Alzheimer's brain vs. normal brain: What to know

What happens to the brain in Alzheimer’s?

Over time, a brain with Alzheimer’s disease shrinks. Neurons die, and plaques accumulate in areas such as the hippocampus. The brain may change for up to a decade or longer, before symptoms of Alzheimer’s present.

Alzheimer’s disease usually begins in the hippocampus, which is the part of the brain that plays a role in memory and thinking.

Typically, the brain processes a chemical called amyloid precursor protein (APP). However, in Alzheimer’s, APP turns into a protein called beta-amyloid, which the brain does not clear away.

Instead, the proteins form clumps and tangles that stick between and damage the neurons. The clumps of beta-amyloid protein can also destroy connections between the neurons, causing them to die.

People with Alzheimer’s also often have atypical tangles of a protein called tau. This protein usually resides inside the neurons of individuals with healthy brains. Evidence suggests that in Alzheimer’s, beta-amyloid interacts with tau proteins to cause atypical clumps and tangles of the protein. This creates plaques in the brain, which are areas of reduced neurons and brain death.

Beta-amyloid and tau

Researchers are still working to fully understand how tau and beta-amyloid interact and why some people’s brains respond atypically to these proteins.

A 2020 study found that the presence and location of tau protein in the brain may predict future brain damage and help with predicting the course of Alzheimer’s. Drawing on brain scans of 32 people with Alzheimer’s disease, researchers concluded that tau might play a more direct role in brain damage than beta-amyloid.

Additionally, those with Alzheimer’s tend to have brain inflammation, which accumulates as people age but is more severe in dementia.

Some research suggests that this happens because the brain becomes less able to clear waste. In healthy brains, cells called microglia destroy toxins, though the brains of those with Alzheimer’s do not do this as effectively.

A gene called TREM2 instructs microglia to remove beta-amyloid plaques in healthy brains, reducing inflammation. However, issues with the function of this gene can reduce the action of microglia, leading to plaques and inflammation.

While research continues to examine the role of beta-amyloid and tau, researchers have also found plaques and tangles in the brains of people without Alzheimer’s. Moreover, some individuals with dementia symptoms do not have these changes in their brains.

This suggests that a complex interaction of many factors is the cause of dementia. Therefore, it may not always be possible, especially in the early stages of the disease, to distinguish an Alzheimer’s brain from a healthy brain.

Blood flow

In some cases, changes in the brain’s blood vessels and blood flow may increase the risk of dementia. People with strokes due to blood vessel disease in the brain are more likely to develop dementia.

Changes in blood flow can further damage the brain, making it even more likely that the brain has difficulty clearing toxins, which can lead to harmful effects. The protein accumulation that occurs in Alzheimer’s can also affect blood vessels, potentially worsening the damage throughout the brain.

Other types of dementia

Alzheimer’s is the most common type of dementia. A few of the other common types include vascular dementia, frontotemporal dementia, and alcohol-induced dementia. Other types of dementia affect the brain in slightly different ways.

For example, frontotemporal dementia affects the frontal or temporal lobes of the brain. This initially affects behavior, speech, or both. As the disease progresses, it may look more like Alzheimer’s, causing memory loss and other forms of brain dysfunction.

To differentiate Alzheimer’s from other dementias, a doctor may look at a combination of symptoms and brain changes.

Differences in function 

Alzheimer’s fundamentally changes how the brain works. Memory loss is the most noticeable symptom, especially in the early stages. As the disease progresses, it can affect other functions, such as self-care, mood regulation, and skills such as eating.

In the early stages, some differences in brain function may include:

• memory problems that begin as short-term memory difficulties and progress to more serious issues, such as not remembering a loved one
• word-finding difficulties
• frequently losing things
• wandering
• getting lost

Read on to learn more about the early signs of Alzheimer’s.

In the middle stages of the disease, some presentations of brain changes may include:

• sleep difficulties, such as not being able to sleep or wandering at night
• confusion about time and place
• becoming withdrawn or apathetic
• incontinence of the bladder and bowels
• personality changes that may cause suspiciousness, anger, or depression
• delusions and hallucinations

As Alzheimer’s progresses, it begins to affect other areas of functioning, including the brain’s ability to coordinate the body’s functions. Some symptoms may include:

• not being able to engage in self-care such as bathing and getting dressed
• needing help with eating
• problems with physical functions such as walking
• swallowing issues
• organ failure
• frequent infections, such as pneumonia
• death

Alzheimer’s progresses in relatively predictable stages based on how the brain damage progresses. A person in late stage Alzheimer’s will always have great difficulty with basic functions. However, the speed at which someone progresses and the specific symptoms most noticeable in each stage varies from person to person.

Frequently asked questions

Below are answers to common questions about Alzheimer’s and the brain.

How is the Alzheimer’s brain different from the regular brain?

As a person ages, the brain may shrink to some degree. But it does not lose a large number of neurons, and most continue functioning typically.

However, with Alzheimer’s disease, damage results in nonfunctioning neurons that lose connections and eventually die. As such, Alzheimer’s disrupts important neuronal processes vital for communication, metabolism, and repair.

What things trigger Alzheimer’s?

Scientists still do not fully understand the causes of Alzheimer’s. Possible causes a person cannot change include older age, family history, and genetics.

However, factors that may relate to Alzheimer’s that a person can change include avoiding head injuries, maintaining good cardiovascular health, eating a nutritious diet, getting regular exercise, limiting alcohol, and avoiding tobacco.

What are the causes of Alzheimer’s?

Researchers are still investigating the possible causes of Alzheimer’s disease. Currently, evidence suggests that causes may include age-related changes in the brain as well as genetic, environmental, and lifestyle factors.

What is the average age of death from Alzheimer’s?

The life expectancy of someone with Alzheimer’s will vary. This will be due to multiple factors such as age and a person’s general health. Typically, people who are 65 years and older may live for 4–8 years after receiving a diagnosis. However, some individuals with the condition may live for 20 years or more.

Read on to learn more about the progression of Alzheimer’s disease.

Summary

Understanding the differences between the brains of people with and without Alzheimer’s may eventually help researchers discover a cure. Current treatments aim to slow Alzheimer’s-related brain changes, such as by slowing the damage to the brain or helping nerve cells better communicate with one another.

However, these treatments do not cure or reverse the condition.

One of the challenges of understanding Alzheimer’s and the brain is that it is difficult to detect changes without invasive testing. Researchers also cannot view all changes until after a person has died.

Additionally, researchers continue to find that there is no clear factor that differentiates a person with Alzheimer’s from one without the disease. This is because some people have plaques and tangles without symptoms, while others have symptoms without brain changes.

Alzheimer’s is a complex disease, and many questions about how it works in the brain remain.