https://www.youtube.com/watch?v=wfLP8fFrOp0 This video from the Alzheimer's Society explains that Alzheimer's disease is the most common cause of dementia. It occurs when abnormal deposits of plaque and tangles — made up of two key proteins, amyloid and tau — occur in the brain. MORE: Six known risk factors for Alzheimer's disease. Plaque and tangles begin to damage nerve cells in the brain and cause them to die, which over time, can lead to cognitive impairment. The hippocampus area of the brain is often the first to be affected by Alzheimer's disease. This is the area where memories are formed, and damage to this area leads to one of the classic symptoms of the disease: short-term memory loss. As the disease progresses, more of the brain is affected by the plaques and tangles. Patients will then begin to present other symptoms of the disease such as long-term memory loss and mood swings. MORE: Ten early symptoms of Alzheimer's you may not be aware of. Alzheimer's News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or another qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.