.SignificanceContinuous, noninvasive monitoring of cerebral blood flow (CBF) at the bedside is a critical unmet clinical need and a long-standing goal of biomedical optics. Despite extensive development, no optical measurement of CBF has achieved routine clinical use.AimWe aim to demonstrate and validate CoMind R1, a time-resolved interferometric neuromonitoring system designed to noninvasively measure CBF at pulsatile rates.ApproachCoMind R1 integrates numerous advances, including a high-power, linearly swept 1064 nm laser, multimode collection, parallelized detection, and real-time processing. Performance is evaluated with homogeneous and dynamic bi-layer phantoms and in vivo studies of adults at rest and during visual stimulation.ResultsCoMind R1 achieves an instrument response function width of 120 ps and exhibits no significant drift over 24 h. In vivo data from 25 adults show consistent pulsatile blood flow waveforms at times-of-flight averaging 1.2 ns, exceeding the prior art. Visual stimulation produces significant, time-of-flight-dependent hyperaemic responses, demonstrating brain sensitivity and selectivity.ConclusionsCoMind R1 consistently achieves time-of-flight resolved measurements of pulsatile blood flow at the late times-of-flight necessary to ensure a brain-dominated signal in the typical adult. CoMind R1 thus provides cerebral sensitivity and tissue specificity in a scalable, cost-effective architecture and advances optical monitoring of CBF toward clinical translation.

Although large field-of-view two-photon microscopy (LF-TPM) is a powerful neuroimaging tool, low signal-to-noise (SNR) poses challenges for high-speed imaging. Increasing the average laser power improves the SNR, but the thermal effect of high laser power on the cortex is not well studied. Further, capturing the curvature of the cortex requires creating an image stack, which also reduces the temporal resolution. Solving these problems would enable mesoscopic mapping with LF-TPM. We aim to study the temperature dynamic of the mouse cortex as a function of the field of view and the average laser power and demonstrate the feasibility of relatively high illumination power. Combining the higher illumination intensity and the curved scanning, we aim to showcase the capability of the LF-TPM system in both stimulated and spontaneous mesoscopic mapping. We developed a combined thermal imaging and LF-TPM system to measure the spatial-temporal dynamics of heat during TPM imaging. We used an electrically tunable lens to vary the focusing depth and track the cortical curvature as a function of the medial distance. We then used the optimized system to image functional activations and resting-state functional connectivity patterns across both hemispheres. The steady-state maximum cortical temperature declines as the FOV increases. For a FOV and 388mW average laser power on the cortical surface, the cortical temperature stayed below 40°C. Using 360mW average power and a curved imaging surface, the custom LF-TPM system can map bilateral hind paw stimulation responses with a single trial and spontaneous bilateral functional connectivity. Concurrent thermal and LF-TPM imaging enables a quantitative optimization of laser power and SNR in LF-TPM systems. We demonstrated the feasibility of bilateral brain mapping using LF-TPM. These findings will help expand the utility of LF-TPMs for mesoscopic brain mapping applications.

.SignificanceDeaf and hard-of-hearing infants’ hemodynamic response function (HRF) has not yet been characterized. However, without an appropriate estimate of their HRF, neuroimaging modalities relying on hemodynamic responses, e.g., functional magnetic resonance imaging (fMRI) or functional near-infrared spectroscopy (fNIRS), cannot be used reliably in this population, e.g., prior to and following cochlear implantation. We contribute to better theoretical models of and more suitable therapeutic interventions for the neural changes induced by auditory and language deprivation in deaf infants.AimWe aim to characterize the parameters of the HRF of deaf and hard-of-hearing infants in response to Italian.ApproachWe measured 2- to 20-month-old Italian-exposed infants’ HRF to Italian using fNIRS in the bilateral temporal, i.e., auditory, cortices. We characterized the HRF for all infants and for three clinically relevant subsets: (i) monolingual Italian infants, (ii) genetically deaf infants, and (iii) infants aged 5 to 12 months. We computed the following parameters: peak amplitude, time-to-peak, full width at half maximum, and where present, the amplitude and latency of the initial dip and/or the final undershoot, using a model-based parameter fitting approach. We statistically compared these HRF parameters to those of typically hearing infants.ResultsDeaf and typically hearing infants showed largely similar HRFs, with both groups reaching comparable main peak amplitudes. Minor differences have been found in the latencies of some response components.ConclusionsOur results provide the first detailed characterization of the hemodynamic response to native-language speech in deaf and hard-of-hearing infants, improving clinical and therapeutic approaches through more accurate analysis of fMRI and fNIRS data.

.SignificanceIn mesoscopic imaging research in neuroscience, achieving high spatial resolution optical imaging across the entire field of view (FOV) remains critical. This directly determines whether researchers can precisely analyze the large-scale dynamic activities of neural circuits at the single-cell or even subcellular level. Consistent optical quality throughout the entire imaging FOV is essential to accurately capture the spatiotemporal patterns of neural activity across brain regions, thereby providing a powerful tool for understanding the circuit mechanisms underlying cognition, behavior, and disease at cellular and subcellular resolution in vivo.AimThis study aims to develop a technology that extends the imaging FOV in a two-photon mesoscope while enhancing the optical quality across the entire FOV in vivo. The key point is to establish a robust method that can significantly extend the FOV beyond what the micro/mesoscope objective had been originally designed for, yet maintain the original resolution specifications. As such, the value of the method also extends beyond improving just one mesoscope, which we use as a demo in this study.ApproachThis study introduces an innovative approach that combines block scanning with adaptive optical (AO) correction through a bioinspired honeycomb-based cellular multipoint adaptive technology (CMAT) to achieve mesoscopic two-photon imaging. This system enables unprecedented large-FOV, high-resolution imaging by dividing an imaging area into subregions, each pre-optimized with deformable mirror (DM) compensation while applying real-time dynamic wavefront correction during scanning. Furthermore, we have designed multiple user-defined sub-region scanning functions. Each sub-region automatically loads the aberration correction compensation values from the nearest reference point relative to its center, thereby ensuring optimal optical performance for every individual sub-region. The robustness of this technology has been systematically verified across multiple neural circuit observation scenarios using transgenic mouse models, demonstrating its capability for reliable single-cell resolution imaging across extensive brain regions.ResultsComprehensive evaluation using standard samples and transgenic mouse models demonstrated that the CMAT significantly enhances the imaging performance of the two-photon mesoscope. This technique extends the effective two-photon imaging FOV from to while markedly improving the optical quality in the peripheral regions. High resolution was maintained at (lateral) and (axial) in the central area, with edge regions achieving improved resolutions of (lateral) and (axial). Quantitative analysis confirmed that multipoint AO not only enhances image contrast and optical resolution but also substantially increases the signal-to-noise ratio (SNR) in imaging. This work delivers a pivotal technical advance for large-scale functional imaging of neural circuits.ConclusionCMAT significantly extends the effective FOV and enhances the optical quality of the two-photon mesoscope system.

.SignificanceNeuroimaging research on child development in low- and middle-income countries (LMICs) remains limited, in part due to substantial implementation challenges. Although functional near-infrared spectroscopy (fNIRS) is a promising tool in these contexts, its use is constrained by barriers that are not yet systematically characterized.AimWe systematically evaluate the challenges encountered during a 3-year longitudinal fNIRS project with children in Dhaka, Bangladesh. We aim to identify the major challenges affecting data quality and collection, compare our findings with similar studies in other LMICs, and gather practical guidance for fNIRS implementation in LMICs.ApproachWe applied failure mode and effects analysis to systematically identify the major challenges in the project. We also polled researchers with experience in similar fNIRS studies in other LMICs and compiled mitigation strategies.ResultsHigh-risk challenges were primarily related to fNIRS headcap fit, onsite staff procedures, and environmentally related fNIRS equipment functionality. Most of these challenges were also reported by other polled sites. Effective mitigation strategies have been compiled based on experience in Dhaka and insights from multiple LMICs.ConclusionsWe provide valuable insights into the challenges of implementing fNIRS in LMICs by identifying high-priority challenges and effective mitigation strategies, ultimately informing more equitable and reliable fNIRS research in global child health.

.SignificanceThe combination of two-photon calcium imaging and targeted two-photon optogenetic stimulation, termed all-optical interrogation, provides spatial and temporal precision when recording and manipulating neural circuit activity in vivo. All-optical experiments often use red-shifted opsins in combination with green fluorescent reporters of neuronal activity. However, their excitation spectra still partially overlap, meaning that the imaging laser can excite the opsin. Although some care has been taken in the past to understand the effects of this spectral overlap; further work is required to understand its impact on the findings of all-optical studies.AimWe aimed to investigate whether two-photon imaging of the green fluorescent calcium reporter GCaMP6s at 920 nm increase the rate of response desensitization in neurons targeted for two-photon stimulation at 1035 nm expressing the red-shifted opsin C1V1.ApproachWe systematically varied either the inter-stimulus interval or the duration of two-photon calcium imaging during targeted two-photon optogenetic stimulation of mouse layer 2/3 barrel cortex or visual cortex neurons.ResultsWe found that two-photon imaging at 920 nm decreases trial-by-trial photostimulation responses in targeted C1V1-expressing neurons—an effect that is exacerbated at shorter inter-stimulus intervals. This is consistent with the imaging laser increasing the rate of opsin desensitization. Reduced photostimulation responses are not limited to targeted cells and are found across the field of view. Such network effects are less pronounced at shorter imaging doses.ConclusionsOur results provide methodological optimizations that enable trial-by-trial decreases in photostimulation response to be mitigated in all-optical experiments. This will reduce an external source of trial-by-trial variability in future all-optical experiments.

.SignificanceTo learn mathematics, young children require accurate interpretations of mathematics vocabulary. When school language differs from children’s home language, mathematics performance often decreases. Little is known about cortical activation during mathematics vocabulary processing in different languages. Although behavioral data highlight a difference in L1 and L2 mathematics learning, neuroimaging insights will help us to better understand how and why there is a difference in children’s mathematical learning in multilingual societies.Aim and ApproachWe investigated behavioral and brain responses (fNIRS) of 42 isiZulu and Sesotho (L1) first graders (6.75 to 7.83 years, 22 girls) who learn mathematics in English (L2) at school when they encounter mathematics vocabulary in L2 compared with L1 and mathematics vocabulary compared with object recognition in L1.ResultsThe results show that higher accuracy in the L1 mathematics vocabulary, as compared with the L2 mathematics vocabulary, comes with the costs of higher cognitive demands in the right superior and middle frontal gyri for first graders. Mathematics vocabulary required longer response time than object recognition and a higher activation in the right superior frontal gyrus. No parietal difference was observed between conditions.ConclusionsNeuroimaging revealed that children engaged additional frontoparietal regions when processing L1 mathematics vocabulary—patterns not detectable through behavioral measures alone. Increased frontal activation suggests that the interpretation of mathematics vocabulary in L2 is not yet automatized. This study demonstrates how educational neuroimaging refines interpretations of behavioral outcomes within multilingual contexts.

.SignificanceAccurate and consistent probe placement is crucial in functional near-infrared spectroscopy (fNIRS) and electroencephalogram (EEG) experiments, especially in longitudinal and group-based studies. Both operator experience and subject head shape variability can affect placement accuracy.AimWe aim to develop an easy-to-use software, NeuroNavigatAR (NNAR), utilizing augmented reality (AR) and machine learning to estimate and display in real-time the subject’s cranial and head landmarks to guide consistent headgear placement.ApproachBy applying a facial recognition toolbox to the image frames extracted from a video camera, we can obtain and continuously track subject-specific three-dimensional facial landmarks. Separately, we have precomputed a robust linear transformation between facial landmarks and key cranial landmarks, including nasion and preauricular points, using a large public head-model library consisting of over 1000 subjects. These allow us to rapidly estimate subject-specific cranial landmarks and subsequently render atlas-derived head landmarks to the subject’s camera stream.ResultsAn open-source graphical user interface implementing this AR system has achieved a speed of 15 frames per second using a laptop. A median 10-20 position error of 1.52 cm was found when using a general adult atlas and is further reduced to 1.33 cm and 0.75 cm when using age-matched atlas models and subject-specific head surfaces, respectively. NNAR demonstrated consistent head-landmark prediction errors across repeated measurement sessions; there is also no statistically significant difference in accuracy across age groups.ConclusionsNNAR is an easy-to-use AR headgear placement monitoring tool that is expected to significantly enhance consistency and reduce setup time for fNIRS and EEG probe donning across a wide range of studies.

.SignificanceThe use of functional near-infrared spectroscopy (fNIRS) is expanding, including examples of devices approved for routine clinical use for specific indications. Instrument standardization is a critical element to facilitate clinical adoption. Currently, there is no published description of a phantom that meets the requirements of IEC 80601-2-71, the IEC/ISO standard for fNIRS equipment.AimWe report an example of the implementation of the fNIRS standard phantom described in IEC 80601-2-71. We further report results from measurement campaigns with this phantom prototype in Japan and Europe.ApproachA phantom prototype was built and circulated among multiple academic and commercial fNIRS groups with diverse instrumentation. The phantom prototype was characterized by wavelength-dependent measurements of its diffuse optical features and utilized in a test for fNIRS signal magnitude as described in IEC 80601-2-71.ResultsThe optical loss of this phantom prototype as well as its change by varying an internal aperture were found to be and between 3.5 and 3.6 dB, respectively. The test for fNIRS signal magnitude based on this phantom was successfully carried out on various commercial fNIRS devices.ConclusionsThe characteristics of the phantom prototype agreed with the specifications in the standard. The phantom prototype proved suitable for the related test in IEC 80601-2-71.

.Neurophotonics Associate Editors Edgar Guevara and Rickson C. Mesquita, along with Felipe Orihuela-Espina, share their perceptions of the evolution of functional near-infrared spectroscopy in Latin America based on a retrospective literature review and the narratives of three other scientists from the region.