Lateral geniculate neurons projecting to primary visual cortex show ocular dominance plasticity in adult mice

Development of ocular dominance columns across rodents and other species: revisiting the concept of critical period plasticity

The existence of cortical columns, regarded as computational units underlying both lower and higher-order information processing, has long been associated with highly evolved brains, and previous studies suggested their absence in rodents. However, recent discoveries have unveiled the presence of ocular dominance columns (ODCs) in the primary visual cortex (V1) of Long-Evans rats. These domains exhibit continuity from layer 2 through layer 6, confirming their identity as genuine ODCs. Notably, ODCs are also observed in Brown Norway rats, a strain closely related to wild rats, suggesting the physiological relevance of ODCs in natural survival contexts, although they are lacking in albino rats. This discovery has enabled researchers to explore the development and plasticity of cortical columns using a multidisciplinary approach, leveraging studies involving hundreds of individuals-an endeavor challenging in carnivore and primate species. Notably, developmental trajectories differ depending on the aspect under examination: while the distribution of geniculo-cortical afferent terminals indicates matured ODCs even before eye-opening, consistent with prevailing theories in carnivore/primate studies, examination of cortical neuron spiking activities reveals immature ODCs until postnatal day 35, suggesting delayed maturation of functional synapses which is dependent on visual experience. This developmental gap might be recognized as 'critical period' for ocular dominance plasticity in previous studies. In this article, I summarize cross-species differences in ODCs and geniculo-cortical network, followed by a discussion on the development, plasticity, and evolutionary significance of rat ODCs. I discuss classical and recent studies on critical period plasticity in the venue where critical period plasticity might be a component of experience-dependent development. Consequently, this series of studies prompts a paradigm shift in our understanding of species conservation of cortical columns and the nature of plasticity during the classical critical period.

An early enriched experience drives targeted microglial engulfment of miswired neural circuitry during a restricted postnatal period

Brain function is critically dependent on correct circuit assembly. Microglia are well-known for their important roles in immunological defense and neural plasticity, but whether they can also mediate experience-induced correction of miswired circuitry is unclear. Ten-m3 knockout (KO) mice display a pronounced and stereotyped visuotopic mismapping of ipsilateral retinal inputs in their visual thalamus, providing a useful model to probe circuit correction mechanisms. Environmental enrichment (EE) commenced around birth, but not later in life, can drive a partial correction of the most mismapped retinal inputs in Ten-m3 KO mice. Here, we assess whether enrichment unlocks the capacity for microglia to selectively engulf and remove miswired circuitry, and the timing of this effect. Expression of the microglial-associated lysosomal protein CD68 showed a clear enrichment-driven, spatially restricted change which had not commenced at postnatal day (P)18, was evident at P21, more robust at P25, and had ceased by P30. This was observed specifically at the corrective pruning site and was absent at a control site. An engulfment assay at the corrective pruning site in P25 mice showed EE-driven microglial-uptake of the mismapped axon terminals. This was temporally and spatially specific, as no enrichment-driven microglial engulfment was seen in P18 KO mice, nor the control locus. The timecourse of the EE-driven corrective pruning as determined anatomically, aligned with this pattern of microglia reactivity and engulfment. Collectively, these findings show experience can drive targeted microglial engulfment of miswired neural circuitry during a restricted postnatal window. This may have important therapeutic implications for neurodevelopmental conditions involving aberrant neural connectivity.

Induction of excitatory brain state governs plastic functional changes in visual cortical topology

Adult visual plasticity underlying local remodeling of the cortical circuitry in vivo appears to be associated with a spatiotemporal pattern of strongly increased spontaneous and evoked activity of populations of cells. Here we review and discuss pioneering work by us and others about principles of plasticity in the adult visual cortex, starting with our study which showed that a confined lesion in the cat retina causes increased excitability in the affected region in the primary visual cortex accompanied by fine-tuned restructuring of neuronal function. The underlying remodeling processes was further visualized with voltage-sensitive dye (VSD) imaging that allowed a direct tracking of retinal lesion-induced reorganization across horizontal cortical circuitries. Nowadays, application of noninvasive stimulation methods pursues the idea further of increased cortical excitability along with decreased inhibition as key factors for the induction of adult cortical plasticity. We used high-frequency transcranial magnetic stimulation (TMS), for the first time in combination with VSD optical imaging, and provided evidence that TMS-amplified excitability across large pools of neurons forms the basis for noninvasively targeting reorganization of orientation maps in the visual cortex. Our review has been compiled on the basis of these four own studies, which we discuss in the context of historical developments in the field of visual cortical plasticity and the current state of the literature. Overall, we suggest markers of LTP-like cortical changes at mesoscopic population level as a main driving force for the induction of visual plasticity in the adult. Elevations in excitability that predispose towards cortical plasticity are most likely a common property of all cortical modalities. Thus, interventions that increase cortical excitability are a promising starting point to drive perceptual and potentially motor learning in therapeutic applications.

A developmental critical period for ocular dominance plasticity of binocular neurons in mouse superior colliculus

Detecting visual features in the environment is crucial for animals' survival. The superior colliculus (SC) is implicated in motion detection and processing, whereas how the SC integrates visual inputs from the two eyes remains unclear. Using in vivo electrophysiology, we show that mouse SC contains many binocular neurons that display robust ocular dominance (OD) plasticity in a critical period during early development, which is similar to, but not dependent on, the primary visual cortex. NR2A- and NR2B-containing N-methyl-D-aspartate (NMDA) receptors play an essential role in the regulation of SC plasticity. Blocking NMDA receptors can largely prevent the impairment of predatory hunting caused by monocular deprivation, indicating that maintaining the binocularity of SC neurons is required for efficient hunting behavior. Together, our studies reveal the existence and function of OD plasticity in SC, which broadens our understanding of the development of subcortical visual circuitry relating to motion detection and predatory hunting.

Microglia are dispensable for experience-dependent refinement of visual circuitry

Microglia are proposed to be critical for the refinement of developing neural circuitry. However, evidence identifying specific roles for microglia has been limited and often indirect. Here we examined whether microglia are required for the experience-dependent refinement of visual circuitry and visual function during development. We ablated microglia by administering the colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX5622, and then examined the consequences for retinal function, receptive field tuning of neurons in primary visual cortex (V1), visual acuity, and experience-dependent plasticity in visual circuitry. Eradicating microglia by treating mice with PLX5622 beginning at postnatal day (P) 14 did not alter visual response properties of retinal ganglion cells examined three or more weeks later. Mice treated with PLX5622 from P14 lacked more than 95% of microglia in V1 by P18, prior to the opening of the critical period. Despite the absence of microglia, the receptive field tuning properties of neurons in V1 were normal at P32. Similarly, eradicating microglia did not affect the maturation of visual acuity. Mice treated with PLX5622 displayed typical ocular dominance plasticity in response to brief monocular deprivation. Thus, none of these principal measurements of visual circuit development and function detectibly differed in the absence of microglia. We conclude that microglia are dispensable for experience-dependent refinement of visual circuitry. These findings challenge the proposed critical role of microglia in refining neural circuitry.

Thalamic regulation of ocular dominance plasticity in adult visual cortex

Experience-dependent plasticity in the adult visual system is generally thought of as a cortical process. However, several recent studies have shown that perceptual learning or monocular deprivation can also induce plasticity in the adult dorsolateral geniculate nucleus (dLGN) of the thalamus. How plasticity in the thalamus and cortex interact in the adult visual system is ill-understood. To assess the influence of thalamic plasticity on plasticity in primary visual cortex (V1), we made use of our previous finding that during the critical period ocular dominance (OD) plasticity occurs in dLGN and requires thalamic synaptic inhibition. Using multielectrode recordings we find that this is also true in adult mice, and that in the absence of thalamic inhibition and plasticity, OD plasticity in adult V1 is absent. To study the influence of V1 on thalamic plasticity, we silenced V1 and show that during the critical period, but not in adulthood, the OD shift in dLGN is partially caused by feedback from V1. We conclude that during adulthood the thalamus plays an unexpectedly dominant role in experience-dependent plasticity in V1. Our findings highlight the importance of considering the thalamus as a potential source of plasticity in learning events that are typically thought of as cortical processes.

Human deprivation amblyopia: treatment insights from animal models

Amblyopia is a common visual impairment that develops during the early years of postnatal life. It emerges as a sequela to eye misalignment, an imbalanced refractive state, or obstruction to form vision. All of these conditions prevent normal vision and derail the typical development of neural connections within the visual system. Among the subtypes of amblyopia, the most debilitating and recalcitrant to treatment is deprivation amblyopia. Nevertheless, human studies focused on advancing the standard of care for amblyopia have largely avoided recruitment of patients with this rare but severe impairment subtype. In this review, we delineate characteristics of deprivation amblyopia and underscore the critical need for new and more effective therapy. Animal models offer a unique opportunity to address this unmet need by enabling the development of unconventional and potent amblyopia therapies that cannot be pioneered in humans. Insights derived from studies using animal models are discussed as potential therapeutic innovations for the remediation of deprivation amblyopia. Retinal inactivation is highlighted as an emerging therapy that exhibits efficacy against the effects of monocular deprivation at ages when conventional therapy is ineffective, and recovery occurs without apparent detriment to the treated eye.

Sensory eye dominance plasticity in the human adult visual cortex

Sensory eye dominance occurs when the visual cortex weighs one eye's data more heavily than those of the other. Encouragingly, mechanisms underlying sensory eye dominance in human adults retain a certain degree of plasticity. Notably, perceptual training using dichoptically presented motion signal-noise stimuli has been shown to elicit changes in sensory eye dominance both in visually impaired and normal observers. However, the neural mechanisms underlying these learning-driven improvements are not well understood. Here, we measured changes in fMRI responses before and after a five-day visual training protocol to determine the neuroplastic changes along the visual cascade. Fifty visually normal observers received training on a dichoptic or binocular variant of a signal-in-noise (left-right) motion discrimination task over five consecutive days. We show significant shifts in sensory eye dominance following training, but only for those who received dichoptic training. Pattern analysis of fMRI responses revealed that responses of V1 and hMT+ predicted sensory eye dominance for both groups, but only before training. After dichoptic (but not binocular) visual training, responses of V1 changed significantly, and were no longer able to predict sensory eye dominance. Our data suggest that perceptual training-driven changes in eye dominance are driven by a reweighting of the two eyes' data in the primary visual cortex. These findings may provide insight into developing region-targeted rehabilitative paradigms for the visually impaired, particularly those with severe binocular imbalance.

Thalamic regulation of a visual critical period and motor behavior

During the visual critical period (CP), sensory experience refines the structure and function of visual circuits. The basis of this plasticity was long thought to be limited to cortical circuits, but recently described thalamic plasticity challenges this dogma and demonstrates greater complexity underlying visual plasticity. Yet how visual experience modulates thalamic neurons or how the thalamus modulates CP timing is incompletely understood. Using a larval zebrafish, thalamus-centric ocular dominance model, we show functional changes in the thalamus and a role of inhibitory signaling to establish CP timing using a combination of functional imaging, optogenetics, and pharmacology. Hemisphere-specific changes in genetically defined thalamic neurons correlate with changes in visuomotor behavior, establishing a role of thalamic plasticity in modulating motor performance. Our work demonstrates that visual plasticity is broadly conserved and that visual experience leads to neuron-level functional changes in the thalamus that require inhibitory signaling to establish critical period timing.

Thalamic neurons drive distinct forms of motor asymmetry that are conserved in teleost and dependent on visual evolution

Brain laterality is a prominent feature in Bilateria, where neural functions are favored in a single brain hemisphere. These hemispheric specializations are thought to improve behavioral performance and are commonly observed as sensory or motor asymmetries, such as handedness in humans. Despite its prevalence, our understanding of the neural and molecular substrates instructing functional lateralization is limited. Moreover, how functional lateralization is selected for or modulated throughout evolution is poorly understood. While comparative approaches offer a powerful tool for addressing this question, a major obstacle has been the lack of a conserved asymmetric behavior in genetically tractable organisms. Previously, we described a robust motor asymmetry in larval zebrafish. Following the loss of illumination, individuals show a persistent turning bias that is associated with search pattern behavior with underlying functional lateralization in the thalamus. This behavior permits a simple yet robust assay that can be used to address fundamental principles underlying lateralization in the brain across taxa. Here, we take a comparative approach and show that motor asymmetry is conserved across diverse larval teleost species, which have diverged over the past 200 million years. Using a combination of transgenic tools, ablation, and enucleation, we show that teleosts exhibit two distinct forms of motor asymmetry, vision-dependent and - independent. These asymmetries are directionally uncorrelated, yet dependent on the same subset of thalamic neurons. Lastly, we leverage Astyanax sighted and blind morphs, which show that fish with evolutionarily derived blindness lack both retinal-dependent and -independent motor asymmetries, while their sighted surface conspecifics retained both forms. Our data implicate that overlapping sensory systems and neuronal substrates drive functional lateralization in a vertebrate brain that are likely targets for selective modulation during evolution.

Atypical brain structure mediates reduced IQ in young adults born preterm with very low birth weight

Preterm birth with very low birth weight (VLBW) confers heightened risk for perinatal brain injury and long-term cognitive deficits, including a reduction in IQ of up to one standard deviation. Persisting gray and white matter aberrations have been documented well into adolescence and adulthood in preterm born individuals. What has not been documented so far is a plausible causal link between reductions in cortical surface area or subcortical brain structure volumes, and the observed reduction in IQ. The NTNU Low Birth Weight in a Lifetime Perspective study is a prospective longitudinal cohort study, including a preterm born VLBW group (birthweight ≤1500 g) and a term born control group. Structural magnetic resonance imaging data were obtained from 38 participants aged 19, born preterm with VLBW, and 59 term-born peers. The FreeSurfer software suite was used to obtain measures of cortical thickness, cortical surface area, and subcortical brain structure volumes. Cognitive ability was estimated using the Wechsler Adult Intelligence Scale, 3rd Edition, including four IQ-indices: Verbal comprehension, Working memory, Perceptual organization, and Processing speed. Statistical mediation analyses were employed to test for indirect effects of preterm birth with VLBW on IQ, mediated by atypical brain structure. The mediation analyses revealed negative effects of preterm birth with VLBW on IQ that were partially mediated by reduced surface area in multiple regions of frontal, temporal, parietal and insular cortex, and by reductions in several subcortical brain structure volumes. The analyses did not yield sufficient evidence of mediation effects of cortical thickness on IQ. This is, to our knowledge, the first time a plausible causal relationship has been established between regional cortical area reductions, as well as reductions in specific subcortical and cerebellar structures, and general cognitive ability in preterm born survivors with VLBW.

Neural circuits for binocular vision: Ocular dominance, interocular matching, and disparity selectivity

The brain creates a single visual percept of the world with inputs from two eyes. This means that downstream structures must integrate information from the two eyes coherently. Not only does the brain meet this challenge effortlessly, it also uses small differences between the two eyes' inputs, i.e., binocular disparity, to construct depth information in a perceptual process called stereopsis. Recent studies have advanced our understanding of the neural circuits underlying stereoscopic vision and its development. Here, we review these advances in the context of three binocular properties that have been most commonly studied for visual cortical neurons: ocular dominance of response magnitude, interocular matching of orientation preference, and response selectivity for binocular disparity. By focusing mostly on mouse studies, as well as recent studies using ferrets and tree shrews, we highlight unresolved controversies and significant knowledge gaps regarding the neural circuits underlying binocular vision. We note that in most ocular dominance studies, only monocular stimulations are used, which could lead to a mischaracterization of binocularity. On the other hand, much remains unknown regarding the circuit basis of interocular matching and disparity selectivity and its development. We conclude by outlining opportunities for future studies on the neural circuits and functional development of binocular integration in the early visual system.

Cortical feedback modulates distinct critical period development in mouse visual thalamus

In primary visual cortex (V1), critical period for ocular dominance (OD) plasticity is a well-defined developmental stage to shape neuronal circuits based on visual experience. Recent studies showed that V1-like OD plasticity existed in mouse dorsal lateral geniculate nucleus (dLGN). It is still unclear what the exact time window is and how neural circuits contribute to OD plasticity in dLGN. Using in vivo electrophysiology, we defined a critical period for OD plasticity in dLGN from eye opening to puberty. There also existed an innate process of OD formation from contralateral to equal bias in dLGN binocular neurons. Instant V1 inactivation with muscimol had no effect on OD bias or plasticity. Short-term V1 inactivation with N-methyl-d-aspartate reversed the formation of equal OD bias, while long-term V1 inactivation retained dLGN development to an immature stage.

Neuroplasticity of the Lateral Geniculate Nucleus in Response to Retinal Gene Therapy in a Group of Patients with RPE65 Mutations

Introduction

Previous works on experience-dependent brain plasticity have been limited to the cortical structures, overlooking subcortical visual structures such as the lateral geniculate nucleus (LGN). Animal studies have shown substantial experience dependent plasticity and using fMRI, human studies have demonstrated similar properties in patients with cataract surgery. However, in neither animal nor human studies LGN has not been directly assessed, mainly due to its small size, tissue heterogeneity, low contrast/noise ratio, and low spatial resolution.

Methods

Utilizing a new algorithm that markedly improves the LGN visibility, LGN was evaluated in a group of low vision patients before and after retinal intervention to reinstate vision and normal sighted matched controls.

Results

Between and within groups comparisons showed that patients had significantly smaller left (p< 0.0001) and right (p < 0.00002) LGN volumes at baseline as compared to the one-year follow-up volumes. The same baseline and one year comparison in controls was not significant. Significant positive correlations were observed between the incremental volume increase after gene therapy of the left LGN and the incremental increase in the right (r = 0.71, p < 0.02) and left (r = 0.72, p = 0.018) visual fields. Incremental volume increase of the right LGN also showed a similar positive slope but did not reach significance.

Discussion

These results show that despite significantly less volume at baseline, retinal gene therapy promotes robust expansion and increase in LGN volume. Reinstating vision may have facilitated the establishment of new connections between the retina and the LGN and/or unmasking of the dormant connections. The exact trajectory of the structural changes taking place in LGN is unclear but our data shows that even after years of low vision, the LGN in RPE65 patients has the potential for plasticity and expansion to a nearly normal volume one year after gene therapy administration.

SpecSeg is a versatile toolbox that segments neurons and neurites in chronic calcium imaging datasets based on low-frequency cross-spectral power

Imaging calcium signals in neurons of animals using single- or multi-photon microscopy facilitates the study of coding in large neural populations. Such experiments produce massive datasets requiring powerful methods to extract responses from hundreds of neurons. We present SpecSeg, an open-source toolbox for (1) segmentation of regions of interest (ROIs) representing neuronal structures, (2) inspection and manual editing of ROIs, (3) neuropil correction and signal extraction, and (4) matching of ROIs in sequential recordings. ROI segmentation in SpecSeg is based on temporal cross-correlations of low-frequency components derived by Fourier analysis of each pixel with its neighbors. The approach is user-friendly, intuitive, and insightful and enables ROI detection around neurons or neurites. It works for single- (miniscope) and multi-photon microscopy data, eliminating the need for separate toolboxes. SpecSeg thus provides an efficient and versatile approach for analyzing calcium responses in neuronal structures imaged over prolonged periods of time.

Mutual interaction between visual homeostatic plasticity and sleep in adult humans

Sleep and plasticity are highly interrelated, as sleep slow oscillations and sleep spindles are associated with consolidation of Hebbian-based processes. However, in adult humans, visual cortical plasticity is mainly sustained by homeostatic mechanisms, for which the role of sleep is still largely unknown. Here, we demonstrate that non-REM sleep stabilizes homeostatic plasticity of ocular dominance induced in adult humans by short-term monocular deprivation: the counterintuitive and otherwise transient boost of the deprived eye was preserved at the morning awakening (>6 hr after deprivation). Subjects exhibiting a stronger boost of the deprived eye after sleep had increased sleep spindle density in frontopolar electrodes, suggesting the involvement of distributed processes. Crucially, the individual susceptibility to visual homeostatic plasticity soon after deprivation correlated with the changes in sleep slow oscillations and spindle power in occipital sites, consistent with a modulation in early occipital visual cortex.

Advantages, Pitfalls, and Developments of All Optical Interrogation Strategies of Microcircuits in vivo

The holy grail for every neurophysiologist is to conclude a causal relationship between an elementary behaviour and the function of a specific brain area or circuit. Our effort to map elementary behaviours to specific brain loci and to further manipulate neural activity while observing the alterations in behaviour is in essence the goal for neuroscientists. Recent advancements in the area of experimental brain imaging in the form of longer wavelength near infrared (NIR) pulsed lasers with the development of highly efficient optogenetic actuators and reporters of neural activity, has endowed us with unprecedented resolution in spatiotemporal precision both in imaging neural activity as well as manipulating it with multiphoton microscopy. This readily available toolbox has introduced a so called all-optical physiology and interrogation of circuits and has opened new horizons when it comes to precisely, fast and non-invasively map and manipulate anatomically, molecularly or functionally identified mesoscopic brain circuits. The purpose of this review is to describe the advantages and possible pitfalls of all-optical approaches in system neuroscience, where by all-optical we mean use of multiphoton microscopy to image the functional response of neuron(s) in the network so to attain flexible choice of the cells to be also optogenetically photostimulated by holography, in absence of electrophysiology. Spatio-temporal constraints will be compared toward the classical reference of electrophysiology methods. When appropriate, in relation to current limitations of current optical approaches, we will make reference to latest works aimed to overcome these limitations, in order to highlight the most recent developments. We will also provide examples of types of experiments uniquely approachable all-optically. Finally, although mechanically non-invasive, all-optical electrophysiology exhibits potential off-target effects which can ambiguate and complicate the interpretation of the results. In summary, this review is an effort to exemplify how an all-optical experiment can be designed, conducted and interpreted from the point of view of the integrative neurophysiologist.

Short-term plasticity in the human visual thalamus

While there is evidence that the visual cortex retains a potential for plasticity in adulthood, less is known about the subcortical stages of visual processing. Here we asked whether short-term ocular dominance plasticity affects the human visual thalamus. We addressed this question in normally sighted adult humans, using ultra-high field (7T) magnetic resonance imaging combined with the paradigm of short-term monocular deprivation. With this approach, we previously demonstrated transient shifts of perceptual eye dominance and ocular dominance in visual cortex (Binda et al., 2018). Here we report evidence for short-term plasticity in the ventral division of the pulvinar (vPulv), where the deprived eye representation was enhanced over the non-deprived eye. This ventral-pulvinar plasticity was similar as previously seen in visual cortex and it was correlated with the ocular dominance shift measured behaviorally. In contrast, there was no effect of monocular deprivation in two adjacent thalamic regions: dorsal pulvinar (dPulv), and Lateral Geniculate Nucleus (LGN). We conclude that the visual thalamus retains potential for short-term plasticity in adulthood; the plasticity effect differs across thalamic subregions, possibly reflecting differences in their cortico-fugal connectivity.

Diverse modes of binocular interactions in the mouse superior colliculus

The superior colliculus (SC) integrates visual and other sensory information to regulate critical reflexive and innate behaviors, such as prey capture. In the mouse, the vast majority of retinal ganglion cells (RGCs) innervate the SC, including inputs from both the contralateral (contra-RGCs) and ipsilateral (ipsi-RGCs) eye. Despite this, previous studies revealed minimal neuronal responses to ipsilateral stimulation and few binocular interactions in the mouse SC. More recent work suggests that ipsi-RGC function and innervation of the SC are critical for efficient prey capture, raising the possibility that binocular interactions in the mouse SC may be more prevalent than previously thought. To explore this possibility, we investigated eye-specific and binocular influences on visual responses and tuning of SC neurons, focusing on the anteromedial region. Although the majority of SC neurons were primarily driven by contralateral eye stimulation, we observed that a substantial proportion of units were influenced or driven by ipsilateral stimulation. Clustering based on differential responses to eye-specific stimulus presentation revealed five distinct putative subpopulations and multiple modes of binocular interaction, including facilitation, summation, and suppression. Each of the putative subpopulations exhibited selectivity for orientation, and differences in spatial frequency tuning and spatial summation properties were observed between subpopulations. Further analysis of orientation tuning under different ocular conditions supported differential modes of binocular interaction between putative subtypes. Taken together, these data suggest that binocular interactions in the mouse SC may be more prevalent and diverse than previously understood.NEW & NOTEWORTHY The mouse superior colliculus (SC) receives binocular inputs, which inform complex behavioral programs. However, we know surprisingly little about binocular tuning in the rodent SC. Here, we characterize responses to eye-specific presentations of visual stimuli and reveal a previously unappreciated diversity of binocularly modulated neurons in the SC. This foundational work broadens our understanding of visual processing in the SC and sets the stage for future studies interrogating the circuit mechanisms underlying binocular tuning.

Orientation and direction tuning align with dendritic morphology and spatial connectivity in mouse visual cortex

The functional properties of neocortical pyramidal cells (PCs), such as direction and orientation selectivity in visual cortex, predominantly derive from their excitatory and inhibitory inputs. For layer 2/3 (L2/3) PCs, the detailed relationship between their functional properties and how they sample and integrate information across cortical space is not fully understood. Here, we study this relationship by combining functional in vivo two-photon calcium imaging, in vitro functional circuit mapping, and dendritic reconstruction of the same L2/3 PCs in mouse visual cortex. Our work reveals direct correlations between dendritic morphology and functional input connectivity and the orientation as well as direction tuning of L2/3 PCs. First, the apical dendritic tree is elongated along the postsynaptic preferred orientation, considering the representation of visual space in the cortex as determined by its retinotopic organization. Additionally, sharply orientation-tuned cells show a less complex apical tree compared with broadly tuned cells. Second, in direction-selective L2/3 PCs, the spatial distribution of presynaptic partners is offset from the soma opposite to the preferred direction. Importantly, although the presynaptic excitatory and inhibitory input distributions spatially overlap on average, the excitatory input distribution is spatially skewed along the preferred direction, in contrast to the inhibitory distribution. Finally, the degree of asymmetry is positively correlated with the direction selectivity of the postsynaptic L2/3 PC. These results show that the dendritic architecture and the spatial arrangement of excitatory and inhibitory presynaptic cells of L2/3 PCs play important roles in shaping their orientation and direction tuning.

Structural and functional plasticity in the dorsolateral geniculate nucleus of mice following bilateral enucleation

Within the nervous system, plasticity mechanisms attempt to stabilize network activity following disruption by injury, disease, or degeneration. Optic nerve injury and age-related diseases can induce homeostatic-like responses in adulthood. We tested this possibility in the thalamocortical (TC) neurons in the dorsolateral geniculate nucleus (dLGN) using patch-clamp electrophysiology, optogenetics, immunostaining, and single-cell dendritic analysis following loss of visual input via bilateral enucleation. We observed progressive loss of vGlut2-positive retinal terminals in the dLGN indicating degeneration post-enucleation that was coincident with changes in microglial morphology indicative of microglial activation. Consistent with the decline of vGlut2 puncta, we also observed loss of retinogeniculate (RG) synaptic function assessed using optogenetic activation of RG axons while performing whole-cell voltage clamp recordings from TC neurons in brain slices. Surprisingly, we did not detect any significant changes in the frequency of miniature post-synaptic currents (mEPSCs) or corticothalamic feedback synapses. Analysis of TC neuron dendritic structure from single-cell dye fills revealed a gradual loss of dendrites proximal to the soma, where TC neurons receive the bulk of RG inputs. Finally, analysis of action potential firing demonstrated that TC neurons have increased excitability following enucleation, firing more action potentials in response to depolarizing current injections. Our findings show that degeneration of the retinal axons/optic nerve and loss of RG synaptic inputs induces structural and functional changes in TC neurons, consistent with neuronal attempts at compensatory plasticity in the dLGN.

Development of Functional Properties in the Early Visual System: New Appreciations of the Roles of Lateral Geniculate Nucleus

In the years following Hubel and Wiesel's first reports on ocular dominance plasticity and amblyopia, much attention has been focused on understanding the role of cortical circuits in developmental and experience-dependent plasticity. Initial studies found few differences between retinal ganglion cells and neurons in the lateral geniculate nucleus and uncovered little evidence for an impact of altered visual experience on the functional properties of lateral geniculate nucleus neurons. In the last two decades, however, studies have revealed that the connectivity between the retina and lateral geniculate nucleus is much richer than was previously appreciated, even revealing visual plasticity - including ocular dominance plasticity - in lateral geniculate nucleus neurons. Here we review the development of the early visual system and the impact of experience with a distinct focus on recent discoveries about lateral geniculate nucleus, its connectivity, and evidence for its plasticity and rigidity during development.

Distinct neuron populations for simple and compound calls in the primary auditory cortex of awake marmosets

Marmosets are highly social non-human primates that live in families. They exhibit rich vocalization, but the neural basis underlying this complex vocal communication is largely unknown. Here we report the existence of specific neuron populations in marmoset A1 that respond selectively to distinct simple or compound calls made by conspecific marmosets. These neurons were spatially dispersed within A1 but distinct from those responsive to pure tones. Call-selective responses were markedly diminished when individual domains of the call were deleted or the domain sequence was altered, indicating the importance of the global rather than local spectral-temporal properties of the sound. Compound call-selective responses also disappeared when the sequence of the two simple-call components was reversed or their interval was extended beyond 1 s. Light anesthesia largely abolished call-selective responses. Our findings demonstrate extensive inhibitory and facilitatory interactions among call-evoked responses, and provide the basis for further study of circuit mechanisms underlying vocal communication in awake non-human primates.

Mechanisms of Plasticity in Subcortical Visual Areas

Visual plasticity is classically considered to occur essentially in the primary and secondary cortical areas. Subcortical visual areas such as the dorsal lateral geniculate nucleus (dLGN) or the superior colliculus (SC) have long been held as basic structures responsible for a stable and defined function. In this model, the dLGN was considered as a relay of visual information travelling from the retina to cortical areas and the SC as a sensory integrator orienting body movements towards visual targets. However, recent findings suggest that both dLGN and SC neurons express functional plasticity, adding unexplored layers of complexity to their previously attributed functions. The existence of neuronal plasticity at the level of visual subcortical areas redefines our approach of the visual system. The aim of this paper is therefore to review the cellular and molecular mechanisms for activity-dependent plasticity of both synaptic transmission and cellular properties in subcortical visual areas.

Bottom-up inputs are required for establishment of top-down connectivity onto cortical layer 1 neurogliaform cells

Higher-order projections to sensory cortical areas converge on layer 1 (L1), the primary site for integration of top-down information via the apical dendrites of pyramidal neurons and L1 GABAergic interneurons. Here we investigated the contribution of early thalamic inputs onto L1 interneurons for establishment of top-down connectivity in the primary visual cortex. We find that bottom-up thalamic inputs predominate during L1 development and preferentially target neurogliaform cells. We show that these projections are critical for the subsequent strengthening of top-down inputs from the anterior cingulate cortex onto L1 neurogliaform cells. Sensory deprivation or selective removal of thalamic afferents blocked this phenomenon. Although early activation of the anterior cingulate cortex resulted in premature strengthening of these top-down afferents, this was dependent on thalamic inputs. Our results demonstrate that proper establishment of top-down connectivity in the visual cortex depends critically on bottom-up inputs from the thalamus during postnatal development.

Nyquist-exceeding high voxel rate acquisition in mesoscopic multiphoton microscopy for full-field submicron resolution resolvability

The Nyquist-Shannon criterion has never been realized in a laser-scanning mesoscopic multiphoton microscope (MPM) with a large field-of-view (FOV)-resolution ratio, especially when employing a high-frequency resonant-raster-scanning. With a high optical resolution nature, a current mesoscopic-MPM either neglects the criterion and degrades the digital resolution to twice the pixel size, or reduces the FOV and/or the raster-scanning speed to avoid aliasing. We introduce a Nyquist figure-of-merit (NFOM) parameter to characterize a laser-scanning MPM in terms of its optical-resolution retrieving ability. Based on NFOM, we define the maximum aliasing-free FOV, and subsequently, a cross-over excitation wavelength, below which the FOV becomes NFOM-constrained irrespective of an optimized optical design. We validate our idea in a custom-built mesoscopic-MPM with millimeter-scale FOV yielding an ultra-high FOV-resolution ratio of >3,000, while securing up-to a 1.6 mm Nyquist-satisfied aliasing-free FOV, a ∼400 nm lateral resolution, and a 70 M/s effective voxel-sampling rate, all at the same time.

•

Nyquist figure-of-merit is introduced to characterize laser-scanning MPM digitization

•

Maximum aliasing-free FOV and cross-over excitation wavelength are formulated

•

High repetition-rate laser can enable high-speed large-FOV high-resolution MPM imaging

•

Up-to 1.6 mm-wide non-aliased FOV and ∼400 nm digital resolution at 8 kHz line-rate

Eavesdropping wires: Recording activity in axons using genetically encoded calcium indicators

Neurons broadcast electrical signals to distal brain regions through extensive axonal arbors. Genetically encoded calcium sensors permit the direct observation of action potential activity at axonal terminals, providing unique insights on the organization and function of neural projections. Here, we consider what information can be gleaned from axonal recordings made at scales ranging from the summed activity extracted from multi-cell axon projections to single boutons. In particular, we discuss the application of different recently developed multi photon and fiber photometry methods for recording neural activity in axons of rodents. We define experimental difficulties associated with imaging approaches in the axonal compartment and highlight the latest methodological advances for addressing these issues. Finally, we reflect on ways in which new technologies can be used in conjunction with axon calcium imaging to address current questions in neurobiology.

Impairment of visual cortical plasticity by amyloid-beta species

INTRODUCTION

A variety of transgenic and knock-in mice that express mutant alleles of Amyloid precursor protein (APP) have been used to model the effects of amyloid-beta (Aβ) on circuit function in Alzheimer's disease (AD); however phenotypes described in these mice may be affected by expression of mutant APP or proteolytic cleavage products independent of Aβ. In addition, the effects of mutant APP expression are attributed to elevated expression of the amyloidogenic, 42-amino acid-long species of Aβ (Aβ42) associated with amyloid plaque accumulation in AD, though elevated concentrations of Aβ40, an Aβ species produced with normal synaptic activity, may also affect neural function.

METHODS

To explore the effects of elevated expression of Aβ on synaptic function in vivo, we assessed visual system plasticity in transgenic mice that express and secrete Aβ throughout the brain in the absence of APP overexpression. Transgenic mice that express either Aβ40 or Aβ42 were assayed for their ability to appropriately demonstrate ocular dominance plasticity following monocular deprivation.

RESULTS

Using two complementary approaches to measure the plastic response to monocular deprivation, we find that male and female mice that express either 40- or 42-amino acid-long Aβ species demonstrate a plasticity defect comparable to that elicited in transgenic mice that express mutant alleles of APP and Presenilin 1 (APP/PS1 mice).

CONCLUSIONS

These data support the hypothesis that mutant APP-driven plasticity impairment in mouse models of AD is mediated by production and accumulation of Aβ. Moreover, these findings suggest that soluble species of Aβ are capable of modulating synaptic plasticity, likely independent of any aggregation. These findings may have implications for the role of soluble species of Aβ in both development and disease settings.

Experience-Dependent Development and Maintenance of Binocular Neurons in the Mouse Visual Cortex

The development of neuronal circuits requires both hard-wired gene expression and experience-dependent plasticity. Sensory processing, such as binocular vision, is especially sensitive to perturbations of experience. We investigated the experience-dependent development of the binocular visual cortex at single-cell resolution by using two-photon calcium imaging in awake mice. At eye-opening, the majority of visually responsive neurons are monocular. Binocular neurons emerge later with visual experience and acquire distinct visual response properties. Surprisingly, rather than mirroring the effects of visual deprivation, mice that lack the plasticity gene Arc show increased numbers of binocular neurons and a shift in ocular dominance during development. Strikingly, acutely removing Arc in the adult binocular visual cortex also increases the number of binocular neurons, suggesting that the maintenance of binocular circuits requires ongoing plasticity. Thus, experience-dependent plasticity is critical for the development and maintenance of circuits required to process binocular vision.

Jenks and Shepherd show that neurons responding to both eyes in the mouse visual cortex develop with experience. These binocular neurons acquire unique visual response properties, such as a preference for horizonal orientations. The neuronal gene Arc limits and maintains the number of binocular neurons, even in the adult cortex.

Functional Differentiation of Mouse Visual Cortical Areas Depends upon Early Binocular Experience

The mammalian visual cortex contains multiple retinotopically defined areas that process distinct features of the visual scene. Little is known about what guides the functional differentiation of visual cortical areas during development. Recent studies in mice have revealed that visual input from the two eyes provides spatiotemporally distinct signals to primary visual cortex (V1), such that contralateral eye-dominated V1 neurons respond to higher spatial frequencies than ipsilateral eye-dominated neurons. To test whether binocular visual input drives the differentiation of visual cortical areas, we used two-photon calcium imaging to characterize the effects of juvenile monocular deprivation (MD) on the responses of neurons in V1 and two higher visual areas, LM (lateromedial) and PM (posteromedial). In adult mice of either sex, we find that MD prevents the emergence of distinct spatiotemporal tuning in V1, LM, and PM. We also find that, within each of these areas, MD reorganizes the distinct spatiotemporal tuning properties driven by the two eyes. Moreover, we find a relationship between speed tuning and ocular dominance in all three areas that MD preferentially disrupts in V1, but not in LM or PM. Together, these results reveal that balanced binocular vision during development is essential for driving the functional differentiation of visual cortical areas. The higher visual areas of mouse visual cortex may provide a useful platform for investigating the experience-dependent mechanisms that set up the specialized processing within neocortical areas during postnatal development.SIGNIFICANCE STATEMENT Little is known about the factors guiding the emergence of functionally distinct areas in the brain. Using in vivo Ca2+ imaging, we recorded visually evoked activity from cells in V1 and higher visual areas LM (lateromedial) and PM (posteromedial) of mice. Neurons in these areas normally display distinct spatiotemporal tuning properties. We found that depriving one eye of normal input during development prevents the functional differentiation of visual areas. Deprivation did not disrupt the degree of speed tuning, a property thought to emerge in higher visual areas. Thus, some properties of visual cortical neurons are shaped by binocular experience, while others are resistant. Our study uncovers the fundamental role of binocular experience in the formation of distinct areas in visual cortex.

Multi-scale network imaging in a mouse model of amyloidosis

The adult neocortex is not hard-wired but instead retains the capacity to reorganise across multiple spatial scales long into adulthood. Plastic reorganisation occurs at the level of mesoscopic sensory maps, functional neuronal assemblies and synaptic ensembles and is thought to be a critical feature of neuronal network function. Here, we describe a series of approaches that use calcium imaging to measure network reorganisation across multiple spatial scales in vivo. At the mesoscopic level, we demonstrate that sensory activity can be measured in animals undergoing longitudinal behavioural assessment involving automated touchscreen tasks. At the cellular level, we show that network dynamics can be longitudinally measured at both stable and transient functional assemblies. At the level of single synapses, we show that functional subcellular calcium imaging approaches can be used to measure synaptic ensembles of dendritic spines in vivo. Finally, we demonstrate that all three levels of imaging can be spatially related to local pathology in a preclinical rodent model of amyloidosis. We propose that multi-scale in vivo calcium imaging can be used to measure parallel plasticity processes operating across multiple spatial scales in both the healthy brain and preclinical models of disease.

Host interneurons mediate plasticity reactivated by embryonic inhibitory cell transplantation in mouse visual cortex

The adult brain lacks sensitivity to changes in the sensory environment found in the juvenile brain. The transplantation of embryonic interneurons has been shown to restore juvenile plasticity to the adult host visual cortex. It is unclear whether transplanted interneurons directly mediate the renewed cortical plasticity or whether these cells act indirectly by modifying the host interneuron circuitry. Here we find that the transplant-induced reorganization of mouse host circuits is specifically mediated by Neuregulin (NRG1)/ErbB4 signaling in host parvalbumin (PV) interneurons. Brief visual deprivation reduces the visual activity of host PV interneurons but has negligible effects on the responses of transplanted PV interneurons. Exogenous NRG1 both prevents the deprivation-induced reduction in the visual responses of host PV interneurons and blocks the transplant-induced reorganization of the host circuit. While deletion of ErbB4 receptors from host PV interneurons blocks cortical plasticity in the transplant recipients, deletion of the receptors from the donor PV interneurons does not. Altogether, our results indicate that transplanted embryonic interneurons reactivate cortical plasticity by rejuvenating the function of host PV interneurons.

Mouse visual cortex areas represent perceptual and semantic features of learned visual categories

Associative memories are stored in distributed networks extending across multiple brain regions. However, it is unclear to what extent sensory cortical areas are part of these networks. Using a paradigm for visual category learning in mice, we investigated whether perceptual and semantic features of learned category associations are already represented at the first stages of visual information processing in the neocortex. Mice learned categorizing visual stimuli, discriminating between categories and generalizing within categories. Inactivation experiments showed that categorization performance was contingent on neuronal activity in the visual cortex. Long-term calcium imaging in nine areas of the visual cortex identified changes in feature tuning and category tuning that occurred during this learning process, most prominently in the postrhinal area (POR). These results provide evidence for the view that associative memories form a brain-wide distributed network, with learning in early stages shaping perceptual representations and supporting semantic content downstream.

Organization, Function, and Development of the Mouse Retinogeniculate Synapse

Visual information is encoded in distinct retinal ganglion cell (RGC) types in the eye tuned to specific features of the visual space. These streams of information project to the visual thalamus, the first station of the image-forming pathway. In the mouse, this connection between RGCs and thalamocortical neurons, the retinogeniculate synapse, has become a powerful experimental model for understanding how circuits in the thalamus are constructed to process these incoming lines of information. Using modern molecular and genetic tools, recent studies have suggested a more complex circuit organization than was previously understood. In this review, we summarize the current understanding of the structural and functional organization of the retinogeniculate synapse in the mouse. We discuss a framework by which a seemingly complex circuit can effectively integrate and parse information to downstream stations of the visual pathway. Finally, we review how activity and visual experience can sculpt this exquisite connectivity.

Subanesthetic Ketamine Reactivates Adult Cortical Plasticity to Restore Vision from Amblyopia

Subanesthetic ketamine evokes rapid and long-lasting antidepressant effects in human patients. The mechanism for ketamine's effects remains elusive, but ketamine may broadly modulate brain plasticity processes. We show that single-dose ketamine reactivates adult mouse visual cortical plasticity and promotes functional recovery of visual acuity defects from amblyopia. Ketamine specifically induces downregulation of neuregulin-1 (NRG1) expression in parvalbumin-expressing (PV) inhibitory neurons in mouse visual cortex. NRG1 downregulation in PV neurons co-tracks both the fast onset and sustained decreases in synaptic inhibition to excitatory neurons, along with reduced synaptic excitation to PV neurons in vitro and in vivo following a single ketamine treatment. These effects are blocked by exogenous NRG1 as well as PV targeted receptor knockout. Thus, ketamine reactivation of adult visual cortical plasticity is mediated through rapid and sustained cortical disinhibition via downregulation of PV-specific NRG1 signaling. Our findings reveal the neural plasticity-based mechanism for ketamine-mediated functional recovery from adult amblyopia.

Cortical Inactivation Does Not Block Response Enhancement in the Superior Colliculus

Repetitive visual stimulation is successfully used in a study on the visual evoked potential (VEP) plasticity in the visual system in mammals. Practicing visual tasks or repeated exposure to sensory stimuli can induce neuronal network changes in the cortical circuits and improve the perception of these stimuli. However, little is known about the effect of visual training at the subcortical level. In the present study, we extend the knowledge showing positive results of this training in the rat's Superior colliculus (SC). In electrophysiological experiments, we showed that a single training session lasting several hours induces a response enhancement both in the primary visual cortex (V1) and in the SC. Further, we tested if collicular responses will be enhanced without V1 input. For this reason, we inactivated the V1 by applying xylocaine solution onto the cortical surface during visual training. Our results revealed that SC's response enhancement was present even without V1 inputs and showed no difference in amplitude comparing to VEPs enhancement while the V1 was active. These data suggest that the visual system plasticity and facilitation can develop independently but simultaneously in different parts of the visual system.

Layer 4 Gates Plasticity in Visual Cortex Independent of a Canonical Microcircuit

Disrupting binocular vision during a developmental critical period can yield enduring changes to ocular dominance (OD) in primary visual cortex (V1). Here we investigated how this experience-dependent plasticity is coordinated within the laminar circuitry of V1 by deleting separately in each cortical layer (L) a gene required to close the critical period, nogo-66 receptor (ngr1). Deleting ngr1 in excitatory neurons in L4, but not in L2/3, L5, or L6, prevented closure of the critical period, and adult mice remained sensitive to brief monocular deprivation. Intracortical disinhibition, but not thalamocortical disinhibition, accompanied this OD plasticity. Both juvenile wild-type mice and adult mice lacking ngr1 in L4 displayed OD plasticity that advanced more rapidly L4 than L2/3 or L5. Interestingly, blocking OD plasticity in L2/3 with the drug AM-251 did not impair OD plasticity in L5. We propose that L4 restricts disinhibition and gates OD plasticity independent of a canonical cortical microcircuit.

Reduced Dendritic Spines in the Visual Cortex Contralateral to the Optic Nerve Crush Eye in Adult Mice

Purpose

To determine alteration of dendritic spines and associated changes in the primary visual cortex (V1 region) related to unilateral optic nerve crush (ONC) in adult mice.

Methods

Adult unilateral ONC mice were established. Retinal nerve fiber layer (RNFL) thickness was measured by spectral-domain optical coherence tomography. Visual function was estimated by flash visual evoked potentials (FVEPs). Dendritic spines were observed in the V1 region contralateral to the ONC eye by two-photon imaging in vivo. The neurons, reactive astrocytes, oligodendrocytes, and activated microglia were assessed by NeuN, glial fibrillary acidic protein, CNPase, and CD68 in immunohistochemistry, respectively. Tropomyosin receptor kinase B (TrkB) and the markers in TrkB trafficking were estimated using western blotting and co-immunoprecipitation. Transmission electron microscopy and western blotting were used to evaluate autophagy.

Results

The amplitude and latency of FVEPs were decreased and delayed at 3 days, 1 week, 2 weeks, and 4 weeks after ONC, and RNFL thickness was decreased at 2 and 4 weeks after ONC. Dendritic spines were reduced in the V1 region contralateral to the ONC eye at 2, 3, and 4 weeks after ONC, with an unchanged number of neurons. Reactive astrocyte staining was increased at 2 and 4 weeks after ONC, but oligodendrocyte and activated microglia staining remained unchanged. TrkB was reduced with changes in the major trafficking proteins, and enhanced autophagy was observed in the V1 region contralateral to the ONC eye.

Conclusions

Dendritic spines were reduced in the V1 region contralateral to the ONC eye in adult mice. Reactive astrocytes and decreased TrkB may be associated with the reduced dendritic spines.

Circuitry Underlying Experience-Dependent Plasticity in the Mouse Visual System

Since the discovery of ocular dominance plasticity, neuroscientists have understood that changes in visual experience during a discrete developmental time, the critical period, trigger robust changes in the visual cortex. State-of-the-art tools used to probe connectivity with cell-type-specific resolution have expanded the understanding of circuit changes underlying experience-dependent plasticity. Here, we review the visual circuitry of the mouse, describing projections from retina to thalamus, between thalamus and cortex, and within cortex. We discuss how visual circuit development leads to precise connectivity and identify synaptic loci, which can be altered by activity or experience. Plasticity extends to visual features beyond ocular dominance, involving subcortical and cortical regions, and connections between cortical inhibitory interneurons. Experience-dependent plasticity contributes to the alignment of networks spanning retina to thalamus to cortex. Disruption of this plasticity may underlie aberrant sensory processing in some neurodevelopmental disorders.

Early Visual Motion Experience Improves Retinal Encoding of Motion Directions

Altered sensory experience in early life often leads to altered response properties of the sensory neurons. This process is mostly thought to happen in the brain, not in the sensory organs. We show that in the mouse retina of both sexes, exposed to a motion-dominated visual environment from eye-opening, the ON-OFF direction selective ganglion cells (ooDSGCs) develop significantly stronger direction encoding ability for motion in all directions. This improvement occurs independent of the motion direction used for training. We demonstrated that this enhanced ability to encode motion direction is mainly attributed to increased response reliability of ooDSGCs. Closer examination revealed that the excitatory inputs from the ON bipolar pathway showed enhanced response reliability after the motion experience training, while other synaptic inputs remain relatively unchanged. Our results demonstrate that retina adapts to the visual environment during neonatal development.SIGNIFICANCE STATEMENT We found that retina, as the first stage of visual sensation, can also be affected by experience dependent plasticity during development. Exposure to a motion enriched visual environment immediately after eye-opening greatly improves motion direction encoding by direction selective retinal ganglion cells (RGCs). These results motivate future studies aimed at understanding how visual experience shapes the retinal circuits and the response properties of retinal neurons.

Longitudinal changes of the macular structure after lens removal combined with anterior vitrectomy after pediatric cataract surgery

PURPOSE

To explore the macular thickness changes after lens removal combined with anterior vitrectomy for pediatric cataract surgery.

SETTING

The Eye Hospital of Wenzhou Medical University, Zhejiang, China.

DESIGN

Prospective study.

METHODS

Thirty children (40 eyes) aged between 3 years and 9 years with pediatric cataracts, including 20 children (20 eyes) with unilateral cataracts and 10 children (20 eyes) with bilateral cataracts, were enrolled. Spectral-domain optical coherence tomography was used to obtain macular images. Central subfield thickness (CST) and retinal thickness in the Early Treatment Diabetic Retinopathy Study subfields (inner 1.0 to 3.0 mm annulus and outer 3.0 to 6.0 mm annulus) were recorded preoperatively as well as at 1, 3, 6, and 12 months postoperatively.

RESULTS

Forty eyes of 30 children were included. Retinal thickness in every subfield significantly thickened at 3 months postoperatively (all P < .05). CST significantly thickened compared with preoperative levels (228.03 ± 18.58 vs 240.35 ± 17.41, P = .005) at 3 months postoperatively; macular thickness gradually decreased in the following months. At 6 months postoperatively, retinal thickness in inner nasal, inferior, temporal, and outer nasal subfields remained significantly thicker compared with preoperative levels (P = .048, P = .036, P = .029, and P = .017, respectively). At 12 months, the retinal thickness in all subfields reached the preoperative level.

CONCLUSIONS

The influence on macular thickness lasted until 12 months after pediatric cataract surgery. The inner macular thickness increased for a longer time than the outer macular thickness postoperatively.

Long-term Monocular Deprivation during Juvenile Critical Period Disrupts Binocular Integration in Mouse Visual Thalamus

Study of the neural deficits caused by mismatched binocular vision in early childhood has predominantly focused on circuits in the primary visual cortex (V1). Recent evidence has revealed that neurons in mouse dorsolateral geniculate nucleus (dLGN) can undergo rapid ocular dominance plasticity following monocular deprivation (MD). It remains unclear, however, whether the long-lasting deficits attributed to MD during the critical period originate in the thalamus. Using in vivo two-photon Ca2+ imaging of dLGN afferents in superficial layers of V1 in female and male mice, we demonstrate that 14 d MD during the critical period leads to a chronic loss of binocular dLGN inputs while sparing response strength and spatial acuity. Importantly, MD leads to profoundly mismatched visual tuning properties in remaining binocular dLGN afferents. Furthermore, MD impairs binocular modulation, reducing facilitation of responses of both binocular and monocular dLGN inputs during binocular viewing. As predicted by our findings in thalamic inputs, Ca2+ imaging from V1 neurons revealed spared spatial acuity but impaired binocularity in L4 neurons. V1 L2/3 neurons in contrast displayed deficits in both binocularity and spatial acuity. Our data demonstrate that critical-period MD produces long-lasting disruptions in binocular integration beginning in early binocular circuits in dLGN, whereas spatial acuity deficits first arise from circuits further downstream in V1. Our findings indicate that the development of normal binocular vision and spatial acuity depend upon experience-dependent refinement of distinct stages in the mammalian visual system.SIGNIFICANCE STATEMENT Abnormal binocular vision and reduced acuity are hallmarks of amblyopia, a disorder that affects 2%-5% of the population. It is widely thought that the neural deficits underlying amblyopia begin in the circuits of primary visual cortex. Using in vivo two-photon calcium imaging of thalamocortical axons in mice, we show that depriving one eye of input during a critical period in development chronically impairs binocular integration in thalamic inputs to primary visual cortex. In contrast, visual acuity is spared in thalamic inputs. These findings shed new light on the role for developmental mechanisms in the thalamus in establishing binocular vision and may have critical implications for amblyopia.

Therapeutic effect of vasoactive intestinal peptide on form-deprived amblyopic kittens

Background

Exploring the role of vasoactive intestinal peptide (VIP) in the lateral geniculate body (LGBd) in visual development and studying the therapeutic effect of VIP on amblyopic kittens.

Methods

Three-week-old domestic cats were divided into a control group (n = 10) and a monocular deprivation group (n = 20), with an eye mask covering the right eye of those in the deprived group. After pattern visual evoked potential (PVEP) recording confirmed the formation of monocular amblyopia, the left LGBd was isolated from 5 kittens in each group. The remaining control kittens continued to be raised, and the remaining deprivation group was divided into a VIP intervention group (n = 5), Sefsol (caprylic acid monoglyceride, VIP solution) intervention group (n = 5) and amblyopia non-intervention group (n = 5) after removal of the eye mask. Three weeks later, PVEPs, VIP immunohistochemistry and VIP mRNA expression in the left LGBd were compared across groups.

Results

At 6 weeks of age, there were significant differences in P100 wave latency and amplitude and VIP immunohistochemistry and in situ hybridization between the control group and the deprivation group (P < 0.05). After 3 weeks of the corresponding interventions, the latency and amplitude in the VIP intervention group were better than that in the Sefsol intervention group and amblyopia non-intervention group (P < 0.05). Furthermore, VIP treatment increased the number of immunohistochemical VIP-positive cells (P < 0.05) and the average optical density of positive cells (P > 0.05), as well as the number (P < 0.05) and average optical density of VIP mRNA-positive cells (P < 0.05).

Conclusions

VIP plays an important role in visual development. Nasal administration of VIP can improve the function of neurons in the LGBd of kittens and has a certain therapeutic effect on amblyopia.

Synaptic plasticity onto inhibitory neurons as a mechanism for ocular dominance plasticity

Ocular dominance plasticity is a well-documented phenomenon allowing us to study properties of cortical maturation. Understanding this maturation might be an important step towards unravelling how cortical circuits function. However, it is still not fully understood which mechanisms are responsible for the opening and closing of the critical period for ocular dominance and how changes in cortical responsiveness arise after visual deprivation. In this article, we present a theory of ocular dominance plasticity. Following recent experimental work, we propose a framework where a reduction in inhibition is necessary for ocular dominance plasticity in both juvenile and adult animals. In this framework, two ingredients are crucial to observe ocular dominance shifts: a sufficient level of inhibition as well as excitatory-to-inhibitory synaptic plasticity. In our model, the former is responsible for the opening of the critical period, while the latter limits the plasticity in adult animals. Finally, we also provide a possible explanation for the variability in ocular dominance shifts observed in individual neurons and for the counter-intuitive shifts towards the closed eye.

During the development of the brain, visual cortex has a period of increased plasticity. Closing one eye for multiple days during this period can have a profound and life-long impact on neuronal responses. A well-established hypothesis is that the absolute level of inhibition regulates this period. In light of recent experimental results, we suggest an alternative theory. We propose that, in addition to the level of inhibition, synaptic plasticity onto inhibitory neurons is just as crucial. We propose a model which explains many observed phenomena into one single framework. Unlike theories considering only the level of inhibition, we can account for both the onset as well as the closure of this period. Furthermore, we also provide an explanation for the small fraction of neurons that show counter-intuitive behaviour and provide some testable predictions.

Visual deprivation independent shift of ocular dominance induced by cross-modal plasticity

There is convincing evidence that the deprivation of one sense can lead to adaptive neuronal changes in spared primary sensory cortices. However, the repercussions of late-onset sensory deprivations on functionality of the remaining sensory cortices are poorly understood. Using repeated intrinsic signal imaging we investigated the effects of whisker or auditory deprivation (WD or AD, respectively) on responsiveness of the binocular primary visual cortex (V1) in fully adult mice. The binocular zone of mice is innervated by both eyes, with the contralateral eye always dominating V1 input over ipsilateral eye input, the normal ocular dominance (OD) ratio. Strikingly, we found that 3 days of WD or AD induced a transient shift of OD, which was mediated by a potentiation of V1 input through the ipsilateral eye. This cross-modal effect was accompanied by strengthening of layer 4 synapses in V1, required visual experience through the ipsilateral eye and was mediated by an increase of the excitation/inhibition ratio in V1. Finally, we demonstrate that both WD and AD induced a long-lasting improvement of visual performance. Our data provide evidence that the deprivation of a non-visual sensory modality cross-modally induces experience dependent V1 plasticity and improves visual behavior, even in adult mice.