Remember that dementia exists when cognitive impairment Cognitive impairment
Difficulty with mental abilities such as judgment, memory, learning, comrehension and reasoning. (e.g. problems with thinking, memory Memory
The ability to process information that requires attention, storage, and retrieval., judgment) is severe enough to interfere with function. Function can relate to complex activities, such as driving or complex hobbies, which are impaired first, but also to more basic activities, such as personal; care, that become impaired later.

The capacity for function does not exist in one part of the brain, but rather requires the integration of several brain activities. Functions like personal care are basic and over learned, so that by the time they become affected, many brain areas are involved. Still, we have some hints based on patterns. For example, the fact that a person can carry out personal care when prompted to do so suggests that the problem in that case is one of initiation, which is characteristically a frontal lobe Frontal lobe
The front part of the brain. It is important for the control of voluntary movement or activity, cognition and feelings. function. Later, as the disease is more widespread, the inability to carry out a motor function because the thinking parts of the brain are affected is known as apraxia Apraxia
Apraxia is defined as the inability to carry out a previously learned motor activity, despite normal function of all the component parts (muscles, nerves, joints, etc.).  For example, experiencing difficulty dressing or using a knife and fork, are often clues that apraxia is present.. Characteristically, the brain's parietal lobes are also involved then.