Ask Doctor K: Research on Alzheimer’s disease yields important insights

DEAR DOCTOR K: My grandmother has Alzheimer’s disease. How does Alzheimer’s wreak so much havoc in the brain?

DEAR READER: Early on, Alzheimer’s disease affects the brain’s limbic system and cerebral neocortex. The limbic system is central to memory and learning. It also links emotions and behavior. It is the line between what we want to do and what we actually do. The cerebral neocortex controls conscious thought. Damage to this area leads to problems with language, math and reasoning.

Ongoing communication between the limbic system and neocortex links thinking and emotions. The back-and-forth between memory and emotion, thought and action, is the foundation of personality. That’s why damage to these two areas is so devastating.

Other parts of the brain are not affected until later in the disease. Examples include the brainstem and cerebellum, which control basic functions needed for survival.

Twenty-five years ago, we knew that the brain cells that do the thinking – neurons – communicate with one another using chemicals called neurotransmitters. As Alzheimer’s disease takes hold, levels of one neurotransmitter, acetylcholine, drop sharply. Without enough acetylcholine, different areas of the brain cannot communicate normally.

We also knew that there were two unusual microscopic structures in the brains of people with Alzheimer’s, called plaques and tangles. We knew that plaques contained a chemical called amyloid beta, and that tangles contained a chemical called tau.

Finally, we knew that areas of the brain with lots of plaques and tangles were most likely to have dead neurons. So there was circumstantial evidence that amyloid beta and tau might be important causes of the death of neurons.

In the past 25 years, scientists have obtained strong evidence that amyloid beta and tau really are important causes of the death of brain cells. And scientists have discovered several other brain molecules that are also important.