Changes in Size

• Big vs. Small Hippocampus
  In a healthy brain, the hippocampus—a key region for memory—is large and structurally intact. But in Alzheimer’s, the hippocampus shrinks significantly. Studies suggest it can reduce in size by 25% to 40%, and the left side is often more affected than the right. This shrinkage is strongly linked to memory loss and cognitive decline.
• Other Memory Areas Also Shrink
  Beyond the hippocampus, regions like the entorhinal cortex, fusiform gyrus, and medial temporal lobe, all of which are important for memory, also shrink and lose surface area due to Alzheimer’s.
• Overall Brain Shrinkage
  Alzheimer’s doesn’t just affect memory-related regions. It causes widespread brain shrinkage, including areas like the frontal lobe and parietal lobe, which are responsible for thinking and processing information. In contrast, normal aging causes much milder brain shrinkage.

Changes in Function

• The Brain is Less Active During Memory Tasks
  Brain scans show that in Alzheimer’s patients, the medial temporal lobe (including the hippocampus) is much less active when trying to remember or recall things, indicating difficulty in processing memory.
• Explicit Memory Declines
  Patients struggle with explicit memory (conscious recall, like remembering an event or recognizing a person). This happens because the hippocampus and related areas that support this type of memory are damaged.
• Implicit Memory Stays Intact (At First)
  In the early stages of Alzheimer’s, implicit memory (unconscious tasks like riding a bike) is usually preserved. That’s because implicit memory doesn’t rely as heavily on the medial temporal lobe.