Neurophotonics最新文献

Significance: Neuronal dendritic spines are central elements for memory and learning. Their morphology correlates with synaptic strength and is a proxy for function. Classic light microscopy cannot resolve spine morphology well, and techniques with higher resolution (electron microscopy and super-resolution light microscopy) typically do not provide spine data in large fields of view, e.g., along entire dendrites. Therefore, it remains unclear if spine types are organized on mesoscopic scales, despite their undisputed importance for understanding the brain.

Aim: Recently, it was shown that the distribution of spine type is dendrite-specific in the turtle cortex, suggesting a mesoscopic organization, but leaving the question open if such a dendrite specificity also exists in mammals. Here, we determine if such a difference in spine-type distribution among dendrites also exists in the mouse brain.

Approach: We used super-resolution stimulated emission depletion microscopy of complete dendrites and advanced morphological analysis in three dimensions to decipher morphological differences of spines on different dendrites.

Results: We found that spines of different shapes decorate different dendrites of the same neuron to a varying extent. Significant differences among the dendrites are apparent, based on spine classes as well as based on quantitative descriptors, such as spine length or head size.

Conclusions: Our findings may indicate that it is an evolutionarily conserved principle that individual dendrites have distinct distributions of spine types hinting at individual roles.

Significance: Despite the availability of various anti-seizure medications, nearly 1/3 of epilepsy patients experience drug-resistant seizures. These patients are left with invasive surgical options that do not guarantee seizure remission. The development of novel treatment options depends on elucidating the complex biology of seizures and brain networks.

Aim: We aimed to develop an experimental paradigm that uses anatomical network information, functional connectivity, and in vivo seizure models to determine how brain networks, and their manipulation, affect seizure propagation.

Approach: Guided by a known anatomical network, we applied widefield calcium imaging to determine how neural activity and seizures spread through the network regions, focusing on the primary somatosensory cortex and secondary motor cortex. We used in vivo microstimulation to induce suprathreshold excitatory activation and compared this reproducible stimulus with acute pharmacologically induced spontaneous seizure propagation. In a proof-of-concept experiment, we ablated a single node within this bilateral network and measured the effect on propagation and recruitment. Similar preliminary experiments were repeated in a chronic seizure model.

Results: The microstimulation of the somatosensory cortex propagated in a distinct pattern throughout the bilateral network with sequential reproducible node recruitment. Seizures recapitulated this same pattern, indicating a hijacking of existing pathways. Ablation of a key node in the network in the secondary motor cortex changed contralateral spread. Early chronic cobalt seizure data are presented.

Conclusion: Here, we demonstrate a paradigm for combining widefield calcium imaging with microstimulation, cortical ablation, and seizure mapping to determine how anatomical networks inform the propagation patterns of cortical seizures. These experiments can be extended to long-term tracking of epilepsy to study epileptogenesis in other cortical networks. Our proof-of-concept findings suggest that this paradigm may be useful in the development of novel therapies for drug-resistant epilepsy patients and can be extended to the study of other disorders involving brain networks.

Internal states involve brain-wide changes that subserve coordinated behavioral and physiological responses for adaptation to changing environments and body states. Investigations of single neurons or small populations have yielded exciting discoveries for the field of neuroscience, but it has been increasingly clear that the encoding of internal states involves the simultaneous representation of multiple different variables in distributed neural ensembles. Thus, an understanding of the representation and regulation of internal states requires capturing large population activity and benefits from approaches that allow for parsing intermingled, genetically defined cell populations. We will explain imaging technologies that permit recording from large populations of single neurons in rodents and the unique capabilities of these technologies in comparison to electrophysiological methods. We will focus on findings for appetitive and aversive states given their high relevance to a wide range of psychiatric disorders and briefly explain how these approaches have been applied to models of psychiatric disease in rodents. We discuss challenges for studying internal states which must be addressed with future studies as well as the therapeutic implications of findings from rodents for improving treatments for psychiatric diseases.

Significance: Cerebral blood flow (CBF) and cerebral blood volume (CBV) are key metrics for regional cerebrovascular monitoring. Simultaneous, non-invasive measurement of CBF and CBV at different brain locations would advance cerebrovascular monitoring and pave the way for brain injury detection as current brain injury diagnostic methods are often constrained by high costs, limited sensitivity, and reliance on subjective symptom reporting.

Aim: We aim to develop a multi-channel non-invasive optical system for measuring CBF and CBV at different regions of the brain simultaneously with a cost-effective, reliable, and scalable system capable of detecting potential differences in CBF and CBV across different regions of the brain.

Approach: The system is based on speckle contrast optical spectroscopy and consists of laser diodes and board cameras, which have been both tested and investigated for safe use on the human head. Apart from the universal serial bus connection for the camera, the entire system, including its battery power source, is integrated into a wearable headband and is powered by 9-V batteries.

Results: The temporal dynamics of both CBF and CBV in a cohort of five healthy subjects were synchronized and exhibited similar cardiac period waveforms across all six channels. The potential use of our six-channel system for detecting the physiological sequelae of brain injury was explored in two subjects, one with moderate and one with significant structural brain damage, where the six-point CBF and CBV measurements were referenced to structural magnetic resonance imaging (MRI) scans.

Conclusions: We pave the way for a viable multi-point optical instrument for measuring CBF and CBV. Its cost-effectiveness allows for baseline metrics to be established prior to injury in populations at risk for brain injury.

Expansion microscopy is a super-resolution technique in which physically enlarging the samples in an isotropic manner increases inter-molecular distances such that nano-scale structures can be resolved using light microscopy. This is particularly useful in neuroscience as many important structures are smaller than the diffraction limit. Since its invention in 2015, a variety of expansion microscopy protocols have been generated and applied to advance knowledge in many prominent organisms in neuroscience, including zebrafish, mice, Drosophila, and Caenorhabditis elegans. We review the last decade of expansion microscopy-enabled advances with a focus on neuroscience.

Significance: Decoding naturalistic content from brain activity has important neuroscience and clinical implications. Information about visual scenes and intelligible speech has been decoded from cortical activity using functional magnetic resonance imaging (fMRI) and electrocorticography, but widespread applications are limited by the logistics of these technologies.

Aim: High-density diffuse optical tomography (HD-DOT) offers image quality approaching that of fMRI but with the silent, open scanning environment afforded by optical methods, thus opening the door to more naturalistic research and applications. Although early visual decoding studies with HD-DOT have been promising, decoding of naturalistic auditory and multisensory stimulus information from HD-DOT data has not been established.

Approach: Audiovisual decoding was investigated using HD-DOT data collected from participants who viewed a library of movie clips. A template-matching strategy was used to decode which movie clip a participant viewed based on their HD-DOT data. Factors affecting decoding performance-including trial duration and number of decoding choices-were systematically evaluated.

Results: Decoding accuracy was 94.2% for four-way decoding utilizing 4 min of data per trial as a starting point. As parameters were made more stringent, decoding performance remained significantly above chance with strong effect sizes down to 15-s trials and up to 32 choices. Comparable decoding accuracies were obtained when cortical sampling was confined to visual and auditory regions and when participants were presented with purely auditory or visual clips.

Conclusions: HD-DOT data sample cortical hemodynamics with sufficient resolution and fidelity to support decoding complex, naturalistic, multisensory stimuli via template matching. These results provide a foundation for future studies on more intricate decoding algorithms to reconstruct diverse features of novel naturalistic stimuli from HD-DOT data.

Significance: Stroke is the leading cause of chronic disability in the United States. How stroke size affects post-stroke repair and recovery is poorly understood.

Aim: We aim to investigate the effects of stroke size on early repair patterns and determine how early changes in neuronal circuits and networks predict functional outcomes after stroke.

Approach: We used wide-field optical imaging, photothrombosis, and the cylinder-rearing assay to examine changes in neuronal circuit and network activity in the context of functional recovery after stroke.

Results: Larger strokes ablating $S{1}_{\mathrm{FP}}$ caused diffuse and widespread forepaw stimulus-evoked cortical activation, including contralesional regions evolving within 4 weeks post-stroke; smaller strokes resulted in more focused ipsilesional activation. Larger strokes decreased neuronal fidelity and bilateral coherence during stimulation of either the affected or unaffected forepaw within this 4-week period. Mice in the larger lesion group demonstrated hyperconnectivity within the contralesional hemisphere at the resting state. Greater degrees of remapping diffusivity, neuronal fidelity degradation, and hyperconnectivity predicted worse 8-week recovery after statistically controlling for the effect of infarct size.

Conclusions: These results suggest that diffuse patterns of remapping, and desynchronization and hyperconnectivity of cortical networks, evolving early after stroke may reflect maladaptive plasticity, predicting poor long-term functional recovery.

Significance: Functional brain imaging experiments in awake animals require meticulous monitoring of animal behavior to screen for spontaneous behavioral events. Although these events occur naturally, they can alter cell signaling and hemodynamic activity in the brain and confound functional brain imaging measurements.

Aim: We developed a centralized, user-friendly, and stand-alone platform that includes an animal fixation frame, compact peripheral sensors, and a portable data acquisition system. The affordable, integrated platform can benefit imaging experiments by monitoring animal behavior for motion detection and alertness levels as complementary readouts for brain activity measurements.

Approach: A custom acquisition system was designed using a powerful, inexpensive microcomputer. We customized an accelerometer and miniature camera modules for efficient, real-time monitoring of animal motion detection and pupil diameter. We then tested and validated the platform's performance with optical intrinsic signal imaging and GCaMP fluorescence calcium imaging in functional activation experiments in awake mice.

Results: The integrated platform shows promise for detecting spontaneous motion and pupil dilation while imaging. Stimulus-induced pupil dilation was found to initiate earlier than cortical hemodynamics with a slower rise time. Compared with neuronal calcium response, stimulus-induced pupil dilation initiated later with a slower rise time.

Conclusions: We developed an integrated platform to monitor animal motion and pupil dynamics. The device can be easily coupled and synchronized with optical brain imaging systems to monitor behavior, alertness, and spontaneous motion for awake animal studies.

Significance: Determining the long-term cognitive impact of infections is clinically challenging. Using functional cortical connectivity, we demonstrate that interhemispheric cortical connectivity is decreased in individuals with acute Zika virus (ZIKV) encephalitis. This correlates with decreased presynaptic terminals in the somatosensory cortex. During recovery from ZIKV infection, presynaptic terminals recover, which is associated with recovered interhemispheric connectivity. This supports the contribution of synapses in the cortex to functional networks in the brain, which can be detected by widefield optical imaging. Although myeloid cell and astrocyte numbers are still increased during recovery, RNA transcription of multiple proinflammatory cytokines that increase during acute infection decreases to levels comparable to mock-infected mice during recovery. These findings also suggest that the immune response and cytokine-mediated neuroinflammation play significant roles in the integrity of brain networks during and after viral encephalitis.

Aim: We hypothesized that widefield optical imaging would allow us to assess functional cortical network disruption by ZIKV, including hippocampal-cortical networks.

Approach: We use widefield optical imaging to measure cortical functional connectivity (FC) in mice during acute infection with, and recovery from, intracranial infection with a mouse-adapted strain of ZIKV.

Results: Acute ZIKV infection leads to high levels of myeloid cell activation, with loss of neurons and presynaptic termini in the cerebral cortex and associated loss of FC primarily within the somatosensory cortex. During recovery, neuron numbers, synapses, and FC recover to levels near those of healthy mice. However, hippocampal injury and impaired spatial cognition persist. The magnitude of activated myeloid cells during acute infection predicted both recovery of synapses and the degree of FC recovery after recovery from ZIKV infection.

Conclusions: These findings suggest that a robust inflammatory response may contribute to the health of functional brain networks after recovery from infection.

Significance: Stimulus-evoked intrinsic optical signal (IOS) changes in retinal photoreceptors are critical for functional optoretinography (ORG). Optical coherence tomography (OCT), with its depth-resolved imaging capability, has been actively explored for IOS imaging of retinal photoreceptors. However, recent OCT studies have reported conflicting results regarding light-induced changes in the photoreceptor outer segments (OSs), with both elongation and shrinkage being observed. These discrepancies may stem from the difficulty in reliably identifying OS boundaries, particularly the inner segment/outer segment (IS/OS) junction and OS tip, as well as potential confusion with subretinal space dynamics. Gaining a better understanding of these light-induced OS changes is essential for accurate interpretation of ORG measurements and for optimizing IOS imaging systems to enhance sensitivity.

Aim: We aim to develop a method for the reliable identification of OS boundaries and to verify light-induced photoreceptor OS shrinkage and subretinal space expansion.

Approach: We employed a polarization-resolved full-field swept-source optical coherence tomography system capable of sequentially capturing parallel-polarization and cross-polarization OCT signals. The parallel-polarization mode is optimized to detect ballistically reflected photons from well-defined retinal boundaries, such as the IS/OS junction and the photoreceptor tips, whereas cross-polarization primarily captures multiply scattered photons. This differentiation enables parallel-polarization OCT to minimize the interference from scattered photons, enhancing the precision of OCT band quantification.

Results: Parallel-polarization OCT revealed photoreceptor OS shrinkage and subretinal space expansion in light conditions compared with dark conditions. Moreover, the overall outer retinal length appeared to swell under light. These observations were consistently confirmed in four healthy adult human subjects.

Conclusions: Parallel-polarization OCT provides a reliable method for identifying the IS/OS junction and OS tip, confirming light-induced photoreceptor OS shrinkage and subretinal space expansion.