Abstract
Recent technological advancements in optical spectroscopy allow for the construction of hyperspectral (broadband) portable tissue oximeters. In a series of our recent papers we have shown that hyperspectral NIRS (hNIRS) has similar or better capabilities in the absolute tissue oximetry as frequency-domain NIRS, and that hNIRS is also very efficient in measuring temporal changes in tissue hemoglobin concentration and oxygenation. In this paper, we extend the application of hNIRS to the measurement of event-related hemodynamic and metabolic functional cerebral responses during simulated driving. In order to check if hNIRS can detect event-related changes in the brain, we measured the concentration changes of oxygenated (HbO2) and deoxygenated (HHb) hemoglobin and of the oxidized state of cytochrome c oxidase, on the right and left prefrontal cortices (PFC) simultaneously during simulated driving on sixteen healthy right-handed participants (aged between 22-32). We used our in-house hNIRS system based on a portable spectrometer with cooled CCD detector and a driving simulator with a fully functional steering wheel and foot pedals. Each participant performed different driving tasks and participants were distracted during some driving conditions by asking general knowledge true/false questions. Our findings suggest that more complex driving tasks (non-distracted) deactivate PFC while distractions during driving significantly activate PFC, which is in agreement with previous fMRI results. Also, we found the changes in the redox state of the cytochrome C oxidase to be very consistent with those in the concentrations of HbO2 and HHb. Overall our findings suggest that in addition to the suitability of absolute tissue oximetry, hyperspectral NIRS may also offer advantages in functional brain imaging. In particular, it can be used to measure the metabolic functional brain activity during actual driving.
Highlights
Near-infrared spectroscopy (NIRS) is a portable non-invasive method for real-time measurement of brain activity in real-life situations without noise and movement limitations or interfering with biological systems [1]
In a series of our recent papers we have shown that hyperspectral NIRS has similar or better capabilities in the absolute tissue oximetry as frequency-domain NIRS, and that hNIRS is very efficient in measuring temporal changes in tissue hemoglobin concentration and oxygenation
We extend the application of hNIRS to the measurement of event-related hemodynamic and metabolic functional cerebral responses during simulated driving
Summary
Near-infrared spectroscopy (NIRS) is a portable non-invasive method for real-time measurement of brain activity in real-life situations without noise and movement limitations or interfering with biological systems [1]. NIRS monitors the concentration changes of tissue chromophores based on changes in the attenuation of near-infrared spectra. CCO is the terminal electron acceptor in the mitochondrial respiratory chain [3] and contains four redox active metal centers; the copper A (CuA) center has a distinct redoxsensitive absorbance band in NIR region of the electromagnetic spectrum; it is responsible for 95% of cellular oxygen metabolism and ATP synthesis [2]. The concentration changes of oxidized CCO (Δ[ox-CCO]) that can be monitored by NIRS represent changes in the CCO redox state and reflect the balance between cerebral oxygen delivery and utilization [4,5]. The brain cells have the highest mitochondrial density among all other body cells the concentration of CCO is significantly higher and easier to measure within brain tissue
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