowing and bladder control become very hard.
For a stage-by-stage chart, see the 7 stages on our Alzheimer's and dementia FAQ.
Alzheimer's brain vs normal brain
If you could see the two side by side, you'd notice:
| Healthy older brain | Brain with severe Alzheimer's | |
|---|---|---|
| Size | Full, with tight folds | Much smaller; tissue has shrunk |
| Memory center (hippocampus) | Normal size | Badly shrunken |
| Fluid spaces inside (ventricles) | Small | Much larger, filling space left by lost tissue |
| Nerve cells and connections | Mostly intact | Many lost |
| Plaques and tangles | Few, if any | Spread throughout |
Why does the brain shrink? When neurons die, the tissue they made up is lost. Doctors call this atrophy. Brain scans can sometimes show it while a person is alive.
What these brain changes mean for everyday life
Memory center damaged: repeating questions
New information can't be stored, so your person truly doesn't remember asking. Answer kindly, or write the answer on a note they can see.
Language areas damaged: lost words
Your person may reach for words and come up empty. Give them time, offer a guess, and watch their face and gestures.
Judgment and planning areas damaged: risky choices
Money mistakes and unsafe decisions aren't carelessness. It may be time to quietly take over bills or the car keys.
Vision and space areas damaged: confusion with objects
Trouble judging steps, finding a chair or using a fork can come from the brain misreading what the eyes see. Good lighting and plain, contrasting colors help.
Emotion areas affected: feelings stay strong
Even when facts are gone, feelings remain. Your person may forget the visit but remember feeling loved.
Questions about Alzheimer's and the brain
Why does my person remember the past but not this morning?
Alzheimer's damages the hippocampus first, and that's the part that makes new memories. Old memories are stored more widely across the brain, so they last longer. That's why your person may tell detailed stories from childhood but not know you visited yesterday.
Does Alzheimer's affect the brain stem?
The brain stem controls automatic functions like breathing, heart rate, swallowing and sleep. It's affected later than the memory areas. In the late stage, problems with swallowing, sleep and other body functions become more common as damage spreads.
How does Alzheimer's affect the nervous system and the body?
Alzheimer's is a disease of the brain, which is the control center of the nervous system. Early on, it mainly affects thinking. As it spreads, it reaches areas that control movement, balance, bladder and bowels, and swallowing, which is why the late stage affects the whole body.
Can the brain damage from Alzheimer's be reversed?
Not at this time. Brain cells that have died can't be brought back. Some medicines may help symptoms for a while, and some newer treatments may slow decline for certain people in the early stages. Ask the doctor what fits your person. Learn more in What is Alzheimer's disease?
Is the brain damage different in other types of dementia?
Yes. Vascular dementia comes from damage to blood vessels, Lewy body dementia from a different protein, and frontotemporal dementia starts in the front and sides of the brain. That's why symptoms differ. See our guide to the types of dementia.
Is Alzheimer's inherited from the mother or father?
Genes can come from either parent. Most Alzheimer's isn't directly inherited, though some genes raise the risk. Read Is Alzheimer's genetic? for what that means for your family.
Why is brain donation important for Alzheimer's research?
Much of what scientists know about plaques and tangles came from studying donated brains. Brain donation also lets families learn exactly what disease their person had. ADRC coordinates enrollment in the State of Florida Brain Bank for Central Florida families, and families receive a report of the findings.
You don't have to understand it all alone
The science is a lot to take in, especially on top of daily caregiving. Our free education workshops explain brain changes in plain language and show you practical ways to respond. A caregiver support group is a place to talk with people who see the same changes at home, and a Care Navigation session can help you plan for what's ahead.
Download Alzheimer's Disease: Unraveling the Mystery
An illustrated book from the National Institute on Aging that shows how the healthy brain works and what changes in Alzheimer's. Based in part on National Institute on Aging guidance.
Alzheimer's & Dementia Resource Center (ADRC)
Alzheimer's & Dementia Resource Center (ADRC)
1470 Gene Street, Winter Park, FL 32789
Serving Orange and Seminole counties and Central Florida since 1984
(407) 436-7750
info@adrccares.org
Monday to Friday, 8:30 AM to 4:30 PM
The Alzheimer's & Dementia Resource Center (ADRC) in Winter Park, Florida, offers free help for caregivers in Orange and Seminole counties; call (407) 436-7750.