Alzheimer’s disease is the most common cause of dementia. But what actually happens to the brain in patients affected by this disease?

The brain is made up of billions of nerve cells. Two key proteins become abnormal in Alzheimer’s disease. The first is called amyloid, which becomes sticky and forms “plaques” around the cells, disrupting electrical signals. The other protein is called tau. This forms tangles inside the cells, stopping them working properly. To complicate matters, more recently we have learned that other proteins and changes in the blood vessels can add to the problems in Alzheimer’s disease (Figure 1).

 

Figure 1. The changes seen in a brain affected by Alzheimer’s disease. The images were used with kind permission from Dr Elizabeth Coulthard and Prof Seth Love, University of Bristol.

When lots of nerve cells die due to these changes, parts of the brain can appear to shrink in size. This can sometimes be seen on brain scans, as shown in Figure 1. The hippocampus is affected very early in Alzheimer’s disease. This part of the brain is vital for making new memories. For this reason, one of the first symptoms can be forgetfulness. The loss of nerve cells can also cause low levels of a chemical messenger in the brain. This messenger is called acetylcholine and it is very important for thinking and memory. Some treatments are used to boost levels of this chemical.

Alzheimer’s disease is a progressive condition, meaning it gets worse over time. New symptoms develop, depending on which brain areas are affected. They may include agitation, depression and wandering. In the later stages, some people may experience hallucinations, such as hearing voices, or delusions, which are false beliefs about the world around them. Treatments are available to help improve symptoms, but we do not have any that stop or reverse the damage caused by Alzheimer’s disease. With the ongoing support of charities, such as BRACE, we remain hopeful that research will help us find the cure that we desperately need.

 - Dr James Selwood, University of Bristol