Functional near-infrared spectroscopy (fNIRS) detects brain changes for apathy and pain in patients with Alzheimer's disease and related dementias: An exploratory study

Alzheimer's Disease and Related Dementias (ADRD) are degenerative and progressive in nature and are often accompanied by chronic pain and neuropsychiatric symptoms, which can be early signs and aggravators of ADRD. This exploratory study explores the relationship between self-reported pain, neuropsychiatric symptoms, and pain-evoked cortical hemodynamic changes measured using functional near-infrared spectroscopy (fNIRS) in the prefrontal and primary motor and somatosensory brain cortices bilaterally, stratified by high or low cognitive function in individuals with ADRD. This study analyzed baseline data of 40 individuals with mild to moderate ADRD with knee osteoarthritis. Baseline data from 40 individuals with mild to moderate ADRD and knee osteoarthritis were analyzed. Measures included self-reported pain, depression, and apathy, along with fNIRS-derived cerebral hemodynamic responses to sub-threshold thermal pain stimulation across five brain regions. The study revealed significant negative correlations for oxyhemoglobin and apathy in the right prefrontal cortex associated with low cognitive function (p = .04) and significant positive correlations for oxyhemoglobin and apathy in the right somatosensory region (p = .04) and for oxyhemoglobin and pain in the medial prefrontal cortex (p = .04) associated with higher cognitive function. Study findings suggest that fNIRS may provide valuable biomarkers for apathy and depression in individuals with ADRD and chronic osteoarthritic pain, with differential patterns based on cognitive function, suggesting neuropsychiatric symptoms may manifest differently depending on the patient's cognitive status. Future studies should explore its utility in larger, diverse samples and clinical interventions targeting neuropsychiatric symptoms.