Epidural fNIRS as a tool for studying local hemodynamic signals and neuro-vascular coupling

Hemodynamic activity is studied using functional Magnetic Resonance Imaging (fMRI), Intrinsic Signal Optical Imaging (ISOI), and functional Near Infrared Spectroscopy (fNIRS). FNIRS is a non-invasive neuroimaging method that uses a near-infrared light source and detector pair (optode pair), to measure changes in concentrations of oxy-hemoglobin (HbO), deoxy-hemoglobin (HbR) and total hemoglobin (HbT), in a small volume of tissue. The advantages of fNIRS include its portability, metabolic specificity, high temporal resolution, high sensitivity in detecting small substance concentrations, affordability, and low susceptibility to movement artefacts. Given these advantages, fNIRS is a good candidate for use in primates, specifically to measure local hemodynamic signals during electrophysiological measurements. To test the feasibility of using epidural fNIRS with concomitant extracellular electrophysiology, we recorded spontaneous and stimulus induced activity from the primary visual cortex in two anesthetized monkeys. To study the relationship between changes in [HbO] and [HbR], and the underlying neuronal activity, we used system identification techniques. Briefly, our results show that epidural fNIRS has much higher SNR than fMRI, and is a promising tool for studying local hemodynamic signals and neuro-vascular coupling