When a person has Alzheimer’s disease or another related dementia, there are noted changes that occur within the brain. These changes are both structural and chemical, and they impact one another to reinforce the damage to the brain. Said another way, most changes in the brain are not the result of one or the other, but a combination of both chemical and structural changes. As the disease progresses, the changes will affect the person’s ability to function as they once did. The individual will have difficulty with their speech, memory, reasoning, and at some point, will lose the ability to function independently.
With the progression of dementia, parts of the brain are damaged. Cells within the brain die, brain tissue is lost, and the overall size of the brain shrinks. The brain of a person in the latest stages of dementia may be 1/3 the size of the brain of an individual without dementia.
The brain is made up of three main parts: the cerebrum, the cerebellum, and the brain stem, which receive oxygen and blood through a network of blood vessels. These components are what we conceive of as separate regions of the brain, due to each region’s unique responsibility for various day-to-day tasks essential for normal functioning. Furthermore, the right side of the brain and the left side of the brain control various functions, including language and movement.
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 that is 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.
Protein clusters, known as “plaques,” gather between nerve cells, and twisted strands of protein, known as “tangles,” gather inside nerve cells. (The protein clusters that gather between nerve cells are called beta-amyloid plaques and the protein that forms inside nerve cells is called tau tangles). Plaques and tangles begin to form in areas of the brain where memory, learning, and thinking occur, and continue to affect other parts of the brain, causing damage to the brain and nerve cells.
During mild to moderate stages of dementia, the plaques and tangles then spread to areas of the brain responsible for communication (speech) and spatial perception. During this time, issues with memory and thought process will typically become apparent, either to the person with dementia, their loved ones, or both. Following these changes, personality and behavior may also become affected.
Inflammation is a normal response to trauma. However, the level of inflammation in an Alzheimer’s brain is excessive and counter-productive, leading to more cell deaths. Such inflammation causes the death or nerve cells, and may also increase tangles.
Within the different regions of the brain, work is being done 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, which carry signals to the brain, are destroyed, signals transmitted between brain cells carried between synapses by neurotransmitters are interrupted, and connections between nerve cells of the brain become interrupted.
Beta-Amyloid Plaques and Tau Tangles
Two toxic proteins appear to be responsible for the cellular brain damage: beta-amyloid and tau. In the initial event that leads to AD, part of the neuron that normally helps promote neuron growth and survival breaks down in an abnormal way to produce a toxic protein called beta-amyloid. Beta-amyloid plaques, which are found 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 of the neurotransmitters are produced and communication between neurons is decreased. 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 due to the damage caused by beta-amyloid plaques and tau tangles.
With the progression of Alzheimer’s disease, the brain shrinks and the individual’s level of functioning on nearly all levels is compromised. One of the big affects of brain changes associated with dementia is an issue with memory. This may include progressive memory loss, lack of orientation to time and place, inability to recall relationships and memories, “confabulation,” or narrative of things that have not occurred, and surfacing of memories from long ago and thinking they are present or relative to the present.
Another big affect of these brain changes is the ability of speech, which encompasses 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 affects of brain changes. In the final stage of dementia, an individual will often lose the ability to communicate and they may no longer able to recognize their loved ones.