Alzheimer's disease (AD), the most common form of dementia, was first described in 1906 by Alois Alzheimer, a German doctor. According to a report by the Alzheimer's Association, approximately 5.1 million Americans over the age of 65 are currently affected by this fatal disease. There is no cure for this illness, and it is the seventh-leading cause of death in the United States. AD causes dramatic changes in brain structure and functions both at the individual cell level and also in large areas of the brain, such as the hippocampus.
Normal Aging Brain
As shown in a study by Dr. Nicholas Bishop published in the Nature journal in March 2010, although both normal, aging people and AD patients may suffer from memory problems, there are drastic differences between these two groups. The hippocampus, an area of the brain responsible for forming new memories, functions quite well in old, but otherwise healthy, people. As a result, they may experience difficulties in retrieving information and need cues to be able to remember things, but they should not have any major difficulties in forming new memories. Yet age does create problems even in healthy people. Dr. Bishop's study discovered age-related regional decreases in cerebral volume. Term plasticity refers to the brain's ability to change its structure and function, and evidence exists that this plasticity decreases as people age. This might be due to age-induced alterations in calcium regulation. Calcium has a crucial role in how information is moved within and from one cell to another.
Alzheimer's Disease and Amyloid Plaques
As demonstrated by the Alzheimer Research Foundation, the prime suspects in damaging and killing neurons in patients with AD are called plaques and tangles. Melanie Meyer-Luehmann, Ph.D., showed in 2007 article in the Nature journal how this abnormal structure builds up between neurons. Even normal, healthy brains produce some of these fragments but they eventually get broken down and eliminated. In a patient with AD, the fragments are not destroyed, but they do form hard, insoluble plaque. This plaque makes it impossible for the neurons to get energy, or to communicate with other cells. Eventually the neurons affected by the plaque will die.
Alzheimer's Disease and Neurofibrillary Tangles
Tangles are twisted fibers of a protein called tau that forms inside of dying cells. Most people develop some tangles as they age but AD patients develop them in greater amounts. Although the exact role of plaque and tangles in AD is not known, it's believed that they somehow prevent communication between neurons and harm other activities, such as cell metabolism or energy formation that cells needs to do in order to survive. The plaques and tangles tend to form in a highly predictable pattern in a brain of a AD patient, beginning in areas important for learning and memory, such as the hippocampus, and eventually spreading to other regions.
Alzheimer's Disease and the Shrinking of the Brain
AD predominantly affects the cerebral cortex and the hippocampus, both of which lose mass and shrink as neurons deteriorate and die. The overall shrinkage of brain tissue is typical for AD. The outer layer of the cortex is folded in a normal, healthy brain. As the AD makes the brain shrink, these folds become noticeably bigger. In addition, the areas in the brain that contain cerebrospinal fluid are noticeably enlarged when the brain itself is shrinking.
Alzheimer's Disease and Neurotransmitters
Neurons communicate with one another by using neurotransmitters. Nerve cells containing one kind of neurotransmitter are usually located in one particular area of the brain. Since AD especially affects the hippocampus, it's natural that the neurotransmitters located in those neurons are affected the most. Thus, it comes as no surprise that lowered concentrations of one neurotransmitter called acetylcoholine (ACh) can be found in AD patients. ACh is responsible for learning and memory in the brain.
References
- "Nature"; Neural mechanisms of ageing and cognitive decline; Bishop, Yanker; vol. 7288, 529-535, 2010
- Alzheimer's Association Report: 2010 Alzheimer's Disease Facts and Figures
- Alzheimer's Disease Research: Brain With Alzheimer's Disease
- "Nature"; Rapid appearance and local toxicity of amyloid; Melanie Meyer-Luehmann; 2008
