Task-Evoked Prefrontal Hemodynamics During Cognitive Assessment in Amyotrophic Lateral Sclerosis Using fNIRS

Background/Objectives: Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease increasingly recognized for extra-motor manifestations, including cognitive dysfunction involving frontal cortical systems. Conventional clinical assessments are primarily behavioral and may not capture subtle alterations in the neural systems that support cognitive performance. This pilot study examined whether wearable functional near-infrared spectroscopy (fNIRS) could detect task-evoked prefrontal hemodynamic differences during the King-Devick Task (KDT), a rapid oculomotor number-naming task that engages visual scanning, attention, processing speed, and verbal response production. Methods: Sixteen participants, including seven individuals with ALS and nine age-matched healthy controls (HC), completed four progressively difficult KDT conditions while prefrontal cortical activity was recorded. Results: As task difficulty increased, response times became slower across participants, while accuracy remained preserved and behavioral performance did not differ significantly between groups. Prefrontal oxygenated hemoglobin (HbO) responses increased with task difficulty across all prefrontal optodes, supporting task-evoked cortical engagement. In contrast, deoxygenated hemoglobin (HbR) responses showed a group-specific pattern in the left dorsolateral prefrontal cortex: individuals with ALS demonstrated progressively increasing HbR responses across difficulty conditions, whereas HC showed relatively stable responses, with group differences emerging at higher difficulty levels. Conclusions: These findings suggest a dissociation between preserved behavioral performance and altered prefrontal hemodynamic regulation in ALS. The observed HbR pattern may reflect differences in cortical recruitment, neurovascular coupling, oxygen extraction, vascular responsiveness, or the efficiency of cortical resource allocation during increasing cognitive-motor demands. Wearable fNIRS may therefore complement behavioral assessments by revealing task-evoked neural alterations that are not evident from performance measures alone.