Abstract
.Significance: Quantitative measurements of cerebral hemodynamic changes due to functional activation are widely accomplished with commercial continuous wave (CW-NIRS) instruments despite the availability of the more rigorous multi-distance frequency domain (FD-NIRS) approach. A direct comparison of the two approaches to functional near-infrared spectroscopy can help in the interpretation of optical data and guide implementations of diffuse optical instruments for measuring functional activation.Aim: We explore the differences between CW-NIRS and multi-distance FD-NIRS by comparing measurements of functional activation in the human auditory cortex.Approach: Functional activation of the human auditory cortex was measured using a commercial frequency domain near-infrared spectroscopy instrument for 70 dB sound pressure level broadband noise and pure tone (1000 Hz) stimuli. Changes in tissue oxygenation were calculated using the modified Beer–Lambert law (CW-NIRS approach) and the photon diffusion equation (FD-NIRS approach).Results: Changes in oxygenated hemoglobin measured with the multi-distance FD-NIRS approach were about twice as large as those measured with the CW-NIRS approach. A finite-element simulation of the functional activation problem was performed to demonstrate that tissue oxygenation changes measured with the CW-NIRS approach is more accurate than that with multi-distance FD-NIRS.Conclusions: Multi-distance FD-NIRS approaches tend to overestimate functional activation effects, in part due to partial volume effects.
Highlights
Using in vivo data from functional activation of healthy human auditory cortex, we demonstrate that hemodynamic responses estimated from CW- and multi-distance FD-near-infrared spectroscopy (NIRS) approaches differ significantly even though they are measured at the same time and from the same physical position
Using finite-element simulations (NIRFAST29), we suggest that frequency domain NIRS (FD-NIRS) estimates of cerebral oxygenation measured using multi-distance methods tend to overestimate focal hemodynamic changes, in part due to the partial volume effect, when compared with single-distance CW approaches
Baseline concentrations were obtained by multi-distance FD-NIRS analysis of phase and amplitude
Summary
Functional near-infrared spectroscopy (fNIRS) has emerged as a reliable non-invasive method for monitoring cortical activity in the brain.[1,2,3] fNIRS has been used for a variety of applications such as to study neuronal activation of brain circuits,[4,5,6] to image functional/resting state connectivity of the human brain,[4,7,8] to examine and characterize cognitive NeurophotonicsDownloaded From: https://www.spiedigitallibrary.org/journals/Neurophotonics on 13 Jan 2022 Terms of Use: https://www.spiedigitallibrary.org/terms-of-useOct–Dec 2021 Vol 8(4)Mohammad et al.: Comparison of functional activation responses from the auditory cortex derived. . .behavior,[9,10,11] and to study/implement brain–computer interfaces.[12,13,14] fNIRS instruments are especially useful for characterizing functional hemodynamic changes associated with the auditory system. It is generally difficult to measure cerebral activity in response to activations of the auditory cortex with clinical imaging modalities such as x-ray computed tomography or magnetic resonance imaging because instrument sounds increase background noise, which could corrupt the careful presentation of auditory stimuli to subjects and thereby significantly bias the results of an experiment. Issa et al.[18] measured the hemodynamic changes in the auditory cortex when presented with a pure tone stimulus of 750 and 8000 Hz as well as broadband noise. The primary auditory cortex in humans spans ∼1650 mm[3] within Heschl’s gyrus of the temporal lobe and is organized along multiple functional dimensions, the most prominent one being tonotopic.[19,20] We, expect that pure tone stimuli will activate a more focal region of the auditory cortex, whereas broadband noise will activate a broader region.[19,21,22]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
