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Two-photon calcium imaging and electron microscopy were used to explore the relationship between structure and function in mouse primary visual cortex, showing that layer 2/3 neurons are connected in subnetworks, that pyramidal neurons with similar orientation selectivity preferentially form synapses with each other, and that neurons with similar orientation tuning form larger synapses; this study exemplifies functional connectomics as a powerful method for studying the organizational logic of cortical networks. The connectomics of excitatory cortical networks To explore the relationship between structure and function in cortical networks, Wei-Chung Allen Lee and colleagues combined two-photon calcium imaging and electron microscopy in mouse primary visual cortex. They found that layer 2/3 neurons are organized into subnetworks, that pyramidal neurons with similar orientation selectivity preferentially form synapses with each other, and that neurons with similar orientation tuning form larger synapses. This study exemplifies functional connectomics as a powerful method for studying the organizational logic of cortical networks. Circuits in the cerebral cortex consist of thousands of neurons connected by millions of synapses. A precise understanding of these local networks requires relating circuit activity with the underlying network structure. For pyramidal cells in superficial mouse visual cortex (V1), a consensus is emerging that neurons with similar visual response properties excite each other 1 , 2 , 3 , 4 , 5 , but the anatomical basis of this recurrent synaptic network is unknown. Here we combined physiological imaging and large-scale electron microscopy to study an excitatory network in V1. We found that layer 2/3 neurons organized into subnetworks defined by anatomical connectivity, with more connections within than between groups. More specifically, we found that pyramidal neurons with similar orientation selectivity preferentially formed synapses with each other, despite the fact that axons and dendrites of all orientation selectivities pass near (<5 μm) each other with roughly equal probability. Therefore, we predict that mechanisms of functionally specific connectivity take place at the length scale of spines. Neurons with similar orientation tuning formed larger synapses, potentially enhancing the net effect of synaptic specificity. With the ability to study thousands of connections in a single circuit, functional connectomics is proving a powerful method to uncover the organizational logic of cortical networks.

Many animals use visual information to navigate 1 – 4 , but how such information is encoded and integrated by the navigation system remains incompletely understood. In Drosophila melanogaster , EPG neurons in the central complex compute the heading direction 5 by integrating visual input from ER neurons 6 – 12 , which are part of the anterior visual pathway (AVP) 10 , 13 – 16 . Here we densely reconstruct all neurons in the AVP using electron-microscopy data 17 . The AVP comprises four neuropils, sequentially linked by three major classes of neurons: MeTu neurons 10 , 14 , 15 , which connect the medulla in the optic lobe to the small unit of the anterior optic tubercle (AOTUsu) in the central brain; TuBu neurons 9 , 16 , which connect the AOTUsu to the bulb neuropil; and ER neurons 6 – 12 , which connect the bulb to the EPG neurons. On the basis of morphologies, connectivity between neural classes and the locations of synapses, we identify distinct information channels that originate from four types of MeTu neurons, and we further divide these into ten subtypes according to the presynaptic connections in the medulla and the postsynaptic connections in the AOTUsu. Using the connectivity of the entire AVP and the dendritic fields of the MeTu neurons in the optic lobes, we infer potential visual features and the visual area from which any ER neuron receives input. We confirm some of these predictions physiologically. These results provide a strong foundation for understanding how distinct sensory features can be extracted and transformed across multiple processing stages to construct higher-order cognitive representations. Electron-microscopy data are used to reconstruct the neurons that make up the anterior visual pathway in the Drosophila brain, providing insight into how visual features are encoded to guide navigation.

Low-level near-infrared light-induced transcranial photobiomodulation (NIR-TPBM) is a promising technology for improving cerebral blood flow and metabolism. However, the effects of NIR-TPBM on the visual pathway's function remain poorly understood. The aim was to assess the visual pathway's function changes in response to NIR-TPBM in young, healthy volunteers. This single-center, randomized, controlled clinical trial included 98 healthy volunteers with a median age of 23.2 years. Participants were randomly assigned to two groups: NIR-TPBM (18 men and 30 women) and sham NIR-TPBM (19 men and 31 women). Eye-tracking procedures were conducted in both groups before and after either PBM or sham intervention. In the NIR-TPBM group, low-fluence NIR-TPBM was applied to the left and right fronto-temporal regions using a NIR-TPBM device (Elmedlife H , Nizhny Novgorod, Russian Federation). In the sham group, participants wore the NIR-TPBM helmet, but the NIR-TPBM mode remained deactivated. The duration of the sessions was identical for both groups. Changes in visual pathway function were evaluated by analyzing the dynamics of vertical and horizontal ocular vergence reactivity indices (VRx) using the EyeTracker application (BVG Software Group LLC, San Francisco, California, United States) on iPadOS 16 before and after the intervention. Statistical analysis was performed using nonparametric methods, with a significance level set at . NIR-TPBM procedures led to a significant increase in both vertical and horizontal VRx values. Post-procedure vertical VRx was significantly higher than pre-procedure values (0.879 [0.761; 0.918] versus 0.774 [0.721; 0.929], ). Similarly, horizontal VRx increased significantly after NIR-TPBM compared with baseline (0.943 [0.848; 0.969] versus 0.772 [0.651; 0.890], ). No adverse effects were observed during or after the NIR-TPBM sessions. NIR-TPBM enhances visual pathways function by increasing both vergence reactivity indices in young healthy volunteers.

Visual input is often noisy and discontinuous, even though the physical environment is generally stable. The authors show that the visual system trades off change sensitivity to capitalize on physical continuity via serial dependence: present perception is biased toward past visual input. This bias is modulated by attention and governed by a spatiotemporally-tuned operator, a continuity field. Visual input often arrives in a noisy and discontinuous stream, owing to head and eye movements, occlusion, lighting changes, and many other factors. Yet the physical world is generally stable; objects and physical characteristics rarely change spontaneously. How then does the human visual system capitalize on continuity in the physical environment over time? We found that visual perception in humans is serially dependent, using both prior and present input to inform perception at the present moment. Using an orientation judgment task, we found that, even when visual input changed randomly over time, perceived orientation was strongly and systematically biased toward recently seen stimuli. Furthermore, the strength of this bias was modulated by attention and tuned to the spatial and temporal proximity of successive stimuli. These results reveal a serial dependence in perception characterized by a spatiotemporally tuned, orientation-selective operator—which we call a continuity field—that may promote visual stability over time.

Most intranasal oxytocin research to date has been carried out in men, but recent studies indicate that females’ responses can differ substantially from males’. This randomized, double-blind, placebo-controlled study involved an all-female sample of 28 women not using hormonal contraception. Participants viewed animations of geometric shapes depicting either random movement or social interactions such as playing, chasing, or fighting. Probe questions asked whether any shapes were “friends” or “not friends.” Social videos were preceded by cues to attend to either social relationships or physical size changes. All subjects received intranasal placebo spray at scan 1. While the experimenter was not blinded to nasal spray contents at Scan 1, the participants were. Scan 2 followed a randomized, double-blind design. At scan 2, half received a second placebo dose while the other half received 24 IU of intranasal oxytocin. We measured neural responses to these animations at baseline, as well as the change in neural activity induced by oxytocin. Oxytocin reduced activation in early visual cortex and dorsal-stream motion processing regions for the social > size contrast, indicating reduced activity related to social attention. Oxytocin also reduced endorsements that shapes were “friends” or “not friends,” and this significantly correlated with reduction in neural activation. Furthermore, participants who perceived fewer social relationships at baseline were more likely to show oxytocin-induced increases in a broad network of regions involved in social perception and social cognition, suggesting that lower social processing at baseline may predict more positive neural responses to oxytocin. •A randomized, double-blind, placebo-controlled fMRI study of intranasal oxytocin.•Neural response of females was measured during animations of interacting shapes.•Oxytocin (OXT) reduced activation in early visual cortex and dorsal stream regions.•OXT reduced perception of social relationships.••OXT increased social cognition networks in females with lower baseline perception

A catalogue of neuronal cell types has often been called a ‘parts list’ of the brain 1 , and regarded as a prerequisite for understanding brain function 2 , 3 . In the optic lobe of Drosophila , rules of connectivity between cell types have already proven to be essential for understanding fly vision 4 , 5 . Here we analyse the fly connectome to complete the list of cell types intrinsic to the optic lobe, as well as the rules governing their connectivity. Most new cell types contain 10 to 100 cells, and integrate information over medium distances in the visual field. Some existing type families (Tm, Li, and LPi) 6 – 10 at least double in number of types. A new serpentine medulla (Sm) interneuron family contains more types than any other. Three families of cross-neuropil types are revealed. The consistency of types is demonstrated by analysing the distances in high-dimensional feature space, and is further validated by algorithms that select small subsets of discriminative features. We use connectivity to hypothesize about the functional roles of cell types in motion, object and colour vision. Connectivity with ‘boundary types’ that straddle the optic lobe and central brain is also quantified. We showcase the advantages of connectomic cell typing: complete and unbiased sampling, a rich array of features based on connectivity and reduction of the connectome to a substantially simpler wiring diagram of cell types, with immediate relevance for brain function and development. An analysis of the Drosophila connectome yields all cell types intrinsic to the optic lobe, and their rules of connectivity.

Animal behaviour arises from computations in neuronal circuits, but our understanding of these computations has been frustrated by the lack of detailed synaptic connection maps, or connectomes. For example, despite intensive investigations over half a century, the neuronal implementation of local motion detection in the insect visual system remains elusive. Here we develop a semi-automated pipeline using electron microscopy to reconstruct a connectome, containing 379 neurons and 8,637 chemical synaptic contacts, within the Drosophila optic medulla. By matching reconstructed neurons to examples from light microscopy, we assigned neurons to cell types and assembled a connectome of the repeating module of the medulla. Within this module, we identified cell types constituting a motion detection circuit, and showed that the connections onto individual motion-sensitive neurons in this circuit were consistent with their direction selectivity. Our results identify cellular targets for future functional investigations, and demonstrate that connectomes can provide key insights into neuronal computations. Reconstruction of a connectome within the fruitfly visual medulla, containing more than 300 neurons and over 8,000 chemical synapses, reveals a candidate motion detection circuit; such a circuit operates by combining displaced visual inputs, an operation consistent with correlation based motion detection. Visual system connectomics — from insects to mammals Three papers in this issue of Nature use the retina as a model for mapping neuronal circuits from the level of individual synaptic contacts to the long-range scale of dendritic interactions. Helmstaedter et al . used electron microscopy to map a mammalian retinal circuit of close to a thousand neurons. The work reveals a new type of retinal bipolar neuron and suggests functional mechanisms for known visual computations. The other two groups study the detection of visual motion in the Drosophila visual system — a classic neural computation model. Takemura et al . used semi-automated electron microscopy to reconstruct the basic connectome (8,637 chemical synapses among 379 neurons) of Drosophila 's optic medulla. Their results reveal a candidate motion detection circuit with a wiring plan consistent with direction selectivity. Maisak et al . used calcium imaging to show that T4 and T5 neurons are divided into specific subpopulations responding to motion in four cardinal directions, and are specific to 'ON' versus 'OFF' edges, respectively.

Social affiliation emerges from individual-level behavioural rules that are driven by conspecific signals 1 – 5 . Long-distance attraction and short-distance repulsion, for example, are rules that jointly set a preferred interanimal distance in swarms 6 – 8 . However, little is known about their perceptual mechanisms and executive neural circuits 3 . Here we trace the neuronal response to self-like biological motion 9 , 10 , a visual trigger for affiliation in developing zebrafish 2 , 11 . Unbiased activity mapping and targeted volumetric two-photon calcium imaging revealed 21 activity hotspots distributed throughout the brain as well as clustered biological-motion-tuned neurons in a multimodal, socially activated nucleus of the dorsal thalamus. Individual dorsal thalamus neurons encode local acceleration of visual stimuli mimicking typical fish kinetics but are insensitive to global or continuous motion. Electron microscopic reconstruction of dorsal thalamus neurons revealed synaptic input from the optic tectum and projections into hypothalamic areas with conserved social function 12 – 14 . Ablation of the optic tectum or dorsal thalamus selectively disrupted social attraction without affecting short-distance repulsion. This tectothalamic pathway thus serves visual recognition of conspecifics, and dissociates neuronal control of attraction from repulsion during social affiliation, revealing a circuit underpinning collective behaviour. A tectothalamic pathway for social affiliation in developing zebrafish dissociates neuronal control of attraction from repulsion during affiliation, revealing a circuit underpinning of collective behaviour