Aging vs Alzheimer's Disease
Research shows that a brain affected by Alzheimer’s disease looks very different from one undergoing normal aging. While all brains shrink in volume as we get older, Alzheimer’s brains lose even more volume than healthy brains. Understanding these differences could lead to better ways to diagnose the disease earlier, even before symptoms appear.
Recent imaging studies show that Alzheimer’s can lead to a 10% shrinkage in the hippocampus over two years, compared to a 4% reduction in volume among healthy people. The disease can also cause changes in the shape of this region, due to the intrusion of abnormal proteins that are linked to Alzheimer’s.
There are about 1010th nerve cells in this part of the brain, which makes up the outer covering of the brain. The cortex is critical for intelligence, personality, planning and motor functions. In Alzheimer’s disease the cortex shrinks because of the loss of nerve cells.
Our brains have four large cavities, each filled with fluid that flows between the brain and the spinal cord. Because Alzheimer’s causes nerve cells to die, Alzheimer’s patients tend to have larger ventricles since more of their brain tissue is destroyed.
This grouping of nerve cells located on each side of the brain’s hemispheres is critical to coordinating cognition and voluntary movement; in Alzheimer’s patients, their activity on both sides of the brain is no longer even, resulting in difficulty organizing thoughts and movements.
White Matter Tracts
Nerve cell tissue is divided into two types—white and grey matter. White matter makes up the bulk of nerve cell volume, and includes the axons and their protective layer, known as myelin. Alzheimer’s patients show signs of reduced white matter in relation to grey matter, particularly in regions important to memory, which suggests that as the disease progresses, nerve cells are losing their axonal links to one another.
How Different is the Alzheimer’s Brain?
By the time Alzheimer’s is well-established, there are distinct differences between an affected brain and one that is aging normally, say experts. But increasingly, they believe it’s important to identify those who are in the early stages of disease, so they might benefit from lifestyle interventions, such as keeping their brains active, that might slow down the progression of Alzheimer’s. But is it possible to select out these patients before their symptoms give them away?
That’s still an open question, but with advances in imaging techniques that can get ever finer resolution of brain structures, researchers are hopeful they can pick out the first signs of Alzheimer’s—or at least the first signs of abnormal aging—so they can study these patients further. They are also working on protein tests, hopefully based on blood, that can detect proteins specific to the disease, even in its earliest stages.