Alzheimer's Brain: What Happens In A Brain With Alzheimer's Disease?

By Patricia Oelze|Updated January 30, 2020
CheckedMedically Reviewed By Erika Schad, LCP, CWLC

Aging brings with it many physical, cognitive, and even emotional changes. Of concern for many people is the increased risk of health problems and certain ailments. While some of these can be treated and managed with medical care, dementia and Alzheimer's Disease are two conditions that are not so easily addressed. Both conditions involve changes in the brain that affect memory and cognitive functioning.

Learn more about the condition of Alzheimer's and what happens in a brain with Alzheimer's Disease:


Normal Brain Vs. Alzheimer's Brain

You likely know that the brain is the most powerful and arguably the most important organ in your body. This is because it runs all the other parts of your body, allows for the ability to think, retains your memories, and governs your personality. The average brain weighs approximately three pounds. Its texture is similar to a firm jelly substance. It is comprised of three main parts:

  • The cerebrum is the largest part of the brain. It is the part that controls cognitive functions such as problem-solving, remembering, thinking, and feeling. It also controls the ability to move.
  • The cerebellum is located at the back of the head, just below the brain. It controls the ability to balance and controls general coordination.
  • The brain stem is located below the cerebrum and in front of the cerebellum. It serves to connect the brain and spinal cord. It controls important automatic body functions. These include breathing, heart rate, blood pressure, and digestion.

Like the other parts of your body, your brain is given oxygen from your blood. In fact, with every heartbeat, the arteries carry approximately 20 to 25 percent of the blood in the body to the brain. The brain has billions of cells that need a good portion of the oxygen found in the blood. Ultimately, on average, your brain uses 20 percent of the oxygen available in the blood. When you are intently concentrating, your brain will use up to 50 of the oxygen flowing through your body.

All that oxygen is needed because of the billions of cells in your brain an important job. Those brain cells are constantly working to keep you alive and carry out various cognitive processes. In fact, various specific parts of the brain are dedicated to different processes. There are parts of the brain that perceive outside stimuli, other parts interpret the sensations received, other parts make plans, other parts initiate action, and other parts move the body to perform actions.

Of particular importance in dementia and Alzheimer's Disease, the hippocampus is a part of the brain that transfers information into long-term memory. It is a part of the limbic system of the brain that assists with the transfer of information and formation of memories. Memories are stored in the temporal lobes of the brain. Damage to the hippocampus can impair the ability to form memories.

How Does Alzheimer's Affect The Brain?


No matter what part of the brain is in action, the work of the brain is done by individual cells. These nerve cells or neurons are connected by branches. The branches are technically called axons. Signals can travel along these axons to carry messages from one neuron to another in the network. Unfortunately, in a brain with Alzheimer's Disease, the neurons become damaged and eventually destroyed. This disrupts and impairs the way that signals can move through the brain.

Researchers think this neuron damage happens because of two processes. One is the formation of neurofibrillary tangles. These are made up of twisted strands of the protein tau. The tau is supposed to be in lines or tracks for the transport of nutrients. However, it collapses into the tangles.

This means that nutrients can no longer go to the nerve cells, which causes them to die. Second, beta-amyloid plaques, which are abnormal clusters of protein fragments, also build up between the brain's nerve cells. Research indicates these plaques seem to block the signaling in the brain's nerve cells.

Scientists are not entirely sure what causes all these changes. However, some changes appear to be the result of genetic and environmental factors. For example, research shows that a genetic mutation increases risk. Studies have also found that a head injury sustained earlier in life may also increase the risk of developing Alzheimer's Disease.

What Part Of The Brain Does Alzheimer's Affect?

As noted above, the hippocampus is the part of the brain responsible for putting information into long-term memory. In fact, this part of the brain is necessary for this process. If the hippocampus becomes damaged, it severely affects memory. Generally, after hippocampal damage, people are unable to form new memories. This can result in individuals living in the past if they still have the ability to access old memories. Consequently, this can result with individuals living in only the present, as they may immediately forget information.

Alzheimer's disease is the single most common cause of dementia and, according to the DSM-5, accounts for 60 to over 90% of all cases. Alzheimer's Disease affects the hippocampus first. This part of the brain is also the most severely affected by the condition. Alzheimer's disease then moves through stages with symptoms worsening over time, as the neuron damage spreads throughout the cortex of the brain. This is why memory is the first cognitive function to be affected in an Alzheimer's Disease brain, and over time other functions are also affected as the damage increases to eventually affect all parts of the brain.

Over time, as more parts of the brain are affected, there will be nerve cell death throughout the brain. There will also be tissue loss that increasingly spreads throughout the brain. As a result of these changes, the brain shrinks over time. This makes the brain appear to shrivel up. This happens first in the hippocampus, which affects memory functioning. It also happens in the cortex, which affects thinking and planning. Meanwhile, the ventricles of the brain, which are fluid-filled spaces, grow larger.

How Is Alzheimer's Disorder Diagnosed?


As neurons send signals to the brain,it leads to thoughts and behaviors. This neuronal firing also creates memories and plays a role in the display of personality. Neurons often fire in patterns for certain activities. These patterns can be seen on brain scans, such as a Positive Emission Tomography Scan (or PET Scan as it is called for short). If someone's brain is scanned while they do different activities (such as reading versus solving math problems) different patterns of activity can be observed.

Dementia or Alzheimer's brain scan would show different patterns in an Alzheimer's brain versus a normal brain. This is because of the changes in neuron function, due to the damage from the plaques and tangles that have been building up in the brain. During the early stages of Alzheimer's Disease, the activity of the brain may appear different around the hippocampus, and that spreads over time.

However, Alzheimer's Disease cannot be diagnosed from a brain scan alone. This is because other disorders and conditions could also account for those changes in brain activity. In fact, there is no definitive way to diagnose Alzheimer's Disease while a person is alive. Instead, doctors do many tests and assessments to rule out other potential problems. When no other diagnosis fits the symptoms, then a diagnosis of Alzheimer's Disease can be used to label the condition. Genetic testing may also show a genetic mutation that could support the diagnosis, although that is also not definitive.

After death, as part of an autopsy, if doctors suspect Alzheimer's Disease, they can examine slices of the brain under a microscope. When this is done, the doctor may observe fewer nerve cells and synapses than is typical. They may also see the tangles and plaques that are so indicative of the disease.



Aging naturally causes some changes in physical and cognitive functioning for everyone. However, if you notice symptoms such as great difficulty recalling information and difficulty finding words/speaking, it could be a sign of more serious dementia or Alzheimer's Disease. When you notice such symptoms, it is important to visit a doctor for a medical evaluation. They will want to assess your physical, cognitive, and psychological symptoms to make a diagnosis and to determine the right treatments.

Suspecting a diagnosis of dementia or Alzheimer's Disease can be upsetting. Once confirmation of a diagnosis is received, there can be grief, anxiety, and depression about the situation. Someone in this situation may seek out therapeutic support to help them adjust and cope. Frequently, those with dementia and Alzheimer's Disease will eventually rely on family members as caregivers. It is usually the case that caregivers could also benefit from the support of counseling.

Trained counselors can help seniors, and their caregivers deal with the logistical and emotional changes that occur during even typical aging. Such supports can help people maintain their independence and quality of life. If you are struggling with age-related changes or you are managing a caregiving role, you can seek out local help or online counseling. Many people now prefer to utilize therapy through online platforms. This allows anyone to access the help they want in a convenient format.

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