Interburst Interval Research Articles

Prevalence, Risk Factors, and Impact of Preoperative Seizures in Neonates With Congenital Heart Disease.

The purpose of this study was to assess the prevalence, risk factors, and impact of electrographic seizures in neonates with complex congenital heart disease before cardiac surgery. A cohort of 31 neonates with congenital heart disease monitored preoperatively with continuous video-EEG (cEEG) was first reviewed for electrographic seizure burden and EEG background abnormalities. Second, cEEG findings were correlated with brain MRI and 18-month outcomes. Continuous video-EEG was recorded preoperatively for a median duration of 20.5 hours (range, 2.5-93.5 hours). The five neonates (16%; 95% confidence interval, 5.5% to 34%) with seizures detected on cEEG in the preoperative period had a diagnosis of transposition of the great arteries or similar physiology, detected in four of five postnatally. None of the 157 recorded electrographic seizures had a clinical correlate. The median time to first seizure was 65 minutes (range, 6-300 minutes) after cEEG hookup. The median maximum hourly seizure burden was 12.4 minutes (range, 7-23 minutes). Before the first electrographic seizure, a prolonged interburst interval (>10 seconds) was not associated with seizures (coefficient 1.2; 95% confidence interval, -1.1 to 3.6). MRI brain lesions were three times more common in neonates with seizures. Sharp wave transients on cEEG were associated with delayed opercular development. In this cohort, preoperative electrographic seizures were common, were all subclinical, and were associated with MRI brain injury and postnatal diagnosis of transposition of the great arteries. The findings motivate further study of the mechanisms of preoperative brain injury, particularly among neonates with a postnatal diagnosis of transposition of the great arteries.

Relationship Between Early Functional and Structural Brain Developments and Brain Injury in Preterm Infants

BackgroundRecent studies explored the relationship between early brain function and brain morphology, based on the hypothesis that increased brain activity can positively affect structural brain development and that excitatory neuronal activity stimulates myelination.ObjectiveTo investigate the relationship between maturational features from early and serial aEEGs after premature birth and MRI metrics characterizing structural brain development and injury, measured around 30weeks postmenstrual age (PMA) and at term. Moreover, we aimed to verify whether previously developed maturational EEG features are related with PMA.Design/MethodsOne hundred six extremely preterm infants received bedside aEEGs during the first 72h and weekly until week 5. 3T-MRIs were performed at 30weeks PMA and at term. Specific features were extracted to assess EEG maturation: (1) the spectral content, (2) the continuity [percentage of spontaneous activity transients (SAT%) and the interburst interval (IBI)], and (3) the complexity. Automatic MRI segmentation to assess volumes and MRI score was performed. The relationship between the maturational EEG features and MRI measures was investigated.ResultsBoth SAT% and EEG complexity were correlated with PMA. IBI was inversely associated with PMA. Complexity features had a positive correlation with the cerebellar size at 30weeks, while event-based measures were related to the cerebellar size at term. Cerebellar width, cortical grey matter, and total brain volume at term were inversely correlated with the relative power in the higher frequency bands.ConclusionsThe continuity and complexity of the EEG steadily increase with increasing postnatal age. Increasing complexity and event-based features are associated with cerebellar size, a structure with enormous development during preterm life. Brain activity is important for later structural brain development.

This Month in Anesthesiology

This Month in Anesthesiology

AC Pulsed Field Ablation Is Feasible and Safe in Atrial and Ventricular Settings: A Proof-of-Concept Chronic Animal Study.

IntroductionPulsed field ablation (PFA) exploits the delivery of short high-voltage shocks to induce cells death via irreversible electroporation. The therapy offers a potential paradigm shift for catheter ablation of cardiac arrhythmia. We designed an AC-burst generator and therapeutic strategy, based on the existing knowledge between efficacy and safety among different pulses. We performed a proof-of-concept chronic animal trial to test the feasibility and safety of our method and technology.MethodsWe employed 6 female swine – weight 53.75 ± 4.77 kg – in this study. With fluoroscopic and electroanatomical mapping assistance, we performed ECG-gated AC-PFA in the following settings: in the left atrium with a decapolar loop catheter with electrodes connected in bipolar fashion; across the interventricular septum applying energy between the distal electrodes of two tip catheters. After procedure and 4-week follow-up, the animals were euthanized, and the hearts were inspected for tissue changes and characterized. We perform finite element method simulation of our AC-PFA scenarios to corroborate our method and better interpret our findings.ResultsWe applied square, 50% duty cycle, AC bursts of 100 μs duration, 100 kHz internal frequency, 900 V for 60 pulses in the atrium and 1500 V for 120 pulses in the septum. The inter-burst interval was determined by the native heart rhythm – 69 ± 9 bpm. Acute changes in the atrial and ventricular electrograms were immediately visible at the sites of AC-PFA – signals were elongated and reduced in amplitude (p < 0.0001) and tissue impedance dropped (p = 0.011). No adverse event (e.g., esophageal temperature rises or gas bubble streams) was observed – while twitching was avoided by addition of electrosurgical return electrodes. The implemented numerical simulations confirmed the non-thermal nature of our AC-PFA and provided specific information on the estimated treated area and need of pulse trains. The postmortem chest inspection showed no peripheral damage, but epicardial and endocardial discolorations at sites of ablation. T1-weighted scans revealed specific tissue changes in atria and ventricles, confirmed to be fibrotic scars via trichrome staining. We found isolated, transmural and continuous scars. A surviving cardiomyocyte core was visible in basal ventricular lesions.ConclusionWe proved that our method and technology of AC-PFA is feasible and safe for atrial and ventricular myocardial ablation, supporting their systematic investigation into effectiveness evaluation for the treatment of cardiac arrhythmia. Further optimization, with energy titration or longer follow-up, is required for a robust atrial and ventricular AC-PFA.

Modeling bursting in neuronal networks using facilitation-depression and afterhyperpolarization

In the absence of inhibition, excitatory neuronal networks can alternate between bursts and interburst intervals (IBI), with heterogeneous length distributions. As this dynamic remains unclear, especially the durations of each epoch, we develop here a bursting model based on synaptic depression and facilitation that also accounts for afterhyperpolarization (AHP), which is a key component of IBI. The framework is a novel stochastic three dimensional dynamical system perturbed by noise: numerical simulations can reproduce a succession of bursts and interbursts. Each phase corresponds to an exploration of a fraction of the phase-space, which contains three critical points (one attractor and two saddles) separated by a two-dimensional stable manifold Σ. We show here that bursting is defined by long deterministic excursions away from the attractor, while IBI corresponds to escape induced by random fluctuations. We show that the variability in the burst durations, depends on the distribution of exit points located on Σ that we compute using WKB and the method of characteristics. Finally, to better characterize the role of several parameters such as the network connectivity or the AHP time scale, we compute analytically the mean burst and AHP durations in a linear approximation. To conclude the distribution of bursting and IBI could result from synaptic dynamics modulated by AHP.

Delta-Frequency Augmentation and Synchronization in Seizure Discharges and Telencephalic Transmission.

SummaryEpileptic seizures constitute a common neurological disease primarily diagnosed by characteristic rhythms or waves in the local field potentials (LFPs) of cerebral cortices or electroencephalograms. With a basolateral amygdala (BLA) kindling model, we found that the dominant frequency of BLA oscillations is in the delta range (1–5 Hz) in both normal and seizure conditions. Multi-unit discharges are increased with higher seizure staging but remain phase-locked to the delta waves in LFPs. Also, the change in synchrony precedes and outlasts the changes in discharging units as well as behavioral seizures. One short train of stimuli readily drives the pyramidal-inhibitory neuronal networks in BLA slices into prolonged reverberating activities, where the burst and interburst intervals may concurrently set a “natural wavelength” for delta frequencies. Seizures thus could be viewed as erroneous temporospatial continuums to normal oscillations in a system with a built-in synchronizing and resonating nature for information relay.

Can Pallidal Deep Brain Stimulation Rescue Borderline Dystonia? Possible Coexistence of Functional (Psychogenic) and Organic Components.

The diagnosis and treatment of functional movement disorders are challenging for clinicians who manage patients with movement disorders. The borderline between functional and organic dystonia is often ambiguous. Patients with functional dystonia are poor responders to pallidal deep brain stimulation (DBS) and are not good candidates for DBS surgery. Thus, if patients with medically refractory dystonia have functional features, they are usually left untreated with DBS surgery. In order to investigate the outcome of functional dystonia in response to pallidal DBS surgery, we retrospectively included five patients with this condition. Their dystonia was diagnosed as organic by dystonia specialists and also as functional according to the Fahn and Williams criteria or the Gupta and Lang Proposed Revisions. Microelectrode recordings in the globus pallidus internus of all patients showed a cell-firing pattern of bursting with interburst intervals, which is considered typical of organic dystonia. Although their clinical course after DBS surgery was incongruent to organic dystonia, the outcome was good. Our results question the possibility to clearly differentiate functional dystonia from organic dystonia. We hypothesized that functional dystonia can coexist with organic dystonia, and that medically intractable dystonia with combined functional and organic features can be successfully treated by DBS surgery.

Synchrony of Spontaneous Burst Firing between Retinal Ganglion Cells Across Species.

Neurons communicate with other neurons in response to environmental changes. Their goal is to transmit information to their targets reliably. A burst, which consists of multiple spikes within a short time interval, plays an essential role in enhancing the reliability of information transmission through synapses. In the visual system, retinal ganglion cells (RGCs), the output neurons of the retina, show bursting activity and transmit retinal information to the lateral geniculate neuron of the thalamus. In this study, to extend our interest to the population level, the burstings of multiple RGCs were simultaneously recorded using a multi-channel recording system. As the first step in network analysis, we focused on investigating the pairwise burst correlation between two RGCs. Furthermore, to assess if the population bursting is preserved across species, we compared the synchronized bursting of RGCs between marmoset monkey (callithrix jacchus), one species of the new world monkeys and mouse (C57BL/6J strain). First, monkey RGCs showed a larger number of spikes within a burst, while the inter-spike interval, burst duration, and inter-burst interval were smaller compared with mouse RGCs. Monkey RGCs showed a strong burst synchronization between RGCs, whereas mouse RGCs showed no correlated burst firing. Monkey RGC pairs showed significantly higher burst synchrony and mutual information than mouse RGC pairs did. Comprehensively, through this study, we emphasize that two species have a different bursting activity of RGCs and different burst synchronization suggesting two species have distinctive retinal processing.

Inhibition of neuronal Na+ currents by lacosamide: Differential binding affinity and kinetics to different inactivated states

Lacosamide is a new-generation anticonvulsant acting on Na+ channels. Compared to the classic anticonvulsants targeting Na+ channels, lacosamide is unique in structure and in its molecular action requiring longer membrane depolarization. Selective binding to the slow inactivated state of Na+ channels was then advocated for lacosamide, although slow binding to the fast inactivated state was alternatively proposed recently. In addition, quantitative characterization of lacosamide action has been deficient. We investigated the interactions between lacosamide and Na+ channels in native mammalian neurons, and found that the apparent dissociation constant (~13.7 μM) of lacosamide to the slow inactivated state is well within the therapeutic concentration range and is much (>15-fold) lower than the dissociation constant of lacosamide to the fast inactivated state. Besides, lacosamide has extremely slow binding rates (<400 M−1sec−1) to the fast but much faster binding rates (>3000 M−1sec−1) to the slow inactivated Na+ channels. Consistent with these biophysical characters, we further demonstrated that lacosamide is much more effective against the repetitive burst discharges with interburst intervals at −60 mV than −80 mV. With preponderant binding to the slow inactivation state in therapeutic concentrations and thus less propensity to affect normal discharges, lacosamide could be a drug of choice for seizure discharges characterized by relatively depolarized interburst intervals, during which more slow inactivated states could be generated and more binding of lacosamide would ensue.

Stochastic Spiking-Bursting Excitability and Transition to Chaos in a Discrete-Time Neuron Model

The randomly forced Rulkov neuron model with the discontinuous 2D-map is considered. We study the phenomena of the stochastic excitement: (i) noise-induced spiking in the parametric zone where the equilibrium is a single attractor; (ii) stochastic generation of the spiking in bistability zone; (iii) noise-induced bursting in the parametric zone where the deterministic model exhibits the tonic spiking. These stochastic effects are investigated numerically by means of probability density functions and mean values of interspike (interburst) intervals. For the parametric study of these noise-induced transformations, we suggest an analytical approach taking into account the stochastic sensitivity of attractors and peculiarities of deterministic phase portraits. In this analysis, we study the mutual arrangement of confidence domains and superthreshold zones near deterministic attractors. This approach gives a prediction of the onset of the noise-induced excitement in the form of the transitions quiescence-spiking or spiking-bursting. A relationship of these phenomena with the order-chaos transformations are discussed.

Distribution of VTA Glutamate and Dopamine Terminals, and their Significance in CA1 Neural Network Activity

Reciprocal connection between the ventral tegmental area (VTA) and the hippocampus forms a loop that controls information entry into long-term memory. Compared with the widely studied VTA dopamine system, VTA glutamate terminals are anatomically dominant in the hippocampus and less understood. The current study employs anterograde and retrograde labeling of VTA dopamine and glutamate neurons to map the distribution of their terminals within the layers of the hippocampus. Also, functional tracing of VTA dopamine and glutamate projections to the hippocampus was performed by photostimulation of VTA cell bodies during CA1 extracellular voltage sampling in vivo. VTA dopamine terminals predominantly innervate the CA1 basal dendrite layer and modulate the firing rate of active putative neurons. In contrast, anatomical dominance of VTA glutamate terminals in the CA1 pyramidal cell and apical dendrite layers suggests the possible involvement of these terminals in excitability regulation. In support of these outcomes, photostimulation of VTA dopamine neurons increased the firing rate but not intrinsic excitability parameters for putative pyramidal units. Conversely, activation of VTA glutamate neurons increased CA1 network firing rate and burst rate. In addition, VTA glutamate inputs reduced the interspike and interburst intervals for putative CA1 neurons. Taken together, we deduced that layer-specific distribution of presynaptic dopamine and glutamate terminals in the hippocampus determinines VTA modulation (dopamine) or regulation (glutamate) of excitability in the CA1 neural network.

Cerebral oxygenation and bioelectrical activity in preterm infants during surfactant replacement therapy with porcine and bovine preparations.

IntroductionSurfactant replacement therapy (SRT) might cause acute changes in cerebral oxygenation and alteration of brain bioelectrical activity. Varying physiologic responses and clinical outcomes were observed when different surfactant preparations were instilled to treat neonatal respiratory distress syndrome (RDS).Material and methodsNeonates born at 26–30 weeks of gestation with RDS requiring intubation and mechanical ventilation were randomized to SRT either with poractant alfa (A) or beractant (B). Saturation (SpO2), heart rate (HR), cerebral tissue oxygenation (StO2) and amplitude-integrated electroencephalography (aEEG) were simultaneously recorded prior to and up to 4 h after SRT.ResultsMean SpO2, HR and StO2 values were comparable between groups at baseline and after SRT. There were differences in mean aEEG voltage before SRT, but amplitudes were within a range considered as normal in both groups. Immediately after SRT and at a few single post-intervention time points mean aEEG voltage was higher in the beractant group. There was a significant difference in the percentage of time with the aEEG signal < 5 μV after SRT between groups (mean 25.7% (A) vs. 16.5% (B), p < 0.05). Quantity of bursts per minute and mean length of inter-burst intervals (IBI) in the aEEG recording varied insignificantly but there was a significant difference in the percentage of IBI > 30 s between groups (52.5% (A) vs. 36.6% (B), p <0.05).ConclusionsThis is the first study assessing brain bioelectrical function and oxygenation while using two different surfactant preparations in a neonate. Cerebral effects of SRT are observed regardless of the type of surfactant, but their magnitude may depend on the preparation and/or dosing used.

GCaMP as an indirect measure of electrical activity in rat trigeminal ganglion neurons

While debate continues over whether somatosensory information is transmitted via labeled line, population coding, frequency coding, or some combination therein, researchers have begun to address this question at the level of the primary afferent by using optical approaches that enable the assessment of neural activity in hundreds to even thousands of neurons simultaneously. However, with limited availability of tools to optically assess electrical activity in large populations of neurons, researchers have turned to genetically encoded Ca2+ indicators (GECIs) including GCaMP to enable the detection of increases in cytosolic Ca2+ concentrations as a correlate for neuronal activity. One of the most widely used GECIs is GCaMP6, which is available in three different versions tuned for sensitivity (GCaMP6s), speed (GCaMP6f), or a balance of the two (GCaMP6m). In order to determine if these issues were unique to GCaMP6 itself, or if they were inherent to more than one generation of GCaMP, we also characterized jGCaMP7. In the present study, we sought to determine the utility of the three GCaMP6 isoforms to detect changes in activity in primary afferents at frequencies ranging from 0.1–30 Hz. Given the heterogeneity of sensory neurons, we also compared the performance of each GCaMP6 isoform in subpopulations of neurons defined by properties used to identify putative nociceptive afferents: cell body size, isolectin B4 (IB4) binding, and capsaicin sensitivity. Finally, we compared results generated with GCaMP6 with that generated from neurons expressing the next generation of GCaMP, jGCaMP7s and jGCaMP7f. A viral approach, with AAV9-CAG-GCaMP6s/m/f, was used to drive GECI expression in acutely dissociated rat trigeminal ganglion (TG) neurons, and neural activity was driven by electrical field stimulation. Infection efficiency with the AAV serotype was high >95 %, and the impact of GCaMP6 expression in TG neurons over the period of study (<10 days) on the regulation of intracellular Ca2+, as assessed with fura-2, was minimal. Having confirmed that the field stimulation evoked Ca2+ transients were dependent on Ca2+ influx secondary to the activation of action potentials and voltage-gated Ca2+ channels, we also confirmed that the signal-to-noise ratio for each of the isoforms was excellent, enabling detection of a single spike in>90% of neurons. However, the utility of the GCaMP6 isoforms to enable an assessment of the firing frequency let alone changes in firing frequency of each neuron was relatively limited and isoform specific: GCaMP6s and 6m had the lowest resolution, enabling detection of spikes at 3 Hz in 15% and 32% of neurons respectively, but it was possible to resolve discrete single spikes up to 10 Hz in 36% of GCaMP6f neurons. Unfortunately, using other parameters of the Ca2+ transient, such as magnitude of the transient or the rate of rise, did not improve the range over which these indicators could be used to assess changes in spike number or firing frequency. Furthermore, in the presence of ongoing neural activity, it was even more difficult to detect a change in firing frequency. The frequency response relationship for the increase in Ca2+ was highly heterogeneous among sensory neurons and was influenced by both the GCaMP6 isoform used to assess it, the timing between the delivery of stimulation trains (inter-burst interval), and afferent subpopulation. Notably, the same deficiencies were observed with jGCaMP7s and 7f in resolving the degree of activity as were present for the GCaMP6 isoforms. Together, these data suggest that while both GCaMP6 and jGCaMP7 are potentially useful tools in sensory neurons to determine the presence or absence of neural activity, the ability to discriminate changes in firing frequency ≥ 3 Hz is extremely limited. As a result, GECIs should probably not be used in sensory neurons to assess changes in activity within or between subpopulations of neurons.

Protein kinase A phosphorylation potentiates cystic fibrosis transmembrane conductance regulator gating by relieving autoinhibition on the stimulatory C terminus of the regulatory domain

Cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel activated by protein kinase A (PKA) phosphorylation on the regulatory (R) domain. Phosphorylation at several R domain residues stimulates ATP-dependent channel openings and closings, termed channel gating. To explore the protein segment responsible for channel potentiation and PKA-dependent activation, deletion mutations were constructed by removing one to three protein segments of the R domain including residues 708-759 (ΔR708-759), R760-783, and R784-835, each of which contains one or two PKA phosphorylation sites. Deletion of R708-759 or R760-783 had little effect on CFTR gating, whereas all mutations lacking R784-835 reduced CFTR activity by decreasing the mean burst duration and increasing the interburst interval (IBI). The data suggest that R784-835 plays a major role in stimulating CFTR gating. For ATP-associated regulation, ΔR784-835 had minor impact on gating potentiation by 2'dATP, CaATP, and pyrophosphate. Interestingly, introducing a phosphorylated peptide matching R809-835 shortened the IBI of ΔR708-835-CFTR. Consistently, ΔR815-835, but not ΔR784-814, enhanced IBI, whereas both reduced mean burst duration. These data suggest that the entirety of R784-835 is required for stabilizing the open state of CFTR; however, R815-835, through interactions with the channel, is dominant for enhancing the opening rate. Of note, PKA markedly decreased the IBI of ΔR708-783-CFTR. Conversely, the IBI of ΔR708-814-CFTR was short and PKA-independent. These data reveal that for stimulating CFTR gating, PKA phosphorylation may relieve R784-814-mediated autoinhibition that prevents IBI shortening by R815-835 This mechanism may elucidate how the R domain potentiates channel gating and may unveil CFTR stimulation by other protein kinases.

Optogenetic manipulations of preBötC μ‐opioid receptor expressing neurons reveal dual mechanisms of opioid‐induced respiratory depression

The analgesic utility of opiates is limited by the risk for adverse and life‐threatening side effects, including respiratory depression. Opioid‐induced respiratory depression (OIRD) is characterized by a pronounced decrease in the frequency and regularity of inspiratory efforts. The inspiratory rhythm originates from the preBotzinger Compex (preBötC), a region in the ventral medulla that contains neurons that express the μ‐opioid receptor (μOR) and is intrinsically sensitive to opioids, including the synthetic μOR agonist DAMGO. However, the cellular‐level mechanisms of opioid‐induced suppression of rhythmogenesis within the preBötC are controversial. Some evidence suggests opiates regulate synaptic transmission while other evidence suggests membrane potential (Vm) is the primary effector. At the network level, the frequency and regularity of the inspiratory rhythm is primarily determined by the interburst interval IBI which is regulated, in part, by excitatory neurons with “pre‐inspiratory” (pre‐I) spiking activity, but the network‐level effects of opiates have not been well defined. To shed light on these cellular‐ and network‐level processes, we utilized Oprm1Cre mice to optogenetically manipulate μOR neurons in vitro and in vivo. In brainstem slice preparations from Oprm1Arch neonatal mice, unit recordings from pre‐I neurons revealed that 37% of these neurons express μOR. In the presence of increasing concentrations of DAMGO, pre‐I spiking was eliminated initially, followed by suppression of spiking activity during inspiratory bursts. Next, using intracellular recordings, laser power was tuned such that photoinhibition hyperpolarized μOR neurons by ~5–10mV, mimicking the effect of DAMGO on Vm when bath applied at concentrations (100–300nm) that dramatically suppress inspiratory frequency (&gt;90%). However, bilateral photoinhibition of μOR neurons reduced frequency by 36%, only partially mimicking the suppression of frequency by DAMGO. In slices from Oprm1ChR2 mice, photostimuation of μOR neurons under control conditions increased frequency by 204%, indicating that these neurons are integrated within this rhythmogenic network. However, following suppression of the rhythm with DAMGO, ChR2‐mediated depolarization of μOR neurons could not rescue inspiratory frequency. These findings in vitro were largely corroborated by experiments in anesthetized mice in vivo, and suggest that hyperpolarization of μOR neurons at the cellular‐level only partially contributes to OIRD in the preBötC. Based on these initial results, we propose a model of preBötC OIRD in which the effects of opioids are twofold: 1) a modest hyperpolarization of μOR neurons at the cellular‐level reduces pre‐I spiking activity within the network and causes the duration between inspirations to become longer and more irregular, followed by 2) a crash in network‐driven rhythmogenesis, potentially through a μOR‐mediated reduction in the efficacy of excitatory synaptic transmission.Support or Funding InformationK99 HL145004 (Baertsch)R01 HL144801 (Ramirez)

Reduction of spontaneous cortical beta bursts in Parkinson's disease is linked to symptom severity.

Parkinson’s disease is characterized by a gradual loss of dopaminergic neurons, which is associated with altered neuronal activity in the beta-band (13–30 Hz). Assessing beta-band activity typically involves transforming the time-series to get the power of the signal in the frequency domain. Such transformation assumes that the time-series can be reduced to a combination of steady-state sine- and cosine waves. However, recent studies have suggested that this approach masks relevant biophysical features in the beta-band—for example, that the beta-band exhibits transient bursts of high-amplitude activity. In an exploratory study, we used magnetoencephalography to record beta-band activity from the sensorimotor cortex, to characterize how spontaneous cortical beta bursts manifest in Parkinson’s patients on and off dopaminergic medication, and compare this to matched healthy controls. We extracted the time-course of beta-band activity from the sensorimotor cortex and characterized bursts in the signal. We then compared the burst rate, duration, inter-burst interval and peak amplitude between the Parkinson’s patients and healthy controls. Our results show that Parkinson’s patients off medication had a 5–17% lower beta bursts rate compared to healthy controls, while both the duration and the amplitude of the bursts were the same for healthy controls and medicated state of the Parkinson’s patients. These data thus support the view that beta bursts are fundamental underlying features of beta-band activity, and show that changes in cortical beta-band power in Parkinson’s disease can be explained—primarily by changes in the underlying burst rate. Importantly, our results also revealed a relationship between beta burst rate and motor symptom severity in Parkinson’s disease: a lower burst rate scaled with increased severity of bradykinesia and postural/kinetic tremor. Beta burst rate might thus serve as a neuromarker for Parkinson’s disease that can help in the assessment of symptom severity in Parkinson’s disease or in the evaluation of treatment effectiveness.

Asymmetric Control of Coexisting Slow and Fast Rhythms in a Multifunctional Central Pattern Generator: A Model Study

Using a simulation approach, we propose a biophysically feasible mechanism describing how a multifunctional central pattern generator (CPG) can produce co-existing slow and fast rhythms of the patterned motor output. This mechanism suggests that the same core elemental CPG can produce either a locomotion or a paw shaking rhythm in mammals (cat). We built a Hodgkin–Huxley-style biophysical model that generates multistability of a locomotion-like regime and a paw shake-like regime. This model is constructed as a half-center oscillator (HCO), in which two inhibitory neurons (representing the respective neuronal populations in real CPGs) reciprocally inhibit each other. We propose that the locomotion rhythm and the paw shaking rhythm are controlled by two different slowly inactivating intrinsic ion currents. In our model, slowly inactivating low voltage-activated calcium current (ICaS) drives the locomotion-like regime, while slowly inactivating sodium current (INaS) drives the paw shakelike regime. We investigated whether asymmetric characteristics of these regimes could be reliably and separately controlled by asymmetric variation of the conductances of these two currents. We found that variation of the conductance of ICaS in only one neuron, while holding this conductance constant in the other neuron, produces asymmetric changes in bursting characteristics, including the burst duration and interburst interval of the locomotion-like regime without producing notable changes of the paw shake-like regime. We also found that similar variation of the conductance of INaS affects the bursting characteristics of both regimes, although the paw shake-like regime is affected more remarkably than the locomotion-like one.

Decoding Neural Metabolic Markers From the Carotid Sinus Nerve in a Type 2 Diabetes Model.

Recent studies showed that the carotid sinus nerve (CSN) and the sympathetic nervous system (SNS) are overactivated in type 2 diabetes and that restoring the correct CSN neural activity can re-establish the proper metabolism. However, a robust characterization of the relationship between CSN and SNS neural activities and metabolism in type 2 diabetes is still missing. Here, we investigated the relationship between neural activity of CSN and SNS in control rats and in rats with diet-induced type 2 diabetes and the animal condition during metabolic challenges. We found that the diabetic condition can be discriminated on the basis of CSN and SNS neural activities due to a high-frequency shift in both spectra. This shift is suppressed in the SNS in case of CSN denervation, confirming the role of CSN in driving sympathetic overactivation in type 2 diabetes. Interestingly, the Inter-Burst-Intervals (IBIs) calculated from CSN bursts strongly correlate with perturbations in glycaemia levels. This finding, held for both control and diabetic rats, indicates the possibility of detecting metabolic information from neural recordings even in pathological conditions. Our results suggest that CSN activity could serve as a marker to monitor glycaemic alterations and, therefore, it could be used for closed-loop control of CSN neuromodulation. This paves the way to the development of novel and effective bioelectronic therapies for type 2 diabetes.

Unique Features of Network Bursts Emerge From the Complex Interplay of Excitatory and Inhibitory Receptors in Rat Neocortical Networks.

Spontaneous network activity plays a fundamental role in the formation of functional networks during early development. The landmark of this activity is the recurrent emergence of intensive time-limited network bursts (NBs) rapidly spreading across the entire dissociated culture in vitro. The main excitatory mediators of NBs are glutamatergic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) and N-Methyl-D-aspartic-acid receptors (NMDARs) that express fast and slow ion channel kinetics, respectively. The fast inhibition of the activity is mediated through gamma-aminobutyric acid type A receptors (GABAARs). Although the AMPAR, NMDAR and GABAAR kinetics have been biophysically characterized in detail at the monosynaptic level in a variety of brain areas, the unique features of NBs emerging from the kinetics and the complex interplay of these receptors are not well understood. The goal of this study is to analyze the contribution of fast GABAARs on AMPAR- and NMDAR- mediated spontaneous NB activity in dissociated neonatal rat cortical cultures at 3 weeks in vitro. The networks were probed by both acute and gradual application of each excitatory receptor antagonist and combinations of acute excitatory and inhibitory receptor antagonists. At the same time, the extracellular network-wide activity was recorded with microelectrode arrays (MEAs). We analyzed the characteristic NB measures extracted from NB rate profiles and the distributions of interspike intervals, interburst intervals, and electrode recruitment time as well as the similarity of spatio-temporal patterns of network activity under different receptor antagonists. We show that NBs were rapidly initiated and recruited as well as diversely propagated by AMPARs and temporally and spatially maintained by NMDARs. GABAARs reduced the spiking frequency in AMPAR-mediated networks and dampened the termination of NBs in NMDAR-mediated networks as well as slowed down the recruitment of activity in all networks. Finally, we show characteristic super bursts composed of slow NBs with highly repetitive spatio-temporal patterns in gradually AMPAR blocked networks. To the best of our knowledge, this study is the first to unravel in detail how the three main mediators of synaptic transmission uniquely shape the NB characteristics, such as the initiation, maintenance, recruitment and termination of NBs in cortical cell cultures in vitro.

Fluctuation Scaling of Neuronal Firing and Bursting in Spontaneously Active Brain Circuits

We employed high-density microelectrode arrays to investigate spontaneous firing patterns of neurons in brain circuits of the primary somatosensory cortex (S1) in mice. We recorded from over150 neurons for10min in each of eight different experiments, identified their location in S1, sorted their action potentials (spikes), and computed their power spectra and inter-spike interval (ISI) statistics. Of all persistently active neurons, 92% fired with a single dominant frequency- regularly firing neurons (RNs)- from1 to8Hz while 8% fired in burst with two dominant frequencies- bursting neurons (BNs)- corresponding to the inter-burst (2-6Hz) and intra-burst intervals (20-160Hz). RNs were predominantly located in layers2/3 and5/6 while BNs localized to layers4 and5. Across neurons, the standard deviation of ISI was a power law of its mean, a property known as fluctuation scaling, with a power law exponent of1 for RNs and1.25 for BNs. The power law implies that firing and bursting patterns are scale invariant: the firing pattern of a given RN or BN resembles that of another RN or BN, respectively, after a time contraction or dilation. An explanation for this scale invariance is discussed in the context of previous computational studies as well as its potential role in information processing.