There are a lot of tests for cognition that physicians can use to determine brain function, but as recent research suggests, one of the most effective tools to see into the inner workings of someone’s mind is through their eyes.
It’s an old expression that the eyes are windows into the brain, but as it turns out, there is some truth to the old adage. According to the Dana Foundation, a New York based philanthropic organization dedicated to brain research, eye movements reflect brain function, but also influence it as they are a part of healthy brain function.
For this reason, researchers are interested in studying the changes in eye movement that accompany the development of neurodegenerative conditions such as Alzheimer’s and Parkinson’s Disease. They believe these may be closely tied to functions such as memory, decision-making and attention span and could serve as markers for the progression of such diseases.
While there are four different types of movements, the one that has drawn the attention of researchers the most is the saccadic eye movement. Saccades are rapid eye movements similar to those that occur during REM sleep. They quickly change the eye’s point of fixation and can be triggered both voluntarily and as a reflex. Humans make up to 100,000 of these eye movements per day, but as we age, these are the most severely affected eye movements as they become less frequent and harder to initiate.
With only 1-2% of the retina’s field of vision available to us in high resolution, eye movements are an important part of how our brain’s form an entire picture of a scene. If a person can’t achieve this through eye movements, they tend to move their heads to obtain the visual information they seek.
Looking Through Saccades
An analysis published by The Japan Academy looked closer at research done on patients with saccade abnormalities in an attempt to further explore the ones common to patient’s suffering from neurological disorders.
According to the analysis, saccades are broken into two different categories, the first being those which occur as part of a response to something visual that has presented itself and the second being internal cues made in the absence of a visual target. The two are actually quite different when it comes to the way our brains process this information.
The analysis looked at visually guided saccades (VGS) and memory guided saccades (MGS), noting that both those suffering from Parkinson’s and Alzheimer’s had near normal VGS responses, but that their MGS (memory based) responses were not as good.
But in the end, the researchers warned against tying things together too quickly as they noted “no reliable associations can be made between any single oculomotor parameter and a single neural system.”
The Importance of Control
A study published in the journal PeerJ by researchers at the University of Liverpool took aim at examining an important facet of eye movements; the ability to inhibit them.
This can be important in the case of patient’s with neurological disorders such as Parkinson’s and schizophrenia, which may be a secondary condition caused by the onset of something such as dementia.
The study examined two cohorts of healthy individuals from significantly different age groups, one older (50-72) and one younger (19-27). Participants were asked to look at a dot in the center of a screen. As they did, another dot would appear to the right or left of that dot. Participants were asked not to look at the other dot until it disappeared again, an act of inhibition given the human tendency to look at something when it enters the field of vision.
Older participants did significantly worse in preventing themselves from looking at the dot too early. This is important, because as these conditions progress, people become less able to inhibit their natural reactions, making them somewhat susceptible to reacting to whatever stimuli comes out of their environment rather than processing situations in a slow and controlled manner.
While no concrete conclusions can be drawn about what eye movements mean for brain health just yet, researchers are actively looking into it as a potential way to create examinations for these conditions that can be done more efficiently and effectively.