Cortical activation and motor-cognitive performance during dual-task walking across healthy aging and Parkinsons disease: a standardized longitudinal fNIRS and gait analysis protocol

BACKGROUND: Aging and Parkinsons disease (PD) reduce gait automaticity and increase cognitive demand during walking. Although dual task (DT) paradigms investigate cognitive motor interference, evidence remains limited by heterogeneous tasks, predominant focus on prefrontal cortex (PFC) activity, and variability in functional near infrared spectroscopy (fNIRS) methods. This study investigates whether longitudinal changes in cortical activation during DT walking differ among young adults, older adults, and individuals with PD, and how these changes relate to DT costs over 5 years. METHODS: This longitudinal observational study follows STROBE and fNIRS guidelines and will be conducted in a controlled laboratory (Rede Amparo, CEPID NeuroMat, University of Sao Paulo). Participants will be evaluated annually under three randomized conditions: motor single-task walking, cognitive single task phonemic verbal fluency and DT walking with phonemic verbal fluency, each repeated 10 times. The primary outcome measure will be longitudinal changes in cortical activation during DT walking, quantified by oxygenated hemoglobin (HbO) signals measured with fNIRS in prefrontal and premotor cortical regions. The main predictors of interest will be motor and cognitive DT costs. Covariates will include age, sex, education, cognition, balance, mood, and disease severity in the PD group. Spatiotemporal gait parameters, including gait speed, step length, stride length, step time, base of support, double support, stance phase, and variability, will be recorded using the GAITRite system, and DT costs will be calculated for selected parameters. Cortical activation will be assessed using a 66 channel wearable fNIRS system with short separation channels. DISCUSSION: By combining randomized task blocks, separate motor and cognitive conditions, broader cortical coverage, and concurrent neural and gait assessment across three groups annually, this protocol is expected to provide a comprehensive characterization of cognitive motor interference during walking and its evolution, supporting interpretation of cortical and behavioral responses. The study may help distinguish age related adaptations from PD specific alterations and clarify whether increased cortical recruitment during DT gait reflects compensation, reduced neural efficiency, or ceiling effects, refining understanding of gait automaticity decline and informing rehabilitation and non invasive brain stimulation approaches.