Abstract
The world population is becoming older now. The boom of the elderly population comes from public health efforts to improve living conditions and prevent disease, and from improved medical interventions. People more than 65-year-old who are representing 12.9% of the population now is expected to grow to be 19% of the population by 2030. Very few numbers of diseases will have such socioeconomic burden on society in the newer world. Although Alzheimer's disease (AD) has been studied very well recently, still its exact etiopathogenesis is unknown. Currently there are no available tests for the definitive diagnosis of AD. So the clinical diagnosis of AD remains a diagnosis of exclusion. This limits the potential for early intervention. The difference between normal degenerative processes of brain and preclinical changes of AD is a gray zone and there is no particular way to distinguish between the two. Now several modalities like functional magnetic resonance imaging (fMRI), positron emission tomography (PET) scan, electrophysiological tests and cerebrospinal fluid (CSF) biomarkers for tauopathy and Aβ have shown to be promising in the development of early diagnostic tools for neurodegenerative changes and help us to differentiate between healthy aging and pathological aging. In this article we tried to discuss about the differences between pathological and physiological aging process from radiological, pathological, biochemical, and electrophysiological point of view. However, differentiating between physiological and pathological dementia still remains a challenge.