As an individual ages into late adulthood, psychological and cognitive changes can sometimes occur. A general decline in memory is very common, due to the decrease in speed of encoding, storage, and retrieval of information. This can cause problems with short-term memory retention and with the ability to learn new information. In most cases, this absent-mindedness should be considered a natural part of growing older rather than a psychological or neurological disorder.
Intelligence
Cognitive ability changes over the course of a person's lifespan, but keeping the mind engaged and active is the best way to keep thinking sharp.
Distinct from a normal decline in memory is dementia, a broad category of brain diseases that cause a gradual long-term decrease in the ability to think and remember to the extent that a person's daily functioning is affected. While the term "dementia" is still often used in lay situations, in the DSM-5 it has been renamed "neurocognitive disorder," with various degrees of severity.
Alzheimer's disease is the most common type of neurocognitive disorder, accounting for 50% to 70% of cases. Neurocognitive disorders most commonly affect memory, visual-spatial ability, language, attention, and executive function (e.g., judgment and problem-solving). Most of these disorders are slow and progressive; by the time a person shows signs of the disease, the changes in their brain have already been happening for a long time. About 10% of people with dementia have what is known as mixed dementia, which is usually a combination of Alzheimer's disease and another type of dementia.
There is no cure for dementia, but for people who suffer from these disorders and for their caregivers, many measures can be taken to improve their lives. These can include education and support for the caregiver and daily exercise programs or cognitive or behavioral therapies for the person with the disorder.