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What is dementia?

Dementia describes a collection of symptoms that are caused by disorders affecting the brain. It is not one specific disease. Dementia affects thinking, behaviour and the ability to perform everyday tasks. Brain function is affected enough to interfere with the person’s normal social or working life. The hallmark of dementia is the inability to carry out everyday activities as a consequence of diminished cognitive ability. Doctors diagnose dementia if two or more cognitive functions are significantly impaired. The cognitive functions affected can include memory, language skills, understanding information, spatial skills, judgement and attention. This means that the disease gradually spreads through the brain and the person’s symptoms get worse over time.

What causes dementia?

In most cases, the reason why people develop these diseases is unknown. Some of the most common forms of dementia are:

Alzheimer’s disease – Alzheimer’s disease is the most common form of dementia, accounting for around two-thirds of cases.

Vascular dementia – Vascular dementia is cognitive impairment caused by damage to the blood vessels in the brain. It can be caused by a single stroke, or by several strokes occurring over time.

Lewy body disease – Lewy body disease is characterised by the presence of Lewy bodies in the brain. Lewy bodies are abnormal clumps of the protein alphasynuclein that develop inside nerve cells. These abnormalities occur in specific areas of the brain, causing changes in movement, thinking and behaviour.

Frontotemporal dementia – Frontotemporal dementia involves progressive damage to the frontal and/or temporal lobes of the brain. Symptoms often begin when people are in their 50s or 60s and sometimes earlier.

What is Alzheimer’s disease?

Alzheimer’s disease is a physical brain disease that causes dementia, resulting in impaired memory, thinking and behaviour. Alzheimer’s disease is a progressive dementia – caused by a progressive degeneration of brain cells. The brain is the control centre for your whole body and different regions of the brain are responsible for different behaviours. The brain degeneration that occurs in Alzheimer’s disease affects memory, thinking skills, emotions, behaviour and mood. As a result, a person’s ability to carry out daily activities becomes impaired. As the disease progresses, symptoms worsen.

Alzheimer’s disease is characterised by specific changes in the brain. There is an abnormal build up of a protein called beta amyloid, which forms “plaques” outside the brain cells. Inside the brain cells, another protein called tau builds up into “tangles”. These abnormal protein accumulations disrupt messages within the brain because they damage connections between brain cells. The brain cells eventually die and brain volume shrinks. These brain changes occur gradually and actually begin many years (on average around 15 years) before symptoms of dementia occur. The brain is able to compensate for the early damage, but eventually the damage becomes too great and brain function is affected. As Alzheimer’s disease affects different areas of the brain, specific functions or abilities are lost. Memory of recent events is often the first to be affected, but as the disease progresses, long-term memory is also lost. The disease also affects many of the brain’s other functions and consequently language, attention, judgement and many other aspects of behaviour are affected.