Neuronal Network Function Research Articles

Antagomir-mediated suppression of microRNA-134 reduces kainic acid-induced seizures in immature mice

MicroRNAs are short non-coding RNAs that negatively regulate protein levels and perform important roles in establishing and maintaining neuronal network function. Previous studies in adult rodents have detected upregulation of microRNA-134 after prolonged seizures (status epilepticus) and demonstrated that silencing microRNA-134 using antisense oligonucleotides, termed antagomirs, has potent and long-lasting seizure-suppressive effects. Here we investigated whether targeting microRNA-134 can reduce or delay acute seizures in the immature brain. Status epilepticus was induced in 21 day-old (P21) male mice by systemic injection of 5 mg/kg kainic acid. This triggered prolonged electrographic seizures and select bilateral neuronal death within the CA3 subfield of the hippocampus. Expression of microRNA-134 and functional loading to Argonaute-2 was not significantly changed in the hippocampus after seizures in the model. Nevertheless, when levels of microRNA-134 were reduced by prior intracerebroventricular injection of an antagomir, kainic acid-induced seizures were delayed and less severe and mice displayed reduced neuronal death in the hippocampus. These studies demonstrate targeting microRNA-134 may have therapeutic applications for the treatment of seizures in children.

The development and physiological and pathophysiological functions of resident macrophages and glial cells.

In the past, brain function and the onset and progression of neurological diseases have been studied in a neuron-centric manner. However, in recent years the focus of many neuroscientists has shifted to other cell types that promote neurodevelopment and contribute to the functionality of neuronal networks in health and disease. Particularly microglia and astrocytes have been implicated in actively contributing to and controlling neuronal development, neuroinflammation, and neurodegeneration. Here, we summarize the development of brain-resident macrophages and astrocytes and their core functions in the developing brain. We discuss their contribution and intercellular crosstalk during tissue homeostasis and pathophysiology. We argue that in-depth knowledge of non-neuronal cells in the brain could provide novel therapeutic targets to reverse or contain neurological diseases.

A simple method defines 3D morphology and axon projections of filled neurons in a small CNS volume: Steps toward understanding functional network circuitry

BackgroundFundamental to understanding neuronal network function is defining neuron morphology, location, properties, and synaptic connectivity in the nervous system. A significant challenge is to reconstruct individual neuron morphology and connections at a whole CNS scale and bring together functional and anatomical data to understand the whole network. New MethodWe used a PC controlled micropositioner to hold a fixed whole mount of Xenopus tadpole CNS and replace the stage on a standard microscope. This allowed direct recording in 3D coordinates of features and axon projections of one or two neurons dye-filled during whole-cell recording to study synaptic connections. Neuron reconstructions were normalised relative to the ventral longitudinal axis of the nervous system. Coordinate data were stored as simple text files. ResultsReconstructions were at 1 μm resolution, capturing axon lengths in mm. The output files were converted to SWC format and visualised in 3D reconstruction software NeuRomantic. Coordinate data are tractable, allowing correction for histological artefacts. Through normalisation across multiple specimens we could infer features of network connectivity of mapped neurons of different types. Comparison with Existing MethodsUnlike other methods using fluorescent markers and utilising large-scale imaging, our method allows direct acquisition of 3D data on neurons whose properties and synaptic connections have been studied using whole-cell recording. ConclusionsThis method can be used to reconstruct neuron 3D morphology and follow axon projections in the CNS. After normalisation to a common CNS framework, inferences on network connectivity at a whole nervous system scale contribute to network modelling to understand CNS function.

Enhanced Neuronal Activity and Asynchronous Calcium Transients Revealed in a 3D Organoid Model of Alzheimer’s Disease

Advances in the development of three-dimensional (3D) brain organoids maintained in vitro have provided excellent opportunities to study brain development and neurodegenerative disorders, including Alzheimer's disease (AD). However, there remains a need to generate AD organoids bearing patient-specific genomic backgrounds that can functionally recapitulate the key features observed in the AD patient's brain. To address this need, we described a strategy to generate self-organizing 3D cerebral organoids which develop a functional neuronal network connectivity. This was achieved by neuroectoderm induction of human pluripotent stem cell (hPSCs) aggregates and subsequent differentiation into desired neuroepithelia and mature neurons in a 3D Matrigel matrix. Using this approach, we successfully generated AD cerebral organoids from human pluripotent stem cells (hPSCs) derived from a familial AD patient with a common mutation in presenilin 2 (PSEN2N141I). An isogenic control with an identical genetic background but wild-type PSEN2 was generated using CRISPR/Cas9 technology. Both control and AD organoids were characterized by analyzing their morphology, the Aβ42/Aβ40 ratio, functional neuronal network activity, drug sensitivity, and the extent of neural apoptosis. The spontaneous activity of the network and its synchronization was measured in the organoids via calcium imaging. We found that compared with the mutation-corrected control organoids, AD organoids had a higher Aβ42/Aβ40 ratio, asynchronous calcium transients, and enhanced neuronal hyperactivity, successfully recapitulating an AD-like pathology at the molecular, cellular, and network level in a human genetic context. Moreover, two drugs which increase neuronal activity, 4-aminopyridine (4-AP) and bicuculline methochloride, induced high-frequency synchronized network bursting to a similar extent in both organoids. Therefore, our study presents a promising organoid-based biosystem for the study of the pathophysiology of AD and a platform for AD drug development.

The Paradox of Astroglial Ca2 + Signals at the Interface of Excitation and Inhibition.

Astroglial networks constitute a non-neuronal communication system in the brain and are acknowledged modulators of synaptic plasticity. A sophisticated set of transmitter receptors in combination with distinct secretion mechanisms enables astrocytes to sense and modulate synaptic transmission. This integrative function evolved around intracellular Ca2+ signals, by and large considered as the main indicator of astrocyte activity. Regular brain physiology meticulously relies on the constant reciprocity of excitation and inhibition (E/I). Astrocytes are metabolically, physically, and functionally associated to the E/I convergence. Metabolically, astrocytes provide glutamine, the precursor of both major neurotransmitters governing E/I in the central nervous system (CNS): glutamate and γ-aminobutyric acid (GABA). Perisynaptic astroglial processes are structurally and functionally associated with the respective circuits throughout the CNS. Astonishingly, in astrocytes, glutamatergic as well as GABAergic inputs elicit similar rises in intracellular Ca2+ that in turn can trigger the release of glutamate and GABA as well. Paradoxically, as gliotransmitters, these two molecules can thus strengthen, weaken or even reverse the input signal. Therefore, the net impact on neuronal network function is often convoluted and cannot be simply predicted by the nature of the stimulus itself. In this review, we highlight the ambiguity of astrocytes on discriminating and affecting synaptic activity in physiological and pathological state. Indeed, aberrant astroglial Ca2+ signaling is a key aspect of pathological conditions exhibiting compromised network excitability, such as epilepsy. Here, we gather recent evidence on the complexity of astroglial Ca2+ signals in health and disease, challenging the traditional, neuro-centric concept of segregating E/I, in favor of a non-binary, mutually dependent perspective on glutamatergic and GABAergic transmission.

Local Secretory Trafficking Pathways in Neurons and the Role of Dendritic Golgi Outposts in Different Cell Models

A fundamental characteristic of neurons is the relationship between the architecture of the polarized neuron and synaptic transmission between neurons. Intracellular membrane trafficking is paramount to establish and maintain neuronal structure; perturbation in trafficking results in defects in neurodevelopment and neurological disorders. Given the physical distance from the cell body to the distal sites of the axon and dendrites, transport of newly synthesized membrane proteins from the central cell body to their functional destination at remote, distal sites represents a conundrum. With the identification of secretory organelles in dendrites, including endoplasmic reticulum (ER) and Golgi outposts (GOs), recent studies have proposed local protein synthesis and trafficking distinct from the conventional anterograde transport pathways of the cell body. A variety of different model organisms, including Drosophila, zebrafish, and rodents, have been used to probe the organization and function of the local neuronal secretory network. Here, we review the evidence for local secretory trafficking pathways in dendrites in a variety of cell-based neuronal systems and discuss both the similarities and differences in the organization and role of the local secretory organelles, especially the GOs. In addition, we identify the gaps in the current knowledge and the potential advances using human induced pluripotent stem cells (iPSCs) in defining local membrane protein trafficking in human neurons and in understanding the molecular basis of neurological diseases.

Overshooting Subcellular Redox-Responses in Rett-Mouse Hippocampus during Neurotransmitter Stimulation.

Rett syndrome (RTT) is a neurodevelopmental disorder associated with disturbed neuronal responsiveness and impaired neuronal network function. Furthermore, mitochondrial alterations and a weakened cellular redox-homeostasis are considered part of the complex pathogenesis. So far, overshooting redox-responses of MeCP2-deficient neurons were observed during oxidant-mediated stress, hypoxia and mitochondrial inhibition. To further clarify the relevance of the fragile redox-balance for the neuronal (dys)function in RTT, we addressed more physiological stimuli and quantified the subcellular redox responses to neurotransmitter-stimulation. The roGFP redox sensor was expressed in either the cytosol or the mitochondrial matrix of cultured mouse hippocampal neurons, and the responses to transient stimulation by glutamate, serotonin, dopamine and norepinephrine were characterized. Each neurotransmitter evoked more intense oxidizing responses in the cytosol of MeCP2-deficient than in wildtype neurons. In the mitochondrial matrix the neurotransmitter-evoked oxidizing changes were more moderate and more uniform among genotypes. This identifies the cytosol as an important reactive oxygen species (ROS) source and as less stably redox buffered. Fura-2 imaging and extracellular Ca2+ withdrawal confirmed cytosolic Ca2+ transients as a contributing factor of neurotransmitter-induced redox responses and their potentiation in the cytosol of MeCP2-deficient neurons. Chemical uncoupling demonstrated the involvement of mitochondria. Nevertheless, cytosolic NADPH- and xanthine oxidases interact to play the leading role in the neurotransmitter-mediated oxidizing responses. As exaggerated redox-responses were already evident in neonatal MeCP2-deficient neurons, they may contribute remarkably to the altered neuronal network performance and the disturbed neuronal signaling, which are among the hallmarks of RTT.

Longitudinal Characterization of Transcriptomic, Functional, and Morphological Features in Human iPSC-Derived Neurons and Their Application to Investigate Translational Progranulin Disease Biology

The disease biology of frontotemporal lobe dementia (FTD) is complex and not fully understood, with limited translational value appreciated from animal models to date. Human cellular systems that can recapitulate phenotypic features of disease offer promise as translational tools to not only increase our understanding of disease processes but also increase the probability of success of translating novel treatment options to patients. However not all researchers may necessarily have access to well-characterized induced pluripotent stem cell (iPSC)-derived human neurons. As an example, we therefore comprehensively profiled phenotypic features over time in one commercially-available IPSC-derived human neuron cell line. This included systems-level assessments of neurite outgrowth dynamics, neuronal network function, and genome-wide gene expression. By investigating progranulin biology as an example we then demonstrated the utility of these cells as a tool to investigate human disease biology. For example, by using the siRNA-mediated knockdown of the progranulin (GRN) gene, we demonstrated the establishment of an isogenic human cellular model to facilitate translational FTD research. We reproduced findings from rodent neurons by demonstrating that recombinant progranulin (rPGRN) mediated neuroprotection. Contrary to previous rodent data, in our human cellular models, growth factor treatment showed no consistent sensitivity to modulate neurite outgrowth dynamics. Our study further provides the first evidence that rRPGRN modulated neuronal firing and synchrony in human neurons. Taken together, our datasets are a valuable systems-level resource demonstrating the utility of the tested commercially-available human iPSC neurons for investigating basic human neurobiology, translational neuroscience, and drug discovery applications in neurodegenerative and other CNS diseases.

Experimentally induced low back pain influences brain networks activity

Purpose of this study was to answer the question whether the recognized patterns of brain activity are likely to change under the influence of experimentally induced low back pain (LBP), and also to determine the functional networks of the brain engaged in this process. Twenty healthy subjects (8 women) participated. An experimental design was applied with repeated measurements of the blood oxygen level-dependent (BOLD) signal from the brain during two different voluntary contractions of the abdominal muscles without and with experimentally induced LBP. Brain areas showing significant differences in activity were identified and ascribed to the three functional neuronal brain networks: default mode network (DMN), pain matrix (PM), and sensorimotor (SM) areas. After implementation of the experimental painful stimulus the overall level of brain activity appears to be higher. No higher brain deactivations are seen in painful conditions and no higher activations in pain-free conditions. During isolated-type of muscular contraction a slight tendency to DMN deactivation may be observed.

Serotonin receptor 4 regulates hippocampal astrocyte morphology and function.

Astrocytes are an important component of the multipartite synapse and crucial for proper neuronal network function. Although small GTPases of the Rho family are powerful regulators of cellular morphology, the signaling modules of Rho-mediated pathways in astrocytes remain enigmatic. Here we demonstrated that the serotonin receptor 4 (5-HT4 R) is expressed in hippocampal astrocytes, both in vitro and in vivo. Through fluorescence microscopy, we established that 5-HT4 R activation triggered RhoA activity via Gα13 -mediated signaling, which boosted filamentous actin assembly, leading to morphological changes in hippocampal astrocytes. We investigated the effects of these 5-HT4 R-mediated changes in mixed cultures and in acute slices, in which 5-HT4 R was expressed exclusively in astrocytes. In both systems, 5-HT4 R-RhoA signaling changed glutamatergic synaptic transmission: It increased the frequency of miniature excitatory postsynaptic currents (mEPSCs) in mixed cultures and reduced the paired-pulse-ratio (PPR) of field excitatory postsynaptic potentials (fEPSPs) in acute slices. Overall, our present findings demonstrate that astrocytic 5-HT4 R-Gα13 -RhoA signaling is a previously unrecognized molecular pathway involved in the functional regulation of excitatory synaptic circuits.

Microglia Provide Structural Resolution to Injured Dendrites after Severe Seizures

Although an imbalance between neuronal excitation and inhibition underlies seizures, clinical approaches that target these mechanisms are insufficient in containing seizures in epileptic patients raising the need for alternative approaches. Brain-resident microglia contribute to the development and stability of neuronal structure and functional networks that are perturbed during seizures. However, the extent of microglial contributions in response to seizures in vivo remain to be elucidated. Using two photon in vivo imaging to visualize microglial dynamics, we show that severe seizures induce microglial process pouch formation that target but rarely engulf beaded neuronal dendrites. Microglial process pouches are stable for hours though they often shrink in size. We further found that microglial process pouches are associated with better structural resolution of beaded dendrites. These findings provide evidence for the structural resolution of injured dendrites by microglia as a form of neuroprotection.

Neuroimaging reveals functionally distinct neuronal networks associated with high-level alcohol consumption in two genetic rat models.

Human imaging data suggest that the motivational processes associated with alcohol reward are reflected in the patterns of neural activation after alcohol or alcohol-related cues. In animal models of alcohol drinking, however, the changes in brain activation during voluntary alcohol ingestion are poorly known. In order to improve the translational utility of animal models, we examined alcohol-induced functional brain activation in Alko Alcohol (AA) and Marchigian-Sardinian alcohol-preferring (msP) rats that drink voluntarily high levels of alcohol, but exhibit widely different neurochemical and behavioral traits cosegregated with alcohol preference. Brain imaging was performed using manganese-enhanced MRI (MEMRI), which is based on accumulation of Mn2+ ions in activated neurons, allowing the identification of functional neuronal networks recruited during specific behaviors in awake animals during a subsequent imaging session under anesthesia. MEMRI was performed following 4 weeks of voluntary alcohol drinking, using water drinking as the control. Despite similar levels of alcohol drinking, strikingly different alcohol-induced neuronal activity patterns were observed in AA and msP rats. Overall, functional activation in the AA rats was more widespread, involving large cortical areas and subcortical structures, such as the bed nucleus of the stria terminalis, preoptic area, hypothalamus, periaqueductal grey, and substantia nigra. In the msP rats, however, alcohol-related activation was largely confined to prefrontal cortical regions and insular cortex, and olfactory areas. Overlapping areas of activation found in both rat lines included the nucleus accumbens, prelimbic, orbital, and insular cortex. In conclusion, our data reveal strikingly different brain circuits associated with alcohol drinking in two genetically different rat lines and suggest innately different motivational and behavioral processes driving alcohol drinking. These findings have important implications for the use of these lines in translational alcohol research.

Three-dimensionality shapes the dynamics of cortical interconnected to hippocampal networks

Objective. The goal of this work is to develop and characterize an innovative experimental framework to design interconnected (i.e. modular) heterogeneous (cortical-hippocampal) neuronal cultures with a three-dimensional (3D) connectivity and to record their electrophysiological activity using micro-electrode arrays (MEAs). Approach. A two-compartment polymeric mask for the segregation of different neuronal populations (cortex and hippocampus) was coupled to the MEA surface. Glass microbeads were used as a scaffold to mimic the 3D brain micro-architecture. Main results. We built a fully functional heterogeneous 3D neuronal network. From an electrophysiological point of view, we found that the heterogeneity induces a global increase of the activity rate, while the 3D connectivity modulates the duration and the organization of the bursting activity. Significance. In vivo, studies of network dynamics and interactions between neuronal populations are often time-consuming, low-throughput, complex, and suffer from reproducibility. On the other hand, most of the commonly used in vitro brain models are too simplified and thus far from the in vivo situation. The achieved results demonstrate the feasibility to build a more realistic and controllable experimental in vitro model of interconnected brain regions on-a-chip whose applications may have impacts on the study of neurological disorders that impair the connectivity between brain areas (e.g. Parkinson disease).

Activity-Dependent Mitochondrial Plasticity and Mitoproteome are Dysregulated in Fragile X Syndrome

Homeostatic plasticity is necessary for the construction and maintenance of functional neuronal networks and becomes disrupted in certain neurodevelopmental disorders. Principal molecular mechanisms required for or modified by homeostatic plasticity are not well understood. We recently reported that homeostatic plasticity induced by activity deprivation is dysregulated in cortical neurons from Fragile X Mental Retardation protein (FMRP) knockout mice (Bulow et al. 2019). These findings suggested to us that proteins responsive to both activity deprivation and modulated by FMRP expression would be robust putative pathways necessary for or modified by homeostatic plasticity. Here, we used unbiased quantitative mass spectrometry to quantify steady-state proteome changes following chronic activity deprivation in wild type and Fmr1-/y cortical neurons. We found that most proteome hits responsive to both activity deprivation and the Fmr1-/y genotype were annotated to mitochondria. Surprisingly, we observed that Fmr1-/y neurons showed exaggerated changes in the expression of mitochondrial proteins following activity deprivation. We identified significant, but compartment specific, changes in the mitochondrial morphology and membrane polarization in dendrites and axons of wild type neurons following activity deprivation. However, these compartmentalized changes were already present in Fmr1-/y neurons at baseline and remained insensitive to activity deprivation. Our findings suggest that mitochondria are required and modified during the induction, establishment or maintenance of homeostatic plasticity. Loss of FMRP exaggerates changes in the mitoproteome during activity deprivation, but Fmr1-/y neurons fail to appropriately regulate mitochondrial morphology and function in an activity dependent and compartmentalized manner. We propose that abnormal compartmentalized mitochondrial plasticity contributes to neurodevelopmental disorders.

Widefield, Spatiotemporal Mapping of Spontaneous Activity of Mouse Cultured Neuronal Networks Using Quantum Diamond Sensors

Quantum diamond sensors containing Nitrogen Vacancy (NV) centers were integrated into the culture of spontaneously electrically active cultures of live mouse primary cortical neurons. Two diamond formats were used enabling extracellular studies of cells cultured directly on a planar diamond plate and intracellular studies via endocytosis mediated integration of nanoscale diamond particles within cells. Over a 14 day culture period functional neuronal networks formed as confirmed by endogenous calcium transients detected via fluorescent imaging of a calcium probe (Fluo-5 AM). Spatially correlated images of photoluminescence from NV centers were also recorded demonstrating successful acquisition of optically detected magnetic resonance from regions of endogenously firing neuronal cultures. Further, a fast and simple measurement protocol based on acquisition of NV photoluminescence without and with the application of near resonant microwaves is presented. This protocol was applied to live signaling cells and dead cells. The relative photoluminescence from NVs with and without microwaves varied for the case of live as compared to dead cells warranting future investigation. Overall this work presents a protocol for integration of NV diamond sensors in a spontaneously active network of neuronal cells of relevance to the field of neuroscience. Photoluminescence from NV centers was detected with high spatiotemporal resolution using measurement protocols potentially capable of single shot detection of neuronal activity. It is anticipated that the methodologies introduced in this work will underpin the establishment of NV diamond sensors as a radically new measurement platform capable of rapid, non-destructive functional studies of cells.

Targeting Vesicular Glutamate Transporter Machinery: Implications on Metabotropic Glutamate Receptor 5 Signaling and Behavior.

Cross talk between both pre- and postsynaptic components of glutamatergic neurotransmission plays a crucial role in orchestrating a multitude of brain functions, including synaptic plasticity and motor planning. Metabotropic glutamate receptor (mGluR) 5 exhibits promising therapeutic potential for many neurodevelopmental and neurodegenerative disorders as a consequence of its modulatory control over diverse neuronal networks required for memory, motor coordination, neuronal survival, and differentiation. Given these crucial roles, mGluR5 signaling is under the tight control of glutamate release machinery mediated through vesicular glutamate transporters (VGLUTs) that ultimately dictate glutamatergic output. A particular VGLUT isoform, VGLUT3, exhibits an overlapping, but unique, distribution with mGluR5, and the dynamic cross talk between mGluR5 and VGLUT3 is key for the function of specific neuronal networks involved in motor coordination, emotions, and cognition. Thus, aberrant signaling of the VGLUT3-mGluR5 axis is linked to various pathologies including, but not limited to, Parkinson disease, anxiety disorders, and drug addiction. We argue that a comprehensive profiling of how coordinated VGLUT3-mGluR5 signaling influences overall glutamatergic neurotransmission is warranted. SIGNIFICANCE STATEMENT: Vesicular glutamate receptor (VGLUT) 3 machinery orchestrates glutamate release, and its distribution overlaps with metabotropic glutamate receptor (mGluR) 5 in regional brain circuitries, including striatum, hippocampus, and raphe nucleus. Therefore, VGLUT3-mGluR5 cross talk can significantly influence both physiologic and pathophysiologic glutamatergic neurotransmission. Pathological signaling of the VGLUT3-mGluR5 axis is linked to Parkinson disease, anxiety disorders, and drug addiction. However, it is also predicted to contribute to other motor and cognitive disorders.

Long-Range Optogenetic Control of Axon Guidance Overcomes Developmental Boundaries and Defects.

Axons connect neurons together, establishing the wiring architecture of neuronal networks. Axonal connectivity is largely built during embryonic development through highly constrained processes of axon guidance, which have been extensively studied. However, the inability to control axon guidance, and thus neuronal network architecture, has limited investigation of how axonal connections influence subsequent development and function of neuronal networks. Here, we use zebrafish motor neurons expressing a photoactivatable Rac1 to co-opt endogenous growth cone guidance machinery to precisely and non-invasively direct axon growth using light. Axons can be guided over large distances, within complex environments of living organisms, overriding competing endogenous signals and redirecting axons across potent repulsive barriers to construct novel circuitry. Notably, genetic axon guidance defects can be rescued, restoring functional connectivity. These data demonstrate that intrinsic growth cone guidance machinery can be co-opted to non-invasively build new connectivity, allowing investigation of neural network dynamics in intact living organisms.

Onset of hippocampal network aberration and memory deficits in P301S tau mice are associated with an early gene signature.

Hyperphosphorylation and deposition of tau in the brain characterizes frontotemporal dementia and Alzheimer's disease. Disease-associated mutations in the tau-encoding MAPT gene have enabled the generation of transgenic mouse models that recapitulate aspects of human neurodegenerative diseases, including tau hyperphosphorylation and neurofibrillary tangle formation. Here, we characterized the effects of transgenic P301S mutant human tau expression on neuronal network function in the murine hippocampus. Onset of progressive spatial learning deficits in P301S tau transgenic TAU58/2 mice were paralleled by long-term potentiation deficits and neuronal network aberrations during electrophysiological and EEG recordings. Gene-expression profiling just prior to onset of apparent deficits in TAU58/2 mice revealed a signature of immediate early genes that is consistent with neuronal network hypersynchronicity. We found that the increased immediate early gene activity was confined to neurons harbouring tau pathology, providing a cellular link between aberrant tau and network dysfunction. Taken together, our data suggest that tau pathology drives neuronal network dysfunction through hyperexcitation of individual, pathology-harbouring neurons, thereby contributing to memory deficits.

Efficient Communication in Distributed Simulations of Spiking Neuronal Networks With Gap Junctions.

Investigating the dynamics and function of large-scale spiking neuronal networks with realistic numbers of synapses is made possible today by state-of-the-art simulation code that scales to the largest contemporary supercomputers. However, simulations that involve electrical interactions, also called gap junctions, besides chemical synapses scale only poorly due to a communication scheme that collects global data on each compute node. In comparison to chemical synapses, gap junctions are far less abundant. To improve scalability we exploit this sparsity by integrating an existing framework for continuous interactions with a recently proposed directed communication scheme for spikes. Using a reference implementation in the NEST simulator we demonstrate excellent scalability of the integrated framework, accelerating large-scale simulations with gap junctions by more than an order of magnitude. This allows, for the first time, the efficient exploration of the interactions of chemical and electrical coupling in large-scale neuronal networks models with natural synapse density distributed across thousands of compute nodes.

Humor‐Associated Mirthful Laughter and Brain Health: Predominance of Beneficial EEG Gamma Frequency and Beta/Gamma Interaction in the Cerebral Cortex

For almost a century, the medical community has been intrigued with the potential health benefits of laughter, as the common phrase notes, “laughter is the best medicine”. However, the science underlying laughter and health is yet to be fully described.ObjectiveWe used electroencephalography (EEG) to explore the potential neurological benefits of humor‐associated mirthful laughter (HAML), compared to stress, and how HAML deferentially modulates brain frequencies (3–40Hz). Specific interests were: 1) increasing beneficial gamma frequency (31–40Hz) during HAML, and 2) identifying a beta/gamma interaction.MethodsIn a randomized crossover design, 31 university students, ages 18–25, were recruited. Subjects watched two 10‐minute videos: 1) HAML task (America’s Funniest Home Videos), and 2) Stress task (Saving Private Ryan movie scene). During each task, EEG data was recorded from nine cortical regions (F3, Fz, F4, C3, Cz, C4, P3, POz, P4). Power spectral density μV2 (PSD) values were calculated and placed into their respective frequency ranges: theta (3–7 Hz), alpha (8–13 Hz), beta (14–30 Hz), and gamma (31–40Hz). PSD values were standardized into Z‐scores for statistical analysis.ResultsTwo‐way ANOVA showed that during HAML, gamma (p<0.001) had the greatest PSD across all assessed cortical regions. When comparing the HAML vs. Stress tasks, the central region showed significant differences between tasks (p<0.05). Specifically, C3 and C4 regions showed the greatest increases in PSD (p<0.05). Stratification of tasks revealed that HAML had significant differences between frequency PSDs; gamma was significantly greater than beta and theta (p=0.001), and beta was greater than theta (p=0.001). In the frontal region, gamma was significantly greater than alpha, beta, and theta PSD (p=0.0001), and beta was greater than theta (p=0.0001). In the parietal region, gamma PSD was significantly greater than alpha and theta PSD (p=0.01). Regression analysis of beta and gamma displayed a strong positive correlation between the two frequencies during both the HAML and Stress task (HAML: p<0.001, R=0.96; Stress: p=0.004, R=0.843).ConclusionDuring HAML, EEG displayed increases in PSD, most remarkably in gamma frequency. Gamma oscillations play a “binding” role in higher cognitive processes, such as memory and processing of sensory stimuli, suggesting gamma’s role in proper neuronal network functions. Interestingly, our previous research has shown that HAML enhances short‐term memory in elderly adults. Relational analysis showed an interplay of beta oscillations dependent on and sub‐harmonic to gamma oscillations. Similar dynamics between beta and gamma underlie working memory. Further, current research has shown that increasing gamma activity through multi‐sensory methods reduces amyloid‐beta levels and modifies microglial activity, both measures associated with Alzheimer’s‐related disease. Based on our research findings and other previous research, we suggest that enhancement of gamma frequency via “humor therapy”/HAML may have adjunctive clinical value in promoting brain health.a–d. Brain Frequency PSD During HAML vs. Stress tasks in the Frontal, Central and Parietal Regions and Heat Map Analysis of Gamma Frequency (N=31)Figure 1Linear Regression Analysis of Beta/Gamma Relationship during HAML and Stress Task (N=31)Figure 2