The term 'dementia' is used to describe the symptoms that occur when the brain is affected by specific diseases and conditions.
Symptoms of dementia include loss of memory, confusion and problems with speech and understanding.
Dementia is progressive, which means the symptoms will gradually get worse.
For more information about dementia visit the Alzheimer's society website.
More top news
The US president, who has not visited the UK since being elected, is reported to be planning a summer trip to Britain.
Mack entered her plea in federal court in Brooklyn. The judge refused a request by her lawyers to release her without bail.
Officers investigating a reported break-in on Friday found 22-year-old Roger Alvarado asleep in the pop star's home in Tribeca.