A new study published in "Neurobiology of Aging" found that how quickly a person's pupil dilates while taking cognitive tests may show if they're at risk for Alzheimer's disease (AD). Scientists at the University of California San Diego School of Medicine say this could be a low-cost, low-invasive method to aid in screening individuals before cognitive decline begins.
In recent years, researchers investigating AD have focused on two factors: the accumulation of protein plaques in the brain called amyloid-beta and tangles of a protein called tau. Both have been linked to damaging and killing neurons, resulting in progressive cognitive dysfunction.
This new study focuses on pupillary responses which are driven by the locus coeruleus (LC), a cluster of neurons in the brainstem involved in regulating arousal and also modulating cognitive function. Tau is the earliest occurring known biomarker for AD; it first appears in the LC, and it is more strongly associated with cognition than amyloid-beta. The study was led by first author William S. Kremen, Ph.D., and senior author Carol E. Franz, Ph.D., both professors of psychiatry and co-directors of the Center for Behavior Genetics of Aging at UC San Diego School of Medicine.
The LC drives pupillary response — the changing diameter of the "eyes'' pupils — during cognitive tasks. Pupils get bigger the more difficult the brain task. Researchers had previously reported that adults with mild cognitive impairment (often a precursor to AD), displayed greater pupil dilation and cognitive effort than cognitively normal individuals. Those findings were still true even if both groups produced equivalent results. In the latest paper, the scientists link pupillary dilation responses with identified AD risk genes.
"Given the evidence linking pupillary responses, LC, tau, and the association between pupillary response and AD polygenic risk scores (an aggregate accounting of factors to determine an individual's inherited AD risk), these results are proof-of-concept that measuring pupillary response during cognitive tasks could be another screening tool to detect Alzheimer's before symptoms appear," said Kremen.
To learn more and to read the full study, visit doi.org/10.1016/j.neurobiolaging.2019.09.001.