Resting state functional near infrared spectroscopy Carlos V. Rizzo-Sierra 1-3 , Singh Deepeshwar 4 , Sanjay Kumar 4 , Hemant Bhargav 4 , Manjunath Krishnamurthy 4 , Nagendra R. Hongasandra 4 1 NeuroniKaS Laboratory, Unicolciencias, Colombia 2 ICMR Center for Advanced Research in Yoga & Neurophysiology, SVYASA Yoga University, India 3 School of Industrial Engineering, St. Thomas University, Colombia 4 Division of Yoga and Life Sciences, Swami Vivekananda Yoga University (S-VYASA), Bangalore, Karnataka, India The present study investigated the spatial-temporal variation of oxygenated hemoglobin (HbO), deoxygenated hemoglobin (Hb), blood volume (BV) and blood oxygenation (BO) concentration changes in the prefrontal cortex, measured with functional near-infrared spectroscopy (fNIRS) during resting state. We examined 36 healthy right handed subjects seating with their minds and body quiet and still, as well as their eyes closed for 5 minutes. The spatial mean concentration change of the four estimated parameters across subjects was found near zero; Moreover, the mean concentration changes across subjects for HbO and Hb were found to be more reduced than those of BV and BO. In addition, there were no statistically voxelwise significant differences for the mean concentration changes related to HbO, Hb, BV, neither BO; This finding strongly suggests for a spatial stability in the mean concentration changes during resting state. Keywords – Brain oxygenation, Continuous wave, Functional near-infrared spectroscopy, NIRS, Optical imaging Introduction: fNIRS has been in development as a useful tool for neuroimaging studies [1-3]. Among these, the instruments for continuous wave (CW) measurements based on the modified Lambert–Beer law (MLB) [4,5] are the most readily available commercially. Instruments of this type allow observation of dynamic changes in regional cerebral blood flow (rCBFs) in real time by monitoring the concentration changes in cerebral HbO and Hb. However, it is difficult to quantitatively measure HbO and Hb concentrations in the cerebral tissue separately from those in the extracerebral tissue. These problems have limited the use of fNIRS. Indeed, proper resting state calibration studies are missing within the fNIRS literature. As a matter of fact, this has not been well understood by many fNIRS users. Here, a common fNIRS-CW system is employed to determine the variation in the spatial-temporal resting state activity in cerebral tissue across healthy subjects. Methods: Thirty six right-handed healthy subjects (27 males and 9 females, with a mean age (± SD) of 27.92 (± 4.78) years and 24.11 (± 2.71) years respectively) volunteered for the study. They seated with their minds quiet as much as possible and their eyes closed; the prefrontal cortex was monitored for 5 minutes employing a fNIRS-CW system first described by Chance et al (1998) [6]. The sensor has a temporal resolution of 500 milliseconds per scan with 2.5 cm source-detector separation allowing for approximately 1.25 cm of penetration depth. The employed fNIRS system is composed of three modules: a flexible headpiece (sensor pad), which holds 4 light sources and 10 detectors to enable a fast placement of all 16 optodes/voxels. Home built-in algorithms in MATLAB were employed for the data analysis. Further, balanced one-way ANOVA was performed voxelwise, for each of the independent four estimated parameters directly related to prefrontal activity: 1. HbO, 2. Hb, 3. BV: HbO + Hb, 4. BO: HbO – Hb. Results: Voxelwise, the spatial mean concentration change of the four estimated parameters across subjects is near zero; although, the variation across them is remarkable, specifically, the voxelwise standard deviation is higher for voxels 8, 9 and 10. These voxels spatially correspond to the center of the frontal lobe. Moreover, the mean of changes across subjects for HbO and Hb concentration are more reduced, with smaller standard deviation than those of BV and BO. Furthermore, there are no statistically voxelwise significant differences for the mean concentration changes related to HbO, Hb, BV, or BO. The highest Std values voxelwise for HbO, Hb, BV and BO are 2 (min: -2.96, max: 7.37), 1.6 (min: -6.26, max: 4.59), 2.8 (min: -3.08, max: 13.08), and 2.0 (min: -3.34, max: 8.09) micromol, relating voxels 9, 8, 9 and 9 respectively. These results show that none of the 16 voxels have means significantly different from each other, across 36 subjects, for none of the four estimated parameters. Conclusion: We investigated the spatial- temporal variation of HbO and Hb concentration changes over the prefrontal cortex during resting state. The present study strongly suggests a spatial stability in the concentration recorded during 5 minutes; the human frontal lobe resting activity follows a spatially homogeneous trend. However, it is evident that the high variation found across subjects, specially at the center of the frontal lobe deserves special attention and detailed research study. REFERENCES [1] Y. Hoshi, M. Tamura, “Detection of dynamic changes in cerebral oxygenation coupled to neuronal function during mental work in man”, Neurosci Lett, 1993; 150: 5–8. [2] K. Kato, A. Kamei, S. Takashima et al, “Human visual cortical function during photic stimulation monitoring by means of near-infrared spectroscopy”, J. Cereb. Blood Flow Metab, 1993; 13: 516–520. [3] A. Villringer, J. Plank, C. Hock et al, “Near-infrared spectroscopy (NIRS): a new tool to study hemodynamic changes during activation of brain function in human adults”, Neurosci Lett, 1993 ; 154: 101–104. [4] B. Chance, Z. Zhuang, C. Unah et al, “Cognition-activated low frequency modulation of light absorption in human brain”, Proc Natl Acad Sci USA, 1993; 90: 3770–3774. [5] D. T. Delpy, M. Cope, P. van der Zee et al, “Estimation of optical pathlength through tissue from direct time of flight measurement”, Phys Med Biol, 1998; 33:1433–1442. [6] B. Chance, E. Anday, S. Nioka et al, “A novel method for fast imaging of brain function, non-invasively, with light”, Optics Express, 1998; 2:411– 423. View publication stats View publication stats