Assessing Brain Function

Sometimes (most times?) how you measure something has a huge impact on the results you get.

My best friend is blessed with a phenomenal memory. In an earlier part of her life, she drove a school bus, and to this day, can rattle off the names of most of the kids she carried. Now that might not be remarkable until you consider that she drove both elementary and high school bus runs every day, in a bus with a capacity of more than 80 students, and did that for 30 years. Do the math: that’s upwards of 4,800 kids. Most people have trouble remembering what they had for breakfast.

How does this related to measurement? Well, drivers are required to get their eyes tested every year, and she in short order memorized the eye chart. She kept getting perfect test results even as she lost the ability to read road signs. As long as she was driving in her normal area, she never needed the signs.

Functionally, was she being tested on eyesight or memory?

A new research study from the University of South Australia offers a different spin on this same issue. (1)

Age-related macular degeneration is a common problem among older adults, often starting in the 50s. It’s a gradual process, often largely unnoticed by the individual, but impacts eyesight just the same. (5)

The problem occurs when visual tasks are used to assess cognitive functioning. That is often done, and in the absence of a separate assessment of vision, can lead to very biased assessments of how well the brain is doing.

It’s common sense, really. If a person can’t see a task and doesn’t know what they can’t see, how are they going to do the task correctly? Then you have to ask, what is the test really measuring — brain function or eyesight? The brain can be in perfect running order while the person fumbles through the task due to fuzzy vision.

The problem is more common among seniors, but isn’t limited to them. Concussions (and other medical conditions) can affect vision, although salient problems such as double vision will be more obvious to the patient than macular degeneration. (3) Still, there can be gradual reductions in vision that might be missed and that brings us to the same situation as with macular degeneration. These kinds of injuries and hearing losses can occur in all age groups.

Of course, if a researcher or clinician uses the same task repetitiously to assess cognitive function, the patient can learn the task — just like my friend and her eye chart. You can get excellent results that in no way represent how the person is actually doing.

An option proposed by the Australian research team is the use of oral testing of cognitive skills. However, hearing is also subject to decline with age or due to injury. So that option really doesn’t solve the problem.

Sources:

1. Anne Macnamara, Victor R. Schinazi, Celia Chen, Scott Coussens, Tobias Loetscher. The effect of age-related macular degeneration on cognitive test performance. Scientific Reports, 2022; 12 (1) DOI: 10.1038/s41598-022-07924-8
2. University of South Australia. “Poor eyesight unfairly mistaken for brain decline.” ScienceDaily. ScienceDaily, 9 May 2022. www.sciencedaily.com/releases/2022/05/220509204939.htm
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6040728/
4. https://www.aoa.org/healthy-eyes/eye-and-vision-conditions/concussions?sso=y
5. https://www.macular.org/about-macular-degeneration/what-is-macular-degeneration