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 every day 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 (thinking) ability.

Doctors diagnose dementia if two or more cognitive functions are significantly impaired.  The cognitive functions that may be affected include:

  • memory
  • language skills
  • understanding of information
  • spatial skills
  • judgement
  • attention

People with dementia may have difficulty solving problems and controlling their emotions. They may experience personality changes, agitation, delusions or hallucinations.

The exact symptoms experienced by a person with dementia depend on the areas of the brain that are damaged by the disease causing the dementia.  With many types of dementia, some of the nerve cells in the brain stop functioning, lose connections with other cells, and die.

Dementia is usually progressive.  This means that the disease gradually spreads through the brain and the person’s symptoms get worse over time.

There are many types of dementia caused by different brain diseases

The most common types of dementia are:

  • Alzheimer’s disease
  • Vascular dementia
  • Lewy body disease
  • Frontotemporal dementia

Mixed dementia, where more than one disease affects the brain, is also very common.

Alzheimer's disease

Alzheimer’s disease is the most common form of dementia, and accounts for around two-thirds of dementia cases.  It causes a gradual decline in cognitive abilities, usually beginning with memory loss.

Other symptoms can include:

  • lapses of judgement
  • personality changes
  • difficulty performing usual activities
  • getting lost
  • becoming disoriented about places and times
  • reduced language skills
  • delusions
  • becoming short-tempered and hostile
  • apathy
  • depression
  • anxiety

Alzheimer’s disease is characterised by two abnormalities in the brain – amyloid plaques and neurofibrillary tangles.  Amyloid plaques are abnormal clumps of a protein called beta-amyloid.  Neurofibrillary tangles are bundles of twisted filaments made up of a protein called tau.  Plaques and tangles stop communication between nerve cells and cause them to die.

Further information about Alzheimer's disease is available here

Vascular dementia

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

Vascular dementia is diagnosed when there is evidence of blood vessel disease in the brain and impaired cognitive function that interferes with daily living.  Symptoms of vascular dementia can begin suddenly after a stroke, or may begin gradually as blood vessel disease worsens.

The symptoms of vascular dementia vary depending on the location and size of brain damage.  It may affect just one or a few specific cognitive functions.

When vascular damage occurs deep in the brain, symptoms can include:

  • diminished motivation and initiative
  • loss of insight and apathy
  • poor planning
  • poor concentration

When vascular damage affects the cortex (outer layer of the brain), symptoms can include:

  • changes in sensory and motor functions
  • language impairment
  • memory loss
  • confusion

Lewy body disease

Lewy body disease is characterised by the presence of abnormal clumps of the protein alpha-synuclein, called Lewy bodies, that develop inside nerve cells.

Typical symptoms can include:

  • attention problems
  • reduced spatial skills
  • memory impairment
  • poor problem solving and planning
  • visual hallucinations
  • depression
  • balance and walking difficulties

People with Lewy body disease may experience large fluctuations in attention and thinking.  They can go from almost normal performance to severe confusion within periods ranging from minutes to days to weeks.

Frontotemporal dementia

Frontotemporal dementia involves damage to the frontal and/or temporal lobes of the brain.  Symptoms often begin gradually and progress slowly over a period of years.

There are two main presentations of frontotemporal dementia – frontal (involving behavioural symptoms) and temporal (involving language impairments).  However, the two often overlap.

Because the frontal lobes of the brain control judgement and social behaviour, people with the frontal or behavioural variant of frontotemporal dementia often have problems maintaining socially appropriate behaviour.  They may:

  • be rude
  • neglect normal responsibilities
  • display compulsive or repetitive behaviour
  • have an increased appetite
  • be aggressive or violent
  • show a lack of inhibition
  • act impulsively

The temporal or language variant of frontotemporal dementia reduces language skills such as:

  • object naming
  • fluency of speech
  • word retrieval
  • comprehension of what others are saying
  • difficulties in reading and writing

Further information about frontotemporal dementia is available from frontier, the frontotemporal dementia research group.

Next ...... Who gets dementia?




Your Brain Matters was supported by funding from the Australian Government under the Chronic Disease Prevention and Service Improvement Fund from July 2012 to June 2015.


The National Dementia Helpline: 1800 100 500

Alzheimer's Australia would like to acknowledge the Aboriginal people as the traditional custodians and carers of the country of Australia. We acknowledge and respect the Aboriginal people of Australia's relationship with country and their cultural and spiritual beliefs.