This Conference Presentation, “Exciting insights into neural coding with sculpted wavefronts,” was recorded at Photonics West 2022, in San Francisco, California.

This Conference Presentation, “Neuroscience of the everyday world,” was recorded at Photonics West 2022, in San Francisco, California.

This Conference Presentation, “Visualization of brain fiber tracts with polarized light,” was recorded at Photonics West 2022, in San Francisco, California.

Fluorescent genetically encoded voltage indicators can be combined with optical imaging to provide high-throughput electrophysiologic recordings with single-spike resolution and subthreshold sensitivity. Such voltage imaging is highly demanding in terms of signal collection; thus, most experiments have been performed with widefield one-photon microscopy. Unfortunately, widefield techniques are susceptible to out-of-focus background and scattering, which degrades SNR, especially in high-density slice or in vivo experiments. In this work, we describe a multi-plane near-kHz-rate confocal microscope that effectively suppresses undesired background. This technique enables more densely labeled in vitro and in vivo imaging experiments, critical for the dissection of neural circuit dynamics.

Recent improvements in genetically encoded voltage indicators have enabled optical imaging of action potentials and subthreshold membrane voltage from single neurons in the mammalian brain. However, most current voltage imaging techniques can only simultaneously sample a few cell, limited either by strong background or small field-of-view. We show that, both theoretically and experimentally, targeted illumination with a widefield microscopy can significantly improve voltage imaging performance by improving signal contrast and reducing background cross-contamination. With such improvements, we demonstrated large-scale voltage imaging with fully genetically encoded voltage indicator SomArchon from tens of neurons over a large anatomical area, while maintaining signal contrast over a prolonged recording duration of several continuous minutes.

We have developed a novel nerve holder, imaging protocol and post-processing routine which enhance OCT imaging by accessing peripheral nerve from 3 sides. Two mirror prisms provide imaging access from sides of a peripheral nerve in addition to conventional volume acquisition from the top. Prism glass compensates for changed focusing and optical pathlength during nerve imaging from its sides Acquired prism sub-volumes and top-bottom imaged nerve sub-volume are merged in two-stage semi-automated postprocessing routine. We demonstrate successful application of this approach on tissue-mimicking phantoms, as well as in vivo rat sciatic nerve imaging.

The anomalous diffusion characteristics of neuronal dynamics are analyzed by label-free, phase-sensitive optical coherence microscopy. The technique provides low-noise images, enabling cellular dynamic characteristics to be measurable. The phase variance is a conventional dynamic parameter that cannot elucidate the ballistic components of neuronal dynamics. Determining the dynamics by phase variance alone omits the ballistic information that can occur from the ion exchange across cellular membranes. The probability density function of phase displacements exerted by cellular dynamics was acquired and the shape of the power-law tail was analyzed. The development of the power-law tail provides a more sensitive dynamic feature.

The quality of speech signals and the inherent contextual cues are essential for effective spoken communication. Our research aims to identify the neural basis of effortful listening for speech altered in linguistic complexity and acoustic clarity. We leverage the strength of HD-DOT to measure cortical responses due to naturalistic stimuli such as stories. Comparisons of stimulus complexity (words vs. stories) and clarity (clear vs. acoustically degraded stories) for seven young adult participants show the recruitment of higher-order brain regions such as the dorsolateral prefrontal cortex and inferior parietal cortex for the more effortful conditions, suggesting the involvement of domain-general processing.

Functional magnetic resonance imaging has decoded complex information about naturalistic stimuli using brain responses, but other non-invasive technologies have not achieved similar decoding capabilities. To evaluate feasibility of naturalistic visual decoding with diffuse optical tomography (DOT), a 6.5-mm-spaced optode grid was employed to decode which of four naturalistic, 90-second movie clips was viewed by human subjects. Over 85% average decoding accuracy was achieved using a template-matching decoder. Average accuracy remained above 60% and above chance using a model-based decoder to identify 4 and 40 clips outside the decoder's training set, respectively. DOT therefore has potential for more-complex neural decoding tasks.

Fast and accurate drug screening can significantly improve the survival rate of cancer patients. Here, we present a new drug screening platform for cancer treatment based on an integrated precision microtome and LiMo microscope. Through this platform, tumor specimens from patients are first sectioned into 100-micron thick tissue slices and cultured for a few days; next, the live tumor tissue array is tested with different anti-cancer drugs for a few weeks and regularly 3D imaged at subcellular resolution, realizing personalized medicine. Our preliminary study on human oral cancer tissue has confirmed the feasibility of the drug screening platform.

Understanding how different central nervous system diseases affect different components of neurovascular coupling will allow for linking changes in neural or metabolic dysfunction to changes in hemodynamic signaling upon which blood-based imaging methods rely. We developed a dual fluorophore imaging system for simultaneous, high-speed mapping of neural, metabolic, and hemodynamic activity. Proof-of-concept measurements of spontaneous and stimulus-evoked dynamics are presented in awake and anesthetized mice. This flexible hardware platform allows for integrating optogenetic stimulation for all optical neural circuit interrogation and readout, and for examining the interaction between multiple cell populations.

Out-of-focus and scattered light often obscure dim fluorescent fibers in widefield neuronal imaging. We solve this obstacle by spatially modulating the excitation light to illuminate different neuronal structures with different light intensities. In this way, we minimize background and enhance the visibility of neuron fibers in the final image. This method significantly improves fiber contrast while maintaining a fast imaging speed and low cost. Using this widefield targeted illumination setup, we demonstrate confocal quality imaging of complex neurons in the nematode C. elegans.

Bessel foci used for two-photon fluorescence excitation have enabled high-speed volumetric imaging. At high numeric aperture, their imaging performances are compromised by substantial side-ring excitation and suffer from reduced image contrast. Here, we describe axially extended Bessel-droplet foci with suppressed side rings and more resistance to optical aberrations. Applying novel phase patterns to generate Bessel-droplet foci of variable NAs at high power throughput, we achieved continuous volume imaging by scanning them interferometrically along the axial direction. With Bessel-droplet foci, we demonstrated high-resolution volumetric imaging of synaptic anatomy and function as well as lymphatic circulations in the mouse brain in vivo.

Light-sheet fluorescence microscopy serves as a fast high-resolution imaging method for neural imaging. However, its 3D imaging ability is often limited by the speed of scanning the detection focal plane in the z-direction. Herein, we develop a rapid random z-access two-photon light-sheet microscope, which incorporates a two-photon Bessel beam light-sheet microscope with a dynamically driven electrical tunable lens (ETL). With a precise ETL calibration process and a novel rapid random z-access method, our system can selectively scan any desired z-section in the 3D imaging volume at the speed of 100 frame-per-second, and allows neural activates monitoring on the living brain tissue at video rate.

Deep-brain stimulation (DBS) of the ventro-intermediate nucleus of the thalamus (VIM) can provide substantial clinical motor benefit to Essential Tremor (ET) patients. However, the DBS impact on the functional connectivity (FC) of networks is difficult to study using standard neuroimaging modalities either due to limited temporal resolution (PET) or safety concerns from contraindications (fMRI). In this study, we tested the feasibility and sensitivity of High-Density Diffuse Optical Tomography (HD-DOT), which avoids these concerns, for mapping cortical blood flow responses to sensory stimuli and measuring resting state cortical FC in ET patients with VIM DBS OFF vs ON.

High density diffuse optical tomography (HD-DOT) is a functional neuroimaging method that uses multiple overlapping and multi-distance functional near-infrared spectroscopy measurements in a dense grid array. Herein, we investigate multiple frequency and matrix scaling strategies to improve frequency domain HD-DOT methods and use simulations of point spread functions in anatomical models to assess the improvement attainable over standard methods. We observe a small improvement in image quality metrics by adding multiple modulation frequencies, and a significant improvement after column scaling sensitivity matrices. These methods may advance image quality of HD-DOT beyond current limitations.

Although the beneficial effects of regular physical exercise on brain aging and neurodegenerative diseases are well recognized, a clear understanding of how exercise leads to such benefits remains elusive. In this work, we investigated the effects of normal aging on cortical microvascular oxygenation, perfusion, and morphology and the impact of four months of voluntary wheel running on cortical microvascular oxygenation in 20 months old mice. We used two-photon microscopy to assess age-related and exercise-induced changes in the distributions of capillary oxygen partial pressure (PO2) and red-blood-cell flux across cortical depth in awake mice. Our finding suggests the mitigating effect of exercise on the progression of age-related changes in capillary oxygenation in deeper cortical layers which may be related to health-enhancing benefits of exercise in elderly individuals.

Obtaining high signal to noise ratio is challenging in wide-field two photon microscopy and one must ensure the mouse brain can be imaged safely under high laser power. Here, we demonstrated a simultaneous thermal imaging and two photon imaging technique. The maximum temperature of the cortex was below 39°C using 400mW laser power with a 5 x 5mm field of view. Together with the brain activities under hind paw stimulation and at rest, we argued that high laser power for wide-field two-photon imaging can potentially be used while keeping the temperature under safety limit.

The fluorescent tracer 5-aminolevulinc acid was introduced to visualize brain tumors intraoperatively, but suffers from drawbacks such as limited sensitivity for certain tumor types. Optical coherence tomography (OCT) is a non-invasive imaging modality, which has recently found its application in neuroscience by contributing label-free tissue information. We present one of the first radiomics-based analyses to capture the form and texture of glioma samples resected during fluorescence-guided surgery in a large cohort of multimodal OCT-based microscopy (OCM) imaging data. Concluding, we report encouraging results for the prediction of tumor infiltration, entity and molecular biomarkers with accuracies as high as 96%.

Focused ultrasound (FUS) is an emerging technology for non-invasive and controlled blood-brain barrier (BBB) opening for drug delivery successfully tested in clinical trials. To improve the safety of this method, we use optical imaging techniques to better understand the relationship between repeated FUS-BBB opening, neuroinflammation, and alteration of neurovascular coupling in an animal model. We perform 1- and 2-photon microscopy in awake mice to image neuronal activity hemodynamics. Before and following FUS treatment, optical imaging sessions access changes in neuronal activity and/or hemodynamics; FUS treatments are repeated several times to approximate a clinical schedule.

Exploring functional brain networks (FBNs) from wide-field calcium imaging (WFCI) data is important to understand the functional architecture and organization of the brain. In the study, an unsupervised deep learning method is implemented for identifying FBNs from WFCI data. Specifically, a recurrent autoencoder is adapted to extract spatial-temporal latent embeddings of brain activity followed by use of ordinary least square regression to establish the corresponding function brain networks. Spatial similarities are shared between FBNs estimated from learned embeddings and those derived by seed-based correlation method. The proposed method allows investigations about the effect of spatial-temporal calcium dynamics on FBNs.