Neurophotonics最新文献

Significance: To 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 approach: We 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.

Results: The 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.

Conclusions: Neuroimaging 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.

Significance: Tone processing is essential in tonal languages such as Mandarin. Understanding how post-stroke aphasia (PSA) affects tone perception can guide targeted rehabilitation, especially in linguistically unique populations.

Aim: We aimed to explore the neural mechanisms of tone perception in Mandarin-speaking PSA patients and examine how brain network reorganization supports or hinders phonological processing.

Approach: Using functional near-infrared spectroscopy (fNIRS) and a tone-based auditory oddball paradigm, we compared cortical activation and functional connectivity (FC) patterns between PSA patients and healthy controls.

Results: Patients with PSA showed reduced/reversed hemodynamic responses in the left Broca's area but increased FC with the right motor cortex. Despite this local hyperconnectivity, overall FC was lower in patients than in controls, especially among highly connected links ( $\left|r\right|>0.7$ ), suggesting either compensatory or maladaptive reorganization. Moreover, deoxygenated hemoglobin changes in the left Broca's area were positively associated with language function, as measured by aphasia quotient scores.

Conclusions: The findings highlight altered auditory-motor network dynamics in PSA, with Broca's area playing a central role in tone-based phonological processing. These results support the potential of fNIRS for clinical assessment and underscore the importance of accounting for network-level changes in aphasia rehabilitation strategies for tonal languages.

Significance: Functional near-infrared spectroscopy (fNIRS) is a valuable neuroimaging technique for auditory-research tasks. However, fNIRS data are influenced by systemic-physiological processes, resulting in noisier signal quality that may compromise test-retest reliability. fNIRS reliability may also be influenced by changes in cap placement across sessions.

Aim: We investigated the effectiveness of systemic-physiology denoising methods on the test-retest reliability of group-level fNIRS data during a passive-listening task.

Approach: Fifteen participants completed two identical sessions of a passive-listening task; source-detector optode locations were digitized for each session. Different denoising methods were compared to investigate the effect of systemic-physiology correction on the consistency of across-session hemodynamic response amplitudes. Test-retest reliability for each method was assessed using the intraclass correlation coefficient (ICC). Changes in optode and channel locations across sessions were calculated to track shifts in cap placement.

Results: Results revealed significant speech-evoked activity in bilateral auditory cortices following stimuli presentation. Group-level test-retest reliability metrics demonstrated good reliability across two identical test sessions. Accounting for the influence of systemic physiology resulted in improved reliability. Slight variations in optode placement did not significantly affect signal repeatability.

Conclusion: This study supports the use of fNIRS for group-level task-evoked studies, demonstrating that systemic-physiology denoising methods can modestly improve test-retest reliability.

Significance: Neonates undergo rapid development, yet the examination of emerging brain markers across paradigms, cognitive domains, and diverse global populations remains limited.

Aim: We investigated whether brain responses at 1 month of age could be interrogated across paradigms to offer deeper context-specific insights into neurodevelopment.

Approach: Functional near-infrared spectroscopy was used to assess frontal and temporal brain responses during natural sleep in 181 infants from a low-income setting (rural Gambia) and 58 infants from a higher-income setting (Cambridge, United Kingdom) during three auditory paradigms: social selectivity, habituation and novelty detection, and functional connectivity. Paradigm-level brain responses were analyzed using threshold-free cluster enhancement and cross-paradigm comparisons of individual responses.

Results: Both Gambian and UK infants showed habituation but not novelty responses, higher inter- versus intra-hemispheric connectivity, stronger inter-hemispheric connectivity in temporal relative to frontal regions, stronger inter-regional connectivity between right temporal and left frontal regions, and nonvocal > vocal selectivity (UK infants only).

Conclusions: Cross-cohort differences in the cross-paradigm analyses suggest that context-specific developmental markers are evident within the first month of life and show high individual variability. Cross-paradigm analyses revealed that greater vocal selectivity (UK) is associated with higher inter-hemispheric connectivity, potentially allowing us to identify biomarkers of more mature neurodevelopment within the first weeks of postnatal life.

Significance: Cellular-resolution retinal imaging in mouse models is hindered by optical aberrations and speckle noise, limiting the ability to visualize and track individual cells in vivo. Overcoming these challenges is critical for advancing preclinical studies of retinal disease and therapy.

Aim: We developed a wavefront sensorless adaptive optics optical coherence tomography (WSAO-OCT) platform designed to achieve reliable cellular-level imaging of the mouse retina.

Approach: The system integrates real-time aberration correction with multivolume averaging to simultaneously improve image quality and suppress speckle noise. Imaging results were validated using immunohistochemistry, and the platform was applied to monitor retinal ganglion cell (RGC) degeneration following optic nerve injury.

Results: WSAO-OCT improved image contrast by 61% and sharpness by 55%, whereas averaging 50 volumes markedly reduced speckle noise. The system enabled visualization of individual cells across all retinal layers and the retinal pigment epithelium. Immunohistochemistry confirmed that 95% of optically detected cells in the RGC layer corresponded to true RGCs. Following optic nerve injury, en face RGC counts enabled by the platform proved more sensitive than conventional layer thickness metrics of RGC loss, detecting significant RGC degeneration earlier (day 3 versus day 5) and with a greater magnitude (62% cell loss versus 8% thickness reduction) over one week.

Conclusions: WSAO-OCT provides a noninvasive, quantitative, and cell-specific imaging tool for preclinical retinal research, offering translational potential for longitudinal monitoring and therapeutic evaluation.

Significance: Elucidating the diurnal differences in cerebral hemodynamics is essential for both advancing our understanding of brain function and improving therapeutic strategies for neurological disorders. However, it remains unclear how the inactive and active diurnal phases influence the microvascular-scale distributions of cerebral blood flow and oxygenation and whether these distributions exhibit brain-region-specific variations.

Aim: We aim to characterize the time-of-day variations in cerebral microvascular blood flow and oxygenation across brain regions in awake mice.

Approach: We used two-photon microscopy and Doppler optical coherence tomography to quantify the resting-state microvascular blood flow and oxygenation parameters in the cerebral middle-cerebral-artery (MCA) territory and adjacent watershed area in the head-restrained, awake mice, during the inactive and active phases.

Results: Microvascular blood flow was consistently higher during the inactive phase compared with the active phase. Specifically, this elevated flow reached statistical significance in the watershed area. Furthermore, oxygen extraction fraction increased in the MCA territory during the active phase but decreased in the watershed area.

Conclusions: We reveal diurnal differences in cerebral microvascular blood flow and oxygenation, with the watershed area exhibiting a greater response to this effect. These findings underscore the potential of chronotherapeutic strategies to enhance treatment efficacy for cerebrovascular disorders.

Significance: Adapting optical imaging technology to avian models can overcome many limitations imposed by functional magnetic resonance imaging (fMRI), which currently restricts the number of species used to study functional connectivity. Developing advanced technology to expand the diversity of species that can be effectively imaged is crucial for addressing significant questions that are currently unreachable, such as understanding the evolution of cognition from a comparative perspective.

Aim: We assessed the potential of optical imaging technology to measure functional connectivity in birds, utilizing pigeons as an avian model. We evaluated whether we could partition the dorsal surface of the pigeon brain into units that correspond to known anatomical regions. Finally, we compared our results with those obtained from a separate dataset acquired using fMRI.

Approach: Using optical intrinsic signal imaging, a widefield optical imaging method, we imaged resting state functional connectivity in scalp-retracted anesthetized pigeons. We then used iterative parcellation and hierarchical clustering to create functional connectivity maps of correlation between parcels at two spatial scales. We recorded a second independent dataset of ten pigeons using a single-shot multi-slice gradient echo EPI sequence fMRI and applied the same parcellation method to compare functional connectivity patterns between the two methodologies.

Results: We successfully partitioned signal activity into clusters of parcels that exhibit left-right symmetry between hemispheres and which align well with known anatomical regions of the dorsal surface of the pigeon brain. Moreover, functional connectivity matrices reveal positive correlations between homotopic regions. These cluster partitions and functional connectivity maps display similar patterns across and within individuals. Finally, WOI imaging results were comparable to resting state data acquired using fMRI.

Conclusions: Taken together, these results demonstrate the potential of optical imaging technology for the reliable and cost-effective characterization of functional connectivity in birds. In addition, they position optical imaging methods as a valuable tool for large-scale comparative and network-level studies in this taxon.

Significance: Neural activation in functional near-infrared spectroscopy (fNIRS) signals is inherently convolved with, and temporally blurred by, a hemodynamic response function (HRF). Accurately modeling HRF variability during deconvolution improves neural activity recovery.

Aim: We present the Python-based HRfunc tool for estimating local HRF distributions and neural activity from fNIRS through deconvolution. HRFs are stored within a tree and a hash table hybrid data structure for efficient spatial and contextual identification of relevant HRFs.

Approach: To test the HRfunc tool, we conducted two analyses with hemoglobin and estimated neural activity, a general linear model (GLM) analysis on a single subject, child executive function task ( $n=79$ ), and a neural synchrony analysis assessing wavelet coherence between child-parent dyads (92 dyads).

Results: Estimated HRFs contained a generally canonical shape. Within estimated neural activity, kurtosis increased, skew remained stable, and signal-to-noise ratio decreased. Neural synchrony lateralization effects emerged, and consistent GLM outcomes were observed.

Conclusions: These results support the use of the HRfunc tool for estimating event-based HRFs and neural activity in fNIRS studies. Through collective sharing of HRFs, an HRF database will be established to provide access to estimated HRFs across brain regions, subject ages, and experimental contexts.

Significance: Although the transmission of auditory information in the brain has been extensively studied, the mechanism underlying fine auditory discrimination remains incompletely understood. The basal region of the ventromedial nucleus of the thalamus (bVM) has recently been found to convey frequency-specific auditory information to the primary auditory cortex (A1). Inhibition of the bVM significantly impairs fine auditory discrimination in mice. These findings indicate that the bVM plays an important role in frequency information processing. However, direct functional evidence for tonotopic organization within the bVM is still lacking.

Aim: We aimed to investigate whether bVM neurons exhibit a spatially ordered frequency preference, using a simple yet efficient in vivo functional mapping strategy.

Approach: To characterize the response properties of bVM neurons projecting to A1, we combined Cre-dependent retrograde viral labeling with fiber photometry in awake mice. Using a "one recording site per animal" strategy, we systematically recorded from 26 distinct locations and successfully reconstructed the tonotopic map of the bVM.

Results: We identified a mediolateral tonotopic gradient within the bVM, with best frequencies progressing from low in medial regions to high in lateral regions.

Conclusions: Our findings provide direct functional evidence of tonotopic organization within the bVM, supporting its role as an auditory relay and its contribution to fine auditory discrimination.