Pupillometry as a Differential Indicator of Cognitive Processing in Alzheimer Disease and Behavioral Variant Frontotemporal Dementia

Introduction: While extensive research has explored cognitive processing with pupillometry in the general population, limited attention has been given to its application in neurodegenerative diseases. This study, for the first time, investigates general cognitive processing using pupillometry in both Alzheimer disease (AD) and behavioral variant frontotemporal dementia (bvFTD). Methods: Pupil diameter was monitored in patients with AD, patients with bvFTD, and control participants under 2 conditions. The first condition involved subtraction (ie, subtracting 9 from 100 and continuing to subtract to a total of 5 subtractions). The second control condition involved counting aloud from 1. Results: Analysis demonstrated increased pupil diameters during subtraction than during counting in patients with bvFTD, patients with AD, and control participants. During both counting and subtraction, smaller pupil diameters were observed in patients with bvFTD compared with patients with AD and in patients with AD compared with control participants. Conclusions: These findings indicate that pupil size can effectively reflect the cognitive load intensity in patients with bvFTD and patients with AD, suggesting the potential of pupillometry as a differential indicator of cognitive processing in neurodegenerative diseases.