Investigating the detailed substructure of the cell is beyond the ability of conventional optical microscopy. Electron microscopy, therefore, has been the only option for such studies for several decades. The recent implementation of several super-resolution optical microscopy techniques has rendered the investigation of cellular substructure easier and more efficient. Nevertheless, optical microscopy only provides an image of the present structure of the cell, without any information on its long-temporal changes. These can be investigated by combining super-resolution optics with a nonoptical imaging technique, nanoscale secondary ion mass spectrometry, which investigates the isotopic composition of the samples. The resulting technique, combined isotopic and optical nanoscopy, enables the investigation of both the structure and the “history” of the cellular elements. The age and the turnover of cellular organelles can be read by isotopic imaging, while the structure can be analyzed by optical (fluorescence) approaches. We present these technologies, and we discuss their implementation for the study of biological samples. We conclude that, albeit complex, this type of technology is reliable enough for mass application to cell biology.

This special section brings together papers presented at the fNIRS 2016 conference (http://www.fnirs2016.org/) held in October 2016 in Paris, as well as other contributed papers on near-infrared spectroscopy. The conference had sessions covering the development and use of NIRS spanning the topics of neurodevelopment, brain and systemic physiology, clinical applications, multimodal monitoring, hardware development, global fNIRS, neonatal and pediatric applications, data analysis, and neurocognition. The following six papers are published as Part 1 of the special section. The second part, expected to appear in the October–December 2017 issue, will contain the rest of the papers and will be accompanied by a full editorial.

Optical intrinsic signal (OIS) imaging has been a powerful tool for capturing functional brain hemodynamics in rodents. Recent wide field-of-view implementations of OIS have provided efficient maps of functional connectivity from spontaneous brain activity in mice. However, OIS requires scalp retraction and is limited to superficial cortical tissues. Diffuse optical tomography (DOT) techniques provide noninvasive imaging, but previous DOT systems for rodent neuroimaging have been limited either by sparse spatial sampling or by slow speed. Here, we develop a DOT system with asymmetric source–detector sampling that combines the high-density spatial sampling (0.4 mm) detection of a scientific complementary metal-oxide-semiconductor camera with the rapid (2 Hz) imaging of a few (<50) structured illumination (SI) patterns. Analysis techniques are developed to take advantage of the system’s flexibility and optimize trade-offs among spatial sampling, imaging speed, and signal-to-noise ratio. An effective source–detector separation for the SI patterns was developed and compared with light intensity for a quantitative assessment of data quality. The light fall-off versus effective distance was also used for in situ empirical optimization of our light model. We demonstrated the feasibility of this technique by noninvasively mapping the functional response in the somatosensory cortex of the mouse following electrical stimulation of the forepaw.

Near infrared (NIR) light has been widely used for measuring changes in hemoglobin concentration in the human brain (functional NIR spectroscopy, fNIRS). fNIRS is based on the differential measurement and estimation of absorption perturbations, which, in turn, are based on correctly estimating the absolute parameters of light propagation. To do so, it is essential to accurately characterize the baseline optical properties of tissue (absorption and reduced scattering coefficients). However, because of the diffusive properties of the medium, separate determination of absorption and scattering across the head is challenging. The effective attenuation coefficient (EAC), which is proportional to the geometric mean of absorption and reduced scattering coefficients, can be estimated in a simpler fashion by multidistance light decay measurements. EAC mapping could be of interest for the scientific community because of its absolute information content, and because light propagation is governed by the EAC for source–detector distances exceeding 1 cm, which sense depths extending beyond the scalp and skull layers. Here, we report an EAC mapping procedure that can be applied to standard fNIRS recordings, yielding topographic maps with 2- to 3-cm resolution. Application to human data indicates the importance of venous sinuses in determining regional EAC variations, a factor often overlooked.

The mechanisms responsible for coupling between relative cerebral blood flow (rCBF), relative cerebral blood volume (rCBV), and relative cerebral metabolic rate of oxygen (rCMRO2), an important function of the microcirculation in preterm infants, remain unclear. Identification of a causal relationship between rCBF–rCBV and rCBF−rCMRO2 in preterms may, therefore, help to elucidate the principles of cortical hemodynamics during development. We simultaneously recorded rCBF and rCBV and estimated rCMRO2 by two independent acquisition systems: diffuse correlation spectroscopy and near-infrared spectroscopy, respectively, in 10 preterms aged between 28 and 35 weeks of gestational age. Transfer entropy was calculated in order to determine the directionality between rCBF–rCBV and rCBF−rCMRO2. The surrogate method was applied to determine statistical significance. The results show that rCBV and rCMRO2 have a predominant driving influence on rCBF at the resting state in the preterm neonatal brain. Statistical analysis robustly detected the correct directionality of rCBV on rCBF and rCMRO2 on rCBF. This study helps to clarify the early organization of the rCBV–rCBF and rCBF−rCMRO2 inter-relationship in the immature cortex.

In diffuse optical tomography (DOT), overlapping and multidistance measurements are required to reconstruct depth-resolved images of oxy- (HbO2) and deoxy- (HHb) hemoglobin concentration changes occurring in the brain. These can be considered an indirect measure of brain activity, under the assumption of intact neurovascular coupling. Broadband systems also allow changes in the redox state of cytochrome c oxidase (oxCCO) to be measured, which can be an important biomarker when neurovascular coupling is impaired. We used DOT to reconstruct images of Δ[HbO2], Δ[HHb], and Δ[oxCCO] from data acquired with a broadband system. Four healthy volunteers were measured while performing a visual stimulation task (4-Hz inverting checkerboard). The broadband system was configured to allow multidistance and overlapping measurements of the participants’ visual cortex with 32 channels. A multispectral approach was employed to reconstruct changes in concentration of the three chromophores during the visual stimulation. A clear and focused activation was reconstructed in the left occipital cortex of all participants. The difference between the residuals of the three-chromophore model and of the two-chromophore model (recovering only Δ[HbO2] and Δ[HHb]) exhibits a spectrum similar to that of oxCCO. These results form a basis for further studies aimed to further optimize image reconstruction of Δ[oxCCO].

Broadband near-infrared spectroscopy (NIRS) can provide an endogenous indicator of tissue temperature based on the temperature dependence of the water absorption spectrum. We describe a first evaluation of the calibration and prediction of brain tissue temperature obtained during hypothermia in newborn piglets (animal dataset) and rewarming in newborn infants (human dataset) based on measured body (rectal) temperature. The calibration using partial least squares regression proved to be a reliable method to predict brain tissue temperature with respect to core body temperature in the wavelength interval of 720 to 880 nm with a strong mean predictive power of R2=0.713±0.157 (animal dataset) and R2=0.798±0.087 (human dataset). In addition, we applied regression receiver operating characteristic curves for the first time to evaluate the temperature prediction, which provided an overall mean error bias between NIRS predicted brain temperature and body temperature of 0.436±0.283°C (animal dataset) and 0.162±0.149°C (human dataset). We discuss main methodological aspects, particularly the well-known aspect of over- versus underestimation between brain and body temperature, which is relevant for potential clinical applications.

Neurofeedback is a method for using neural activity displayed on a computer to regulate one’s own brain function and has been shown to be a promising technique for training individuals to interact with brain–machine interface applications such as neuroprosthetic limbs. The goal of this study was to develop a user-friendly functional near-infrared spectroscopy (fNIRS)-based neurofeedback system to upregulate neural activity associated with motor imagery, which is frequently used in neuroprosthetic applications. We hypothesized that fNIRS neurofeedback would enhance activity in motor cortex during a motor imagery task. Twenty-two participants performed active and imaginary right-handed squeezing movements using an elastic ball while wearing a 98-channel fNIRS device. Neurofeedback traces representing localized cortical hemodynamic responses were graphically presented to participants in real time. Participants were instructed to observe this graphical representation and use the information to increase signal amplitude. Neural activity was compared during active and imaginary squeezing with and without neurofeedback. Active squeezing resulted in activity localized to the left premotor and supplementary motor cortex, and activity in the motor cortex was found to be modulated by neurofeedback. Activity in the motor cortex was also shown in the imaginary squeezing condition only in the presence of neurofeedback. These findings demonstrate that real-time fNIRS neurofeedback is a viable platform for brain–machine interface applications.

Pulsed infrared (IR) laser energy has been shown to modulate neurological activity through both stimulation and inhibition of action potentials. While the mechanism(s) behind this phenomenon is (are) not completely understood, certain hypotheses suggest that the rise in temperature from IR exposure could activate temperature- or pressure-sensitive ion channels or create pores in the cellular outer membrane, allowing an influx of typically plasma-membrane-impermeant ions. Studies using fluorescent intensity-based calcium ion ( Ca 2 + ) sensitive dyes show changes in Ca 2 + levels after various IR stimulation parameters, which suggests that Ca 2 + may originate from the external solution. However, activation of intracellular signaling pathways has also been demonstrated, indicating a more complex mechanism of increasing intracellular Ca 2 + concentration. We quantified the Ca 2 + mobilization in terms of influx from the external solution and efflux from intracellular organelles using Fura-2 and a high-speed ratiometric imaging system that rapidly alternates the dye excitation wavelengths. Using nonexcitable Chinese hamster ovarian ( CHO - hM 1 ) cells and neuroblastoma-glioma (NG108) cells, we demonstrate that intracellular IP 3 receptors play an important role in the IR-induced Ca 2 + , with the

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