ORIGINALLY PUBLISHED BY JOHN SCHMID ON JANUARY 12, 2016
How Alzheimer’s Affects the Brain
To understand why different activities and treatments for dementia work it is beneficial to look at the Alzheimer’s brain, and how the disease affects memory, cognition, perception, and behavior. Different areas of the brain control different functions. As each area is affected, the functions related to that area are lost or hampered.(Click here to see more about Alzheimer’s and dementia.)
We are often asked, “Is dementia part of the normal aging process?”
Age is the number one factor influencing the development of dementia, so the confusion is understandable. Adding to the confusion are those senior moments, when an older gentleman, for example, can’t remember where he left his keys. He usually finds them soon enough and that minor, annoying forgetfulness can be a normal part of aging. Having his keys in his hand and forgetting what they are for is not normal and might be an indication of something more serious.
Our senses also suffer from the process of aging. As we get older our eyes don’t see as far or as clearly as they used to, or without the light being bright. Hearing, taste, our sense of smell; all of our senses become less acute as we grow older. This is the normal wear and tear that years of use bestow upon our sense organs (as well as on the rest of our body).
A person with dementia is most likely older and probably experiences the same age-related deterioration, but in addition the disease is damaging the brain in areas that affect perception. A sensory signal might be getting to the brain, but if the Alzheimer’s brain isn’t processing the signal it can be very difficult to make sense of the world. Perceptual problems caused by dementia are much more pronounced than perceptual problems that result only from the aging process.
So, no! Although dementia seems to be getting more common with time, dementia is not a part of the normal aging process.
Another area of confusion is how exactly dementia affects the brain and behavior. Everyone knows that Alzheimer’s disease causes memory problems, but there is much more. Different types of dementia (there are more than 100) affect the brain differently. Many, including Alzheimer’s will eventually affect virtually every part of the brain and every brain function.
Click Spinning Heads (Below) to Enlarge Image
The hippocampus is responsible for forming memories and for spatial navigation. This is one of the first areas of the brain to be affected by Alzheimer’s disease.
The Alzheimer’s Brain — The Hippocampus
Alzheimer’s disease starts in the hippocampus, deep within and part of the temporal lobe of the brain. The hippocampus is the structure responsible for creating new memories from our experiences. This organ receives input from the various sensory centers of the cortex in the form of perceptions (more about perception later).
These “sensations” are combined by the hippocampus into a complete experience. For example, the perception of an ocean sunset combines a multitude of visual impressions; a vast color palette with numerous shapes (a round red sun, the line of the horizon, purple clouds of all shapes and sizes, etc.). But the experience is more than just visual. The sound of the waves and the gulls flying overhead. The smell and the taste of the salt water and the way the warm breeze feels against your face. You may be enjoying the moment with friends, and this also becomes a part of the overall experience, and of the memory.
It is the hippocampus that sorts and compares these impressions (like the sunset) and creates a memory. Memories at this stage are short-term memories. The hippocampus then decides if a particular memory will be committed to long-term memory.
So it is not surprising that forgetting a recent event (short-term memory) is one of the very first symptoms of this disease. In addition to creating memories, the hippocampus also helps with spatial memory which allows us to navigate our world. Getting lost, even in familiar places, is another early sign of the disease.
The temporal lobes are responsible for encoding language and visual input
The Alzheimer’s Brain — The Temporal Lobes
From the hippocampus the disease moves outward into the cerebral cortex, the outer layer of the brain, beginning in the temporal lobes. The temporal lobes, along with the prefrontal cortex, play an important role in processing sounds and in language comprehension. Communication becomes difficult once this part of the brain in affected. If you have worked with people who have Alzheimer’s disease I am sure you have seen them struggle to find a word, or to string words together into a sentence. This difficulty with language gets more pronounced as the disease moves toward the front of the brain.
The frontal lobes are responsible for voluntary movement and have an important function in memory
The Alzheimer’s Brain — The Frontal Lobes and the Prefrontal Cortex
The frontal lobes and the prefrontal cortex are the parts of the human brain most associated with making us who we are. The frontal lobes lie directly behind the forehead and in large part control voluntary movement like walking and finger tapping. It plays an important role in preserving memories, especially emotion based memories arriving from the brain’s limbic system. The frontal lobe contains the dopamine system which is associated with reward, attention, short-term memory tasks, planning, and motivation. It moderates responses so that our behavior is appropriate and acceptable in social situations.
The prefrontal cortex covers the forward part of the frontal lobes. It is responsible for our executive functioning. Many researchers believe it to be the center of our personality. Executive functions include our ability to differentiate between conflicting thoughts, between good and bad, for example. It is the prefrontal cortex that gives us the ability to choose between alternatives and to make decisions.
The Prefrontal Cortex is the seat of executive functioning
This is the part of the brain that allows us to project possible future outcomes from current actions. Those of you who have raised teenagers know that the prefrontal cortex is not fully developed at that age. ( A little joke, but one based in fact) To a large extent, the prefrontal cortex is the part of the brain that makes us who we are. Most of our conscious thinking is done here. It should be evident that this brain structure is very important to Once Alzheimer’s disease progresses to this point a person will begin to lose the ability to care for himself or herself.
I have been describing the way that Alzheimer’s disease moves through the brain, but the word “moves” is not entirely accurate. “Spreads” would be a better choice. When the disease gets to the front of the brain, for example, it continues to do damage to the hippocampus and the temporal lobes. And it not only damages brain cells, it damages connections. Much of our ability to think and process information is a result of the interconnectedness of all of the different areas of the brain.
From the prefrontal cortex Alzheimer’s disease spreads toward the back of the brain, into the parietal, then the occipital lobes. These structures process much of the information coming in from our sense organs, and when these areas are damaged it becomes harder to make sense of the world. Alzheimer’s is now progressing into its later stages. Language processing, movement, perception, and memory are being radically affected due to the areas of the brain damaged by the disease. At this point safety becomes a primary concern, and the individual needs almost constant care.
The parietal lobes are chiefly responsible for the somatic senses and proprioception
The Alzheimer’s Brain — The Parietal Lobes
Our sense of touch, the somatic sense, is located in the parietal lobe. This structure is responsible for processing information coming in from various receptors under our skin, in our bones and in our organs that collectively make up our sense of touch. “Touch” is not the best word to describe this sense because it includes awareness of sensations like hunger, heat and cold, and the spatial awareness of our bodies (proprioception). Like so many other parts of the brain, the parietal lobes play a role in language processing.
It seems that people in the later stages of dementia can often be engaged through these somatic senses when other sensory stimulation fails. This has given rise to a category of therapy that we call Comfort Care. Comfort Care includes dolls and stuffed animals, soft gloves and socks containing skin conditioners, and items containing attachment to be “fiddled” with.
The occipital lobe is responsible for processing information coming from the eye
The Alzheimer’s Brain — The Occipital Lobes
The occipital lobes contain the visual cortex, responsible for processing information coming from the eyes. Damage to the occipital lobe compromises visual perception, and often causes visual hallucinations. Hallucinations of any of the senses can occur with dementia.
A dark tile in this patterned floor can become a hole, an obstacle to avoid. A mis-perception that may cause a fall
Compromised visual perception doesn’t just result in poor vision or blindness, or in hallucinations, though those are all possible outcomes. Perceptual problems can cause an alternating pattern in carpeting or tile to be interpreted a holes in the floor. A beautiful bathroom like the one pictured here can become an obstacle course. Lines in the carpet becomes steps, and walking becomes very tenuous. These changes in perception need to be considered when designing and decorating for a person with dementia. Read more about safety considerations.
Finally the disease reaches the base of the brain, the cerebellum and the brain stem.
The cerebellum is largely responsible for movement and balance
The Alzheimer’s Brain — The Cerebellum
Located under the occipital lobes the cerebellum is responsible in large part for our kinesthetic sense, and controls balance and how we move. It is also believed to add something to cognitive functioning and language.
Movement is initiated in the frontal lobes, primarily in the motor cortex, but the cerebellum “fine tunes” that movement. It adds coordination and precision to motion.
“Cerebellum” is latin for “little brain”, and indeed it looks like something separate from the rest of the brain. It does not have the familiar cortical convolutions we associate with the brain, but looks a bit more like muscle. Like the rest of the brain it is a highly complex structure and not completely understood, but it is clear that movement is its primary function.
“A standard test of cerebellar function is to reach with the tip of the finger for a target at arm’s length: A healthy person will move the fingertip in a rapid straight trajectory, whereas a person with cerebellar damage will reach slowly and erratically, with many mid-course corrections.”† You have probably noticed this type of motion if you have worked with people in the later stages of Alzheimer’s, and be sure, once the disease reaches the base of the brain it is nearing the end of its progression.
The brainstem connects the brain and the spine
The Alzheimer’s Brain—The Brainstem
Finally the path of destruction reaches the brainstem. The brainstem connects the brain with the spinal cord and is the conduit through which signals are passed back and forth between the brain and the body, including the organs. The brainstem is the last area to be affected, and when damage here becomes severe enough autonomic functions including breathing and heart rate will cease.
The brain is an extremely complex organ and does much more than we have discussed here. The process by which memories are created and stored is much more involved too. If you are interested in digging deeper I suggest you visit †Wikipedia and The Human Memory. I have relied heavily on these websites in the preparation of this document. Also, a special thanks to BodyParts3D, © The Database Center for Life Science licensed under CC Attribution-Share Alike 2.1 Japan, for the images on this page.
Organizations & Affiliations
Purple Angel Ambassador
Dementia Friendly America
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