Seeing and Believing

On July 28 of this year, we posted regarding the four syndromes of Alzheimer's disease; the memory, language, visual, and frontal syndromes.  These point to different ways that Alzheimer's disease and dementia first asserts itself, and they vary based on which part of the brain is being attacked first.  Most common and most familiar is the memory syndrome, but mine may actually have been the visual syndrome.  It is known as posterior cortical atrophy or Benson's syndrome.  Benson's syndrome is referred to as "an atypical variant" of Alzheimer's disease.  In my case, I had to stop driving because I sometimes failed to see a car in the lane I wanted to move into, or I didn't see a pedestrian in a crosswalk.  (This problem has not recurred since 2016.)

Today, Firefox offered me an interesting article on how the brain processes vision that discussed how vision changes in the elderly ("Your Brain Chooses What to Let You See").  It discussed how changes in the brain affect the way the brain processes information delivered by the eye to assess the environment for threats or access to food.  First and foremost, it must screen out distractions, so that you focus on what's important.

The principal idea was that something moving is more important than something stationary, so your brain will be interested in that first.  Also, something small that's moving may be more important than something big that's moving.  They give as an example that a raptor must distinguish a moving mouse from the windblown grass and tree branches.

One of the research findings they discussed was that elderly people have a harder time separating smaller moving objects from larger moving objects.  This is consistent with Benson's syndrome, in that evidence of Benson's syndrome includes difficulty in distinguishing the relative sizes of objects.

I will speculate that we will see something here that is similar to distinguishing memory issues in normal aging from Alzheimer's disease and other dementias.  In normal aging, the brain is atrophying.  If you're a Baby Boomer you know this, regardless of your Alzheimer's disease status.  In normal aging, the word you want to use is still in your memory, you just have trouble pulling it up for use.  It will come back to you later, but too late to have been used in the conversation.  In Alzheimer's disease, it has been erased from your memory.  You may be able to re-learn it, but it's gone.  I have met several people recently who's own names have been erased from their memories.

The authors of the article discuss limitations of seniors on their brains' ability to distinguish relative sizes of objects in motion.  I speculate that the article is referring to the consequences of normal aging.  In Benson's syndrome of Alzheimer's disease, the damage to the areas of the brain responsible for interpreting the information from the eye are much more seriously damaged, and the visual function of the brain is more seriously degraded.