It’s natural for your brain to change during the aging process. In some cases, these changes affect the brain’s ability to function properly.
During the aging process:
- Abnormal structures may develop within the brain
- Blood flow to the brain may be restricted
- Free radical damage may increase
- Inflammation may occur
- Parts of the brain may shrink.
These changes can account for a general decline in your thinking abilities and memory capacity.
How Alzheimer’s Disease Affects the Brain
In individuals with Alzheimer’s disease, brain damage can occur that’s not part of the normal aging process. In such cases, brain tissue degeneration tends to affect the cortex and hippocampus more than other areas of the brain. The cortex is involved with memory recall, reasoning and personality. The hippocampus processes new information.
Two types of neuron damage are common in people with Alzheimer’s disease. These are:
- Amyloid plaques
- Neurofibrillary tangles (aka “tau protein tangles”).
Both plaques and tangles can occur as part of the normal aging process of the brain, but they are much more abundant in individuals with symptoms of Alzheimer’s. It is yet unknown whether these structures are causes or symptoms of Alzheimer’s disease.
Amyloid Plaques in the Brain and Alzheimer’s
Beta-amyloid is a naturally occurring protein that is formed from amyloid precursor protein (APP), one of the proteins of the cell membrane. Clumps of beta-amyloid can build up in the brain of an individual with Alzheimer’s, forming a protein plaque between the neurons in the brain. This interferes with the neurons’ ability to communicate with one another, which in turn interferes with normal brain function.
According to the U.S. Institutes of Health National Institute of Aging, research suggests that beta-amyloid may inhibit the communication between neurons by:
- Attaching to a receptor site on dendrites (the part of the neuron that receives electrochemical messages) and blocking incoming messages
- Blocking a particular molecular pathway for a protein (nitric oxide/cGMP/cAMP-responsive element-binding protein) that appears to influence the ability of the brain to alter its behavior in response to neural activity (or “synaptic plasticity”).
Neurofibrillary Tangles in the Brain and Alzheimer’s
Tau protein plays an important role in maintaining the internal structure of neurons. In many cases of Alzheimer’s disease, tau protein strands are altered and become twisted. This creates neurofibrillary “tangles.” As the protein strands twist, the neuron’s internal transport network collapses. This prevents neural communication and inhibits brain function. These tangles tend to develop in a pattern; first in areas of the brain associated with learning and memory, then in other regions.
Alzheimer’s Disease: Brain Inflammation
Some Alzheimer’s patients show evidence of brain inflammation. This may be the result of the immune cells’ attempts to repair areas of the brain that are affected by plaques and tangles. The resulting inflammation may actually further degrade brain functions.
Acetylcholine Levels, the Brain and Alzheimer’s
Low levels of the neurotransmitter acetylcholine also affect brain function in Alzheimer’s sufferers. Acetylcholine is necessary for memory and other cognitive functions. Maintaining acetylcholine levels is often the goal of Alzheimer’s treatment.
American Health Assistance Foundation. (n.d.) Common Alzheimer’s treatments. Retrieved on April 24, 2010, from http://www.ahaf.org/alzheimers/treatment/common/.
Fisher Center for Alzheimer’s Research Foundation. (n.d.) Alzheimer’s research on causes and risk factors. Retrieved on April 23, 2010, from http://www.alzinfo.org/alzheimers-research-causes.asp#2.
Mayo Clinic. (2009). Causes. Retrieved on April 24, 2010, from http://www.mayoclinic.com/health/alzheimers-disease/DS00161/DSECTION=causes.
U.S. National Institutes of Health National Institute of Aging. (2006). Beta-amyloid and its damaging effects on neurons. Retrieved on April 24, 2010, from http://www.nia.nih.gov/Alzheimers/Publications/ ADProgress2005_2006/Part2/beta_amyloid.htm.htm.
U.S. National Institutes of Health National Institute of Aging. (2008). The hallmarks of AD. Retrieved on April 24, 2010, from http://www.nia.nih.gov/Alzheimers/Publications/Unraveling/Part2/hallmarks.htm.