How Structural & Chemical Changes in a Brain with Alzheimer’s Affects Level of Functioning

Last Updated: June 03, 2021


When a person has Alzheimer’s disease or another related dementia, there are noted changes that occur within the brain. These changes are structural and chemical.

Structural: Brain cells die and brain tissue is lost. The overall size of the brain shrinks.
Chemical: Tiny electrical signals between the cells become weak and break down.

These changes reinforce one another, so damage to the brain is both chemical and structural. As the disease progresses, the individual loses the ability to function like someone who is healthy. The breakdown of cells and their ability to communicate makes thinking more difficult as bodily functions become harder to control. The individual will have difficulty with speech, memory, reasoning, and eventually loses the ability to be independent because activities of daily living (ADLs) like getting dressed or eating become too hard.


Structural Changes to the Brain

Alzheimer’s, vascular, frontotemporal, Lewy body, and other dementias are progressive diseases, meaning they get worse over time. As dementia progresses, parts of the brain are damaged. Cells within the brain (neurons) die, brain tissue is lost, and the overall size of the brain shrinks. The brain of a person in the late stages of dementia may be 1/3 the size of the brain of an individual without dementia. Gaps between folds in the brain are also significantly wider for a person with dementia.

In healthy brains, the neurons are constantly repairing themselves to maintain the ability to transmit messages for thoughts and movement. In brains with dementia, however, damaged neurons stay damaged. Often, a brain with dementia can’t receive its normal amount of blood and oxygen. Metabolism, which is the ability to break down nutrients and chemicals into energy, breaks down significantly.

 Watch a brief video that shows the differences between a normal brain and the brain of a person with dementia.


Main Parts of the Brain

The brain is made up of three main parts: the cerebrum, the cerebellum, and the brain stem. These components receive oxygen and blood through a network of blood vessels. Because each region has a unique job that makes us able to function and do various day-to-day tasks, we see them as separate.

– Cerebrum: The part that fills most of the skull and is traditionally pictured when we think of a brain. It does the thinking. More generally, the cerebrum controls memory, problem solving, feelings, and movement.
– Cerebellum: Located under the cerebrum in the backs of our heads, the cerebellum controls balance and coordination.
– Brain stem: Under the cerebellum, the brain stem connects our brains to our spinal cords. Automatic body functions like breathing, heartbeat, and digestion are controlled by the brain stem.

The cerebrum contains the cerebral cortex, which has four lobes: frontal, parietal, temporal, and occipital. The hippocampus, located within the temporal lobe, is responsible for making new memories and is often one of the first areas of the brain damaged by dementia. The outer layer of the cerebellum is the cortex, which is involved with memory, interpretation of sights and sounds, and thought generation.



Inflammation is a normal response to trauma. However, the level of inflammation in a brain with dementia is excessive and counter-productive:. The deaths of cells causes inflammation, and that inflammation in turn causes more cells to die. And inflammation not only damages and kills nerve cells, it may also increase tangles and the buildup of proteins described in Chemical Changes below. Those tangles and proteins cause all sorts of mental and physical impairments, and are believed to be the main cause of Alzheimer’s disease and related dementias.


Chemical Changes to the Brain

Within the different regions of the brain, the work of forming thoughts and moving our bodies happens on a cellular level. Chemically, tiny electrical charges or “signals” move through individual cells and parts of the brain. When these processes are compromised, so too are basic brain tasks, such as thinking, feeling, and forming and recalling memories.

In an individual with dementia, neurons carrying signals to and from the brain are destroyed. Signals transmitted between brain cells carried by neurotransmitters are interrupted, and connections between nerve cells of the brain become broken. This is why someone with dementia has problems with thoughts and movement: The communication between cells in their bodies has broken down.

Beta-Amyloid Plaques and Tau Tangles
Two toxic proteins appear to be responsible for the cellular brain damage: beta-amyloid and tau.

When Alzheimer’s disease begins to develop, part of the neuron that normally helps promote cell growth and survival breaks down in an abnormal way and begins producing a toxic protein called beta-amyloid. Beta-amyloid plaques, which form between neurons, damage neurons in at least two ways: They affect the neuron’s receptor for a particular neurotransmitter, and that, in turn, interferes with the cell’s ability to function and send messages to other neurons.

Beta-amyloid also interferes with another protein that is important for neurons to respond to signals in the hippocampus, a part of the brain that is very important in memory. As the neuron’s function is reduced, less neurotransmitters are produced, and communication between neurons decreases. Tau tangles (strands of protein that are twisted) are found inside the neurons and also contribute to cell death, blocking cells from receiving needed nutrients. Eventually, brain cells die from the damage caused by beta-amyloid plaques and tau tangles.

Changes caused by these plaques and tangles become most pronounced in the middle stages of dementia, usually after two or three years, when they have spread enough to begin impairing speech and spatial perception. During this time, issues with memory and thought process will become outwardly apparent, either to the person with dementia, their loved ones, or both. Following these changes, personality and behavior may also become affected.


Effect of Brain Changes on Functioning

With the progression of Alzheimer’s disease, the brain shrinks and the individual’s ability to function on nearly all levels is compromised. One of the big effects of brain changes associated with dementia is memory problems. This may include progressive memory loss, lack of orientation to time and place, inability to recall relationships, “confabulation” (remembering or believing things that have not occurred), and the belief that memories from long ago are present or relatively recent.

Another big effect of these brain changes is speech problems, including difficulty finding the correct words to use, vagueness of speech, very limited language ability, and garbled speech.

Changes in personality and behavior, inability to organize thoughts, and difficulty or inability to perform daily living activities are also common effects of brain changes. In the final stage of dementia, an individual will often lose the ability to communicate and they may no longer be able to recognize their loved ones.

  Communicating with someone with Alzheimer’s disease can be challenging. Click here to learn how to communicate with someone with dementia.