A slow and gradual deterioration of brain cells of a human is called dementia. The patient affected by dementia is unable to function normally. There are various causes for a person to get affected by dementia; it could be a brain injury this could be categorized as fixed cognitive impairment. The brain injury may cause irreversible but a fixed impairment. There is another way that dementia affects is slow progressive dementia.
Dementia which begins gradually and worsens progressively over several years, this is usually caused by neurodegenerative disease. In this condition generally the neurons of the brain gradually and slowly lose function and this is irreversible. Dementia leads to memory loss, loss of familiarity to the surroundings, repetition of actions and many other disfunctions. The patient with dementia does not behave as normal person anymore and to recognize that he/she is affected by dementia in the initial stage is quite difficult. If the symptoms occur for more than six months or so then it is possible to diagnose dementia.