Digital biomarkers for Alzheimer's disease: the mobile/ wearable devices opportunity

Abstract

Alzheimer's Disease (AD) represents a major and rapidly growing burden to the healthcare ecosystem. A growing body of evidence indicates that cognitive, behavioral, sensory, and motor changes may precede clinical manifestations of AD by several years. Existing tests designed to diagnose neurodegenerative diseases, while well-validated, are often less effective in detecting deviations from normal cognitive decline trajectory in the earliest stages of the disease. In the quest for gold standards for AD assessment, there is a growing interest in the identification of readily accessible digital biomarkers, which harness advances in consumer grade mobile and wearable technologies. Topics examined include a review of existing early clinical manifestations of AD and a path to the respective sensor and mobile/wearable device usage to acquire domain-centric data towards objective, high frequency and passive digital phenotyping.

Fig. 1

Consumer wearable and mobile devices offer a large personalized, direct, and high frequency sensing potential. Microphones can sense ambient noise and voice. Touch screens can probe for fine motor skills in swiping and typing. Cameras can register eye movements, gaze, and pupillary reflexes as well as capture facial expression traits. Altimeters offer useful information with respect to activity and barometers provide atmospheric pressure readings and weather data. PPG (Photoplethysmography) provides beat-to-beat heart rate measurements (HRM), heart rate variability (HRV) and oxygen saturation (SpO₂). IMU (Inertia Measurement Unit) includes accelerometer, gyroscope and magnetometer (9 spatial values) and is used by numerous applications to track activity. Geopositioning sensors (GPS and WiFi localization) provide accurate location information. Light sensors read ambient visible or UV radiation levels. Thermometers on rings, patches or watches provide body temperature readings. Electromyograph sensors (EMG) found on patches or suits yield muscle group activity signals. Electrodermograph (EDG) or Galvanic Skin Response (GSR) sensors equip patches and watches to measure the skin conductance and potential or the skin resistance/impendance. Social interactions can be monitored using proximity to Bluetooth or Wi-Fi enabled devices as well as by monitoring overall phone use (calls, texts) and social network activity. Finally, wearable/mobile devices are equipped with logic components that can probe the executive function and memory of a user