A multimodal neuroimaging study of cerebrovascular regulation: Protocols and insights of combining electroencephalography, functional near-infrared spectroscopy, transcranial Doppler ultrasound, and physiological parameters

The current paper describes the creation of a simultaneous trimodal neuroimaging protocol. The authors detail their methodological design for a subsequent large-scale study, demonstrate the ability to obtain the expected physiologically induced responses across cerebrovascular domains, and describe the pitfalls experienced when developing this approach. Approach: Electroencephalography (EEG), functional near-infrared spectroscopy (fNIRS), and transcranial Doppler ultrasound (TCD) were combined to provide an assessment of neuronal activity, microvascular oxygenation, and upstream artery velocity, respectively. Real-time blood pressure, capnography, and heart rate were quantified to control for the known confounding influence of cardiorespiratory variables. The EEG-fNIRS-TCD protocol was attached to a 21-year-old male who completed neurovascular coupling/functional hyperemia (finger tapping and "Where's Waldo/Wally?"), dynamic cerebral autoregulation (squat-stand maneuvers), and cerebrovascular reactivity tasks (end-tidal clamping during hypocapnia/hypercapnia). Main Results: In a pilot participant, the Waldo task produced robust hemodynamic responses within the occipital microvasculature and the posterior cerebral artery. A ~90% decrease in alpha band power was seen in the occipital cortical region compared between the eyes closed and eyes opened protocol, compared to the frontal, central, and parietal regions (~80% reduction). A modest increase in motor oxygenated hemoglobin was seen during the finger tapping task, with a harmonious alpha decrease of ~15% across all cortical regions. No change in the middle or posterior cerebral arteries were noted during finger tapping. During cerebral autoregulatory challenges, sinusoidal oscillations were produced in hemodynamics at 0.05 and 0.10 Hz, while a decrease and increase in TCD and fNIRS metrics were elicited during hypocapnia and hypercapnia protocols, respectively. Significance: All neuroimaging modalities have their inherent limitations; however, these can be minimized by employing multimodal neuroimaging approaches. This EEG-fNIRS-TCD protocol enables a comprehensive assessment of cerebrovascular regulation across the association between electrical activity and cerebral hemodynamics during tasks with a mild degree of body and/or head movement.