This PDF file contains the editorial “2016 List of Reviewers” for NPh Vol. 4 Issue 01

Measuring changes in cerebral oxygen in tissue microdomains during epilepsy is important to identify hypoxic potential. Here, using a custom-built two-photon microscopy system, we present microscopic measurements of oxygen partial pressure (PO2) in cortical microvessels and tissue of anesthetized mice during 4-aminopyridine (4-AP)-induced epileptic seizures. Investigating epileptic events, we characterized the distribution of the “initial dip” in PO2 in arterioles, venules, and tissue near the 4-AP injection site. Our results reveal a correlation between the percent change in PO2 during the “initial dip” and the diameter of nearest arterioles and venules.

This PDF file contains the editorial “Special Section Guest Editorial: Brain Mapping and Therapeutics” for NPh Vol. 4 Issue 01

Optogenetic methods developed over the past decade enable unprecedented optical activation and silencing of specific neuronal cell types. However, light scattering in neural tissue precludes illuminating areas deep within the brain via free-space optics; this has impeded employing optogenetics universally. Here, we report an approach surmounting this significant limitation. We realize implantable, ultranarrow, silicon-based photonic probes enabling the delivery of complex illumination patterns deep within brain tissue. Our approach combines methods from integrated nanophotonics and microelectromechanical systems, to yield photonic probes that are robust, scalable, and readily producible en masse. Their minute cross sections minimize tissue displacement upon probe implantation. We functionally validate one probe design in vivo with mice expressing channelrhodopsin-2. Highly local optogenetic neural activation is demonstrated by recording the induced response—both by extracellular electrical recordings in the hippocampus and by two-photon functional imaging in the cortex of mice coexpressing GCaMP6.

Impaired facial processing may contribute to social dysfunction in certain individuals with autism spectrum disorder (ASD). Prior studies show that electroencephalogram-based and functional magnetic resonance imaging-based neurofeedback might help some individuals with ASD learn to modulate regional brain activity and thus reduce symptoms. Here, we report for the first time the feasibility of employing functional near-infrared spectroscopy (fNIRS)-based neurofeedback training in children with ASD. We developed a method to study physiological self-regulation of oxy-hemoglobin using real-time feedback. The paradigm is illustrated with initial data from four subjects who engaged in a facial-identity recognition training program during which an implicit reinforcement was given based on the participant’s brain activity and behavioral performance. Two participants had a confirmed diagnosis of ASD, and the other two were typically developing (TD). One participant with ASD and one TD participant received real-feedback (real-FB) during the training, whereas the other two received sham-feedback (sham-FB). After five training sessions, the subjects who received real-FB showed more improvement in facial recognition performance compared with those receiving sham-FB, particularly in the participant with ASD. These results suggest fNIRS-based neurofeedback could enhance therapeutic intervention in children with ASD.

Palmar and plantar grasp are the foremost primitive neonatal reflexes and functions. Persistence of these reflexes in infancy is a sign of evolving cerebral palsy. Our aims were to establish measurement feasibility in a clinical setting and to characterize changes in oxyhemoglobin (HbO) and deoxyhemoglobin (HbD) concentration in the bilateral frontoparietal cortex in unsedated neonates at the crib-side using functional near-infrared spectroscopy (fNIRS). We hypothesized that bilateral concentration changes will occur upon somatic central and peripheral somatic stimulation. Thirteen preterm neonates (five males) underwent time 1, and six (two males) returned for time 2 (mean PMA=41.6 and 47.0 weeks, respectively). Signals from a total of 162 somatic stimuli responses were measured. Response amplitude, duration, and latency were log-transformed and compared between palmar, plantar, and oromotor stimuli using linear mixed models, adjusted for cap, electroencephalogram abnormality, time (1 versus 2), and Sarnat score, if necessary. The oromotor stimulus resulted in a 50% greater response than the palmar or plantar stimuli for HbO left and right hemisphere duration (p<0.0001). There were no other statistically significant differences between stimuli for any other outcome (p>0.05). Utilizing fNIRS in conjunction with occupational and physical therapy maneuvers is efficacious to study modifiable and restorative neurophysiological mechanisms.

Some very transparent cells in the optical tract of vertebrates, such as the lens fiber cells, possess certain types of specialized intermediate filaments (IFs) that have essential significance for their transparency. The exact mechanism describing why the IFs are so important for transparency is unknown. Recently, transparency was described also in the retinal Müller cells (MCs). We report that the main processes of the MCs contain bundles of long specialized IFs, each about 10 nm in diameter; most likely, these filaments are the channels providing light transmission to the photoreceptor cells in mammalian and avian retinas. We interpret the transmission of light in such channels using the notions of quantum confinement, describing energy transport in structures with electroconductive walls and diameter much smaller than the wavelength of the respective photons. Model calculations produce photon transmission efficiency in such channels exceeding 0.8, in optimized geometry. We infer that protein molecules make up the channels, proposing a qualitative mechanism of light transmission by such structures. The developed model may be used to describe light transmission by the IFs in any transparent cells.

We present the visualization of the mouse cerebellum and adjacent brainstem using a serial optical coherence scanner, which integrates a vibratome slicer and polarization-sensitive optical coherence tomography for ex vivo imaging. The scanner provides intrinsic optical contrasts to distinguish the cerebellar cortical layers and white matter. Images from serial scans reveal the large-scale anatomy in detail and map the nerve fiber pathways in the cerebellum and brainstem. By incorporating a water-immersion microscope objective, we also present high-resolution tiled images that delineate fine structures in the cerebellum and brainstem.

Visualization of whole brain activity during epileptic seizures is essential for both fundamental research into the disease mechanisms and the development of efficient treatment strategies. It has been previously discussed that pathological synchronization originating from cortical areas may reinforce backpropagating signaling from the thalamic neurons, leading to massive seizures through enhancement of high frequency neural activity in the thalamocortical loop. However, the study of deep brain neural activity is challenging with the existing functional neuroimaging methods due to lack of adequate spatiotemporal resolution or otherwise insufficient penetration into subcortical areas. To investigate the role of thalamocortical activity during epileptic seizures, we developed a new functional neuroimaging framework based on spatiotemporal correlation of volumetric optoacoustic hemodynamic responses with the concurrent electroencephalogram recordings and anatomical brain landmarks. The method is shown to be capable of accurate three-dimensional mapping of the onset, spread, and termination of the epileptiform events in a 4-aminopyridine acute model of focal epilepsy. Our study is the first to demonstrate entirely noninvasive real-time visualization of synchronized epileptic foci in the whole mouse brain, including the neocortex and subcortical structures, thus opening new vistas in systematic studies toward the understanding of brain signaling and the origins of neurological disorders.

High-resolution three-dimensional (3-D) imaging (stereo imaging) by endoscopes in minimally invasive surgery, especially in space-constrained applications such as brain surgery, is one of the most desired capabilities. Such capability exists at larger than 4-mm overall diameters. We report the development of a stereo imaging endoscope of 4-mm maximum diameter, called Multiangle, Rear-Viewing Endoscopic Tool (MARVEL) that uses a single-lens system with complementary multibandpass filter (CMBF) technology to achieve 3-D imaging. In addition, the system is endowed with the capability to pan from side-to-side over an angle of ±25  deg, which is another unique aspect of MARVEL for such a class of endoscopes. The design and construction of a single-lens, CMBF aperture camera with integrated illumination to generate 3-D images, and the actuation mechanism built into it is summarized.

Understanding the functional wiring of neural circuits and their patterns of activation following sensory stimulations is a fundamental task in the field of neuroscience. Furthermore, charting the activity patterns is undoubtedly important to elucidate how neural networks operate in the living brain. However, optical imaging must overcome the effects of light scattering in the tissue, which limit the light penetration depth and affect both the imaging quantitation and sensitivity. Laminar optical tomography (LOT) is a three-dimensional (3-D) in-vivo optical imaging technique that can be used for functional imaging. LOT can achieve both a resolution of 100 to 200  μm and a penetration depth of 2 to 3 mm based either on absorption or fluorescence contrast, as well as large field-of-view and high acquisition speed. These advantages make LOT suitable for 3-D depth-resolved functional imaging of the neural functions in the brain and spinal cords. We review the basic principles and instrumentations of representative LOT systems, followed by recent applications of LOT on 3-D imaging of neural activities in the rat forepaw stimulation model and mouse whisker-barrel system.

Advances in image-guided therapy enable physicians to obtain real-time information on neurological disorders such as brain tumors to improve resection accuracy. Image guidance data include the location, size, shape, type, and extent of tumors. Recent technological advances in neurophotonic engineering have enabled the development of techniques for minimally invasive neurosurgery. Incorporation of these methods in intraoperative imaging decreases surgical procedure time and allows neurosurgeons to find remaining or hidden tumor or epileptic lesions. This facilitates more complete resection and improved topology information for postsurgical therapy (i.e., radiation). We review the clinical application of recent advances in neurophotonic technologies including Raman spectroscopy, thermal imaging, optical coherence tomography, and fluorescence spectroscopy, highlighting the importance of these technologies in live intraoperative tissue mapping during neurosurgery. While these technologies need further validation in larger clinical trials, they show remarkable promise in their ability to help surgeons to better visualize the areas of abnormality and enable safe and successful removal of malignancies.

Surgical removal of tumor mass is a common approach in the management of brain tumors. However, the precise delineation of normal tissue from tumor tissue for a complete resection of tumor mass in brain tumor surgery remains a difficult task for neurosurgeons. Aminolevulinic acid (ALA)-mediated exgogenous fluorescence of protoporphyrin IX (PpIX) is a sensitive approach for tumor imaging. Recent studies suggest that the use of ALA/PpIX-mediated fluorescence-guided resection (FGR) or fluorescence-guided surgery can enable more accurate and complete resection of brain tumors, especially when used in quantitative fashion. This review will highlight the current progress in PpIX-mediated FGR and discuss technical challenges in intraoperative quantification of intracellular PpIX fluorescence during FGR of brain tumor.

Historically, regular drusen and geographic atrophy (GA) have been recognized as the hallmarks of nonneovascular age-related macular degeneration (AMD). Recent imaging developments have revealed another distinct nonneovascular AMD phenotype, reticular pseudodrusen (RPD). We develop an approach to semiautomatically quantify retinal surfaces associated with various AMD lesions (i.e., regular drusen, RPD, and GA) in spectral domain (SD) optical coherence tomography (OCT) images. More specifically, a graph-based algorithm was used to segment multiple retinal layers in SD-OCT volumes. Varying surface feasibility constraints based on the presegmentation were applied on the double-surface graph search to refine the surface segmentation. The thicknesses of these layers and their correlation with retinal functional measurements, including microperimetry (MP) sensitivity and visual acuity (VA), were investigated. The photoreceptor outer segment layer demonstrated significant thinning with a reduction in MP sensitivity and VA score when atrophic AMD lesions were present. Regular drusen and RPD were separately segmented on SD-OCT images to allow their characteristics and distribution to be studied separately. The mean thickness of regular drusen was found to significantly correlate with the VA score. RPD appeared to be distributed evenly throughout the macula and regular drusen appeared to be more concentrated centrally.

The brain is equipped with a complex system for processing sensory information, including retinal circuitry comprising part of the central nervous system. Retinal stimulation can influence brain function via customized eyeglasses at both subcortical and cortical levels. We investigated cortical effects from wearing therapeutic eyeglasses, hypothesizing that they can create measureable changes in electroencephalogram (EEG) tracings. A Z-Bell^SM test was performed on a participant to select optimal lenses. An EEG measurement was recorded before and after the participant wore the eyeglasses. Equivalent quantitative electroencephalography (QEEG) analyses (statistical analysis on raw EEG recordings) were performed and compared with baseline findings. With glasses on, the participant’s readings were found to be closer to the normed database. The original objective of our investigation was met, and additional findings were revealed. The Z-bell^SM test identified lenses to influence neurotypical brain activity, supporting the paradigm that eyeglasses can be utilized as a therapeutic intervention. Also, EEG analysis demonstrated that encephalographic techniques can be used to identify channels through which neuro-optomertric treatments work. This case study’s preliminary exploration illustrates the potential role of QEEG analysis and EEG-derived brain imaging in neuro-optometric research endeavors to affect brain function.

Infrared (IR) imaging is used to detect the subtle changes in temperature needed to accurately detect and monitor disease. Technological advances have made IR a highly sensitive and reliable detection tool with strong potential in medical and neurophotonics applications. An overview of IR imaging specifically investigating quantum well IR detectors developed at Jet Propulsion Laboratory for a noninvasive, nonradiating imaging tool is provided, which could be applied for neuroscience and neurosurgery where it involves sensitive cellular temperature change.

Functional near-infrared spectroscopy (fNIRS) is a noninvasive neuroimaging technique, which uses light to measure changes in cerebral blood oxygenation through sensors placed on the surface of the scalp. We recorded concurrent fNIRS with magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) in order to investigate the group-level correspondence of these measures with source-localized fNIRS estimates. Healthy participants took part in both a concurrent fNIRS-MEG and fNIRS-fMRI neuroimaging session during two somatosensory stimulation tasks, a blocked design median nerve localizer and parametric pulsed-pair median nerve stimulation using interpulse intervals from 100 to 500 ms. We found the spatial correlation for estimated activation patterns from the somatosensory task was R=0.54, 0.57, and −0.48 and the amplitude correlation was R=0.80, 0.52, and −0.70 for fMRI-MEG, fMRI-fNIRS oxy-hemoglobin, and fMRI-fNIRS deoxy-hemoglobin signals, respectively. Taken together, these results show good correspondence among the fMRI, fNIRS, and MEG with the great majority of the difference across modalities being driven by lower sensitivity for deeper brain sources in MEG and fNIRS. These results provide an important validation of source-localized fNIRS in the context of concurrent multimodal imaging for future studies of the relationship between physiological effects in the human brain.

Neuronal activity results in the release of K+ into the extracellular space (ECS). Classically, measurements of extracellular K+ ([K+]o) are carried out using K+-sensitive microelectrodes, which provide a single point measurement with undefined spatial resolution. An imaging approach would enable the spatiotemporal mapping of [K+]o. Here, we report on the design and characterization of a fluorescence imaging-based K+-sensitive nanosensor for the ECS based on dendrimer nanotechnology. Spectral characterization, sensitivity, and selectivity of the nanosensor were assessed by spectrofluorimetry, as well as in both wide-field and two-photon microscopy settings, demonstrating the nanosensor efficacy over the physiologically relevant ion concentration range. Spatial and temporal kinetics of the nanosensor responses were assessed using a localized iontophoretic K+ application on a two-photon imaging setup. Using acute mouse brain slices, we demonstrate that the nanosensor is retained in the ECS for extended periods of time. In addition, we present a ratiometric ve

Diffuse optical tomography (DOT) measures concentration changes in both oxy- and deoxyhemoglobin providing three-dimensional images of local brain activations. A pilot study, which compares both DOT and functional magnetic resonance imaging (fMRI) volumes through t-maps given by canonical statistical parametric mapping (SPM) processing for both data modalities, is presented. The DOT series were processed using a method that is based on a Bayesian filter application on raw DOT data to remove physiological changes and minimum description length application index to select a number of singular values, which reduce the data dimensionality during image reconstruction and adaptation of DOT volume series to normalized standard space. Therefore, statistical analysis is performed with canonical SPM software in the same way as fMRI analysis is done, accepting DOT volumes as if they were fMRI volumes. The results show the reproducibility and ruggedness of the method to process DOT series on group analysis using cognitive paradigms on the prefrontal cortex. Difficulties such as the fact that scalp–brain distances vary between subjects or cerebral activations are difficult to reproduce due to strategies used by the subjects to solve arithmetic problems are considered. T-images given by fMRI and DOT volume series analyzed in SPM show that at the functional level, both DOT and fMRI measures detect the same areas, although DOT provides complementary information to fMRI signals about cerebral activity.

Functional near-infrared spectroscopy (fNIRS) has recently been suggested for monitoring cortical hemodynamic response to experimental and clinical acute pain. However, the hemodynamic response to a tonic, noxious cold stimulus, and its relation with subjective pain sensation is not fully characterized. We investigated the relationship between pain threshold and tolerance and the evoked hemodynamic response to cold pressor tests (CPTs) at varying intensities and explored the gender effect. Twenty-one healthy individuals (10 males and 11 females) performed four CPTs at 1°C, 5°C, 10°C, and 15°C. Deoxyhemoglobin (HHb) and oxyhemoglobin (HbO2) were measured continuously on the forehead by two “far” and two “near” channels in addition to pain scores, threshold, and tolerance. We found a significant within-subject correlation between pain threshold and the immediate HbO2 response at the right frontal region. Gender difference and asymmetrical activation were observed in the “far” channels but not the “near” channels, suggesting a hemispheric preference in response to noxious cold stimuli. No gender difference was found in pain threshold, tolerance, or scores. This research adds to the body of literature suggesting the use of fNIRS for bedside assessment of pain in addition to behavioral and subjective measures for comprehensive, multimodal pain management.

This PDF file contains the errata for “NPh Vol. 4 Issue 01 Paper NPh-2016-0829-ERR” for NPh Vol. 4 Issue 01