Targeting brain regions of interest in functional near-infrared spectroscopy-Scalp-cortex correlation using subject-specific light propagation models.

Targeting specific brain regions of interest by the accurate positioning of optodes (emission and detection probes) on the scalp remains a challenge for functional near-infrared spectroscopy (fNIRS). Since fNIRS data does not provide any anatomical information on the brain cortex, establishing the scalp-cortex correlation (SCC) between emission-detection probe pairs on the scalp and the underlying brain regions in fNIRS measurements is extremely important. A conventional SCC is obtained by a geometrical point-to-point manner and ignores the effect of light scattering in the head tissue that occurs in actual fNIRS measurements. Here, we developed a sensitivity-based matching (SBM) method that incorporated the broad spatial sensitivity of the probe pair due to light scattering into the SCC for fNIRS. The SCC was analyzed between head surface fiducial points determined by the international 10-10 system and automated anatomical labeling brain regions for 45 subject-specific head models. The performance of the SBM method was compared with that of three conventional geometrical matching (GM) methods. We reveal that the light scattering and individual anatomical differences in the head affect the SCC, which indicates that the SBM method is compulsory to obtain the precise SCC. The SBM method enables us to evaluate the activity of cortical regions that are overlooked in the SCC obtained by conventional GM methods. Together, the SBM method could be a promising approach to guide fNIRS users in designing their probe arrangements and in explaining their measurement data.

Deficiency of a pyrroline-5-carboxylate reductase produces the yellowish green cocoon 'Ryokuken' of the silkworm, Bombyx mori.

The silkworm cocoon colour has attracted researchers involved in genetics, physiology and ecology for a long time. 'Ryokuken' cocoons are yellowish green in colour due to unusual flavonoids, prolinylflavonols, while 'Sasamayu' cocoons are light green and contain only simple flavonol glucosides. We found a novel gene associated with the cocoon colour change resulting from a change in flavonoid composition and named it Lg (light green cocoon). In the middle silk glands of the + Lg /+ Lg larvae, 1-pyrroline-5-carboxylic acid (P5C) was found to accumulate due to a decrease in the activity of pyrroline-5-carboxylate reductase (P5CR), an enzyme reducing P5C to proline. Sequence analysis of BmP5CR1, the candidate gene for Lg, revealed a 1.9 kb insertion and a 4 bp deletion within the 1st intron, a 97 bp deletion within the 4th intron, and a > 300 bp insertion within the 3'-UTR, in addition to two amino acid changes on exons 3 and 4 in + Lg /+ Lg compared to Lg/Lg. Decreased expression of BmP5CR1 was observed in all of the investigated tissues, including the middle silk glands in + Lg /+ Lg , which was probably caused by structural changes in the intronic regions of BmP5CR1. Furthermore, a BmP5CR1 knockout strain exhibited a yellowish green cocoon with the formation of prolinylflavonols. These results indicate that the yellowish green cocoon is produced by a BmP5CR1 deficiency. To our knowledge, this is the first report showing that the defect of an enzyme associated with intermediate metabolism promotes the conjugation of phytochemicals derived from foods with endogenously accumulating metabolites in animal tissues.

Quantitative evaluation of deep and shallow tissue layers' contribution to fNIRS signal using multi-distance optodes and independent component analysis.

To quantify the effect of absorption changes in the deep tissue (cerebral) and shallow tissue (scalp, skin) layers on functional near-infrared spectroscopy (fNIRS) signals, a method using multi-distance (MD) optodes and independent component analysis (ICA), referred to as the MD-ICA method, is proposed. In previous studies, when the signal from the shallow tissue layer (shallow signal) needs to be eliminated, it was often assumed that the shallow signal had no correlation with the signal from the deep tissue layer (deep signal). In this study, no relationship between the waveforms of deep and shallow signals is assumed, and instead, it is assumed that both signals are linear combinations of multiple signal sources, which allows the inclusion of a "shared component" (such as systemic signals) that is contained in both layers. The method also assumes that the partial optical path length of the shallow layer does not change, whereas that of the deep layer linearly increases along with the increase of the source-detector (S-D) distance. Deep- and shallow-layer contribution ratios of each independent component (IC) are calculated using the dependence of the weight of each IC on the S-D distance. Reconstruction of deep- and shallow-layer signals are performed by the sum of ICs weighted by the deep and shallow contribution ratio. Experimental validation of the principle of this technique was conducted using a dynamic phantom with two absorbing layers. Results showed that our method is effective for evaluating deep-layer contributions even if there are high correlations between deep and shallow signals. Next, we applied the method to fNIRS signals obtained on a human head with 5-, 15-, and 30-mm S-D distances during a verbal fluency task, a verbal working memory task (prefrontal area), a finger tapping task (motor area), and a tetrametric visual checker-board task (occipital area) and then estimated the deep-layer contribution ratio. To evaluate the signal separation performance of our method, we used the correlation coefficients of a laser-Doppler flowmetry (LDF) signal and a nearest 5-mm S-D distance channel signal with the shallow signal. We demonstrated that the shallow signals have a higher temporal correlation with the LDF signals and with the 5-mm S-D distance channel than the deep signals. These results show the MD-ICA method can discriminate between deep and shallow signals.

Correlating functional near-infrared spectroscopy with underlying cortical regions of 0-, 1-, and 2-year-olds using theoretical light propagation analysis.

Significance: The establishment of a light propagation analysis-based scalp-cortex correlation (SCC) between the scalp location of the source-detector (SD) pair and brain regions is essential for measuring functional brain development in the first 2 years of life using functional near-infrared spectroscopy (fNIRS). Aim: We aimed to reveal the optics-based SCC of 0-, 1-, and 2-year-olds (yo) and the suitable SD distance for this age period. Approach: Light propagation analyses using age-appropriate head models were conducted on SD pairs at 10-10 fiducial points on the scalp to obtain optics-based SCC and its metrics: the number of corresponding brain regions ( N C B R ), selectivity and sensitivity of the most likely corresponding brain region (MLCBR), and consistency of the MLCBR across developmental ages. Moreover, we assessed the suitable SD distances for 0-, 1-, and 2-yo by simultaneously considering the selectivity and sensitivity of the MLCBR. Results: Age-related changes in the SCC metrics were observed. For instance, the N C B R of 0-yo was larger than that of 1- and 2-yo. Conversely, the selectivity of 0-yo was lower than that of 1- and 2-yo. The sensitivity of 1-yo was higher than that of 0-yo at 15- to 30-mm SD distances and higher than that of 2-yo at 10-mm SD distance. Notably, the MLCBR of the fiducial points around the longitudinal fissure was inconsistent across age groups. An SD distance between 15 and 25 mm was found to be appropriate for satisfying both sensitivity and selectivity requirements. In addition, this work provides reference tables of optics-based SCC for 0-, 1-, and 2-yo. Conclusions: Optics-based SCC will be informative in designing and explaining child developmental studies using fNIRS. The suitable SD distances were between 15 and 25 mm for the first 2 years of life.

Theoretical and experimental investigation of the influence of frontal sinus on the sensitivity of the NIRS signal in the adult head.

The sensitivity of the near-infrared spectroscopy signal to the brain activation depends on the thickness and structure of the superficial tissues. The influence of the frontal sinus, which is void region in the skull, on the sensitivity to the brain activation is investigated by the time-resolved experiments and the theoretical modelling of the light propagation in the head. In the time-resolved experiments, the mean-time of flight for the forehead scarcely depends upon the existence of the frontal sinus when probe spacing was shorter than 30 mm. The partial optical path length in the brain, which indicates the sensitivity of the near-infrared spectroscopy signal to the brain activation, in a simplified head model is predicted by Monte Carlo simulation. The influence of the frontal sinus on the sensitivity of the signal depends on the thickness of the skull and the depth of the frontal sinus.

Ex Vivo Assessment of Various Histological Differentiation in Human Carotid Plaque with Near-infrared Spectroscopy Using Multiple Wavelengths.

We previously reported that near-infrared hyperspectral imaging enabled the localization of atherosclerotic plaques from outside the vessels, but not the optical characteristics of each histological component. Therefore, the near-infrared spectrum of each component was collected from the sliced section of the human carotid plaque obtained with endarterectomy and the optical characteristics were confirmed in several wavelengths. Based on this information, we assessed the diagnostic accuracy for ex vivo chemogram in each plaque component created with near-infrared spectroscopy (NIRS), using multiple wavelengths. The chemogram projected on the actual image of plaque was created based on light intensity and transmittance change at three wavelengths. The wavelengths that were mainly were 1440, 1620, 1730, and 1930 nm. We evaluated the accuracy of histological diagnosis in chemogram compared with pathological findings, analyzing interobserver agreement with κ-statistics. The chemograms that we created depicted the components of fibrous tissue, smooth muscle, lipid tissue, intraplaque hemorrhage, and calcification. Diagnostic odds ratio in each component was as follows: 259.6 in fibrous tissue, 144 in smooth muscle, 1123.5 in lipid tissue, 29.3 in intraplaque hemorrhage, and 136.3 in calcification. The κ-statistics revealed that four components, excluding intraplaque hemorrhage, had substantial or almost perfect agreement. Thus, this study demonstrated the feasibility of using chemogram focused on specific component during the histological assessment of atherosclerotic plaques, highlighting its potential diagnostic ability. Chemograms of various target components can be created by combining multiple wavelengths. This technology may prove to be useful in improving the histological assessment of plaque using NIRS.

In situ estimation of optical properties of rat and monkey brains using femtosecond time-resolved measurements.

An accurate knowledge of tissue optical properties (absorption coefficients, µa, and reduced scattering coefficients, µs') is critical for precise modeling of light propagation in biological tissue, essential for developing diagnostic and therapeutic optical techniques that utilize diffusive photons. A great number of studies have explored the optical properties of various tissue, and these values are not known in detail due to difficulties in the experimental determination and significant variations in tissue constitution. Especially, in situ estimates of the optical properties of brain tissue, a common measurement target in optical imaging, is a challenge because of its layer structure (where the thin gray matter covers the white matter). Here, we report an approach to in situ estimates of the µa and µs' of the gray and white matter in living rat and monkey brains by using femtosecond time-resolved measurements and Monte Carlo simulation. The results demonstrate that the µa of the gray matter is larger than that of the white matter, while there was no significant difference in the µs' between the gray and white matter. The optical properties of the rat brain were very similar to those of the monkey brain except for the µa of the gray matter here.

Non-contact acquisition of brain function using a time-extracted compact camera.

A revolution in functional brain imaging techniques is in progress in the field of neurosciences. Optical imaging techniques, such as high-density diffuse optical tomography (HD-DOT), in which source-detector pairs of probes are placed on subjects' heads, provide better portability than conventional functional magnetic resonance imaging (fMRI) equipment. However, these techniques remain costly and can only acquire images at up to a few measurements per square centimetre, even when multiple detector probes are employed. In this study, we demonstrate functional brain imaging using a compact and affordable setup that employs nanosecond-order pulsed ordinary laser diodes and a time-extracted image sensor with superimposition capture of scattered components. Our technique can simply and easily attain a high density of measurement points without requiring probes to be attached, and can directly capture two-dimensional functional brain images. We have demonstrated brain activity imaging using a phantom that mimics the optical properties of an adult human head, and with a human subject, have measured cognitive brain activation while the subject is solving simple arithmetical tasks.

Genetic mapping of a food preference gene in the silkworm, Bombyx mori, using restriction fragment length polymorphisms (RFLPs).

The domesticated silkworm, Bombyx mori, has strict food preferences and grows by feeding on mulberry leaves. However, "Sawa-J", an abnormal feeding habit strain selected from the genetic stock, feeds on an artificial diet without mulberry leaf powder. In this study, the food preference gene in Sawa-J was genetically identified using restriction fragment length polymorphisms (RFLPs) of a cDNA clone on each linkage group. Taking advantage of a lack of genetic recombination in females, reciprocal backcrossed F1 (BC1) progenies were independently prepared using a non-feeding strain, C108, as a mating partner of Sawa-J. Our results of linkage analysis and mapping proved that the feeding behavior is primarily controlled by a major recessive gene mapped at 20.2 cM on RFLP linkage group 9 (RFLG9), and clone e73 at a distance of 4.2 cM was found as the first linked molecular marker.

Room-temperature isolation of V(benzene)2 sandwich clusters via soft-landing into n-alkanethiol self-assembled monolayers.

The adsorption state and thermal stability of V(benzene)2 sandwich clusters soft-landed onto a self-assembled monolayer of different chain-length n-alkanethiols (Cn-SAM, n = 8, 12, 16, 18, and 22) were studied by means of infrared reflection absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD). The IRAS measurement confirmed that V(benzene)2 clusters are molecularly adsorbed and maintain a sandwich structure on all of the SAM substrates. In addition, the clusters supported on the SAM substrates are oriented with their molecular axes tilted 70-80 degrees off the surface normal. An Arrhenius analysis of the TPD spectra reveals that the activation energy for the desorption of the supported clusters increases linearly with the chain length of the SAMs. For the longest chain C22-SAM, the activation energy reaches approximately 150 kJ/mol, and the thermal desorption of the supported clusters can be considerably suppressed near room temperature. The clear chain-length-dependent thermal stability of the supported clusters observed here can be explained well in terms of the cluster penetration into the SAM matrixes.

Wavelength dependence of crosstalk in dual-wavelength measurement of oxy- and deoxy-hemoglobin.

In near-IR spectroscopy, the concentration change in oxy- and deoxyhemoglobin in tissue is calculated from the change in the detected intensity of light at two wavelengths by solving the simultaneous equation based on the modified Lambert-Beer law. The wavelength-independent constant or mean optical path length is usually assigned to the term of partial optical path length in the simultaneous equation. This insufficient optical path length in the calculation causes crosstalk between the concentration change in oxy- and deoxyhemoglobin. We investigate the crosstalk in the dual-wavelength measurement of oxy- and deoxyhemoglobin theoretically by Monte Carlo simulation to discuss the optimal wavelength pair to minimize the crosstalk. The longer wavelength of the dual-wavelength measurement is fixed at 830 nm and the shorter wavelength is varied from 650 to 780 nm. The optimal wavelength range for pairing with 830 nm for the dual-wavelength measurement of oxy- and deoxyhemoglobin is from 690 to 750 nm. The mean optical path length, which can be obtained by time- and phase-resolved measurement, is effective to reduce the crosstalk in the results of dual-wavelength measurement.

Interpretation of principal components of the reflectance spectra obtained from multispectral images of exposed pig brain.

The spatial variation in reflectance such as the blood-vessel pattern can be observed in the image of cerebral cortex. This spatial variation is mainly caused by the difference in concentrations of oxy- and deoxyhemoglobin in the tissue. We analyze the reflectance spectra obtained from multispectral images of pig cortex by principal component analysis to extract information that relates to physiological parameters such as the concentrations of oxy- and deoxyhemoglobin and physical parameters such as mean optical path length. The light propagation in a model of exposed pig cortex is predicted by Monte Carlo simulation to estimate the interpretation of physiological and physical meanings of the principal components. The spatial variance of reflectance spectra of the pig cortex can be approximately described by the first principal component. The first principal component reflects the spectrum of hemoglobin in the cortical tissue multiplied by the mean optical path length. These results imply that the wavelength dependence of mean optical path length can be experimentally estimated from the first principal component of the reflectance spectra obtained from multispectral image of cortical tissue.

Magnetic resonance imaging appropriate for construction of subject-specific head models for diffuse optical tomography.

Subject-specific head models of which their geometry is based on structural magnetic resonance images are essential to accurately estimate the spatial sensitivity profiles for image reconstruction in diffuse optical tomography. T1-weighted magnetic resonance images, which are commonly used for structural imaging, are not sufficient for the threshold-based segmentation of the superficial tissues. Two types of pulse sequences, which provide a high contrast among the superficial tissues, are introduced to complement the segmentation to construct the subject-specific head models. The magnetic resonance images acquired by the proposed pulse sequences are robust to the threshold level and adequate for the threshold-based segmentation of the superficial tissues compared to the T1- and T2-weighted images. The total scan time of the proposed pulse sequences is less than one-fourth of that for the T2-weighted pulse sequence.

Theoretical evaluation of accuracy in position and size of brain activity obtained by near-infrared topography.

Near-infrared (NIR) topography can obtain a topographical distribution of the activated region in the brain cortex. Near-infrared light is strongly scattered in the head, and the volume of tissue sampled by a source-detector pair on the head surface is broadly distributed in the brain. This scattering effect results in poor resolution and contrast in the topographic image of the brain activity. In this study, a one-dimensional distribution of absorption change in a head model is calculated by mapping and reconstruction methods to evaluate the effect of the image reconstruction algorithm and the interval of measurement points for topographic imaging on the accuracy of the topographic image. The light propagation in the head model is predicted by Monte Carlo simulation to obtain the spatial sensitivity profile for a source-detector pair. The measurement points are one-dimensionally arranged on the surface of the model, and the distance between adjacent measurement points is varied from 4 mm to 28 mm. Small intervals of the measurement points improve the topographic image calculated by both the mapping and reconstruction methods. In the conventional mapping method, the limit of the spatial resolution depends upon the interval of the measurement points and spatial sensitivity profile for source-detector pairs. The reconstruction method has advantages over the mapping method which improve the results of one-dimensional analysis when the interval of measurement points is less than 12 mm. The effect of overlapping of spatial sensitivity profiles indicates that the reconstruction method may be effective to improve the spatial resolution of a two-dimensional reconstruction of topographic image obtained with larger interval of measurement points. Near-infrared topography with the reconstruction method potentially obtains an accurate distribution of absorption change in the brain even if the size of absorption change is less than 10 mm.

Arranging optical fibres for the spatial resolution improvement of topographical images.

Optical topography is a method for visualization of conical activity. Ways of improving the spatial resolution of the topographical image with three arrangements of optical fibres are discussed. A distribution of sensitivity is obtained from the phantom experiment, and used to reconstruct topographical images of an activation area of the brain with the fibres in each arrangement. The correlations between the activated area and the corresponding topographical images are obtained, and the effective arrangement of the optical fibres for improved resolution is discussed.

Pial arteries respond earlier than penetrating arterioles to neural activation in the somatosensory cortex in awake mice exposed to chronic hypoxia: an additional mechanism to proximal integration signaling?

The pial and penetrating arteries have a crucial role in regulating cerebral blood flow (CBF) to meet neural demand in the cortex. Here, we examined the longitudinal effects of chronic hypoxia on the arterial diameter responses to single whisker stimulation in the awake mouse cortex, where activity-induced responses of CBF were gradually attenuated. The vasodilation responses to whisker stimulation under prehypoxia normal conditions were 8.1% and 12% relative to their baselines in the pial arteries and penetrating arterioles, respectively. After 3 weeks of hypoxia, however, these responses were significantly reduced to 5.5% and 4.1%, respectively. The CBF response, measured using laser-Doppler flowmetry (LDF), induced by the same whisker stimulation was also attenuated (14% to 2.6%). A close linear correlation was found for the responses between the penetrating arteriolar diameter and LDF, and their temporal dynamics. After 3 weeks of chronic hypoxia, the initiation of vasodilation in the penetrating arterioles was significantly extended, but the pial artery responses remained unchanged. These results show that vasodilation of the penetrating arterioles followed the pial artery responses, which are not explainable in terms of proximal integration signaling. The findings therefore indicate an additional mechanism for triggering pial artery dilation in the neurovascular coupling.

Dynamic phantom with two stage-driven absorbers for mimicking hemoglobin changes in superficial and deep tissues.

In near-infrared spectroscopy (NIRS) for monitoring brain activity and cerebral functional connectivity, the effect of superficial tissue on NIRS signals needs to be considered. Although some methods for determining the effect of scalp and brain have been proposed, direct validation of the methods has been difficult because the actual absorption changes cannot be known. In response to this problem, we developed a dynamic phantom that mimics hemoglobin changes in superficial and deep tissues, thus allowing us to experimentally validate the methods. Two absorber layers are independently driven with two one-axis automatic stages. We can use the phantom to design any type of waveform (e.g., brain activity or systemic fluctuation) of absorption change, which can then be reproducibly measured. To determine the effectiveness of the phantom, we used it for a multiple source-detector distance measurement. We also investigated the performance of a subtraction method with a short-distance regressor. The most accurate lower-layer change was obtained when a shortest-distance channel was used. Furthermore, when an independent component analysis was applied to the same data, the extracted components were in good agreement with the actual signals. These results demonstrate that the proposed phantom can be used for evaluating methods of discriminating the effects of superficial tissue.

The influence of frontal sinus in brain activation measurements by near-infrared spectroscopy analyzed by realistic head models.

Adequate modeling of light propagation in the head is important to predict the sensitivity of NIRS signal and the spatial sensitivity profile of source-detector pairs. The 3D realistic head models of which the geometry is based upon the anatomical images acquired by magnetic resonance imaging and x-ray computed tomography are constructed to investigate the influence of the frontal sinus on the NIRS signal and spatial sensitivity. Light propagation in the head is strongly affected by the presence of the frontal sinus. The light tends to propagate around the frontal sinus. The influence of the frontal sinus on the sensitivity of the NIRS signal to the brain activation is not consistent and depends on the depth of the frontal sinus, the optical properties of the superficial tissues and the relative position between the source-detector pair and the frontal sinus. The frontal sinus located in the shallow region of the skull tends to reduce the sensitivity of the NIRS signal while the deep frontal sinus can increase the sensitivity of the NIRS signal.

Genetic analysis of the electrophysiological response to salicin, a bitter substance, in a polyphagous strain of the silkworm Bombyx mori.

Sawa-J is a polyphagous silkworm (Bombyx mori L.) strain that eats various plant leaves that normal silkworms do not. The feeding preference behavior of Sawa-J is controlled by one major recessive gene(s) on the polyphagous (pph) locus, and several minor genes; moreover, its deterrent cells possess low sensitivity to some bitter substances including salicin. To clarify whether taste sensitivity is controlled by the pph locus, we conducted a genetic analysis of the electrophysiological characteristics of the taste response using the polyphagous strain Sawa-J·lem, in which pph is linked to the visible larval marker lemon (lem) on the third chromosome, and the normal strain Daiankyo, in which the wild-type gene of pph (+(pph)) is marked with Zebra (Ze). Maxillary taste neurons of the two strains had similar dose-response relationships for sucrose, inositol, and strychnine nitrate, but the deterrent cell of Sawa-J·lem showed a remarkably low sensitivity to salicin. The F(1) generation of the two strains had characteristics similar to the Daiankyo strain, consistent with the idea that pph is recessive. In the BF(1) progeny between F(1) females and Sawa-J·lem males where no crossing-over occurs, the lem and Ze phenotypes corresponded to different electrophysiological reactions to 25 mM salicin, indicating that the gene responsible for taste sensitivity to salicin is located on the same chromosome as the lem and Ze genes. The normal and weak reactions to 25 mM salicin were segregated in crossover-type larvae of the BF(1) progeny produced by a reciprocal cross, and the recombination frequency agreed well with the theoretical ratio for the loci of lem, pph, and Ze on the standard linkage map. These results indicate that taste sensitivity to salicin is controlled by the gene(s) on the pph locus.

Optical scanning system for light-absorption measurement of deep biological tissue.

A noncontact near-infrared scanning system for multi-distance absorption measurement of deep biological tissue was developed. An 808-nm laser, whose focal point on the surface of biological tissue is controlled by a galvano scanner, is used as a light source. A phosphor is placed at a detection focal point on the tissue surface. The light that propagates through tissue and exits from the tissue surface beneath the phosphor excites the phosphor. The fluorescence emitted from the phosphor is detected by an avalanche photodiode. The system is used to measure 20 points on tissue surface at which source-detector (S-D) distances are 7-45 mm (with 2-mm intervals). Neither the light source nor the detector contacts the tissue surface. The system was validated by using it to measure the absorption change of an absorber (which is embedded in a deep layer of a tissue-simulating phantom) while the surface-layer thickness of the phantom was changed from 1 to 12 mm. It was demonstrated that both the relative absorption change of the absorber and the absolute thickness of the surface layer can be estimated from the measured optical-density change (ΔOD) and the dependence of ΔOD on S-D distance, respectively.