Acquired or hereditary, severely impaired thinking and emotional life.

The term "dementia" thus denotes a condition in which a person's mental faculties are blunted and eventually disappear. Memory deteriorates, learning becomes increasingly difficult, forgetfulness gets worse, a general disorientation grows, depression and the individual eventually loses the ability to take care of himself. The self dissolves and interaction with the environment ceases.

Dementia is due to the destruction of nerve cells in the cortex of the cerebrum, i.e. degenerating. This causes the cerebral cortex to decrease in thickness and the brain to shrink together. The causes of degeneration and how fast it progresses vary. Alzheimer's disease is an example of an increasingly common and sometimes rapidly progressing form of dementia, which in some cases begins as early as the age of 50.