To determine the alterations in optical characteristics and cerebral blood oxygenation (CBO) during activation and deactivation, we evaluated the changes in mean optical pathlength (MOP) and CBO induced by a verbal fluency task (VFT) and driving simulation in the right and left prefrontal cortex (PFC), employing a newly developed time-resolved near infrared spectroscopy, which allows quantitative measurements of the evoked-CBO changes by determining the MOP with a sampling time of 1 s. The results demonstrated differences in MOP in the foreheads with the subjects and wavelength; however, there was no significant difference between the right and left foreheads (p > 0.05). Also, both the VFT and driving simulation task did not affect the MOP significantly as compared to that before the tasks (p > 0.05). In the bilateral PFCs, the VFT caused increases of oxyhemoglobin and total hemoglobin associated with a decrease of deoxyhemoglobin, while the driving simulation task caused decreases of oxyhemoglobin and total hemoglobin associated with an increase of deoxyhemoglobin; there were no significant differences in evoked-CBO changes between the right and left PFC. The present results will be useful for quantitative measurement of hemodynamic changes during activation and deactivation in the adults by near infrared spectroscopy.
"The principle behind fNIRS is that near-infrared light penetrates the skull and brain and is absorbed by the chromophores O 2 Hb and HHb, which have different absorption spectra. Assuming constant scattering (Sakatani et al., 2006) and by using the modified Lambert–Beer Law, it is possible to calculate the concentration changes of these chromophores in the penetrated brain tissue based on changes in the detected light intensity. Both increases in [O 2 Hb] and decreases in [HHb] are indicators of cortical activation. "
[Show abstract][Hide abstract] ABSTRACT: Spontaneous slow oscillations occur in cerebral hemodynamics and blood pressure (BP), and may reflect neurogenic, metabolic or myogenic control of the cerebral vasculature. Aging is accompanied by a degeneration of the vascular system, which may have consequences for regional cerebral blood flow and cognitive performance. This degeneration may be reflected in a reduction of spontaneous slow oscillations of cerebral hemodynamics and BP. Therefore, we aimed to establish the dependency of slow oscillations of cerebral hemodynamics and BP on the factors age and cognitive load, by using functional Near-Infrared Spectroscopy (fNIRS). Fourteen healthy young (23-32 years) and 14 healthy older adults (64-78 years) performed a verbal n-back working-memory task. Oxygenated and deoxygenated hemoglobin concentration changes were registered by two fNIRS channels located over left and right prefrontal cortex. BP was measured in the finger by photoplethysmography. We found that very-low-frequency oscillations (0.02-0.07 Hz) and low-frequency oscillations (0.07-0.2 Hz) of cerebral hemodynamics and BP were reduced in the older adults compared to the young during task performance. In young adults, very-low-frequency oscillations of cerebral hemodynamics and BP reduced with increased cognitive load. Cognitive load did not affect low-frequency oscillations of the cerebral hemodynamics and BP. Transfer function analysis indicated that the relationship between BP and cerebral hemodynamic oscillations does not change under influence of age and cognitive load. Our results suggest aging-related changes in the microvasculature such as declined spontaneous activity in microvascular smooth muscle cells and vessel stiffness. Moreover, our results indicate that in addition to local vasoregulatory processes, systemic processes also influence cerebral hemodynamic signals. It is therefore crucial to take the factors age and BP into consideration for the analysis and interpretation of hemodynamic neuroimaging data.
"The responses we observed may have been influenced by mental stability and excitability because they indicate control of sophisticated mental functions that are produced by complex networks. Because brain activity in the frontal cortex increases when subjects are speaking and decreases when they play TV games , we suggest that the phenomenon has a profound effect on the parasympathetic or sympathetic activity. Specifically, we suggest that such brain activity during conscious speaking is associated with a sympathetic effect and that playing a TV game is associated with responsive movement, under a nonsympathetic effect. "
[Show abstract][Hide abstract] ABSTRACT: We previously found that the greatest salivation response in healthy human subjects is produced by facial vibrotactile stimulation of 89 Hz frequency with 1.9 μ m amplitude (89 Hz-S), as reported by Hiraba et al. (2012, 20011, and 2008). We assessed relationships between the blood flow to brain via functional near-infrared spectroscopy (fNIRS) in the frontal cortex and autonomic parameters. We used the heart rate (HRV: heart rate variability analysis in RR intervals), pupil reflex, and salivation as parameters, but the interrelation between each parameter and fNIRS measures remains unknown. We were to investigate the relationship in response to established paradigms using simultaneously each parameter-fNIRS recording in healthy human subjects. Analysis of fNIRS was examined by a comparison of various values between before and after various stimuli (89 Hz-S, 114 Hz-S, listen to classic music, and "Ahh" vocalization). We confirmed that vibrotactile stimulation (89 Hz) of the parotid glands led to the greatest salivation, greatest increase in heart rate variability, and the most constricted pupils. Furthermore, there were almost no detectable differences between fNIRS during 89 Hz-S and fNIRS during listening to classical music of fans. Thus, vibrotactile stimulation of 89 Hz seems to evoke parasympathetic activity.
"Recently we used near-infrared spectroscopy (NIRS) to obtain numerous noninvasive measurements of regional cerebral blood oxygenation (CBO) in vivo [23−25]. This is advantageous because the portable nature of NIRS also enables reproduction of natural experimental conditions when providing continuous and repetitive stimuli to subjects  . "
[Show abstract][Hide abstract] ABSTRACT: Working memory (WM) performance is considered to change according to the nature of the task by adequate and prompt activation of corresponding functional connectivity in the brain. In the present study, we examined continuous prefrontal hemodynamic changes depending on reciprocal disposition of WM and non-WM tasks using two-channel near-infrared spec-troscopy. To investigate possible functional connectivity deficits in autism spectrum disorder (ASD) during these tasks, relative concentration changes in oxygenated hemoglobin (Hb), deoxygenated Hb, and total Hb were compared between high-func-tioning ASD subjects (n = 11) and controls (n = 22). Instant evoked cerebral blood oxygenation changes were observed in re-sponse to the task switch in controls but not in ASD subjects, although the task performance rate was almost equivalent. Delayed or altered response of functional connectivity to incoming stimuli is considered a characteristic feature of ASD.
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