Mapping functional hemodynamic and metabolic responses to dementia: a broadband spectroscopy pilot study

SIGNIFICANCE: Broadband near-infrared spectroscopy (bNIRS) can simultaneously monitor several chromophores, including the oxidative state of cytochrome c-oxidase (oxCCO), an oxygen metabolism biomarker, the activity of which is altered in Alzheimer's disease. Being a portable and noninvasive neuromonitoring technique, bNIRS could provide accessibility to brain-specific biomarkers and aid in the dementia diagnostic pathway.

AIM: We use bNIRS-recorded functional hemodynamic and oxCCO changes to assess their relevance in Alzheimer's disease diagnosis.

APPROACH: Using a visual stimulus paradigm, we recorded functional changes in oxy-, deoxy-hemoglobin and oxCCO in three similarly aged cohorts: healthy controls ( n = 5 ), individuals with mild cognitive impairment ( n = 7 ), and individuals with early Alzheimer's dementia ( n = 7 ). We then selected features from these functional responses to find the best correlation with clinical cognitive markers (cognitive and behavioral test scores and clinical diagnoses) using canonical correlation analysis (CCA).

RESULTS: We found individual variations in peak amplitude and time-to-peak for all the stimulus-evoked bNIRS signals across the three cohorts. CCA showed a strong correlation between bNIRS features and the clinical cognitive markers ( r = 0.902 ). However, repeating the same analysis by excluding the bNIRS oxCCO features leads to a significantly lower correlation ( r = 0.687 ) with the clinical markers.

CONCLUSIONS: oxCCO could be a crucial biomarker, partly explaining cognitive differences with dementia. bNIRS uniquely provides a portable and noninvasive technique to monitor several chromophores simultaneously, including oxCCO, with potential future applications in diagnosing and tracking dementia progression.