Patients with Alzheimer's disease suffer from memory loss, emotional changes, and impairment of language and judgment; these symptoms are a result of brain cell deterioration and a loss of brain mass. As the disease progresses, patients have a noticeable decrease in brain size when compared to an average adult brain; these changes can be observed with magnetic resonance imaging (MRI) or through post mortem examination. However, the difference between an Alzheimer's brain and average brain takes years to be significant.
Decrease in Size
The University of Washington states that the average adult human brain weighs 1,300 to 1,400 grams. Researchers at the Oregon Health and Science University studied the brain volume of Alzheimer's disease patients and found that their brain size was 10 percent less compared to non-Alzheimer's disease brains, which would make it approximately 1,170 to 1,260 grams.
Affected Brain Structures
The decrease in brain size is localized to certain areas of the brain. The Alzheimer's Association states that the disease affects the cerebral cortex, which is the neural tissue surrounding the cerebrum---the largest part of the brain. Alzheimer's disease destroys the brain cells, causing significant shrinkage of the cortex. One area of the cortex, the hippocampus, is targeted in particular. The hippocampus is located in the medial temporal lobe, and receives its name from its shape (a seahorse). The Alzheimer's Association adds that the ventricles, which are fluid-filled areas of the brain that resemble small gaps, are enlarged. These physiological changes result in the Alzheimer's brain appearing shrunken with deep holes.
Additional Changes
Besides the changes to the cerebral cortex and the ventricles, patients with Alzheimer's disease have abnormal protein formations in the brain; these also result in deterioration of neurological function. The Alzheimer's Association states that these two formations are plaques and tangles. Plaques are a buildup of a protein, beta amyloid, between nerve cells. Tangles are twisted strands of the tau protein that ensnare themselves among dead and dying nerve cells.
Changes in Function
All the changes to the Alzheimer's brain result in the symptoms of the disease, which are a loss of normal function. The American Health Assistance Foundation states that the first neurological change is a decline in short-term memory; the reason that memory loss is significant in Alzheimer's disease is the severe damage to the hippocampus. As the volume of the cerebral cortex decreases, cognitive function further declines, resulting in judgment problems, impaired language and emotional changes.
Progression of Deterioration
The changes in brain size occur over a long period of time. With early Alzheimer's, which can last up to 20 years before diagnosis, according to the Alzheimer's Association, the size difference may not appear on an MRI image. Changes become noticeable during moderate Alzheimer's disease, which can last two to 10 years. During severe Alzheimer's, which can last between one and five years, the physiological changes are apparent with imaging and symptoms.
