Diverse coupling of neurons to populations in sensory cortex.

In order to localize cerebral cognitive or sensorimotor function, activation paradigms are being used in conjunction with PET measures of cerebral activity (e.g., rCBF). The changes in local cerebral activity have two components: a global, region independent change and a local or regional change. As the first step in localizing the regional effects of an activation, global variance must be removed by a normalization procedure. A simple normalization procedure is division of regional values by the whole brain mean. This requires the dependence of local activity on global activity to be one of simple proportionality. This is shown not to be the case. Furthermore, a systematic deviation from a proportional relationship across brain regions is demonstrated. Consequently, any normalization must be approached on a pixel-by-pixel basis by measuring the change in local activity and change in global activity. The changes associated with an activation can be partitioned into global and local effects according to two models: one assumes that the increase in local activity depends on global values and the other assumes independence. It is shown that the increase in activity due to a cognitive activation is independent of global activity. This independence of the (activation) condition effect and the confounding linear effect of global activity on observed local activity meet the requirements for an analysis of covariance, with the "nuisance" variable as global activity and the activation condition as the categorical independent variable. These conclusions are based on analysis of data from 24 scans: six conditions over four normal subjects using a verbal fluency paradigm.(ABSTRACT TRUNCATED AT 250 WORDS)

Luminance and spatial contrast provide information on the surfaces and edges of objects. We investigated neural responses to black and white surfaces in the primary visual cortex (V1) of mice and monkeys. Unlike primates that use their fovea to inspect objects with high acuity, mice lack a fovea and have low visual acuity. It thus remains unclear whether monkeys and mice share similar neural mechanisms to process surfaces. The animals were presented with white or black surfaces and the population responses were measured at high spatial and temporal resolution using voltage-sensitive dye imaging. In mice, the population response to the surface was not edge-dominated with a tendency to center-dominance, whereas in monkeys the response was edge-dominated with a "hole" in the center of the surface. The population response to the surfaces in both species exhibited suppression relative to a grating stimulus. These results reveal the differences in spatial patterns to luminance surfaces in the V1 of mice and monkeys and provide evidence for a shared suppression process relative to grating.

Event Abstract Back to Event High-speed imaging of local population activity in mouse visual cortex A fundamental goal in systems neuroscience is to understand how local populations of neurons coordinate their firing to encode external events and to generate internal states. Much of what is known on the subject has been inferred from multi-electrode recordings which can only sparsely sample neural populations. Recently, two-photon calcium imaging has made it possible to measure spiking from a large number of neurons in a local region. Two-photon calcium imaging is an optical microscopic technique that allows visualization and simultaneous measurement of the activity of nearly every neuron in a local plane or volume of the living brain. Spiking activity induces large calcium influxes into the cell body which can be measured by loading a fluorescent calcium indicator into the cell and exciting the indicator with high intensity infrared laser pulses. While two-photon calcium imaging routinely yields high-resolution activity maps, it has remained a challenge to use it to study how neural responses evolve as a function of time, or how they vary from one trial to the next. In theory, its temporal resolution should only depend on the time course of the calcium influx, limited by diffusion, which has a rise time of a few tens of milliseconds. In practice, two-photon imaging is limited by both the ability to scan the sample quickly and also by signal-to-noise. Scan speed is affected by the technology used to deflect the laser. Signal-to-noise is primarily affected by the number of collected photons since this type of imaging works at low light levels where shot noise dominates. To address these problems we have developed a two-photon microscope which uses a high-speed resonant galvanometer and an optimized excitation and collection light path which increases photon flux. We can continuously image large populations (up to several hundreds of neurons) in the living brain at rates of >30 Hz with high signal-to-noise. We find that we can reliably detect the presence or absence spontaneous and stimulus-evoked calcium transients, and that we can measure their onset of with a temporal resolution of ~30 milliseconds. This yields the ability to analyze trial-to-trial responses of a large population of neurons. We are examining how populations of neurons in visual cortex respond to repeated presentation of visual stimuli. Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster Presentation Topic: Poster Presentations Citation: (2009). High-speed imaging of local population activity in mouse visual cortex. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.239 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Feb 2009; Published Online: 03 Feb 2009. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Google Google Scholar PubMed Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Neuronal connectivity is fundamental to information processing in the brain. Understanding the mechanisms of sensory processing, therefore, requires uncovering how connection patterns between neurons relate to their function. On a coarse scale long range projections can preferentially link cortical regions with similar responses to sensory stimuli1-4. But on the local scale, where dendrites and axons overlap substantially, the functional specificity of connections remains unknown. Here we determine synaptic connectivity between nearby layer 2/3 pyramidal neurons in vitro whose response properties were first characterized in mouse visual cortex in vivo. We found that connection probability was related to the similarity of visually driven neuronal activity. Neurons with the same preference for oriented stimuli connected at twice the rate of neurons with orthogonal orientation preferences. Neurons responding similarly to naturalistic stimuli formed connections at much higher rates than those with uncorrelated responses. Bidirectional synaptic connections were found more frequently between neuronal pairs with strongly correlated visual responses. Our results reveal the deg of functional specificity of local synaptic connections in visual cortex, and point to the existence of fine-scale subnetworks dedicated to processing related sensory information.

In this article, we make use of large-scale municipal border changes in Germany to provide the first evidence on the effect of local border changes on the distribution of activity in space. To allow for a comparison of economic activity within unique geographical units over time, we use geo-coded light data as well as local land-use data. Applying a difference-in-differences approach, we find evidence that municipalities absorbing their merger partners and hosting the new administrative center experience a significant increase in local activity, while the municipalities that are being absorbed and are losing the administrative center experience a decrease in such activity. The difference between the gains in activity from absorbing municipalities and the losses from absorbed ones is positive. These previously undocumented results point to the importance of distance to the administrative center as a determinant of the spatial distribution of economic activity.

Characterizing Inscapes and resting-state in MEG: Effects in typical and atypical development

Local Border Reforms and Economic Activity

Calcium imaging is a powerful tool for recording from large populations of neurons in vivo. Imaging in rhesus macaque motor cortex can enable the discovery of fundamental principles of motor cortical function and can inform the design of next generation brain-computer interfaces (BCIs). Surface two-photon imaging, however, cannot presently access somatic calcium signals of neurons from all layers of macaque motor cortex due to photon scattering. Here, we demonstrate an implant and imaging system capable of chronic, motion-stabilized two-photon imaging of neuronal calcium signals from macaques engaged in a motor task. By imaging apical dendrites, we achieved optical access to large populations of deep and superficial cortical neurons across dorsal premotor (PMd) and gyral primary motor (M1) cortices. Dendritic signals from individual neurons displayed tuning for different directions of arm movement. Combining several technical advances, we developed an optical BCI (oBCI) driven by these dendritic signalswhich successfully decoded movement direction online. By fusing two-photon functional imaging with CLARITY volumetric imaging, we verified that many imaged dendrites which contributed to oBCI decoding originated from layer 5 output neurons, including a putative Betz cell. This approach establishes new opportunities for studying motor control and designing BCIs via two photon imaging.

The enteric nervous system (ENS) contains millions of neurons essential for organization of motor behavior of the intestine. It is well established that the large intestine requires ENS activity to drive propulsive motor behaviors. However, the firing pattern of the ENS underlying propagating neurogenic contractions of the large intestine remains unknown. To identify this, we used high-resolution neuronal imaging with electrophysiology from neighboring smooth muscle. Myoelectric activity underlying propagating neurogenic contractions along murine large intestine [also referred to as colonic migrating motor complexes, (CMMCs)] consisted of prolonged bursts of rhythmic depolarizations at a frequency of ∼2 Hz. Temporal coordination of this activity in the smooth muscle over large spatial fields (∼7 mm, longitudinally) was dependent on the ENS. During quiescent periods between neurogenic contractions, recordings from large populations of enteric neurons, in mice of either sex, revealed ongoing activity. The onset of neurogenic contractions was characterized by the emergence of temporally synchronized activity across large populations of excitatory and inhibitory neurons. This neuronal firing pattern was rhythmic and temporally synchronized across large numbers of ganglia at ∼2 Hz. ENS activation preceded smooth muscle depolarization, indicating rhythmic depolarizations in smooth muscle were controlled by firing of enteric neurons. The cyclical emergence of temporally coordinated firing of large populations of enteric neurons represents a unique neural motor pattern outside the CNS. This is the first direct observation of rhythmic firing in the ENS underlying rhythmic electrical depolarizations in smooth muscle. The pattern of neuronal activity we identified underlies the generation of CMMCs.SIGNIFICANCE STATEMENT How the enteric nervous system (ENS) generates neurogenic contractions of smooth muscle in the gastrointestinal (GI) tract has been a long-standing mystery in vertebrates. It is well known that myogenic pacemaker cells exist in the GI tract [called interstitial cells of Cajal (ICCs)] that generate rhythmic myogenic contractions. However, the mechanisms underlying the generation of rhythmic neurogenic contractions of smooth muscle in the GI tract remains unknown. We developed a high-resolution neuronal imaging method with electrophysiology to address this issue. This technique revealed a novel pattern of rhythmic coordinated neuronal firing in the ENS that has never been identified. Rhythmic neuronal firing in the ENS was found to generate rhythmic neurogenic depolarizations in smooth muscle that underlie contraction of the GI tract.

Hub GABA Neurons Mediate Gamma-Frequency Oscillations at Ictal-like Event Onset in the Immature Hippocampus

Requirement of keratan sulfate proteoglycan phosphacan with a specific sulfation pattern for critical period plasticity in the visual cortex

Some neurotransmitters can diffuse freely across cell membranes, influencing neighbouring neurons regardless of their synaptic coupling. This provides a means of neural communication, alternative to synaptic transmission, which can influence the way in which neural networks process information. Here, we ask whether diffusive neurotransmission can also influence the structure of synaptic connectivity in a network undergoing plasticity. We propose a form of Hebbian synaptic plasticity which is mediated by a diffusive neurotransmitter. Whenever a synapse is modified at an individual neuron through our proposed mechanism, similar but smaller modifications occur in synapses connecting to neighbouring neurons. The effects of this diffusive plasticity are explored in networks of rate-based neurons. This leads to the emergence of spatial structure in the synaptic connectivity of the network. We show that this spatial structure can coexist with other forms of structure in the synaptic connectivity, such as with groups of strongly interconnected neurons that form in response to correlated external drive. Finally, we explore diffusive plasticity in a simple feedforward network model of receptive field development. We show that, as widely observed across sensory cortex, the preferred stimulus identity of neurons in our network become spatially correlated due to diffusion. Our proposed mechanism of diffusive plasticity provides an efficient mechanism for generating these spatial correlations in stimulus preference which can flexibly interact with other forms of synaptic organisation.

The production of distinct and appropriate behaviors under different circumstances requires that an organism’s neural circuitry be flexible and, at times, multifunctional. One means by which neural circuits or networks are accorded flexibility is through the release of neuromodulatory substances

Leech ganglia maintained in organ culture were used to follow regeneration and the formation of synaptic connections by individual neurons. From earlier physiological studies on operated animals it is known that the c. n. s. of the leech is able to regenerate and that specific connections can be reformed. The present experiments show that specific regeneration also occurs in vitro but that axons do not simply grow directly back to their targets. (1) Axons were severed by crushing the connectives linking pairs of ganglia at the time of removal from the animal. Light and electron microscopy indicated that the procedure of crushing severed all the axons within the connectives. For several days after the lesion had been made, conduction of impulses from one ganglion to the next was abolished. (2) After 5–10 days in culture, stimulation of the connectives with external electrodes gave rise to impulses that were once again conducted beyond the site of the lesion. Characteristic excitatory and inhibitory synaptic potentials were evoked in identified sensory and motor cells in both ganglia by this indiscriminate stimulation of axons. Electron micrographs of the crushed region showed not only regenerated axons traversing the site of the lesion but also synaptic profiles similar to those seen in the neuropile of normal ganglia. Thus, pre- and post-synaptic specializations had been formed during regeneration in a part of the c. n. s. where they are not normally present. (3) Individual sensory neurons were injected with horseradish peroxid­ase to reveal the course taken by their regenerating axons. At the site of the crush profuse branching occurred by 7 days. The arborization of a single axon was highly complex, with many varicosities present on fine branches. After two weeks in culture, one or more of the processes had usually grown beyond the crush and in certain instances had reached the next ganglion. Other branches ran back towards the ganglion in which the cell body was situated. During the period of the experiments (up to 45 days) no retraction of the sprouted fibres or of the arborization at the crush was observed. In addition to sprouting at the site of the lesion considerable sprouting also occurred within the ganglion, close to the cell body. (4) Individual mechanosensory neurons regenerated and would once again evoke synaptic potentials in their original targets after two weeks in culture. Thus, intracellular stimulation of single sensory cells in one ganglion gave rise to synaptic potentials in the appropriate motor neuron of the neighbouring ganglion. Injection of such sensory cells with horse­radish peroxidase showed that their axons had extended beyond the lesion and ramified in the neuropile of the next ganglion. (5) It is concluded that neurons in leech ganglia are able to regenerate and reform appropriate synaptic connections in culture. The degree of precision is hard to assess because of novel synaptic interactions and numerous additional sprouts that develop during regeneration.

Local activity could be the source for complexity. In this study, a multistable locally active memristor is proposed, whose nonvolatile memory, as well as locally active characteristics, is validated by the power-off plot and DC [Formula: see text]–[Formula: see text] plot. Based on the two-dimensional Hindmarsh–Rose neuron and a one-dimensional Hopfield neuron, a simple neural network is constructed by connecting the two neurons with the locally active memristor. Coexisting multiple firing patterns under different initial conditions are investigated according to the controlled coupling factor. The results suggest that the system exhibits coexisting periodic and chaotic bursting with different firing patterns. Complex firing only occurs in the locally active area of the defined memristor, meanwhile the system shows a periodic oscillation in the passive area. Beyond this, the coupled neurons exhibit the specific phenomenon of attractor growing in the locally active region of the memristor. The circuit simulations by Power Simulation (PSIM) are included confirming the numerical simulations and theoretic analysis.