Dementia is a degenerative brain condition affecting memory, cognition, mood, and other brain functions. If you or someone in your family has been diagnosed with dementia, it can be helpful to understand the biological mechanisms behind the condition.
There are several types of dementia, all of which are caused by damage to nerve cells in the brain. However, different types of dementia affect areas of the brain differently. Moreover, brain cell damage differs from one form of dementia to another.
This article explores the main types of dementia and their effect on the brain. We’ll be answering the following questions:
- What parts of the brain are affected by dementia?
- How does damage to different areas of the brain affect behaviour and cognition?
- What are the underlying biological causes of different types of dementia?
How does dementia affect the brain?
It’s normal for brain cells to die off as a person ages, even in a healthy brain. This is why older adults sometimes have minor short-term memory difficulties and slightly slower cognition – these symptoms do not necessarily indicate dementia.
In a brain affected by dementia, cell death happens more rapidly and worsens over time. The damaged brain cells have difficulty transmitting messages to each other. This affects the clarity of thought, logic, behaviour, communication and mood. The symptoms do not usually develop simultaneously, and may appear fairly mild at first.
The progression of symptoms associated with dementia and the order in which symptoms appear differ slightly from person to person. The type of dementia also plays a role in determining symptom development, as different dementias are more likely to affect certain brain areas.
Different “lobes” of the brain have other functions. For instance:
- The frontal lobes deal with movement, problem solving and judgement.
- The temporal lobes deal with memory and hearing.
- The parietal lobes deal with sensation, body position, and handwriting.
- The occipital lobes deal with vision and processing of visual information.
The specific symptoms a person with dementia experiences will depend on the areas of the brain that have sustained the most cell damage.
What does dementia look like on a brain scan?
There are physical signs of dementia which you can pick up on a brain scan. The cell death associated with the condition will eventually lead to shrinkage in affected brain areas, which may be visible on a CT scan. Early-stage dementia may not be detectable via a brain scan, as significant shrinkage may not yet have occurred.
Blood clots and infections in the brain are also associated with dementia. A doctor may look for these markers when using a brain scan to determine if dementia is present.
What part of the brain does Alzheimer’s affect?
Alzheimer’s Disease is caused by an abnormal build-up of specific proteins around brain cells. These proteins (amyloid and tau) are present in healthy brains but not in harmful amounts. As the protein deposits form around cells, they cluster into “plaques” and “tangles”, restricting blood flow and impairing normal brain cell function. Eventually, affected nerve cells will die off, and brain function will be affected.
In most people with Alzheimer’s disease, the temporal lobes are the first areas of the brain to be affected. As a result, the earliest sign of Alzheimer’s dementia is usually memory loss.
Alzheimer’s brain vs normal brain
In addition to temporal lobe shrinkage, people with Alzheimer’s disease typically have far lower levels of a neurotransmitter called acetylcholine. Other neurotransmitters may also be affected. This means that – compared to a healthy brain – a brain with Alzheimer’s disease may have difficulty sending messages and receiving messages between lobes.
Atypical Alzheimer’s Disease
There are two atypical (less common) types of Alzheimer’s disease, called Frontal Variant Alzheimer’s disease (fvAD) and Posterior Cortical Atrophy (PCA).
Frontal Variant Alzheimer’s disease affects around 1 in 50 people who have Alzheimer's. This condition affects the frontal lobes of the brain first, which wouldn’t happen in a typical Alzheimer’s brain until much later.
Frontal lobe damage can cause:
- Executive function problems (trouble with self-control, flexible thinking, and understanding processes).
- Behavioural changes and mood swings.
Posterior cortical atrophy affects around 5 per cent of people living with Alzheimer’s disease. People with PCA experience early cell degeneration in their occipital lobes and other deep brain structures. As the occipital lobe is responsible for processing visual information, people with PCA typically develop problems understanding images or making sense of things they see. This form of Alzheimer’s can also cause issues with spacial awareness and spatial reasoning (i.e. the ability to visually and physically negotiate the distance between objects).
Vascular dementia is caused by reduced blood flow to the brain. When blood flow is restricted, brain cells can become starved of oxygen and damaged. Reduced blood flow to the brain can be caused by:
- Narrowing of blood vessels in the brain
- Blockage of blood vessels in the brain
- A stroke, or series of mini-strokes
Vascular dementia is usually linked to underlying health problems like high blood pressure, diabetes, obesity or high cholesterol. The areas of the brain affected by vascular dementia vary. As a result, the symptoms a person with vascular dementia may initially experience differs too.
The blood vessels supplying the frontal lobe are often susceptible to restrictions and blockages, so frontal lobe functions are often the first to be impaired. As with fvAD, the earliest symptoms may include slowed thinking and impaired executive function.
In a brain affected by Frontotemporal Dementia (FTD), cell death primarily occurs in the frontal and/or temporal lobes. The initial symptoms of dementia vary based on the pattern in which damage occurs. There are two FTD variants:
*** Semantic Dementia:** Affects verbal and semantic memory. This can lead to difficulty remembering specific words, but speech is otherwise undisturbed in the early stages. Cell damage in the right temporal lobe can also cause problems recognising objects and faces.
*** Behavioural variant FTD:** Affects specific frontal lobe of the brain areas, resulting in loss of motivation and reduced inhibitions. The person experiencing this type of dementia may appear withdrawn. Making inappropriate or out-of-character comments is another common symptom.
In a brain affected by dementia with Lewy bodies (DLB), small protein deposits known as Lewy bodies form around nerve cells. People with this form of dementia tend to have less brain shrinkage. Instead, a brain scan will reveal deposits in the cerebral cortex and limbic system.
The initial symptoms of Lewy body dementia are fairly typical. They include memory problems and difficulty thinking clearly. In later stages, Lewy body dementia is more likely to cause issues with movement and posture – similar to Parkinson’s Disease Dementia.
Staying independent with dementia
While dementia cannot be cured, the onset of symptoms can be managed or slowed by taking steps to remain mentally active. At Relish, we offer a range of craft, game and puzzle activities specifically designed for people living with dementia. Browse our dementia-friendly products to find something that’s a good fit for you or your loved one.