Synaptic Information Processing Research Articles

Self-Adhesive, Stretchable, and Thermosensitive Iontronic Hydrogels for Highly Sensitive Neuromorphic Sensing-Synaptic Systems.

Artificial sensory afferent nerves that emulate receptor nanochannel perception and synaptic ionic information processing in chemical environments are highly desirable for bioelectronics. However, challenges persist in achieving life-like nanoscale conformal contact, agile multimodal sensing response, and synaptic feedback with ions. Here, a precisely tuned phase transition poly(N-isopropylacrylamide) (PNIPAM) hydrogel is introduced through the water molecule reservoir strategy. The resulting hydrogel with strongly cross-linked networks exhibits excellent mechanical performance (∼2000% elongation) and robust adhesive strength. Importantly, the hydrogel's enhanced ionic conductance and heterogeneous structure of the temperature-sensitive component enable highly sensitive strain information perception (GFmax = 7.94, response time ∼ 87 ms), temperature information perception (TCRmax = -1.974%/°C, response time ∼ 270 ms), and low energy consumption synaptic plasticity (42.2 fJ/spike). As a demonstration, a neuromorphic sensing-synaptic system is constructed integrating iontronic strain/temperature sensors with fiber synapses for real-time information sensing, discrimination, and feedback. This work holds enormous potential in bioinspired robotics and bioelectronics.

Postsynaptic GABAB-receptor mediated currents in diverse dentate gyrus interneuron types.

The processing of rich synaptic information in the dentate gyrus (DG) relies on a diverse population of inhibitory GABAergic interneurons to regulate cellular and circuit activity, in a layer-specific manner. Metabotropic GABAB-receptors (GABABRs) provide powerful inhibition to the DG circuit, on timescales consistent with behavior and learning, but their role in controlling the activity of interneurons is poorly understood with respect to identified cell types. We hypothesize that GABABRs display cell type-specific heterogeneity in signaling strength, which will have direct ramifications for signal processing in DG networks. To test this, we perform in vitro whole-cell patch-clamp recordings from identified DG principal cells and interneurons, followed by GABABR pharmacology, photolysis of caged GABA, and extracellular stimulation of endogenous GABA release to classify the cell type-specific inhibitory potential. Based on our previous classification of DG interneurons, we show that postsynaptic GABABR-mediated currents are present on all interneuron types albeit at different amplitudes, dependent largely on soma location and synaptic targets. GABABRs were coupled to inwardly-rectifying K+ channels that strongly reduced the excitability of those interneurons where large currents were observed. These data provide a systematic characterization of GABABR signaling in the rat DG to provide greater insight into circuit dynamics.

A Dendritic Architecture‐Based Deep Learning for Tumor Detection

Brain tumor detection typically involves classifying various tumor types. Traditional classifiers, based on the McCulloch‐Pitts model, have faced criticism due to their oversimplified structure and limited capabilities in detecting brain tumor images with complex features. In this study, we propose a multiclassification model inspired by dendritic architectures in neurons, which leverages synaptic and dendritic nonlinear information processing capabilities. Experimental results using brain tumor detection datasets demonstrate that our proposed model outperforms other state‐of‐the‐art models across all evaluation metrics. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Acute stress modulates hippocampal to entorhinal cortex communication.

Feed-forward inhibition is vital in the transfer and processing of synaptic information within the hippocampal-entorhinal loop by controlling the strength and direction of excitation flow between different neuronal populations and individual neurons. While the cellular targets in the hippocampus that receive excitatory inputs from the entorhinal cortex have been well studied, and the role of feedforward inhibitory neurons has been attributed to neurogliafom cells, the cortical interneurons providing feed-forward control over receiving layer V in the entorhinal cortex remain unknown. We used sharp-wave ripple oscillations as a natural excitatory stimulus of the entorhinal cortex, driven by the hippocampus, to study the function of synaptic interactions between neurons in the deep layers of the entorhinal cortex. We discovered that CB1R-expressing interneurons in the deep layers of the entorhinal cortex constitute the major relay station that translates hippocampal excitation into efficient inhibition of cortical pyramidal cells. The impact of inhibition provided by these interneurons is under strong endocannabinoid control and can be drastically reduced either by enhanced activity of postsynaptic targets or by stress-induced elevation of cannabinoids.

Electromagnetic-field theories of qualia: can they improve upon standard neuroscience?

How do brains create all our different colors, pains, and other conscious qualities? These various qualia are the most essential aspects of consciousness. Yet standard neuroscience (primarily based on synaptic information processing) has not found the synaptic-firing codes, sometimes described as the "spike code," to account for how these qualia arise and how they unite to form complex perceptions, emotions, et cetera. Nor is it clear how to get from these abstract codes to the qualia we experience. But electromagnetic field (versus synaptic) approaches to how qualia arise have been offered in recent years by Pockett, McFadden, Jones, Bond, Ward and Guevera, Keppler and Shani, Hunt and Schooler, et cetera. These EM-field approaches show promise in offering more viable accounts of qualia. Yet, until now, they have not been evaluated together. We review various EM field theories of qualia, highlight their strengths and weaknesses, and contrast these theories with standard neuroscience approaches.

How synaptic strength, short-term plasticity, and input synchrony contribute to neuronal spike output

Neurons integrate from thousands of synapses whose strengths span an order of magnitude. Intriguingly, in mouse neocortex, the few 'strong' synapses are formed between similarly tuned cells, suggesting they determine spiking output. This raises the question of how other computational primitives, including 'background' activity from the many 'weak' synapses, short-term plasticity, and temporal factors contribute to spiking. We used paired recordings and extracellular stimulation experiments to map excitatory postsynaptic potential (EPSP) amplitudes and paired-pulse ratios of synaptic connections formed between pyramidal neurons in layer 2/3 (L2/3) of barrel cortex. While net short-term plasticity was weak, strong synaptic connections were exclusively depressing. Importantly, we found no evidence for clustering of synaptic properties on individual neurons. Instead, EPSPs and paired-pulse ratios of connections converging onto the same cells spanned the full range observed across L2/3, which critically constrains theoretical models of cortical filtering. To investigate how different computational primitives of synaptic information processing interact to shape spiking, we developed a computational model of a pyramidal neuron in the excitatory L2/3 circuitry, which was constrained by our experiments and published in vivo data. We found that strong synapses were substantially depressed during ongoing activation and their ability to evoke correlated spiking primarily depended on their high temporal synchrony and high firing rates observed in vivo. However, despite this depression, their larger EPSP amplitudes strongly amplified information transfer and responsiveness. Thus, our results contribute to a nuanced framework of how cortical neurons exploit synergies between temporal coding, synaptic properties, and noise to transform synaptic inputs into spikes.

Upregulation of astroglial connexin 30 impairs hippocampal synaptic activity and recognition memory.

Astrocytes crucially contribute to synaptic physiology and information processing. One of their key characteristics is to express high levels of connexins (Cxs), the gap junction-forming protein. Among them, Cx30 displays specific properties since it is postnatally expressed and dynamically upregulated by neuronal activity and modulates cognitive processes by shaping synaptic and network activities, as recently shown in knockout mice. However, it remains unknown whether local and selective upregulation of Cx30 in postnatal astrocytes within a physiological range modulates neuronal activities in the hippocampus. We here show in mice that, whereas Cx30 upregulation increases the connectivity of astroglial networks, it decreases spontaneous and evoked synaptic transmission. This effect results from a reduced neuronal excitability and translates into an alteration in the induction of synaptic plasticity and an in vivo impairment in learning processes. Altogether, these results suggest that astroglial networks have a physiologically optimized size to appropriately regulate neuronal functions.

Calcium signaling in astrocytes and gliotransmitter release.

Glia are as numerous in the brain as neurons and widely known to serve supportive roles such as structural scaffolding, extracellular ionic and neurotransmitter homeostasis, and metabolic support. However, over the past two decades, several lines of evidence indicate that astrocytes, which are a type of glia, play active roles in neural information processing. Astrocytes, although not electrically active, can exhibit a form of excitability by dynamic changes in intracellular calcium levels. They sense synaptic activity and release neuroactive substances, named gliotransmitters, that modulate neuronal activity and synaptic transmission in several brain areas, thus impacting animal behavior. This "dialogue" between astrocytes and neurons is embodied in the concept of the tripartite synapse that includes astrocytes as integral elements of synaptic function. Here, we review the recent work and discuss how astrocytes via calcium-mediated excitability modulate synaptic information processing at various spatial and time scales.

Ferroelectric memristor based on Li-doped BiFeO3 for information processing

As a nanoscale semiconductor memory device, a ferroelectric memristor has promising prospects to break through the von Neumann framework in terms of artificial synaptic function, information processing, and integration. This study presents the fabrication of Li0.09Bi0.91FeO3 as the functional layer for a memristor device based on the Si substrate, enabling the integration of silicon complementary metal oxide semiconductor technology. In addition, it exhibits bipolar resistance switching characteristics in a direct current mode and can rapidly achieve stable conductance tunability at higher frequencies through the applied pulse for biosynapse simulation. More importantly, multiple devices are connected into electrical circuits to realize storage functions with information processing and programmable characteristics. This work paves the way for near-future applications of ferroelectric memristors in information processing.

Trafficking of NMDA receptors is essential for hippocampal synaptic plasticity and memory consolidation.

NMDA receptor (NMDAR) plays a vital role in brain development and normal physiological functions. Surface trafficking of NMDAR contributes to the modulation of synaptic functions and information processing. However, it remains unclear whether NMDAR trafficking is independent of long-term potentiation (LTP) and whether it regulates behavior. Here, we report that LTP of AMPAR and NMDAR can occur concurrently and that NMDAR trafficking can regulate AMPAR trafficking and AMPAR-mediated LTP. By contrast, AMPAR trafficking does not impact NMDAR-mediated LTP. Using SAP97-interfering peptide and SAP97 knockin (KI) rat, we show that the effect is mediated by GluN2A-subunit-containing NMDARs. At the behavior level, impaired NMDAR trafficking results in deficits in consolidation, but not acquisition, of fear memory. Collectively, our results suggest the essential role of NMDAR trafficking in LTP and memory consolidation.

A Computational Study on Synaptic Plasticity Regulation and Information Processing in Neuron-Astrocyte Networks.

Postsynaptic ionotropic receptors critically shape synaptic currents and underpin their activity-dependent plasticity. In recent years, regulation of expression of these receptors by slow inward and outward currents mediated by gliotransmitter release from astrocytes has come under scrutiny as a potentially important mechanism for the regulation of synaptic information transfer. In this study, we consider a model of astrocyte-regulated synapses to investigate this hypothesis at the level of layered networks of interacting neurons and astrocytes. Our simulations hint that gliotransmission sustains the transfer function across layers, although it decorrelates the neuronal activity from the signal pattern. Overall, our results make clear how astrocytes could transform neuronal activity by inducing a lowfrequency modulation of postsynaptic activity.

Two Suggested Probabilistic and Kinetic Models for Astrocytic Network in Spiking Neural Networks

Astrocytes, the predominant glial cell type in the brain, were traditionallyconsidered as merely passive supportive cells without any important roles in synaptic information processing. In contrast, the contemporary view was given rise to show that astrocytes play active roles in synaptic neurotransmissionand information processing. Hence, recently two terms have been emerged, tripartite synapse, to describe the communication between an astrocyte and two neurons, and the term astrocytic syncytium or astrocytic network to describe the communication among the astrocytesby gap junction. Therefore, we propose mathematical models for tripartite synapseand astrocytic syncytium basedontwo-state kinetics models, several probabilistic methods and Spiking Neural Network (SNN) to introducenew Artificial Astrocytic Syncytium (AAS) model. The simulation results have shown that proposed model could represent the cellular intrinsic properties of astrocyte based on the spatial and temporal aspects to emulate the astrocytic network functions related to cognitive, learning and memory.

Ca2+- and Phospholipid-Dependent Mechanisms for the Coupling of Synaptic Vesicle Consumption and Re-Supply Rates

The efficacy and reliability of synaptic transmission depend on the ability of the transmitter release machinery to replenish the releasable pool of synaptic vesicles (SV) during and following activity. To sustain transmitter release during periods of high-frequency activity, a mechanism must exist that increases the recovery rate of the releasable SV pool. We sought to identify Ca2+-dependent SV replenishment mechanisms that operate in vivo, study how they dynamically interact during periods of synaptic activity, and illustrate how they affects transmitter release dynamics and short-term synaptic plasticity. Munc13s are a family of presynaptic proteins with three domains that are directly or indirectly regulated by Ca2+. Munc13s are functionally absolutely essential for the priming of SVs, and have a central role in the organization of SVs prior to and during transmitter release. Here, we present novel genetically modified mouse lines in which Ca2+- and phospholipid sensing by the regulatory domains of Munc13-1 is altered. Our analyses demonstrate that the SV replenishment rates can be controlled bi-directionally by Munc13-1, with consequent effects on short-term synaptic plasticity and information processing.

Region- and Cell Type-Specific Facilitation of Synaptic Function at Destination Synapses Induced by Oligodendrocyte Depolarization.

The axonal conduction of action potentials affects the absolute time it takes to transmit nerve impulses as well as temporal summation at destination synapses. At the physiological level, oligodendrocyte depolarization facilitates axonal conduction along myelinated fibers in the hippocampus; however, the functional significance of this facilitation is largely unknown. In this study, we examined the physiology of the facilitation of axonal conduction by investigating the changes in synaptic responses at destination synapses using male and female mice in which channelrhodopsin-2 expression was restricted to oligodendrocytes. The subiculum, one of the projection areas of the examined axons at the alveus of the hippocampus, is divided into three regions (proximal, mid, and distal) and contains two types of principal neurons: regular firing and bursting pyramidal cells. We found a significant increase in excitatory synaptic responses following optogenetic oligodendrocyte depolarization in bursting neurons at two of the three regions, but not in regular firing neurons at any region. The long-term potentiation (LTP) induced by theta burst stimulation at the synapses showing a significant increase was also enhanced after oligodendrocyte depolarization. Conversely, the reduction of oligodendrocyte depolarization during theta burst stimulation, which was achieved by photostimulation of archaerhodopsin-T expressed selectively on oligodendrocytes, reduced the magnitude of LTP. These results show that oligodendrocyte depolarization contributes to the fine control of synaptic activity between the axons they myelinate and targets subicular cells in a region- and cell type-specific manner, and suggest that oligodendrocyte depolarization during conditioning of stimuli is involved in the induction of LTP.SIGNIFICANCE STATEMENT All activity in the nervous system depends on the propagation of action potentials. Changes in the axonal conduction of action potentials influence the timing of synaptic transmission and information processing in neural circuits. At the physiological level, oligodendrocyte depolarization facilitates axonal conduction along myelinated fibers. In this study, we investigated the functional significance of the facilitation of axonal conduction induced by physiological oligodendrocyte depolarization. Using optogenetics and electrophysiological recordings, we demonstrated that oligodendrocyte depolarization in mice expressing channelrhodopsin-2 on oligodendrocytes increased excitatory synaptic responses and enhanced the induction of long-term potentiation at destination synapses in a region- and cell type-specific manner. This facilitation may have a hitherto unappreciated influence on the transfer of information between regions in the nervous system.

Disintegration of the Astroglial Domain Organization May Underlie the Loss of Reality Comprehension in Schizophrenia: A Hypothetical Model

A pathophysiological model of the loss of reality comprehension in schizophrenia is proposed. Based on a formalism it is hypothesized that astroglial domains exert an information-categorizing function which becomes progressively lost in the schizophrenic process, caused by functional and structural disintegration of astroglial domains. Unconstrained synaptic neurotransmission functionally disintegrates the astroglial domains. Microdomains located between perisynaptic astroglial processes and the synaptic membrane are interpreted as elementary functional units categorizing synaptic information processing. Unconstrained diffusion of neurotransmitters into the extrasynaptic space leads to the dysfunction of microdomain formation. In parallel, atrophic processes of astroglia progressively break up the connectivity between synaptic and extrasynaptic compartments disrupting astroglial domains. Basically, the organization of astroglia into definite functional and structural units (modules) of astroglial-synaptic information processing may enable the brain to comprehend ontological realms such as subjects and objects in the environment and their distinct qualities. This fundamental capability of cognition is lost in schizophrenia. It is suggested that this ontological confusion of astroglial domain boundaries progressively disorganizes reality comprehension and may represent the basic pathology in schizophrenia underlying the main symptoms of the disorder. Finally, the testing of the model is shortly discussed.

Active Sampling State Dynamically Enhances Olfactory Bulb Odor Representation

SummaryThe olfactory bulb (OB) is the first site of synaptic odor information processing, yet a wealth of contextual and learned information has been described in its activity. To investigate the mechanistic basis of contextual modulation, we use whole-cell recordings to measure odor responses across rapid learning episodes in identified mitral/tufted cells (MTCs). Across these learning episodes, diverse response changes occur already during the first sniff cycle. Motivated mice develop active sniffing strategies across learning that robustly correspond to the odor response changes, resulting in enhanced odor representation. Evoking fast sniffing in different behavioral states demonstrates that response changes during active sampling exceed those predicted from feedforward input alone. Finally, response changes are highly correlated in tufted cells, but not mitral cells, indicating there are cell-type-specific effects on odor representation during active sampling. Altogether, we show that active sampling is strongly associated with enhanced OB responsiveness on rapid timescales.

Towards a Comprehensive Psychobiological Model of Major Depressive Disorder

A psychobiological model of the etiopathology of major depression is proposed. It is hypothesized that a hyperintentional personality structure, if faced with non-feasible intentional programs in the environment, suffers from inner and outer stress. This stress situation leads to an excess of astrocytic receptors in glial-neuronal synaptic units, called tripartite synapses, and an overexpression of gap junctions in astroglial networks. The imbalance of synaptic information processing caused by the excess of astrocytic receptors leads to a protracted information processing which affects the behavior generating systems in the reticular formation in the brainstem. Since the activation of these systems is delayed, they cannot decide in real time which mode of behavior (e.g. eating, working, communicating, etc.) is appropriate to a specific sensory information from the environment. The modes of behavior comprise all psychobiological action patterns occurring in circadian time periods. A delay of synaptic activation of the systems in the brainstem reticular formation may lead to a displacement of the modes of behavior in the sense of a persistence of some modes (“must do”) and the inability to produce others (”cannot do”). Such a severe behavioral disorder also affects the self-understanding of the patient resulting in a depressive mood. The mechanism of the displacement of the modes of behavior is shown in a computer simulation. Preliminary clinical data may support the model proposed and is briefly discussed.

Psychobiological Model of Bipolar Disorder: Based on Imbalances of Glial-Neuronal Information Processing

A psychobiological model of the etiopathology of bipolar disorder is proposed. Based on genetic-epigenetic and chronobiological factors a hyperintentional personality structure, if faced with non-feasible intentional programs in the environment, suffers from inner and outer stress. This stress situation leads to imbalances in information processing in glial-neuronal synaptic units, called tripartite synapses. In depression the overexpression of astrocytic receptors and of gap junctions in the astroglial network causes a prolonged information processing which affects the behavior generating systems in the brainstem reticular formation. Because the activation of the behavior generating systems is protracted, they are unable to select an appropriate mode of behavior (e.g. communicating, eating, working, sleeping, etc.) from sensory information in real time. Inversely, in mania astrocytic receptors and gap junctions are underexpressed causing a shortened synaptic information processing with rapid changes in behavior. Switching may represent a coping-attempt with depression by mania and vice versa. Towards a comprehensive model of the pathophysiology of bipolar disorder the role of microglia and their devastating effects on glial-neuronal interactions are outlined. Finally, the testing of the model is discussed.

Marked bias towards spontaneous synaptic inhibition distinguishes non-adapting from adapting layer 5 pyramidal neurons in the barrel cortex

Pyramidal neuron subtypes differ in intrinsic electrophysiology properties and dendritic morphology. However, do different pyramidal neuron subtypes also receive synaptic inputs that are dissimilar in frequency and in excitation/inhibition balance? Unsupervised clustering of three intrinsic parameters that vary by cell subtype – the slow afterhyperpolarization, the sag, and the spike frequency adaptation – split layer 5 barrel cortex pyramidal neurons into two clusters: one of adapting cells and one of non-adapting cells, corresponding to previously described thin- and thick-tufted pyramidal neurons, respectively. Non-adapting neurons presented frequencies of spontaneous inhibitory postsynaptic currents (sIPSCs) and spontaneous excitatory postsynaptic currents (sEPSCs) three- and two-fold higher, respectively, than those of adapting neurons. The IPSC difference between pyramidal subtypes was activity independent. A subset of neurons were thy1-GFP positive, presented characteristics of non-adapting pyramidal neurons, and also had higher IPSC and EPSC frequencies than adapting neurons. The sEPSC/sIPSC frequency ratio was higher in adapting than in non-adapting cells, suggesting a higher excitatory drive in adapting neurons. Therefore, our study on spontaneous synaptic inputs suggests a different extent of synaptic information processing in adapting and non-adapting barrel cortex neurons, and that eventual deficits in inhibition may have differential effects on the excitation/inhibition balance in adapting and non-adapting neurons.

Three-dimensional spatial modeling of spines along dendritic networks in human cortical pyramidal neurons

We modeled spine distribution along the dendritic networks of pyramidal neurons in both basal and apical dendrites. To do this, we applied network spatial analysis because spines can only lie on the dendritic shaft. We expanded the existing 2D computational techniques for spatial analysis along networks to perform a 3D network spatial analysis. We analyzed five detailed reconstructions of adult human pyramidal neurons of the temporal cortex with a total of more than 32,000 spines. We confirmed that there is a spatial variation in spine density that is dependent on the distance to the cell body in all dendrites. Considering the dendritic arborizations of each pyramidal cell as a group of instances of the same observation (the neuron), we used replicated point patterns together with network spatial analysis for the first time to search for significant differences in the spine distribution of basal dendrites between different cells and between all the basal and apical dendrites. To do this, we used a recent variant of Ripley’s K function defined to work along networks. The results showed that there were no significant differences in spine distribution along basal arbors of the same neuron and along basal arbors of different pyramidal neurons. This suggests that dendritic spine distribution in basal dendritic arbors adheres to common rules. However, we did find significant differences in spine distribution along basal versus apical networks. Therefore, not only do apical and basal dendritic arborizations have distinct morphologies but they also obey different rules of spine distribution. Specifically, the results suggested that spines are more clustered along apical than in basal dendrites. Collectively, the results further highlighted that synaptic input information processing is different between these two dendritic domains.