Alzheimer’s disease is a neurodegenerative disease that damages a person’s ability to think, remember and perform basic functions. According to the National Institutes of Health, Alzheimer’s disease affects more than 6 million Americans, mostly aged 65 and older. Although the neurological damage of the disease is irreversible, early detection and intervention have been shown to slow its progression.
Before the onset of physical symptoms of Alzheimer’s disease, the most common method used to measure the risk of developing the disease is to measure the levels of certain proteins, such as beta-amyloid and tau proteins, in the fluid cerebrospinal. This test is invasive, painful and expensive.
Now, a team from Caltech and the Huntington Institutes of Medical Research has made progress toward developing a simple behavioral test to measure an individual’s risk of developing Alzheimer’s disease before any symptoms appear.
The research was conducted in the lab of Shinsuke Shimojo, Gertrude Baltimore Professor of Experimental Psychology. An article describing the results appears in the journal Alzheimer’s and dementia September 20. Shimojo is an affiliate faculty member of the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech.
“Early detection of Alzheimer’s disease is important in order to take interventions that can slow disease progression,” says study first author Shao-Min Sean Hung, a former postdoctoral researcher at the Shimojo lab and now assistant professor at Waseda University. in Japan. “Before disease onset, by definition, cognitively healthy people do not show behavioral symptoms – and so it is not possible to do traditional behavioral assessments for disease because there are not yet What we’re trying to do is develop a test to detect behavioral abnormalities long before any symptoms appear and in a way that’s less invasive than measuring cerebrospinal fluid.
The study involved 40 people with an average age of 75 and all in good cognitive health, who underwent a myriad of tests linked to Alzheimer’s risk: magnetic resonance imaging (MRI) of the brain, genome sequencing and measurements invasive cerebrospinal fluid mentioned above. Based on these biomarkers, individuals could be categorized as high risk or low risk. The researchers aimed to develop a behavioral test whose results would correlate with these biological measurements.
The team developed a task in which a participant undergoes a so-called Stroop Paradigm test. In this common test, a person is shown a word – the name of a color – displayed in colored ink. However, the word itself does not necessarily match the color of the printed word. For example, the word “RED” is printed in green. At each iteration of the task, the participant is asked to name either the color of the word or the word itself. Compared to naming the word itself, naming the text color is considered “high effort” – it’s harder than it looks. (You can try it yourself below.)
In this study, the researchers also added a hidden element to the Stroop paradigm. Just before the actual target is displayed, a colorless word rapidly flashes across the screen, so rapidly that a participant cannot consciously detect it.
The colorless word is intended to subconsciously distract the participant and measure “implicit cognition”. In addition to conscious and intentional collection of information or “explicit cognition”, our brain has a separate system in which sensory information is digested without consciousness – this is called implicit cognition.
“Participants in our study are cognitively healthy at the explicit level, and we measure this through a battery of neuropsychological tests,” Hung says. “But the central question of this study is: what about their implicit cognition? Could it be that their implicit cognition is more sensitive to show the cognitive decline linked to Alzheimer’s disease? The study tested the hypothesis that high-risk and low-risk cognitively healthy participants would be distracted differently by an invisible word.