So, let’s start with the first part. Dementia is a progressive loss of mental function due to certain diseases that affect the brain. The losses are substantial. Over time, all types of dementia will lead to loss of memory, loss of reasoning and judgment, personality and behavioral changes, physical decline, and death. But the course dementia takes can vary widely from person to person. It's influenced by many factors, including age and other conditions a person may have. The most of people. The next common dementias are vascular dementia, or tiny strokes in the brain. Dementia is usually caused by degeneration in the cerebral cortex, the part of the brain responsible for thoughts, memories, actions, and personality. Death of brain cells in this region leads to the cognitive impairments that characteristic dementia.